hello and welcome today we're going to do a run through of the whole of the first topic for AQA gcsc biology we're starting with cell structure so in terms of cell structure we have our ukari and our ukar are animals and plants here is a cell from an animal and here is a cell from a plant we need to know the labels for each of these they both have a nucleus the job of the nucleus is to control the cell activities remember it also contains DNA which is for protein synthesis which we'll look at later the cytoplasm this is where chemical reactions take place the cell membrane we can see is on the outside of the animal cell and just inside the gray cell wall on the plant cell this controls what goes in and out of the cell we often call it partially permeable we then have these parts here that are very tiny so I've magnified further the top one here is the ribosomes these make proteins from amino acids called protein synthesis and these are mitochondria they release energy by respiration remember not to say produce energy do not say produce energy they release energy by respiration these are too small to be seen with a light microscope we need something called an electron microscope which we'll look at shortly plant cells only have a cell wall which is for strength and support and it's made of a substance called cellulose this is the sap vacu this contains something called cell sap a sugary solution and this is a chloroplast it contains a green substance called chlorophyll to absorb sunlight for photosynthesis all these parts are referred to as subcellular structures let's take a look at the procario these are usually bacterial cells they have no nucleus they have no mitochondria in fact they don't have any subcellular structures that have a membrane here is a diagram of a procaryotic cell lots of labels we know already the cytoplasm where the chemical reactions take place these are ribosomes which make proteins from amino acids this is the cell membrane which controls what goes into and out of the cell this is the cell wall this is for strength and support this is not made of cellulose not made of cellulose but its job is for strength and support it's called the cell wall this is what's called circular DNA this is the DNA of the procaryotic cell and this controls the cell activities makes proteins for the procaryote and this is what's called a plasmid a small ring of DNA that's separate from the main DNA contains a few genes we also need to know the relative sizes in other words the sizes in comparison to each other approximately 10 micrometers for our animal cell approximately 50 micrometers for our plant cell and about 5 micrometers for our procario this is just to give you an idea of of the size of each of these in comparison to each other and these are rough values for the sizes of these cells next we're going to take a look at cell differentiation and specialization cell differentiation let's start at the beginning here a sperm cell is fertilizing an egg cell here in Plants we have a pollen grain fertilizing an XL this results in a small ball of cells and these are undifferentiated cells these can then go by a process of cell differentiation to make specialized cells in animals a common set of specialized cells are nerve cells muscle cells and sperm cells and of course lots of others in Plants we have xylm flm root hair cells and of course lots of others in Plants as well in animals when these specialized cells divide is usually for repair and replacement of those cells these cells cannot differentiate into any other kind of cell once it's already differentiated into those specialized cells with plants many plant cells do keep the ability to differentiate into any other type of plant cell let's take a look at some specialized cells in humans this is a nerve cell this part of the cell is called the cell body contains the cytoplasm and all that stuff here we have dendrites these connect to other nerve cells this is the axon and the axon is down the center of that blue region there it's a long projection that carries impulses around the body along the nerve cell we then have an insulating sheath some insulation this has the job of speeding up the electrical impulse at the end we have axon terminals often synapses are joined onto that and we'll take a look at that in a later video then we have a sperm cell here's a diagram of a sperm cell we have a mid piece here this has lots of mitochondria which provide energy for the tail to move if we look in there we can see the mitochondria there this is the tail this is for swimming towards the egg at the top or the tip of the sperm cell we have something called an acrosome this contains enzymes for penetrating the egg cell membrane so the nucleus can get into the egg cell here's the nucleus contains 23 chromosomes in humans human sperm cells contain 23 chromosomes another cell we need to know about is the muscle cell here is a diagram of some muscle cells they have fibers that can shorten for muscle contraction to allow movement of the body they have lots of mitochondria that provide energy for the contraction and they contain a store of something called glycogen for stored energy we have some cells in plants that we need to know about xylm cells they have no end plates they are long tube shaped cells but they have no plates at the end of them this is so that water can can pass through the xylem tissue there is no cytoplasm xylem cells are dead but that helps to allow more water to flow through the xylem cells we also have these rings of a Woody material called lignin this helps to support the xylem cells and stops them from collapsing and remember xylm is dead tissue is non-living has no cytoplasm we have flum next remember both xylm and flum are made of elongated cells cells that are long tube