Transcript for:
GCSE Biology Overview and Key Concepts

this video is for paper one of GCSE biology and combined science you can get extra help with this exam by downloading my revision workbooks and my maps from Emma DT ChiCom the link is in the description below I really hope you find this video useful if you do you can support me by giving me a thumbs up and subscribing GCSE these are tough but the fact that you're watching this means that you care and are putting effort in and that always pays off good luck for your exams and thanks again for watching [Music] our first topic is cell biology and we're starting with number one microscopy we're going to look at two types of microscopes as you need to understand how microscopy has developed and the differences between these two first up is a light microscope which you'll have seen and used in school it was first developed in the mid 17th century and it uses light to form an image because of this it can be used to view live specimens for example bugs it's also pretty cheap and it's easy to use which is a big advantage the best ones can magnify up to 2,000 times which means that it zooms in two thousand times resolution is all about the details you can see it is the ability to see two things as separate objects a high resolution means you can see lots of detail and everything is clear and separated the light microscope has quite a low resolution with a resolving fire of around 200 nanometers now let's look at the electron microscope it was developed by scientists in the 1930s and it uses electrons to form an image it does this by firing electrons through the specimen which means that the specimens must be dead first so it can't be used to view living specimens it's a very expensive microscope and it has a lot of conditions so that needs to be capped on there however the rewards are really good as the magnification can be up to two million times and it has a really high resolution of just 0.2 nanometers the magnification and the resolution are the two big ones you need to remember to be able to compare these microscopes in both cases the electron microscope is much better it has really high magnification and resolution and this is a lie scientists to see and understand lots more about the subcellular structures of cells we'll look at these in more detail in the next video number 2 animal and plant cells we're going to start with animal cells and we'll look at the organelles that it contains and the functions of each so the first organelle is called the nucleus that's this big black blob it controls the cells activities so basically everything and it also contains genetic material which in animal cells is DNA on the outside of the cell is a cell membrane this is responsible for controlling the passage of substances in and out of the cell so that's things like glucose and water down here we've got the cytoplasm this is a liquid gel that fills up the entire cell and it's where chemical reactions occur so make sure you learn chemical reactions happen there this squiggly guy is a mitochondrion that's the singular and if you had a few of them we'd call them mitochondria not suppl ok their function is super-important they are where aerobic respiration occurs and that releases energy for the cell so there really important now we've got a little tiny black dot over here and we call this little guy a ribosome you can also sometimes see the ribosomes attached to this structure and you'll learn more about this if you do a level biology but for now I just look for the little tiny black dots its function is protein synthesis which is just a fancy way of saying making proteins so these are all the parts you need to learn for an animal cell now let's look at a plant cell I want you to pause the video and see which parts you can already label you'll know some from what we've just covered ready okay so the big black blob is the nucleus that's the same in the animal cell and we've also got the little tiny black blobs which are the ribosomes over here we have got the squiggly guy which is a mitochondrion we've also got our liquid gel which is the cytoplasm okay we have got the cell membrane and that is the inner layer of the two layers that you can see and I'll go over how you remember that a little bit later so now let's swap colors and we'll do the parts that are specific to plant cells starting with this green blob this is a chloroplast now not every plant cell has these but when they do have it their function is to continue or aful which is that green pigment that makes it look that way and chlorophyll is really important because it absorbs light for photosynthesis you're going to do a lot more on photosynthesis later on in paper wom we've also got this big white blob which is a permanent vacuole its function is to be filled with cell sap and that's important because it helps keep the cell rigid you'll notice that plants don't have skeletons so they need this to help support them and down here we've got the outer layer which is the cell wall my trick to remembering this is that the wall is always the outside layer of your house and it's the same in a plant cell it's on the outside in plants it's made of cellulose but in fungi it's made of a different material okay and just like the wall of your house it strengthens it and gives it support so it's really vital also vital is that you learn the differences between plant and animal cells three eukaryotic and prokaryotic cells [Music] animal and plant cells are both eukaryotic cells as well as fungi and protesta we call them eukaryotic cells because they all have some features in common they all have a cell membrane a cytoplasm and genetic material that is found inside a nucleus prokaryotic cells are different all bacteria are prokaryotes so we're going to look at a bacterial cell to see the organelles that it contains so they've still got a cell membrane and they still have a cytoplasm and they've still got ribosomes they always have a cell wall unlike eukaryotes which only sometimes have a cell wall and unlike plant cells it is not made of cellulose the next big difference is that their genetic material is not enclosed in a nucleus instead it's find as a single loop of DNA inside the cytoplasm there may also be one or more small rings of extra DNA which are called plasmids and some bacterial cells may also have a slime layer which is for protection and they may have a flagellum or plural flagella for movement it's important to learn the differences between eukaryotic and prokaryotic cells notice that prokaryotic cells also don't have any chloroplasts or mitochondria as they're just so small that these can't fit inside them for specialized cells [Music] when a new organism is growing initially all of the cells are the same ie they are undifferentiated as the organism develops the cells do differentiate this means that they change by developing different sub cellular structures we'll look at examples of these in just a moment we call these cells that have developed the subcellular structures specialized cells as they are able to carry out a particular function or that's just a fancy word for a job this will be in the tissue organ or whole organism in which they are find we're going to look at three specialized animal cells you need to be able to explain are the structure of a cell relates to its function so we'll cover this for each cell and you can expect to be given some information to use for these types of questions so first up we've got a sperm cell and its function is to reach and fertilize an egg cell can you spot any structures that would help it do this well first up we've got a teal that helps it swim or move through the reproductive system to the egg then it's mid piece has got many mitochondria to release energy for the movement of the teal up here in the head we've got what we call an acrosome which contains digestive enzymes to break down the egg and allow the sperm cell to penetrate it and of course we need a large nucleus to contain DNA which can then be passed on to create offspring down below we've got some muscle cells their function is to contract and relax causing movement can you spot anything that would help them do this well over here you can see that we've got lots of tiny little pink things which our mitochondria these release energy needed for the contractions over here we've also got some special proteins these caused contractions by sliding across each other and finally these cells can also store glycogen this is broken down into glucose to live respiration to happen you're going to learn more about respiration in the bioenergetics topic so don't worry too much about that and I finally up here we got a nerve cell its function is to carry electrical impulses around the body what can you spot that would help it do this well this is called an axon and it's very long to lie the impulse to be carried along it and over here you can see we've got lots of these little spiky things which are called dendrites dendrites allow the nerve cell to connect to lots of other nerve cells and finally we've got nerve endings these release chemical messengers that will cause an electrical impulse to be carried in the next nerve cell so the nerve endings have lots of mitochondria to release the energy needed to meet these chemical messengers now we've got our specialized plant cells for starting with the RIT hair cell and its function is the absorption of water and mineral ions from the soil what can you spot that would help it carry out this job well first of all this little protrusion provides a large surface area for the greater absorption of the water and mineral ions we've also got a large permanent vacuole this speeds up osmosis which overall will bring more water into the cell and again we've got lots of these guys many mitochondria these are going to be for the active transport of mineral ions and you'll learn a lot more about this in the active transport part of this topic later on next up we've got the xylem these cells are responsible for the movement of water and mineral ions up from the Ritz through the rest of the plant what can you see that would help them do this well you can see that they form long hollow tubes so the cell walls have been removed which alized the easy movement of water and mineral ions through them they also have spirals of lignin this allows it to strengthen the cells to withstand the pressure of the water moving through it and also supports the plant as it doesn't have a skeleton our sixth and final specialized cell is the phloem cell what can you spot that would help it move dissolve food up and down the plant well first of all you can see that the cell wall has been replaced by these funny little things called sieve plates and just like a sieve they've got holes in them till I dissolve food to move easily up and down through them we've got another type of cell here which is called a companion cell and it's adjacent to the phloem cells these have lots of mitochondria and they release the energy that allows the dissolve food to be moved up and down through the plant by diffusion let's start with a definition diffusion is the spreading out of particles of any substance in solution ie a liquid or a gas resulting in a net movement which just means overall movement from an area of higher concentration to an area of lower concentration let's look at an example of diffusion so here we've got a beaker of water water is a liquid so it's particles can move freely around now let's imagine that you drop some food coloring into it like this the food coloring is really concentrated in one place initially so this area is a higher concentration everywhere else in the beaker is a lower concentration since there's no food coloring there yet so we can label it like this because it is in solution the food coloring particles can also move around the movement of these particles is random and they spread out from a higher concentration to a lower concentration this can also be described as down a concentration gradient as we're moving from high to low so we can show it like this eventually all of the food coloring has completely diffused throughout the beaker so that the concentration is equal everywhere if you were looking at this it would look like a peel purple color the particles will still continue to move around randomly it's worth noting that diffusion is called a passive process and this is because no additional energy is needed to move the particles down a concentration gradient there are three factors that can affect the rate of diffusion the first is temperature higher temperatures cause particles to move more quickly so diffusion will happen faster as they spread out much more quickly using a Bunsen burner here would make the food coloring diffuse much more quickly similarly if there were a cold temperature this would slow down the rate of diffusion the second factor affecting the rate of diffusion is the concentration gradient this is the difference in concentration the greater the difference in concentration the faster diffusion will occur look at these two boxes in which one will diffusion of the orange gas happen the fastest box a or box B Falls and see if you can work a type ready well we can see in both boxes that the high concentration is up here in the top left corner so we can label it as such and then we'll need to compare the rest of the area of gasses so here we have got a lower concentration than the top-left corner but in B it is even lower as there are no orange gas molecules and therefore it's a steeper concentration gradient so diffusion will be much much faster it will still happen in box a but the diffusion will be a lot slower okay finally our third factor affecting the rate of diffusion is surface area having a larger surface area provides a bigger area for diffusion to take place across and therefore speeds it up let's take a look at both of these diagrams in these diagrams food molecules are being absorbed into the bloodstream in which one do you think this will happen fastest well if we take a look at the one at the top we can see it's got a very flat membrane surface and therefore this is a lower surface area than the diagram below where the membranes are highly folded so we can call this a higher surface area now let's look at the impact that this has in the top diagram the molecules will only be absorbed when they're right next to the membrane in the bottom one many many more of the food molecules are in proximity and therefore a much higher rate of diffusion will happen the bottom one is a chi a diagram of your small intestines and they're shaped like this to maximize the food absorption in your body six osmosis osmosis is a special type of diffusion because it involves the movement of water molecules only and like diffusion it still occurs down a concentration gradient with the water moving from a dilute solution ie one that has a high concentration of water molecules to a more concentrated solution ie one has a lower concentration of water an important part of osmosis is that it happens through a partially permeable membrane this is a membrane that has tiny holes in it so only very small molecules like water can pass through the membrane but bigger molecules for example sucrose can pass through because they get stuck most cell membranes are partially permeable so to sum up our definition of osmosis it is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane it is worth noting that just like diffusion it is a passive process because it happens down a concentration gradient and therefore no extra energy is needed now let's take a look at osmosis in action in which direction in this diagram will the net movement of water molecules be left to right or right to left pause the video and see if you can work it out well to answer this question we need to identify which side is more dilute and which is more concentrated the dilate side is the one with the higher concentration of water molecules which in this case is the left side of the membrane the right side of the membrane has got less water molecules and more sucrose or solute molecules and therefore it is the concentrated side of the membrane so just to recap osmosis occurs down a concentration gradient or from a dilute solution to a more concentrated solution so this means the net movement of water is from the left side over to the right side eventually the water concentration will be equal on both sides the water molecules will continue to move back and forth across the parsley permeable membrane but there's no further net movement of water ie the water is balanced on both sides osmosis is important in animal cells for making sure that the solutes like glucose and salts are at the right concentration inside the cell this internal environment needs to be kept just right for the cell to work the difference in concentration between the cells internal environment I'm the solution art sighted will determine how much as Moses occurs we're going to look at what happens when a red blood cell is put into three solutions that have different concentrations so you can see the impacts of this on the cell the first one is a hypotonic solution this means that it is more dilute in the cells internal environment what do you think will happen when the red blood cell is put into this solution pause and see if you can work it out well remember that osmosis is the diffusion of water from a dilute solution to a more concentrated solution so it's going to go from the hypertonic solution into the red blood cell as the water moves into the cell it will stretch it and if a lot of the water moves in the cell may even burst this happens if there's a big difference in concentration of course this kills the cell so next up we've got an isotonic solution this means that it is at the same concentration as the red blood cell pause again and see if you can think about what will happen when the red blood cell is put into this solution well nothing happens because the two solutions are the same there is no net movement of water ie no osmosis occurs and finally we've got a hypertonic solution this means it is a lot more concentrated than the red blood cells internal environment pause once more and see if you can work out what will happen in this case well this time the water will move out of the red blood cell and into the beaker as the red blood cell solution is more dilated and the water moves by osmosis so the more concentrated solution if it's a really big difference in concentration lot of water will leave the cell and this time the cell will shrink and the same thing happens is when it bursts it just won't function properly anymore neither is a required practical a by osmosis that looks at the effect of concentration of salt or sugar on the mass of plant tissue you'll get to apply your understanding of osmosis a lot more in this practical seven active transport using the diagrams on the left can you work out what active transport is pause and have a go well hopefully you've spotted that this time around that arrow is reversed so substances are moving from where they are in a low concentration to where there are a high concentration I II against the concentration gradient you might also have spotted that this movement is taking place across a partially permeable membrane just like osmosis because active transport moves substances against the concentration gradient it requires energy and this energy comes from respiration can you remember the name of this organelle where respiration happens yep it's a mitochondrion well done if you remembered that before we move on to the definition we'll look at an example as it will help us understand the process of active transport in the terms of the key words dilute and concentrated so here we've got a plant root and in the soil around it there are mineral ions these are in solution and plants need to absorb them so that they can grow properly often plants are in soil that has a low concentration of mineral ions and because the solute is low we say it's a dilute solution inside the plant roots are ever there are quite a lot of mineral ions so a lot of solute or a high concentration which therefore means it's a concentrated solution in active transport the mineral ions move from the dilute solution in the soil into the more concentrated solution in the root hair cells moving against the concentration gradient requires energy from respiration in the root hair cells this allows the plants to continue to grow even when they're in per quality soil returning to our definition we can now say that active transport moves substances from a more dilute solution to a more concentrated solution ie against a concentration gradient this requires energy from respiration another common example of active transport is in the small intestines if we zoom in on these we can see that they are absorbing dissolve food molecules for example glucose that's the little yellow molecule their glucose is very important as it can be used in respiration to carry out lots of processes in your body so the body wants to absorb as much of it as possible and to do this it uses active transport if we zoom in a little further we'll see how this works in the small intestines so over here we can see we've got a low concentration of glucose as there is less of it therefore this is the dilute solution inside the blood vessels we've got a high concentration of glucose and therefore this is called the concentrated solution your body is able to move the glucose from where it is in a dilute solution to where it is in a more concentrated solution and this allows it to move the glucose against the concentration gradient bringing it inside your bloodstream and transporting it to tissues where respiration can then take place it mitosis and the cell cycle to understand the process of mitosis we first need to understand the nucleus a little bit better so let's look inside an adult body cell the nucleus is this little black blob and if we zoom inside it we can see it's made up of these structures called chromosomes there are 23 pairs of chromosomes in an adult body cell or 46 in total if we zoom inside a chromosome we can see that it's actually made up of DNA this is a molecule of DNA right here DNA codes for genes you're going to learn a lot more about this in the inheritance topic in paper 2 but this is all that you need to know for paper 1 now that you understand that the nucleus contains chromosomes we can look at mitosis and the cell cycle the cell cycle is split into 3 parts stage 1 stage 2 and stage 3 we're going to look each stage in turn to understand how they work together to produce new cells let's start with stage one you can see from the pie chart that stage one is the longest of the three stages in preparation for cell division it has a lot to do first of all the cell will grow gaining mass secondly it will also increase the number of sub cellular structures such as ribosomes and mitochondria amongst others really importantly is then that the DNA replicates by doing this it forms two copies of each chromosome in a human body cell this would mean that by the end of stage one the cell contains 92 chromosomes instead of 46 we can see this here that there are two copies of each chromosome Stage two is mitosis in mitosis one set of chromosomes is pulled to each end of the cell you can see this happening in the diagram above with half of the chromosomes having gone to the top of the cell and half of the chromosomes having gone to the bottom of the cell as well as this the nucleus will also need to divide into splitting the chromosomes in half you can see this here that the nucleus is starting to pinch in and that will completely split off and finally in stage three the cytoplasm and cell membranes divide to form two identical cells these cells are genetically identical to each other and also to the parent cell which was the initial body cell just a quick note to mention that if you take a level biology you'll learn about mitosis in a lot more detail if you've come across this already then remember that you don't need this level of detail at GCSE you just need what I've already covered you're probably wondering what the importance of mitosis and the cell cycle actually is why do we need new cells well there are three main reasons the first is development when you're first conceived you're just a single cell you're going to need to make a lot of new cells for you to develop all the way from being an embryo to actual little-bitty secondly during child on puberty you need the ability to grow and therefore you need to be able to make new cells and finally sometimes we do need to repair ourselves imagine you God agrees and you're going to lose some of your skin your body can therefore make new skin cells through mitosis to repair the damage as you can see it's a really important process 9 stem cells we're going to start with recapping what differentiation is we looked at this in this specialized cells video when a cell differentiates it means it changes by acquiring different sub cellular structures like mitochondria and ribosomes by doing this it becomes a specialized cell can you name these 3 specialized cells below on the Left we've got a nerve cell in the middle our muscle cells and on the right is a red blood cell this unspecialized cell is a stem cell a stem cell is an undifferentiated cell and they've got two main functions the first we've already covered which is differentiation to produce different cell types and the second function is that it is capable of giving rise to many other stem cells ie it can regenerate new stem cells we're going to look at the uses of stem cells in animals and plants let's start with animals most animal stem cells will differentiate at a very early stage this means that more stem cells can be found in an animal when it is still an embryo we call these embryonic stem cells an embryo forms when a fertilized egg cell divides and this forms a hollow ball of cells on the inside of this we find the embryonic stem cells the function of these is to differentiate to make all of the specialized cells in the body but scientists have come up with another use embryonic stem cells can be cloned they can then be induced to differentiate into lots of different cell types like the ones you see here and these can then be used for the treatment of conditions or cells in the body aren't working properly for example paralysis is when nerves are damaged the body kamek new nerve cells on its own so using stem cells to make more could potentially cure paralysis similarily type 1 diabetes is when cells of the pancreas are damaged replacing them with working pancreatic cells could cure this condition there are other applications as well like new heart cells to repair heart damage but paralysis and diabetes are the two conditions that you need to learn for this specification although most animal stem cells differentiate at the early stage of development there are some that remain into adulthood we call these adult stem cells one place where adult stem cells are find is in the Morrow these stem cells can differentiate for many other types of cells including blood cells for example they could differentiate to make white blood cells and red blood cells adult stem cells are more limited in their uses as they tend to only make a small number of different cell types whereas embryonic stem cells can make almost any cell in the body neuron to plant stem cells plant cells can differentiate throughout their entire life as they continue to grow for their whole life meristem tissue is found in the shoots and root tips of plants and this is where you'll find the stem cells you can see down here that a lot of mitosis is taking place and this actually happens constantly so that the plant is continuing to grow because plant stem cells can differentiate into all cell types even in adulthood we can use them to clone plants this has got some real advantages the first is that using stem cells to clone plants is very quick and economic ie cheaper than other methods for example the bananas that we eat are all cloned from a single plant cloning plants for commercial sale is also known as horticulture we can also use stem cells including rare plants saving them from extinction as you'll see in the ecology topic extinction is an ever growing concern in our world so the ability to save rare plants from this is very important a big benefit for farmers is the ability to clone crops with special features like disease resistance and lastly cloning large numbers of genetically identical plants for research is really useful as the plants are all the same the effects of the research procedure can be tested more easily finally we need to look at the issue surrounding stem cells adult stem cells have a risk of carrying viruses which could in fact the patient receiving them and if a patient receives stem cells from an unrelated person there's a chance that their body will reject them they'll have to use immunosuppressant drugs to prevent this one solution to this is therapeutic cloning in this process cells from the patient are used to create an embryo which then has the CM DNA as the patient so there's absolutely no rejection risk the embryonic stem cells could then in theory be used to treat conditions and even grow entire organs this process is still in the research stages but there are high hopes for the future of stem cells in medicine other issues of stem cells include ethical issues embryos cannot give consent to be used in research so some people think it is against their human rights to use them one counter-argument is that most of the embryos used are left over from fertility treatments and would otherwise be discarded another issue is that it is against some people's religious beliefs as they think we shouldn't interfere with the natural reproduction process at all in some countries the use of embryos and research is banned here in the UK it's a light but there are some very strict regulations around it and finally 10 culturing microorganisms bacteria x type of simple cell division which is called binary fission it's very similar to normal cell division first up the genetic material replicates in this case it's a loop of DNA as we're talking about bacteria the two copies then move apart to opposite ends of the cell next new cell walls form and in addition to this the cytoplasm will divide eventually on the walls formed in the center they split off into two cells you'll notice that there are plasmids and these aren't split equally between the two cells so each cell is slightly different you can remember the name binary fission by thinking of it like this by means to like bicycle has two wheels and fission means splitting you may have learned to fight this in physics when looking at nuclear fission so putting the two together binary fission means splitting in two it's a very quick process and it can take as little as twenty minutes for the bacterial cell to split into that's provided it has enough nutrients and a suitable warm temperature you need to know how to calculate the number of bacteria in a population you'll be given the mean time and ask to work out how many there are after a certain length of time so let's look at an example Staphylococcus aureus divides once every 30 minutes what is the population size after 3.5 hours the first step is to check that our units are the same at the moment we've got minutes and ours and you need to be the same so let's turn 30 minutes into ours which is 0.5 hours you get this by doing 30 divided by 60 or just think of it as half an hour next we'll work out how many times it has divided so to get the divisions we're going to do the time that we've been given in this case it's three and a half hours and we divide it by the length of 1 division which in this case is 0.5 so we take our numbers and we pop them in and 3.5 divided by 0.5 gives us seven divisions so that's seven divisions