shaped these Form Tubes for transport FL cells have very little cytoplasm they are not dead they do have cytoplasm but only very little cytoplasm this is to allow more solution to be able to pass through the flow cells they also have end plates but these end plates have tiny little holes called pores to allow dissolved substances through the dissolved substances in solution they also have these cells called companion cells these provide energy for the transport of the sugars in the solution passing through the flm we have root hair cells these are found on the surface of roots they have lots of mitochondria to provide energy for active transport there's our mitochondria and they have a large surface area for the maximum absorption of water and mineral ions so these are the types of cell that we need to know about next we're going to take a look at microscopy microscopes started off being very simple a few hundred years ago they were just very simple devices over time they developed into slightly more complex devices like the light microscope that you might see in school and after a further amount of time we've developed even better microscopes for example electron microscopes the differences are however that the simple microscope would have low magnification and the electron microscope actually has very high magnification the simple microscope has a low resolving power whereas the electron microscope has a high resolving power what's the consequence of that well electron microscopes with their higher magnification and higher resolving power provide images with higher resolution and higher magnification this has enabled biologists to see and understand many more subcellular structures for example mitochondria and ribosomes next let's take a look at the scale and size of subcellular structures we deal with sizes in millimet in micrometers and in nanometers millimeters are 1,000th of a meter micrometers are 1,000 of a millimeter and nanometers are 1,000th of a micrometer if we want to convert millimeters into micrometers we Times by a th000 if we want to convert micrometers into Nan nanometers we Times by a th000 if we want to go the other way convert nanometers into micrometers we divide by a th000 and going from micrometers into millimeters again we divide by a th000 that's how we should do our conversions which are very useful for many types of questions to do with microscopes magnification calculations magnification is equal to the size of an image the size of a picture divided by the real size of the real object some people like to use a formula triangle and a formula triangle triangle might look like this don't forget when we're doing the size of the image and the size of the real object we have to convert the units so they are the same and our size and scale in the bottom left will help us do that here's an example here's a root hair cell the projection is 5 mm on the image says calculate the magnification of the root hair the real root hair ha is 20 micromet so firstly let's convert 5 mm into micromet So based on what we have learned in the bottom left there we times 5 by 1,000 that gives us 5,000 micromet and then we divide by the 20 micrometers given in the question that gives us an answer of 250 so the magnification is times 250 don't forget to put a little time sign there example number two here is the sperm cell the magnification is given as time 2000 it says calculate the real length of the sperm cell the image size is 10 mm and it asks you to give your answer in micrometers the size of the real object is equal to 10 / 2,000 if we use our formula triangle this gives us an answer of 0.005 mm we want the answer in micrometers so to convert that we times that by 1,000 so we get 5 micromet two examples of where we might use the magnification formula next is mitosis and the cell cycle cells can divide and one of the reasons they divide is to repair any damaged tissue in the body it's also for growth so it's also for the growth and development of of an organism cells go through a cell cycle there are three stages stage one stage two which is mitosis and stage three we know we need to know the details of those stages here is a parent cell I've just drawn an enlarged nucleus with chromosomes of DNA inside and this is part of stage one we need to know remember that in stage one the cell grows and increases the number of sub cellular structures for example ribosomes and mitochondria the DNA also repli replicates to form two copies of each chromosome in the cell this is stage two this is what we call mitosis the key things to remember about this are that the chromosomes line up along the center and then are pulled to each end of the cell and the nucleus divides this is stage three this is where the cytoplasm and cell membranes divide to form two genetically identical cells those cells are genetically identical to each other and genetically identical to the parent cell I've seen this as a formark question in an exam in the past and the marks would be for saying those four points there the cell cycle let's now take a look at stem cells we'll start with embryonic stem cells again here's a sperm cell fertilizing an egg cell this is the fertilized egg this will then grow into a small group of cells and these are stem cells they are undifferentiated in other words they are not yet specialized they can be cloned and these clones of cells can actually be used in medical research these are called embryonic stem cells these can differentiate into most other cell types these specialized cells and tissues can be used potentially for medical treatment for example paralysis or diabetes we can also find stem cells in adults a common example is in bone marrow so here is a bone inside the bone there is some tissue called bone marrow these are stem cells from