in three and a half hours it's important to remember that each new salla is created will also divide in this time so each new cell will divide to give two new cells because of this we're able to use the number two to work out our answer and we just do two to the part of the number of divisions so in this case it's going to be two to the power of seven this just means you're multiplying two by itself seven times but it's easier to do it in your calculator and you get 128 okay try the next question on your own and then press play when you're ready to go through the answer ready so Helicobacter pylori divides once every 45 minutes calculate the population of the colony after 9 hours so again our units aren't the same so we're going to turn the minutes into ours and that gives us zero point seven five hours when we divide 45 by 60 then we're gonna work out the number of divisions we're going to divide the time given which here is nine hours by the length of the division which reaches work died was zero point seven five hours and when we pop that inter calculator it gives us 12 divisions so we take our magic two and put it to the power of 12 from our calculator we get 4096 now you could be asked to give your answer in standard form this is a higher tier skill and it's one of the mathematical parts of your paper so pop on over to my math skills and biology if you haven't learned how to do this skill yet when you're done come back here and see if you're not able to do it okay so what we're gonna do is make a number that's between 1 and 10 by placing a decimal point somewhere in this number that would go here to give us 4 point 0 9 6 and now we're just going to work out what our 10 is ^ so we count 1 2 3 back to the original decimal place and that's going to give us 4 point 0 9 6 times 10 to the 3 I remember that's higher-tier only now we're going to look at how you can prepare uncontaminated bacteria cultures using aseptic technique for the aseptic techniques you need to be able to explain why those steps are done so I'll do those parts in blue firstly bacteria are grown in a culture medium that supplies them with nutrients to grow this can be supplied by either a nutrient broth or a solid agar jelly these are both found inside a petri dish the petri dishes and culture media must be sterilized before use this ensures that any unwanted microorganisms are killed this wire loop is called an inoculating loop just like before the inoculating loop must be sterilized before use by passing it through a hot flame like a Bunsen burner flame this of course kills any microorganisms that were on it it's then allowed to cool down and then used to spread your bacteria after transferring and spreading the bacteria the light of the petri dish should be secured lightly with adhesive tape this is important as it prevents any microorganisms that are in the air from entering your petri dish and culture the petri dish is then stored upside down this looks odd but it stops any drops of condensation forming on the lids and dropping down onto the agar surface which could damage or prevent growth of the bacterial cultures finally in school laboratories culture should be incubated at 25 degrees Celsius or lower if a higher temperature were used harmful pathogens would be more likely to grow so 25 degrees Celsius and lower is safer for skills in industrial conditions cultures may be incubated at higher temperatures so that they grow faster neither is a required practical on the culturing of microorganisms and in this you'll look at the effect of antiseptics or antibiotics on bacterial growth you'll learn more about zones of inhibition and calculations for this then so we won't cover it here our second topic is organization and we're starting with number one principles of organization like many things in life there's a natural hierarchy to the organization of living things in the last topic you learned all about cells cells are the basic building blocks of life and they are first in the hierarchy examples include sperm cells nerve cells which are also called neurons and red hair cells amongst others next up are tissues a tissue is a group of cells with a similar structure and function let's look at an example here we've got muscular tissue and its function is to contract causing movement and you can see that all of the cells have a similar structure then we have organs these are collections of tissues performing specific functions for example the stomach care has got three different types of tissue firstly we've got muscular tissue to churn and move the food we've got glandular tissue over here that can release digestive juices and the stomach has got epithelial tissue this covers the surfaces the stomach both inside and out lots of organs combine to form an organ system the organs in an organ system work together to carry out a specific function for example down here we've got a diagram of the digestive system the digestive system organs are all working together to digest food you've also got a respiratory system and these organs work to bring oxygen into the body and remove the co2 from it let's take a look at the final hierarchy at the bottom we've got cells which build up into tissues which build up into organs and lots of organs make an organ system and what do you think is at the top yep it's the whole organism itself for example a human T the human digestive system the process of digestion is really important because the food that we eat can't be absorbed immediately it's too large and insoluble but digestion breaks it down into smaller soluble molecules which can then be absorbed into the bloodstream the GCSE specification assumes knowledge of the digestive system from Key Stage three science so it's important that we recap that first let's start by going over what each organ does to start we've got the mouth this takes in the food and mechanically breaks it dine with the teeth it then gets mixed with saliva speaking of saliva over here we've got the saliva guns these are what produced the saliva the fifth end gets swallowed and passed down through the esophagus this tube transports food to the stomach the stomach over here is where the food is then turned unmixed with hydrochloric acid it's important that you learned the name of this acid so we'll highlight it here if then passes into the small intestine here it continues to digest the food and then absorbs the resulting small soluble molecules we're going to take a minute to see how the small intestine is adapted for its function as this is one of the exchange surfaces you need to know there are three main adaptations to learn firstly the small intestines have a very large surface area this is achieved by having villi if you zoom in on the small intestines you'll see the villi and each one is called a villus that's a singular these are just folds in the surface of the small intestine the large surface area is also achieved by micro villi if we zoom in on just one villus we can see it's covered in loads of micro villi these folds on the surface of the villi really increase the surface area secondly the small intestines have a good blood supply there are loads of capillaries supply the villi this ensures that any food molecules absorbed are quickly taken away to other tissues maintaining a steep concentration gradient which results in faster diffusion this is also covered in the diffusion video thirdly the small intestines have got a short diffusion distance this is the distance from the food molecules to the bloodstream as the food molecules don't have to travel very far this means it's a faster rate of diffusion okay let's carry on with our journey through the digestive system after the small intestines the food passes to the large intestines this is where water is absorbed from any undigested material we call this undigested material feces and it gets stored in the rectum then finally it gets excreted through the anus now we're going to add the new bits that you need to know for GCSE level so we mentioned this library glands produce saliva but they also produce a digestive enzyme called amylase you'll learn a lot more by enzymes in the next three videos the stomach also produces a digestive enzyme and this one is called protease now we've got a new organ called the pancreas this small organ produces all three digestive enzymes amylase protease and lipase and over here we've got the liver it's a large organ that produces bile bile helps by speeding up enzyme action we will talk a lot more about bile in the video factors affecting enzymes so look out for that finally we've got the gallbladder and this is where the bile is stored before it's finally released into the small intestines three enzymes lock-and-key theory catalyst speed up the rate of chemical reactions and they do this without being used up or changed themselves because of this they can be used again and again enzymes have a similar function they are biological catalysts and they speed up the reactions in living organisms they can be used again and again as well they're actually just a special type of protein all proteins are made from chains of amino acids amino acids are small organic molecules and you'll learn more about them if you take a level chemistry the folding of the amino acid chains is what gives a protein its specific shape and structure in enzymes this folding is particularly important it determines the shape of the enzymes active site let's look at what this actually is enzymes are like a padlock and the active site is the key hole it's got a specific shape and this is really important as it's going to allow just one key to fit inside it the key is called the substrate this is a word you need to learn because enzymes and substrates work together like a lock and key we call this the locking key theory of enzymes okay so now let's take a look at an example one example of a substrate is starch and the enzyme that it binds to is called amylase so if they come into contact with each other the starch will bind to the active site of the amylase when this happens the amylase catalyzes the reaction which means it speeds it up and in this case the reaction taking place is the breakdown of the starch into its products and starch breaks down into glucose so here you can see we've got two glucose molecules and those are the products different enzymes have different active site shapes this is because their amino acid chains have folded differently giving a different 3d structure because enzymes affect the rate of reactions they fact the metabolism of a cell or organism this is a term that comes up in the specification under the fundamental concepts and principles of biology section will cover again in the bioenergetics topic but for now here's the definition for metabolism it is the sum of all of the reactions that take place in a cell or organism hopefully this little picture will help you remember it by affecting the speed of reactions enzymes control the metabolism of a cell or organism now it's important to note that not all enzymes break down substrates some enzymes are able to catalyze reactions that build large molecules from smaller molecules other enzymes can change one molecule into another for factors affecting enzymes I've mentioned before that enzymes are a special type of protein that can catalyze reactions in living organisms they do this by having an active site that is a specific shape for a substrate molecule to bind to keeping this specific shape is vital to the enzyme working properly if the active site changes shape the substrate can no longer bind to it there are two factors that can alter the shape of the active site and therefore affect enzyme function the first is temperature this graph shows our temperature affects the rate of reaction and you need to be able to explain every part of it just like in normal reactions increasing the temperature will increase the rate of reaction this is because the enzyme and substrate molecules have got more kinetic energy resulting in more successful collisions and therefore more reactions the optimum temperature is where enzyme activity is at its highest in humans this temperature is around 37 degrees Celsius as this is a temperature at which our enzymes work best in other organisms it can be different increasing the temperature beyond the optimum temperature will cause the enzyme activity to decrease this is because the enzyme has been denatured let's take a moment to see what this word means hopefully you recall from the locking key theory video the enzymes are made from chains of amino acids that have been folded to give them their specific shape this structure is actually held together by weak forces between the amino acids high temperatures can break these forces causing the amino acid chains to change ship this alters the shape of the active site which we call denatured this is an important word to learn when enzyme is denatured the substrate molecules can no longer bind to the active site and the reaction will slow down or stop altogether enzymes are also affected by pH this is high acidic or alkaline their environment is each enzyme will have an optimum pH and this can vary in the digestive system for example the protease produced in the stomach has a low optimal pH the stomach secretes hydrochloric acid to maintain the acidic environment so the protease can function efficiently changing the pH to far above or below and enzymes optimal pH can also denature the enzyme it does this by changing the shape of its active site changing the pH affects the charges on amino acids and this changes their folding structure maintaining the right pH is important for efficient digestion speaking of efficient digestion let's talk about bile in the digestive system video we mentioned that bile is produced in the liver stored in the gallbladder and acts in the small intestine now let's look at what it actually does enzymes produced in the pancreas over here and the small intestine over here work best in alkaline conditions when food leaves the stomach and enters a small intestine some of the hydrochloric acid comes along with it bile is an alkaline liquid so it is able to neutralize this HCL that comes from the stomach this maintains the right alkaline conditions needed for the enzymes in the small intestines to work properly file another function it helps with the digestion of fats by emulsifying them this means that they're physically broken down from larger droplets into smaller droplets this provides a much larger surface area for enzymes to act upon and this increases the rate of digestion hopefully you can see this in the diagram here it's important to note the bile is not an enzyme as it isn't chemically breaking down the fat molecule into different molecules it's just physically making it into smaller pieces five digestive enzymes in the digestive system video you heard the names of three digestive enzymes today we're going to look at what they break down and the products of this breakdown so let's take a look at the names of them first up we've got amylase and this is an example of a carbohydrates enzyme what do you think carbohydrate is break dawn taking a look at the picture it's things like bread and pasta which we call carbohydrates amylase in particular break star in the carbohydrate that's called starch you may have heard of this already and the products of this are simple sugars for example glucose our next enzyme is protease what do you think it breaks down well the start of the word is a hint they break down proteins for example these chickpeas now for the products see if you can remember what proteins are made from well done if you remembered they're made from amino acids so when they're broken down they turn back into amino acids our third enzyme is lipase any ideas of what it breaks dyeing well the start of the word is another hint it's lipids otherwise known as fats and oils for example this cheese the products of lipids are fatty acids and glycerol as well as knowing what each enzyme does you also need to know where they are produced and the site of action ie where they work I'm going to start with a top tip for you all three enzymes are purchased in the pancreas let's change those integrating to match the color of the pancreas another top tip is the site of action for all three enzymes is the small intestines that means they all work in this organ this is really good to know for any exam questions okay but they do also get produced in other places amylase for example also gets produced in this library glands it's then no surprise that the site of action is the mice as that's where the saliva glands are located protease on the other hand is produced in the stomach and therefore it also works in this stomach and is also produced in the small intestines lipase is also produced in the small intestines now different to the others it's only site of action is the small intestines and this kind of makes sense when you look at the fact that the pancreas empties its digestive enzymes into the small intestine and that's the only other place that they are meat so that's the only place where it works 6 the blood the blood is part of the human circulatory system along with the blood vessels and the heart you'll learn more about these in separate videos there are four components of the blood you need to know what each part does and what it looks like it may surprise you that over half of your blood isn't actually made of cells it's made of plasma plasma is a peel straw yellow colored liquid its function is to transport your blood cells around the body along with some other chemicals such as carbon dioxide urea and proteins then we've got red blood cells these have the important function of carrying oxygen around the body bringing it to the cells that need it to do this they have some special adaptations first up they've got a pigment called hemoglobin this combines strongly to oxygen which helps them hold on to it and carry it around the body it's also what makes the red blood cells red secondly they have no nucleus this allows more space for the hemoglobin pigment and thirdly their biconcave which means they have a dip on each side this increases their surface area to volume ratio so they can carry more oxygen red blood cells make up around 45% of the blood and the remaining less than 1% are white blood cells and platelets white blood cells are covered in the infection and response topic you'll go over them in a lot more detail then so for now we'll just cover their main function which is to protect the body against infection unlike red blood cells they do have a nucleus and they're normally larger they're also not as strongly pigmented so if you're asked to identify them in a photograph they'll just be the color of whatever stain has been used finally we've got platelets these are fragments of cells and their function is to help the blood clot this is important when a person gets wounded as it helps prevent blood loss and forms a scab that prevents bacteria from entering the body as their fragments of cells they're quite a lot smaller than red or white blood cells so this is how you can identify them seven blood vessels there are three types of blood vessels you need to know the structure and function of each the arteries carry blood away from the heart and I remember this with a four away there carrying it to the organs of the body the blood is under high pressure as it's just being pumped out of the heart because of this the arteries have thick muscular walls with elastic fibers and this allows the walls to stretch as the blood is forced through them this is actually what you're feeling when you take your own pulse over here the hole in the middle is called the lumen arteries have a relatively small lumen and that keeps the blood under high pressure the arteries will eventually branch out into capillaries capillaries are tiny blood vessels that you can actually see with the naked eye their job is to bring the blood to the cells of the body once I've done that substances can then easily diffuse out of the blood and into the cells for example oxygen and glucose may diffuse into the body cells and waste products like carbon dioxide will diffuse out of the body cells capillaries have very thin walls and you can see that they're just one cell thick this short distance makes diffusion much much easier and therefore faster the blood will then pass from the capillaries to the veins they carry the blood from the body's organs back to the heart at this point the blood is under lower pressure this means that fiends can have thinner walls as they don't need to maintain a high pressure they also have a wider lumen to allow the blood to flow easily through it with less resistance and they've got valves these allow the blood to flow forward to the heart but prevent any backflow of blood which is really important it's the lungs and gas exchange in the previous video on blood vessels we saw that capillaries allow oxygen to diffuse out of the blood and into the body cells where it's used and they allow a carbon dioxide to diffuse out of the cells and into the blood this co2 needs to be removed from the blood and the oxygen needs to be replenished this happens in the process of gas exchange which takes place here in the lungs you need to know the structure and adaptations of the lungs so let's start by labeling this diagram why not pause and see how many parts you can already name well up here we have the nose and the mouth and those bring air into the body and then here we have the trachea or the windpipe this has rings of cartilage to keep it open it then branches into the bronchi or bronchus for singular which then itself branches into bronchioles at the end of the bronchioles we've got tiny little air sacs called the alveoli we'll look at these more in a second over here we've got the ribs they make up the ribcage which protects the lungs and between them our intercostal muscles these help move the ribcage and finally down here we've got the diaphragm this muscular tissue also helps with breathing now let's look at the adaptations for gas exchange here is one alveolus this is where gas exchange takes place and you can see that it is surrounded by a capillary the first adaptation is data is ventilated this means the air is actively brought in an out of the lungs this helps maintain a steep concentration gradient as fresh oxygen-rich air is brought into the lungs with each breath gas exchange then takes place and the co2 that entered the alveolus from the blood will then leave with each exhaled breath secondly it has a good blood supply as it's surrounded by a capillary network that covers 70% of the alveolus let's look at what's happening in the blood the blood that arrives to the alveolus has got a high concentration of co2 this diffuses out of the blood and into the alveolus where it has a lower concentration of co2 the blood that is arriving also has a low concentration of oxygen whereas the alveolus has a high concentration of oxygen that means it diffuses out and into the blood this maintains a really steep concentration gradient as the blood quickly transports that new oxygen away and that keeps that diffusion gradient going our third adaptation is that the walls of the alveoli are very thin providing a short diffusion pathway between the air and the blood so it's much faster if we take a look at the shape of the alveolus we can see it's a spherical shape and it's tiny so they have a large surface area to volume ratio this maximizes the rate of diffusion now that we've looked at gas exchange in humans we're going to briefly look at it in fish you may have already covered this with your teacher in topic 1 when learning about diffusion fish get their oxygen from water which only holds very low concentrations of oxygen they therefore need a really efficient gas exchange process here's how it works water enters through the mouth of the fish and then passes over the gills which are inside the body it then leaves by a special flap called a per Coulomb gas exchange happens in the gills the diagram below shows you what the gills are made of these are stacks of filaments and these help provide adaptations the first is that the filaments provide a large surface area they also have a good blood supply with lots of capillaries along them the gill filaments and capillaries are just one cell thick that provides a shorter path for diffusion and they are ventilated as water containing oxygen is actively moved over the gills and finally they maintain a counter current this just means that the blood moves in the opposite direction to the flow of the water this is good because it maintains a steep concentration gradient for diffusion hopefully you can spot that there are some similarities between gas exchange in the human lungs and the gills of the fish 9 the heart the heart is an organ the pumps blood around the body in a double circulatory system this means that each side of the heart pumps the blood to a different place the right side of the heart has deoxygenated blood so it needs to pump the blood to the lungs and up here you can see the capillary network of the lungs this is where gas exchange takes place providing the blood with oxygen the oxygenated blood then returns the left side of the heart which pumps his blood to the rest of the body and down here you can see the capillary network of the rest of the body in the capillaries oxygen can diffuse out of the blood and into the body's cells where it's used for aspiration carbon dioxide is produced and this will get transported up to the right side of the heart to be taken to the lungs the double circulatory system works really well as it means the oxygenated blood is pumped separately and so it's sent under a really high pressure so it can reach all parts of the body now let's look at the structure of the heart you'll notice that it says right side over here on the left side of the diagram and it says left side on the right side of the diagram when we look at a diagram of the heart the sides are flipped this is because it's labeled as though it's facing you the heart has four chambers the top two chambers are called atria so we've got the right atrium and the left atrium and the bottom chambers are called the ventricles so we've got the right ventricle and the left ventricle my tip to remember which way Ron the Chamber's are is that the bottom chambers look a little bit like a v4 ventricle and then the top chambers you just need to remember are the atria the blood comes from the body and it enters the heart through a vein called the vena cava you can remember this by V 4 V n is V 4 vena cava remember veins always bring blood back to the heart the blood then travels down through the right atrium into the right ventricle where it gets pumped out through an artery called Neri artery remember arteries take blood away and in this case they're taking it to the lungs gas exchange takes place there and the oxygenated blood returns to the heart by the pulmonary vein pulmonary just means that it's relating to the lungs the blood then travels down through the left atrium and the left ventricle before getting pumped out of the heart and through the aorta the aorta is a major artery and it takes the blood to the rest of the body one way to remember this blood vessel is that it's a four artery and a four aorta now down here you'll notice that the left side of the heart has got thicker muscle tissue than the right side this allows it to pump the blood under a higher pressure to make sure that it gets to all the parts of the body that it needs to the last thing to note is that we've got some special cells here in the right atrium these cells are called the natural peacemaker cells of the heart they release an electrical signal that causes the heart to contract and this then pumps the blood out of it these control the resting heart rate of the heart also known as your pulse 10 coronary heart disease the heart pumps blood to all of our body's cells it works very hard and requires lots of oxygen and glucose for its own cells these are supplied by the coronary arteries and you can see them here covering the heart sometimes the coronary arteries can become narrow usually caused by a buildup of fatty deposits this is called coronary heart disease or CHD this is dangerous because the fatty deposits restrict the blood flow to the heart less blood flow means less oxygen is being supplied which can cause pain and even heart attacks there are two methods of treatment for CHD you need to be able to evaluate methods of treatment so we'll discuss the benefits and risks as we go through them the first method is stents these are little mesh tubes that can be put inside the blocked artery where they then squash down the fatty deposit opening the artery wider there left in place allowing the blood vessel to work properly the issues are that the stents can cause a risk of clotting after they've been put in the second method is statins these are a drug that lower blood cholesterol levels slowing the build-up of fatty deposits they don't unblock any blocked arteries so they're generally only used for people who are at risk of CHD besides the main benefit of reducing the build-up they also lower the risk of some other diseases but as their tablets people need to remember to actually take them and they're a little bit slower to have an effect there are also some possible side effects that are quite serious now we'll take a look at some other cardiovascular diseases in some people the heart valves may become faulty particularly in older people this means they may not open fully or they could be leaky when this happens the blood can flow in both directions so that less oxygenated blood is pumped to the tissues of the body this results in people feeling breathless or tired as their cells aren't receiving enough oxygen for respiration without treatment faulty valves can result in death fortunately doctors can replace the faulty valves with either mechanical valves or biological valves mechanical valves are man-made and the good news is that they last forever the bad news is is that patients will need to take medication to prevent any blood clotting forming around the valves biological valves on the other hand are valves from donors so the patient's don't need any medication but they only last forever in 10 to 15 years next up are peacemakers in the last video about the heart you will have learned that the natural pacemaker cells of the heart are in the right atrium but sometimes these cells aren't functioning properly they can make the heart beat too fast or too slow and both cases this causes problems so if the heart is beating irregularly an artificial pacemaker needs to be implanted into the chest this is attached to the heart with two wires and then it can release an electrical signal which causes the heart to contract at the rate that's needed these devices are tiny and life-saving if a patient has heart failure they may require a heart transplant or a heart and lungs transplant this requires a donor heart which isn't always available doctors may use an artificial heart to try and keep the patient alive until a donor heart is find the big advantage of this is that it's less likely to be rejected by the patient's body and of course it prolongs their life but it can cause the blood to stick and clot leading to strokes and to prevent this the patient needs to take blood thinners which have their own complications like extended bleeding if they're in an accident there's also a lot of machinery involved in keeping the artificial heart working that means that patients need to stay in hospital until a donor heart is farmed natural heart transplants work a lot better and there's a much lower chance of the blood clotting it also allows the patients to live a more normal life but as with any organ transplant there's a risk that the heart will be rejected as the patient's body may detect it as foreign eleven health