the bone marrow these can differentiate as well and they can differentiate into many cell types mainly blood cells these are two white blood cells we have stem cells in plants and they are found somewhere called meristem tissue this is in the root and Chute tips and one or two other areas of the plant these can differentiate into any plant cell throughout the plant's lifetime there are some examples there that we've already looked at but also stem cells from Mery stems can also be used to clone whole plants quickly and economically this is so that rare species can be cloned to protect them from Extinction or plants with special features can be produced in large numbers for example nice or attractive flowers we can produce those in large numbers using stem cells from Mery stems now we go back to humans something called therapeutic cloning this is when we have a patient body cell removed often a skin cell we have a human egg cell and what we do is we remove the nucleus from the patient body cell there's the nucleus with all the DNA inside it and we discard the rest of the cell we remove the nucleus from the human egg cell and we discard that nucleus and what we do is we place the patient body cell into the empty human egg cell this is the patient nucleus inserted into the egg cell this can be cloned and it produces stem cells these can be made to differentiate through differentiation to make specialized cells and tissues for medical treatment the big advantage of doing it this way is that the tissues that are made for treatment are not rejected by the patient there is a negative you can potentially transfer viral infections and some people have moral or religious objections to this kind of procedure these are the key things we need to know about stem cells adult stem cells stem cells in plants and something called therapeutic cloning next is diffusion and active transport we'll start with diffusion some substances move into and out of cells by diffusion this is a very important definition diffusion is the spreading out of the particles in a solution or in a gas giving a net movement from an area of higher concentration to an area of lower concentration this is sometimes asked in exams key things about this are the spreading of the particles with a net movement from an area of higher concentration to an area of lower concentration here is an example we have net movement from the left to the right on the left the particles in a higher concentration on the right they're in a lower concentration we end up with equilibrium there is no more net movement of particles examples of diffusion in living things here we have some cells in a body only two drawn there this is a blood supply through some capillaries and these are particles of oxygen these will diffuse from an area of high concentration in the blood to an area of lower concentration in the cells that's oxygen diffusing into the cells from blood the cells produce carbon dioxide in respiration we can see there's a higher concentration of carbon dioxide particles in the cell so they will diffuse out into the blood that's another example of diffusion in living things a waste product called Ura is made in cells and this also diffuses out of cells factors that affect the rate of diffusion one is the concentration difference between the particles in other words the concentration gradient also known as a diffusion gradient so on the example here we've got on the left hand side a much bigger difference in the concentrations of the particles between the inside and the outside of the cell so we're going to get a higher rate of diffusion on the left and a lower rate of diffusion on the right because there is a smaller diffusion gradient a bigger difference in concentration gives a faster rate of diffusion second factor is temperature the higher the temperature the faster the rate of diffusion that's because particles have more kinetic energy at higher temperatures so there is more rapid diffusion the surface area of a membrane if something is diffusing into or out of a cell this cell here will have a lower rate of diffusion compared to this one which has a much higher surface area so therefore a higher rate of diffusion the bigger the surface area the faster the rate of diffusion we know we need to know these three factors and why they affect the rate of diffusion next we're going to take a look at active transport this is the movement of particles from an area of lower concentration to an area of higher concentration this requires energy from respiration unlike diffusion diffusion requires no energy whereas active transport does require energy one example is sugar absorption in the small intestine here is the small intestine magnified slightly there is a lower concentration of sugars in the digested food as it gets absorbed into the blood there's going to be a higher concentration of sugars in the blood so sugars are actively transported into the blood so that they are absorbed and and can be transported around the body another example is in Plants this is root hair cells here is our root hair cell earlier we talked about the presence of mitochondria for energy for active transport well here we have a lower concentration of mineral ions in the soil we have a higher concentration of mineral ions inside the root hair cell so the mineral ions are actively transported into the root hair cell again using energy from respiration released by the mitochondria next it's diffusion and adaptations for the exchange of substances the first thing we need to know about is this idea of surface area to volume ratio single celled organisms have a high surface area to volume ratio this allows sufficient transport of molecules into and out of the cell to meet the needs of the organism we need to know how to calculate