issues health is a state of physical and mental well-being it's important to remember that it is both physical and mental not just one or the other diseases are major causes of ill health and they can be split into two groups communicable and non-communicable communicable means the disease is infectious and can be passed on from one person to another non communicable means it cannot be transmitted you'll learn about some non communicable diseases in the next video and you'll find out about communicable diseases in the infection and response topic other factors affecting physical and mental health include diet stress and difficult life situations diet could mean a lack of food or certain nutrients this could cause diseases like anemia scurvy and starvation or it could mean too much food or too much of specific unhealthy foods this can cause conditions like type 2 diabetes and obesity we all experience stress and some of this is okay the high levels of it can affect mental health and even increase a risk of certain diseases like heart disease life situation includes things like income where in the world you live access to health care and clean water etc many people have little or no control over their life situation and it can have a big effect on mental and physical health different types of diseases may interact with each other there are four examples you need to know defects in the immune system mean that an individual is more likely to suffer from infectious diseases these defects could be caused by genetics or by something like HIV viruses living inside body cells can be the trigger for certain cancers for example the human papilloma virus or HPV can trigger cervical cancer immune reactions initially caused by a pathogen can trigger allergies such as skin rashes and even asthma severe physical ill health can lead to depression and other mental illnesses particularly if they affect the person's ability to do everyday activities for example if somebody is bedridden now you need to be able to use graphs frequency tables bar charts histograms and scatter diagrams to analyze information about diseases these skills are all covered in my maths and biology video and they can come up in other topics I suggest you take some time to practice these skills as it's quite likely they'll come up with this topic 12 non communicable diseases non communicable diseases are ones that aren't infectious this means they can't be transmitted from person to person these diseases caused 71 percent of deaths globally which far outweighs the number of deaths caused by communicable diseases at just 29% both of these diseases not just communicable diseases apology's affect the individual their family which is supporting them and their country countries spend huge amounts of monies trying to treat ill people and not only that affects the global economy because people who are ill aren't able to contribute to the work force what's crazy about these diseases is that most of them are preventable as they are caused by some lifestyle factors like smoking or a lack of exercise or they can be caused by substances in the person's body or environment for example UV light that comes from the Sun lifestyle choices and substances that increase the risk of disease are called risk factors they increase the rate of disease incidents which just means how many people have the disease now sometimes there is a correlation between something like a lifestyle factor and a disease for example here the number of ice creams eaten per hundred people increases as does the incidence of sunburn per hundred people but just because there's a correlation doesn't mean there's a causation we know the eating ice cream doesn't make you sunburned it just so happens that eating ice cream and getting sunburned both happen on sunny days to find out if certain factors really cause diseases doctors and scientists need to do a lot of research to understand the biological mechanism causing this when this is proven we call it a causal mechanism a causal mechanism has been proven for some risk factors but not in others there are six proven causal mechanisms that you need to know the first is cardiovascular disease which has the risk factors of diet smoking and exercise a per diet can increase the levels of blood cholesterol smoking can increase the blood pressure and damage the lining of the arteries and a lack of exercise can lead to a buildup of fatty deposits in the arteries type 2 diabetes can be caused by obesity the result of this is the body stops responding to an increase in blood glucose levels which is dangerous liver and brain damage are both caused by alcohol this can cause liver cancer and cirrhosis which is scarring of the liver it can also cause brain damage which stops the brain functioning properly even when sober lung disease and cancer are both caused by smoking tar is a carcinogen and it turns the lungs gray and increases the risk of lung cancer and damage to the fetus is caused by both smoking and alcohol the results of this can be a low birth weight a premature birth or even a still birth this is when the baby is born dead now it cancer is something you're going to learn about in the next video but for now you just need to know that it's an uncontrolled cell division it can be caused by Kirstin engines in a person's environment including ionizing radiation like UV light from the Sun and radioactive metals like uranium it can be other substances as well like tar or possibly even in excess of red meat in the diet which is linked to boil cancer many non communicable diseases are caused by multiple factors interacting so it can be hard to find a causal mechanism thirteen cancer cancer occurs when changes in a cell cause abnormal or uncontrolled cell growth and vision this can lead to the formation of tumors in the body like the one you see here benign tumors are contained in one area of the body usually within a membrane they don't spread to other parts of the body however they can still be dangerous as they grow very quickly and can put pressure and other organs which damages them this happens if there's no space for them to grow into for example tumors in the brain have nowhere else to grow as the skull surrounds them so they can put pressure on the brain which is very dangerous so these types of tumors can still be life-threatening malignant tumors are different small parts that then can break off and these cells can travel in the blood this allows them to spread to different parts of the body and they can also invade neighboring tissues once there they can then cause secondary tumors malignant tumors are difficult to treat because of how they spread around the body the two main methods of treating cancer are radiotherapy and chemotherapy you don't need to know the details of these so we'll just look at this very briefly radiotherapy uses radiation to target and kill cancer cells but it can't harm healthy cells to chemotherapy uses chemicals these can be taken either through tablets or through avian in the hand or arm these chemicals work by halting mitosis in rapidly dividing cells ie cancer cells unfortunately cells like your hair cells are also rapidly dividing which is why patients undergoing chemotherapy can often lose their hair both treatments have many side effects and the results can be quite variable from person to person there are certain lifestyle factors that increase the risk of different cancers for example we have smoking obesity exposure to UV light and common viruses like HPV all of these will increase the risk of a specific cancer for example HPV increases the risk of cervical cancer there are also genetic risk factors for cancers for example breast cancer and ovarian cancer 14:12 tissues and organs plump organs include the root stem flowers and leaves we're going to look at the tissues of the leaves and hardly help it carry out photosynthesis this is a cross section diagram of a leaf so you can imagine that we've cut through it and are looking at it from the side so first up we have the epidermal tissues we have got the upper epidermis and the lower epidermis these both cover the surface of the plant unprotected they can also secrete a waxy substance which we call the waxy cuticle this waterproofs leaf which minimizes water loss you'll also notice that the upper epidermis is quite thin this allows light to penetrate through to the next layer the next layer is the policy of musa phil this tissue is responsible for photosynthesis you can remember it by P for Policy as P for photosynthesis to carry out this function it has lots of chloroplasts and these contain chlorophyll to absorb the light for photosynthesis this tissue is tightly packed and this maximizes the amount of light that gets absorbed for photosynthesis the next issue is a spongy mesophyll just like a normal sponge it has lots of air spaces this allows gas exchange via diffusion to take place easily this is important as carbon dioxide needs to diffuse into the plant cells for photosynthesis and oxygen that is produced needs to be able to diffuse out on the underside of the leaf or the bottom of the leaf we've got tiny little pores called stomata stoma is a singular for just one of these little holes the size of this hole is determined by guard cells that are find on either side of the stoma these are important for controlling water loss which we'll learn more about in the next video now we're going to look at the transport systems of the plant this consists of the xylem and the phloem this eylem transports water and mineral ions these are absorbed from the soil in the ribs and are then transported up through the plant to the stem and the lead therefore the direction of travel is in just one way upwards only no energy is needed as this is a physical process the flume transports dissolve food ie glucose which is made in the process of photosynthesis in the leaves this needs to be transported up through the phloem to the developing tissue or the meristem and dying the phloem to the ribs the roots can't carry out photosynthesis so they need to get their glucose that comes from the leaves therefore the direction of travel is up and don't the plant and finally yes energy is needed for this process and this is supplied by the companion cells adjacent to the phloem cells just to note you do need to be able to link structure to function which is covered in the specialized cells video of topic one another note is that the merry stamp tissue is another tissue you need to know this is find in the chute and the roots and again hopefully you've already covered this in topic one stem cells fifteen transpiration plants require carbon dioxide for photosynthesis this comes from the air around them and enters the leaves through small pores called stomata these can be open like this one which shows the stoma which is a singular of stomata or they can be closed so you can't see it this opening and closing is controlled by the guard cells which are find on either side of the stomata here in this diagram that guard cells are turgid that means they're full of water and this gives them this particular shape that causes the stoma to open when the guard cells lose water they become flaccid and their shape becomes more rectangular which closes the stoma the guard cells control gas exchange when the stomata are open carbon dioxide diffuses into the leaf where it's then used for photosynthesis oxygen is produced in this process and it will then diffuse out of the leaf at least the excess that isn't needed for aspiration unfortunately water vapor is also able to escape through these open pores let's take a look at this in more detail water evaporates from the surface of cells in the air spaces of the spongy mesophyll when it evaporates it turns into water vapour and this water vapor then leaves through the stomata this process of water loss through the stomata is called transpiration that's a key word to learn now let's look at the effect it has the orange arrows show the path of water through the plant water is getting pulled up through the xylem through the stem and the leaves to replace the lost water so more water will need to be taken up by the roots in the process of osmosis this movement of water through the whole plant is referred to as the transpiration stream it's important to remember the transpiration is driven by the evaporation of water in the leaves 16 factors affecting the rate of transpiration we learned in the previous video that stomata allowed gas exchange to take place but they also allow water vapor to escape this is called transpiration and certain factors affect the rate of transpiration because the stomata open to a low carbon dioxide to diffuse in for photosynthesis conditions that affect the rate of photosynthesis will also affect the rate of transpiration these factors include light intensity and temperature you'll learn how these affect the rate of photosynthesis in the bioenergetics topic but for now you need to know that increasing each of these increases the rate of photosynthesis up to a point which therefore increases the rate of transpiration temperature also gives the water vapor molecules more energy so they're able to move around more rapidly resulting in faster diffusion and when there's faster diffusion there's a faster rate of transpiration conditions that affect evaporation also affect the rate of transpiration as it's the evaporation of water from the cells inside the leaf that results in transpiration humidity is one of these factors this is how much water vapor is in the air the air on the Left is very humid as there's lots of water molecules this means there's a lower concentration gradient between the leaves and the outside air so diffusion and therefore the rate of transpiration will happen more slowly if the air is really dry like you see here then there's going to be a steeper concentration gradient between the leaves on the outside air so diffusion and transpiration occur more rapidly finally we've got air movement or how windy it is take a look at what the wind does here it moves the water molecules quickly away from the surface of the leaf that leaves a higher concentration inside the leaf than outside the leaf so we can say that lots of air movement or wind maintains a steep concentration gradient which means a faster rate of evaporation and therefore a higher rate of transpiration as well it's important to remember these four factors that are affecting the rate of transpiration plants want to reduce water loss while still caring I as much photosynthesis as possible this is especially important for plants living in hot dry windy and bright environments one adaptation they have to do this is the waxy cuticle this waterproofs the leaf preventing water loss it can be very thick depending on the plant's environment secondly they can wilt this means that the leaves drip down this is protective as it reduces the surface area for transpiration to occur it also means that less direct sunlight is absorbed by the leaves and finally an extreme solution is to close the stomata this of course prevents water loss but it also prevents photosynthesis without gas exchange no carbon dioxide can diffuse in and therefore no photosynthesis can occur the plant will reopen them when the conditions are more favorable okay so it's really likely that you're going to get a mass scale question when you're talking about the rate of transpiration so let's take a look at this piece of apparatus that's used to calculate the rate of transpiration and then we'll do the questions to practice this skill so this apparatus is called a pedometer at one end you've got a chute and you're going to introduce an air bubble into the capillary tube you just do this by taking the pedometer out of the water I'm blotting it with some paper towel then over here we have a ruler that's going to measure how far the air bubble moves and we've got a reservoir of water to flush out the air bubble and start again ask transpiration occurs water is drawn up and this pulls the air bubble along with it the rate of transpiration can then be calculated by how quickly the air bubble moves when we say quickly we mean the speeds which is calculated with distance divided by time okay now we've understood how to use the apparatus let's try these questions calculate the rate of transpiration for this chute under a normal conditions and be windy conditions okay so for a the air bubble moves five millimeters in eight minutes so we're going to do speeds equals distance divided by time and the distance is five millimeters and the time is eight minutes on our calculator this comes like to 0.625 millimeters per minute now let's look at B this is under windy conditions how do you think you would create these conditions in the lab well you could simply use a fun this can generate some wind speeds why not pause the video and then try this question yourself first ready so again we're going to do speed equals distance which here is 12 millimeters divided by time which in this case is 9 minutes when we do this on the calculator we get one point three three recurring millimeters per minute now it's more than possible that you will get a question that asks you to compare the different rates of transpiration so be prepared to say which one is faster and give a reason why our third topic is infection and response and we're starting with number one communicable diseases [Music] communicable diseases are ones that can be transmitted from one organism to another ie they are infectious pathogens or microorganisms that cause infectious diseases these include microorganisms from for grips we've got bacteria viruses protists and fungi you'll learn specific diseases from each grip leader in this topic pathogens can affect plants or animals and they spread by three different methods the first is direct contact this is when the infected individual directly touches a healthy individual and this passes the disease on this is very common in plant diseases but can also happen in humans with things like STDs secondly we've got water some pathogens can spray it in the water and in fact the individual when they drink the contaminated water it enters the body through the digestive system and thirdly we've got the air many diseases can spread in the air including droplet infection when you have a cold and sneeze millions of droplets containing pathogens are spread into the air and other people may breathe them in the majority of communicable diseases are caused by bacteria and viruses let's look at these two groups of pathogens and how they differ bacteria are larger than viruses and there are many good bacteria that play an important role in our digestive system it's actually estimated that the average human has roughly the same number of bacterial cells as human cells in their body it's no surprise then the bacteria can reproduce rapidly in the process of binary fission they can purchase poisons called toxins and these damage the tissues of the body this is what actually makes us feel ill viruses then are a lot smaller than bacteria they're teeny-tiny and these actually live inside the body cells of the hosts once there they also reproduce rapidly but they require the hosts body cell to actually do this they damage and eventually destroy the host cell this happens when they've reproduced enough times they burst out of the cell and infect more cells there are four main ways to reduce the spread of disease the first is simple hygiene measures these include things like washing your hands after using the bathroom using disinfectants to clean kitchen and bathroom surfaces and food safety things like keeping raw meats appart from other foods and using tissues when sneezing or coughing this minimizes pathogens spreading in the air secondly is destroying vectors vectors are organisms that carry disease for example mosquitoes carry the protists that causes malaria if the mosquito is destroyed then the disease cannot spread we can also isolate infected individuals until they're better this is done when the disease is highly infectious or dangerous for example Ebola isolating them reduces the number of healthy people who come into contact with them and finally we've got vaccinations you'll learn a lot more about this in the vaccinations video but this prevents disease by introducing a small amount of a dead or harmless pathogen into the body the immune system then learns hard to destroy the pathogen and can do this if it ever comes into contact with the full disease - viral diseases viruses lids and reproduce inside host body cells this makes treating viral diseases very hard as to destroy the viruses you have to damage and destroy your own body cells instead the focus is on preventing the spread of viral diseases so we'll look at how this is done for each of the three diseases first up is measles the measles virus is spread by droplet infection in the air this happens when an infected person sneezes or coughs and another person in heals the virus symptoms of this disease include fever under red skin rash that covers the whole body it's a serious illness and it can even be fatal if complications arise because of this infected individuals are advised to be isolated and most young children are vaccinated against measles HIV is spread by sexual contact or by the exchange of body fluids such as blood this can happen when drug users share needles you can see in this picture here that there's some residual blood on the needle HIV initially causes flu-like symptoms if it's caught early enough antiretroviral drugs can suppress the virus but they don't cure it if it's not caught early then it can develop into late stage HIV or AIDS this is when the body's immune system becomes very badly damaged and it means it can no longer deal with other infections or cancers patients can ultimately die from something like the common cold as er immune system cannot fight it off because of this people with AIDS have a much lower life expectancy to prevent the spread of HIV blood transfusions should be screened for this disease needles should never be shared and condoms should be used before any sexual contact is made including oral sex mothers can also be screened for HIV during pregnancy if found to be positive they'll receive specialist care and should not breastfeed their babies tobacco mosaic virus or tmv affects many species of plants including tobacco plants and tomatoes it's spread by direct contact and vectors which are other organisms that can carry the disease pathogen this means that the disease can spread easily and quickly tmv damages leaves by giving them a distinct mosaic pattern of discoloration you can see this here this reduces photosynthesis so the plant growth is really restricted and therefore farmers will get a smaller yield for their crops to reduce the spread farmers can use some form of pest control and they may grow tmv resistant crops three bacterial diseases salmonella is a common form of food poisoning it's a bacterium find in the guts of many different animals and can also be find in eggs and raw meat it spreads when undercooked meat is eaten or when food has been prepared in unhygenic conditions for example if a knife or chopping board were used for raw meat and then used to prepare a solid without being washed the salad would get contaminated with the Salmonella bacteria this is spreading by direct contact the symptoms of salmonella food poisoning include fever vomiting abdominal cramps and diarrhea not very nice at all to prevent this from happening in the UK poultry are vaccinated against salmonella to control the spread practicing safe food hygiene is also important cooking meat thoroughly keeping raw meat separate from other foods and washing hands and utensils properly after contact with raw meat this means using warm water and soap gonorrhea is a sexually transmitted disease also known as an STD this means the bacteria spread when there is any sexual contact between people this includes unprotected vaginal oral and anal sex the symptoms are a thick yellow or green discharge from the vagina or penis and there's pain upon urinating which just means peeing and this isn't on the specification but around one in ten infected men and almost half of infected women do not experience any symptoms so a lack of symptoms doesn't necessarily mean that a person is disease-free gonorrhea can be treated with antibiotics like penicillin however many antibiotic resistant strains have since emerged so it's becoming a lot more difficult to treat the spread of gonorrhea can be prevented by using condoms dental dams etc during sexual contact for fungal and protist diseases [Music] fungal diseases aren't that common in humans with the exception of athlete's foot they're much more common in plants the one you need to know is rose black spots this affects the leaves of roses the spores of this fungus spread in the environment by wind and by water the symptoms of rose black spot are in the name there are purple or black spots developing on plant leaves the leaves often turn yellow and can drop off the plant earlier than normal both of these symptoms result in less photosynthesis having purple or black spots means there's less chlorophyll in the leaf and having less leaves or yellow leaves also reduces the amount of chlorophyll this results in less growth of the plant and can even mean that there are less or smaller roses this disease can be treated in two ways firstly we've got chemical fungicides that kill the spores and secondly is removing and destroying any affected leaves this is usually done by burning them malaria is a deadly disease caused by protists the malarial protest has a lifecycle that involves the mosquito mosquitoes are factors for malaria meaning that they carry the disease only female mosquitoes bite humans and if the mosquito is infected it passes the protest into the human's bloodstream once there it circulates around the body and damages both the blood cells and the liver cells the symptoms of malaria are recurring episodes of fever and shaking it can be fatal if it isn't treated promptly in many countries where malaria is prevalent like sub-saharan Africa the medicine isn't easily accessible or it's very expensive so unfortunately many people die from this disease the spread of malaria is controlled by dealing with the vectors ie dealing with mosquitoes first up is preventing mosquitoes from biting humans this can be done using mosquito nets and insecticide secondly is preventing mosquito from breeding they require standing water to breed which is just still water so removing any standing water from areas around the home can prevent them breeding near humans this reduces their population five human defense systems the first line of defense is nonspecific meaning it's used against all types of pathogens there are four parts to this first up is the nose your nose contains hairs and mucus which can trap any pathogens that enter through it then we've got the skin you're probably aware that the skin acts as a barrier preventing pathogens from entering the body if it gets cut the body repairs it by forming a scab a new skin but the skin does more than just this it also produces antimicrobial secretions that can destroy some bacteria healthy skin is also covered with a layer of microorganisms that act as an extra barrier to the entry of pathogens over here we've got the trachea and bronchi which we learned to fight in the lungs and gas exchange video both of these chips produce mucus to trap pathogens they also have lots of cilia cilia are tiny hairs which line all the way down the tubes these can waft the mucus back up to the throat where it can then be swallowed when it is followed it goes down the esophagus which is a big long tube and into the stomach and the stomach is number four this organ contains hydrochloric acid which is strong enough to kill most pathogens that enter it these come from the mucus and from food and drinks if any pathogens get past the first line of defense they will meet the immune system the immune system is made up of different white blood cells and they can do three things to defend against pathogens first up is phagocytosis this is when a white blood cell engulfs which means it sort of surrounds and absorbs it engulfs the pathogen and then digests it which breaks it down and ultimately destroys it next up is antibody production pathogens have antigens on their surface you can see some of these over here these alert the immune system to the fact that the pathogen is foreign to the body some white blood cells can make antibodies these are special proteins and they have a specific shape that means that they can attach to the antigen when they attach to it they label it for destruction there's a unique antibody for each type of pathogen and lastly we've got antitoxin production antitoxins are able to counteract or in other words neutralize the toxins released by the pathogens and this means they can't harm you or make you feel ill over here you can see them locking together six vaccinations in the previous video we learned to fight hard the immune system defends the body against infection the issue is that some diseases act quickly before the white blood cells have time to make the right antibodies some of these are deadly diseases like meningitis but thanks to Edward Jenner and other scientists we have vaccinations to prepare the immune system here's how they work number one a small quantity of dead or inactive pathogen is put into the body this is called a vaccine and it's normally delivered via an injection the white blood cells will then detect the antigens of the pathogen and begin producing the correct antibodies this takes some time so it's a pretty slow response but that's okay because if the real pathogen re-enters the body as the full disease then the white blood cells can produce the antibodies much more rapidly this time it's a fast response the pathogen will be destroyed quickly before they can cause any symptoms of illness vaccinations have saved millions of lives around the world if a large enough proportion of a population is immune to a communicable disease then the disease will not be able to spread easily and may even be eradicated over here in this picture you can see that this pathogen is struggling to spread because if you look at the members of the population they've all been vaccinated this only works if it's many people in the population but if there are a very small number of people who haven't been vaccinated for example if they're very young or very old or have an illness then they'll still gain immunity as the disease cannot spread to them from the other people this is known as herd immunity that's an important phrase to remember so let's highlight it and it's also important to remember that this only works if there's a very small number of people who aren't vaccinated in this example here let's say that this lady hasn't been vaccinated because she has an illness that prevents her from doing so she'll still be protected from catching this pathogen if everybody around her is vaccinated the World Health Organization is aiming to establish global herd immunity for a number of diseases ongoing education and financial support is necessary to make this possible seven empty products and painkillers antibiotics are widely used in medicine to cure bacterial diseases and have greatly reduced the number of deaths from these pathogens they're normally taken orally which means they're swallowed through the mice as pills or syrup once they've entered the body they kill the infectious bacteria while leaving your body cells unharmed one example of an antibiotic is penicillin you need to learn this example so we'll highlight it specific antibiotics or kick and specific bacteria so it's important to use the right antibiotic to cure each disease for example this amoxicillin syrup would be able to work against this little bacteria here but that doesn't mean it'll work against this other species of bacteria some strains of bacteria have developed antibiotic resistance meaning that the antibiotics aren't effective at killing them this is a real concern as it takes many years and huge sums of money to develop new antibiotics many deaths could occur from antibiotic resistant bacteria you'll learn more about this including how it could be prevented in the antibiotic resistance video which is paper to content antibiotics cannot kill viruses they only work in bacteria viruses reproduce inside your body cells because of this it's hard to develop drugs that destroy viruses without also damaging the body's tissues the symptoms of disease can be treated with painkillers and other medicines these don't actually kill the pathogen so they don't cure the disease but they do help you feel a wee bit better while your immune system actually overcomes it for example this girl here has a viral infection that's causing her to have a headache she can take painkillers for this to help her relieve her symptoms while her immune system destroys the viruses it's the discovery and development of drugs drugs are used in medicine to cure diseases and treat symptoms traditionally drugs were extracted from plants and microorganisms there are three examples of this to learn the hard drug digitalis originates from foxgloves this plant is pretty common in the UK but it's poisonous if eaten directly the painkiller aspirin originates from willow trees which look like this and the antibiotic penicillin which he learned to buy in the previous video originates from the penicillin mold Alexander Fleming discovered this accidentally when he left some bacterial cultures open for a while he later found that those that had mold growing on them had clear rings around the mold where the bacteria had been killed he struggled to extract the penicillin from the mold but luckily two other scientists called Florey and chin followed up on his work and were able to extract the world's first antibiotic nowadays most new drugs are synthesized by chemists in the pharmaceutical industry however the starting point may still be a chemical extracted from a plant this is one reason why maintaining biodiversity is so important new medical drugs have to be tested and trialed before being used to check three things first is toxicity this means checking if it's poisonous or not secondly is efficacy which means it has the intended effect ie it treats the disease and thirdly is the dosage this is checking the amount of drug that needs to be taken to work best so I have a tip for you you can remember these three with the word Ted this is just the first letter of each of the words and you can make the link that Teddy's need to be tested to to make sure they're safe before they're sold to children see if it helps okay the first stage of testing is preclinical testing this is testing the drug in a laboratory using cells tissues sometimes whole organs and live animals cells and tissues are used first before testing on live animals there are a lot of strict rules before testing can be done on real animals if the drug passes the test for the preclinical trials then clinical trials may begin these use healthy volunteers and patients so first up very low doses are given to healthy volunteers to check if their see if or if there are any side effects if they are see if then they're tested on a small number of patients this is to see if it actually treats the disease and if it does then larger further trials are carried out to find the optimum dose for the drug clinical trials are double-blind trials this means that some patients are given a placebo while other patients are given the real drug the placebo and the real drug look identical and they're delivered in the same way ie both as pills or both as injections neither the doctor nor the patient know what they've been given this is what makes it a double-blind trial only the researcher knows and this is done to check if the drug really works or if any improvements in health are just due to the placebo effect the results of drugs testing and trials are only published after scrutiny by peer review this is when other scientists check the results to make sure they're robust untrue if they are they'll get published in a scientific journal and their national health bodies will look at the results and decide which drugs should be produced and offered on the NHS nine monoclonal antibodies in a previous video we covered her antibodies work these are proteins made by white blood cells that can attach to antigens antigens are proteins often find on the surfaces of cells today we're looking at how large amounts of antibodies can be made in the lab these are monoclonal antibodies in the first stage a mouse is stimulated so that it's white blood cells make antibodies for a particular antigen as you're studying biology only or triple you need to learn that these white blood cells are called lymphocytes these lymphocytes are then combined with a particular type of tumor cell this makes a new cell called a hybrid uma hybridoma cells have the properties of both cell types it can produce antibodies like a lymphocyte and it can divide rapidly like a tumor cell single hybridoma cells are then cloned to produce many identical cells these can all divide rapidly to produce the same antibody a large amount of the monoclonal antibodies can then be collected and purified for use the uses of monoclonal antibodies are all possible because the antibodies will only bind to one specific type of antigen which allows it to target specific cells in the body or chemicals like hormones you need to be able to describe some of the uses of monoclonal antibodies and you can also expect an application question with this topic to explain how the monoclonal antibodies work there are afford to learn the first is pregnancy tests a specific hormone is made during the early stages of pregnancy and if it's present monoclonal antibodies or ma B's will bind to it and cause a color change to indicate pregnancy like this they can also be bond to a fluorescent dye and they're then used in research to locate or identify specific molecules in a Cell or the whole cells themselves monoclonal antibodies can also be used to detect diseases this can be done by binding to the pathogens antigens like this they can also bind to other chemicals or hormones in the blood that are only produced in high levels if a person has a disease and finally they can be used to treat some diseases like cancer in this case a substance such as a toxic drug a radioactive substance or a chemical that stops the growth of the cells can all be attached to the monoclonal antibody when it then binds to the tumor cells antigens it delivers the substance to the cell monoclonal antibodies deliver substances to disease cells without damaging the body's healthy cells this is a huge advantage of monoclonal antibodies conventional drugs are carried all over the body and are much harder to target to specific cells or tissues resulting in damage to healthy cells targeting cells based on their antigens allows a much more specific response there is one big disadvantage to monoclonal antibodies because they were made using mice lymphocytes monoclonal antibodies have created more side effects than expected because of this they're not yet as widely used as hoped when they were first developed researchers are continuing to improve the production of monoclonal antibodies to try and reduce the side effects and doctors are also able to anticipate and treat side effects so it's hoped that they will be more widely used in the future 10 plant diseases earlier in the infection and response topic you learn to buy plant diseases including tmv and rose black spot viral bacterial and fungal pathogens can infect puns but there are other ways that plants can be damaged the first is by insects in particular a fits aphids are small green insects that have a sharp mouthpiece they insert this into the plant stem and penetrate the phloem vessel sucking the sap out of it this deprives the plant of the sugar it made during photosynthesis which damages the plant and reduces its growth aphids can also be vectors for disease this means they carry the pathogens to the plant gardeners can destroy if AIDS by using chemical pesticides or biological pesticides this is when predators like ladybirds are released into the area the plants are grown in here they eat the aphids removing the pests ion deficiency can also damage plants this is when the soil doesn't have enough of certain ions and there are two you need to know nitrate ions are needed for protein synthesis and therefore growth so nitrate ion deficiency causes stunted growth ie the plant is smaller magnesium ions are used to make chlorophyll when there isn't enough magnesium less chlorophyll is made and the leaves look peel or yellow colored there is reduced growth as a result this condition is called chlorosis knowing about the ions needed for plants to grow at their best alloys gardeners and horticulturists to provide the optimum conditions for plants by enriching the soil with all of the ions that they need this next part is for higher-tier only so if you're studying foundation just skip ahead to the questions okay you need to know how plant diseases can be detected pause the video and see how many you can spot in the picture below alright there are seven indicators of disease let's see how many you spotted here we've got discoloration presence of pets spots on leaves like rose black spot areas of decay or rot malformed leaves or stems and here we've got abnormal growths and finally stunted growth so there are seven to memorize once you've spotted an indicator of a disease the next step is to identify which disease is causing it this can be tricky as many plant diseases have overlapping symptoms there are three main ways to identify disease first is using a gardening manual or website you can compare the disease plant with descriptions and pictures of each disease secondly is taking infected plants or samples to laboratory to identify the pathogens using something like microscopy or DNA analysis this may be done for crop plants or forests when the disease affects many plants and finally we can use testing kits that contain monoclonal antibodies these will bind to antigens on certain pathogens if they are present you learn to buy this in the previous video once the disease has been identified appropriate action to treat or contain it can happen I'm finally 11-1 defenses plant defenses can be split into three groups physical chemical and mechanical let's start with physical defenses plants have a cellulose cell wall that makes harder for pathogens to enter the cells the leaves can have a tough waxy cuticle that acts as an additional barrier to pathogens trees have a thick bark and plants without this have layers of dead cells around the stem this is an extra layer of protection and it helps remove pathogens when the dead cells are shed or the bark falls off now let's look at chemical defenses many plants produce antimicrobial chemicals that can protect them against pathogens in the developing drugs video we saw that chemicals from plants form the basis of many traditional medicines based on this property some plants produce poisons for example foxgloves and nettles this deters herbivores from eating them herbivores include large animals like cars and smaller animals like insects if the animal feels unwell or ill after eating the plant then it's unlikely to eat the same type of Punt again now we'll look at mechanical defenses hairs like the ones you see on nettle leaves and thorns like the ones you see on rose plant stems to tear animals from eating the plant by hurting them additionally insects find it harder to lay eggs on plants if they've got hairs on the leaves mimicry is something that's used to trick animals the plant copies something to make it appear off pitting for example the passion flower vine has evolved to have small yellow spots on its leaves these look like butterfly eggs this deters butterflies from laying eggs on the leaves as it appears there will be more competition from other caterpillars when the eggs hatch the butterflies will lay their eggs on different plant leaves reducing damage to the passionflower vine and finally leaves that can drip or curl when touched can scare animals away and so cause insects to fall off or fly away from the plant our fourth and final topic is bioenergetics and we'll be kicking it off with number one photosynthesis photosynthesis is a fundamental process that has already come up in lots of earlier topics like cell biology it's how a plant's harness the sun's energy to make fit and this happens in the green parts of the plant like the leaves and the stem in the chloroplasts these little green bits here this is the word equation carbon dioxide plus water arrow and light can go along the arrow glucose plus oxygen we put light along the arrow because it's not a chemical but it is a condition needed for photosynthesis to happen if you're given a word fill it with just two spaces make sure you put in the chemicals and not light okay let's look at where each of the reactants comes from co2 comes from the air around the leaf and diffuses in through the stomata and water comes from the soil and is absorbed by osmosis you also need to know the chemical symbols for each of these substances carbon dioxide is just co2 water is h2o light we don't need to know because it's not a chemical glucose is c6h12o6 and oxygen is owed to so make sure you have a go at memorizing those now it isn't on the spec but if you want to practice some chemistry skills pause the video and try and balance this equation we just put a six in front of everything that isn't glucose now I because light from the environment needs to be taken into the chloroplasts for photosynthesis to occur we can describe it as an endothermic reaction that's an important phrase to learn its endothermic because n means in and light needs to be ticket into the chloroplasts and just a reminder that the chloroplasts contain chlorophyll the green pigment that's what's actually absorbing the light leaves are adopted to maximize the amount of photosynthesis that can take place pause the video and see how many adaptations you can spot in these two diagrams we'll start with their shape you can see that it gives them a large surface area to more light they are thin to allow gases to diffuse in a night easily and they have beans which contain the xylem to transport water and the flume to transport glucose it's important that glucose can move dying the plant as well to the roots as they can't make their own glucose they also have lots of guard cells on the underside of the leaf and these regulate gas exchange the spongy mesophyll has air spaces and again these are like gases to diffuse easily and finally the policy in Mesa filled tissue has many chloroplasts to maximize photosynthesis number two the rate of photosynthesis one factor that can affect the rate of photosynthesis is light intensity in the previous video we learned the photosynthesis is an endothermic reaction so light is needed to transfer energy to the chloroplasts for photosynthesis to occur it makes sense then that the higher the light intensity the faster the rate of photosynthesis this doesn't increase at a steady rate so the line is a curve because the rate increases as we increase the light intensity it means that light was limiting at the lower intensities so we call light a limiting factor at these points that's an important phrase to learn and all of the other factors we're going to look at are also limiting factors at a certain point the rate of photosynthesis plateaus which means it stops increasing no matter how much brighter it becomes the rate doesn't increase because light intensity isn't limiting it anymore another limiting factor has been reached this means that something else is preventing the rate of photosynthesis from increasing this could be any one of the three remaining factors that we're going to look at for example carbon dioxide concentration carbon dioxide is a reactant in photosynthesis so as we increase the concentration of it the rate of photosynthesis will also increase this can be shown on the graph like so at the low concentrations of carbon dioxide this is limiting so we say the co to concentration is a limiting factor at these concentrations beyond a certain concentration carbon dioxide stops being the limiting factor and instead it's a different factor that limits the rate of photosynthesis the third factor that can affect the rate of photosynthesis is temperature all chemical reactions are affected by temperature increasing the temperature increases the rate of photosynthesis until it reaches the optimum temperature after this point the enzymes that catalyze this reaction become denatured you can learn more about this in the factors affecting enzymes video the final limiting factor is the amount of chlorophyll in the leaves of the plant chlorophyll is the green pigment find in the chloroplasts that can absorb light for photosynthesis reduced chlorophyll means that less photosynthesis can take place and the rate is reduced this can happen in variegated leaves like this spider plant which have got white stripes and therefore reduced chlorophyll it can also happen when a plant is deficient in magnesium ions and this causes chlorosis graphs aren't normally used for this as chlorophyll isn't a variable that can be easily changed or measured externally but it would follow a similar shape to the light and carbon dioxide graphs this next bit is higher tier content only if you're studying foundation skip to the quick questions at the end so the first thing to note is that limiting factors can and do interact with each other it's important to be able to identify which factor is limiting the rate of photosynthesis for example if you were making a cake and had 100 eggs but only 200 grams of flyer then the flower is limiting the size of the cake and is our limiting factor it works the same way for photosynthesis if a plant receives a high light intensity but has a low concentration of carbon dioxide then overall the rate of photosynthesis will be low this is because a carbon dioxide centration has limited it we can show multiple limiting factors on the same graph like this in this graph we've got light intensity and carbon dioxide concentration temperature was controlled which means it was kept the same for example at 20 degrees Celsius so let's take a look at our graph at this part of the graph light intensity is the limiting factor because as it increases the rate of photosynthesis also increases let's take a look at the next part of the graph what do you think is the limiting factor here pause and see if you can work it out the answer is that carbon dioxide is the limiting factor here's how we know this the blue line is 0.04 percent carbon dioxide when the carbon dioxide concentration increases to 0.08 the rate of photosynthesis increases that means that the lower concentration of carbon dioxide was a limiting factor now let's look up here when it's 0.08 percent of carbon dioxide what's the limiting factor here pauls and have a think well the truth is we can't work it out unless we do another experiment let's say for example that we increase the carbon dioxide concentration again and this time we change it to 0.12 percent carbon dioxide you can see that the lines on the graph are pretty much the same that means the increase in the carbon dioxide concentration had no effect on the rate of photosynthesis so the limiting factor is not carbon dioxide concentration therefore it must either be temperature or chlorophyll you could do another experiment to find art which as I mentioned chlorophyll is hard to change externally so instead we'll change the temperature and here we are you can see that the early investigations were done at 20 degrees Celsius but our final investigation has been increased to 30 degrees Celsius we can compare this result but only to the investigation that had the same concentration of co2 otherwise we have two different independent very Abel's so we can actually see that when we compare these the rate of photosynthesis does increase when we increase the temperature therefore temperature was the limiting factor in the earlier investigation now I know these graphs may look hard but with practice I promise they'll become easier and just one thing to point out again is that you cannot compare results with two different independent variables so in this situation we were only able to compare the two highlighted results because they had the CM co2 concentration three making the most of photosynthesis we learned two by limiting factors in the previous video and hardly can affect the rate of photosynthesis farmers and gardeners can remove limiting factors to maximize the rate of photosynthesis this is often done in a greenhouse which looks like this pause the video and see if you can spot some ways in which this greenhouse increases the rate of photosynthesis well first of all green house is naturally trap heat from the Sun which increases the temperature and warm temperatures cause a higher rate of photosynthesis if it gets too hot green houses can be ventilated using open windows this lets wind in and cools the green house time in very cold conditions they can use heaters to provide warmth ensuring that the optimum temperature for photosynthesis is maintained gardeners can also provide higher co2 concentrations within greenhouses this is commonly done using paraffin heaters these release carbon dioxide as they burn and also provide Heat the higher co2 concentration increases the rate of photosynthesis photosynthesis doesn't happen without light so in natural conditions plants only photosynthesize during daylight artificial lights allow farmers and gardeners to extend the length of time that plants can photosynthesize by turning on lights after the Sun has gone down or when it is cloudy all of these methods of increasing the rate of photosynthesis cost money the car and farmers need to be sure that the profits from the extra yield of their crops exceeds the costs here's one example this graph shows the yield of tomatoes as the plants receive increasing ARS of artificial light just looking at this graph you would say the 10 hours of artificial light is the best because 10 ARS gives the highest yield in tomatoes but this doesn't take into account the costs we know that artificial lights use electricity and therefore cost the gardener or farmer money we would probably therefore change our answer and choose the point in the graph where the increase in yield really slows down this happens at about six hours of artificial light so this is actually going to be a better number of hours for the farmer because it will increase their profits now let's say we had access to the information in this graph this graph looks at the actual profit we can see that the profit Peaks at four hours of artificial light a different answer than what we came up with previously but when we look at the previous graph we can see the between three and four hours of artificial lights was the steepest increase in yield so it makes sense that this would give the most profit for the farmer data analysis questions are really common in this topic so make sure you practice interpreting graphs and tables I've got videos for this from exam style questions in my bioenergetics workbook will also focus on this skill for power plants use glucose plants make glucose in the process of photosynthesis while we often say this is food for the plant in reality this simple sugar has got many uses it can be tricky to remember them all so I use the meetup word false RAC this doesn't mean anything but somehow it sticks in my mind to help me remember the uses when I'm teaching it here's what each letter stands for F and O are fats and oils glucose is used to produce these for storage in the plant they are energy stores if the plant needs it S is for starch glucose can be converted into starch which is another storage material this can be converted back into glucose when the plant requires it for example at night when it isn't photosynthesizing r is for respiration and in this process glucose is broken down to release energy for the plant you'll learn more about this in the next video a and a are for amino acids glucose is used to make amino acids along with nitrate ions that plants get from the soil the amino acids are then used in protein synthesis which just means making proteins and finally C is for cellulose glucose is used to produce cellulose which is a molecule that strengthens the cell walls of plants which is this part here and that is pretty much it if you don't like the word fosroc or it doesn't stick in your head then try coming up with your own mnemonic this is a brilliant way to remember lots of linked content like this and if you're using my bioenergetics workbook i've provided an extra page for you to have a go and making up your mnemonic and an explanation of how to do this v respiration [Music] respiration is an exothermic reaction which means energy is transferred to the environment ie it is released this energy supplies all of the energy needed for living processes in organisms for example movement keeping warm and carrion are chemical reactions to build larger molecules note that the keeping warm aspect largely applies to mammals if we were asked about how a plant uses the energy transferred in respiration then this wouldn't apply instead we could mention hi active transport in the RIT's requires energy to bring mineral ions against a concentration gradient that's a good link across topics to supply enough energy for all of these processes respiration happens continuously in cells aerobic respiration can occur when there's adequate oxygen present and this happens in the mitochondria of the cell here's the word equation for it glucose plus oxygen arrow carbon dioxide plus water this equation for aerobic respiration is actually the reverse of the photosynthesis equation so this might help you remember it photosynthesis was also an endothermic reaction but respiration is exothermic that's another important difference okay you also need to know the symbols for each of these chemicals so pause the video and see how many you can remember ready glucose is c6h12o6 oxygen is o2 carbon dioxide is co2 and water is h2o now I will look at anaerobic respiration this occurs in the absence of oxygen and it can happen in our bodies when the muscles are working very hard for example when were sprinting less energy is transferred than in aerobic respiration because the oxidation of glucose is incomplete this means that the glucose isn't fully broken down so less energy is released here's the word equation for anaerobic respiration in the muscles of animals glucose is broken down to give us lactic acid and a small amount of energy is released anaerobic respiration implant and yeast cells produces different products so here's the word equation for it glucose brickstone to give carbon dioxide plus ethanol anaerobic respiration in yeast cells is called fermentation that's an important word to learn and this process has economic importance as it's used in the manufacture of alcoholic drinks for example beer this is possible because ethanol is released which is a type of alcohol it's also used to make bread as the co2 helps the bread rise and the ethanol just evaporates as the bread is bit six response to exercise exercise involves the contraction and relaxation of our muscles to move the body this increases the demand for energy which is transferred during respiration as we learned in the previous video more energy is transferred during aerobic respiration than anaerobic respiration so our bodies will try to respire aerobic Li for as long as possible to help with this three main changes occur firstly our heart rate increases this means more blood is pumped to the muscles each minute secondly our breathing rate increases this means we take more breaths per minute getting more air and therefore more oxygen into our body and finally our breathing volume increases this means we're breathing more deeply taking more air into our lungs resulting in more oxygen entering the bloodstream the overall result is that our muscles receive more oxygenated blood so the mitochondria can carry out more aerobic respiration long periods of vigorous activity calls muscles to become fatigued and stop contracting efficiently you've probably experienced this yourself when exercising your muscles get sore and tired one cause of this is lactic acid this is produced during anaerobic respiration due to insufficient oxygen and as we saw in the previous video the incomplete oxidation of glucose causes a buildup of lactic acid this also causes an oxygen depth the explanation of oxygen debt is higher to your content so if you're studying foundation feel free to skip ahead to the questions ok lactic acid is a waste product that the body needs to remove it isn't a gas so it can't just be pre thought like carbon dioxide instead blood flowing through the muscles will pick it up and transport it to the liver once there the lactic acid is converted back into glucose using oxygen the amount of extra oxygen needed to do this is called the oxygen debt that's an important phrase to learn this is the reason why we continue to breathe heavily on quickly after exercise the body still requires a higher amount of oxygen to repay the oxygen debt and convert the lactic acid back into glucose and their very last section is number seven metabolism I've briefly mentioned metabolism in my enzymes video if you've seen it pause the video and see if you can think of the definition for metabolism metabolism is the sum of all the reactions in a cell or organism you can remember this with this little graphic here these are reactions in which molecules are made or broken down there are quite a few examples for this across the specification and in this video we're linking them together there are six to learn the first is the digestion and synthesis of carbohydrates lipids and proteins can you remember what each one breaks down into you pause the video and see okay carbohydrates break down into sugars lipids break down into glycerol and fatty acids and proteins break down into amino acids an extra bit of detail to learn is that lipids are synthesized from one glycerol molecule and three fatty acid molecules synthesis is the opposite of digestion or breaking down so it's just going in the reverse and the small molecules build up the bigger molecules our next process is that glucose can be converted into starch or cellulose in plant cells in animal cells it can be converted into class ojen this is an energy store for later use glucose and nitrate ions are used to form amino acids these are then used to synthesize proteins as we saw previously proteins are just chains of amino acids excess proteins in the body are broken down to form urea for excretion this is turned into urine in the kidneys and it then leaves the body as urine or key next up is respiration this is a metabolic process in which the breakdown of glucose transfers energy to the cell and finally we've got photosynthesis this is also a metabolic process and occurs in plants and algae to produce food using light there are hundreds of thousands of metabolic processes but these are the examples you need to learn for the exams if you finished your revision notes or are using my study along workbooks then I suggest going through them and finding these examples then mark the pages with the little M for metabolism to remind you when you next revise it I hope you find that video useful and you're feeling prepared for your exams if you did find it helpful and please hit my icon over there to subscribe or the big red button down below thanks again for watching and good luck for your exams [Music]