surface area to volume ratio we often do it with simple shapes like cubes here is Cube number one 2 mm in length all sides are 2 mm because it's a cube to work out surface area it's the surface area of one side * 6 sides so it's 2 * 2 * 6 an answer of 24 mm the volume is length * width * height this is 2 * 2 * 2 this gives us an answer of 8 the ratio is 24 to8 but in biology we take it one step further we divide 24 by 8 to give us a single number of three here is a second Cube this is a larger Cube this is 4 mm the surface area is 4 * 4 * 6 which is 96 mm s the volume is 4 * 4 * 4 this is 64 mm cubed the surface area to volume ratio is 96 to 64 we can make that into a single number by dividing 96 by 64 gives us 1.5 therefore the larger the organism the smaller the surface area to volume ratio you could do some more calculations with with bigger cubes to see that this actually is the case this means larger organisms cannot transport sufficient molecules into their bodies across their surface area because they have a small surface area to volume ratio we need an exchange and transport system here are the adaptations for exchange systems in larger organisms one example is a small intestine we have a small intestine there a cross-section we can magnify that area there and we can see two structures that look like this these are called Villi one by itself is called a villis more than one is called or are called Villi there are many blood vessels inside the Villi and if we look at the surface of of the Villi we can see there are even smaller structures these are called microvilli Villi and micro increased surface area for more absorption of food molecules Villi and microvilli have very thin walls to provide a short diffusion distance microvilli have many mitochondria to provide energy for active transport which we looked at a moment ago they also have a good blood supply to maintain a high concentration gradient in other words the blood constantly takes away the digested food molecules keeping the concentration in the blood very low to maintain a high concentration gradient next we look at the lungs here are some lungs at the ends of the tubes in the lungs we have something called alvioli one by itself is called an Alvis there's a diagram of alveolus and here is a simple version of an alvus they are covered by many capillaries there are many Alvi to provide a large surface area for gas exchange there's a good blood supply to maintain a high concentration gradient of oxygen and carbon dioxide the Alvi walls are very thin or you could say they're only one cell thick to provide a short diffusion distance and the lungs in this case are ventilated in other words fresh air is brought in bringing in oxygen to maintain a concentration gradient there will always be a high concentration of oxygen in the lungs because they are ventilated next we have leaves key thing about leaves is that they have cells in the structures as shown below we're going to look at this in more detail in a later video there are stamata at the bottom side of leaves the leaves are flat and wide to provide a large surface area leaves are thin to provide a short diffusion pathway for gases there are air spaces between the cells to increase rate of diffusion and there are stamato that can open and close to increase or decrease gas exchange the last one we want to look at is gills found in fish so here is our fish here are some structures in the gills these are gill filaments if we enlarge one of those filaments it might look a little something like this there's our Gill filament there are many Gill filaments to provide a large surface area for gas exchange there's a good blood supply to maintain a concentration gradient of oxygen and carbon dioxide there are capillary walls which are very thin or only one cell thick to provide a short diffusion distance and we have fresh water flowing over the filaments all the time to maintain a high concentration of oxygen in the water next we have osmosis this is the final part to look at osmosis is the diffusion of water from a dilute solution to a concentrated solution through a par partially permeable membrane this is the definition which often gives you two or three marks if you're asked for it let's take an example of a cell that is in a solution there is my cell there in the green but what I'm going to do is remove the cell and just simplify the whole diagram I've got a dilute Solution on the outside of the cell that has a high water concentration so we say it's dilute here's our partially permeable membrane and we have a concentrated solution inside the cell in other words a low water concentration water only water will move into the cell this is what the cell will look like water moves into the plant cell the plant cell becomes turgid there is a example of a turgid plant cell turgid cells help support a plant and helps keep it upright there's our turgid cell underneath worth noting here that plant cells don't burst because they have a cell wall that prevents them from bursting if it was an animal cell movement of water inside could cause it to burst there is no cell wall in animal cells let's take another look example of where osmosis happens this is in root hair cells a very common feature of this unit we've got a dilute solution in the soil outside the cell and we have a more concentrated solution inside the cell that means water moves into the root hair cells from the soil by osmosis let's take a look at the investigation of the effect of a range of solutions of salt or sugar Solutions on the mass of plant tissue we very commonly use potato we use something called a cork Bor to get samples of our tissue that cork Bor will produce equal sizes or equal cylinder shapes we just need to cut them to the right length so they have an equal shape and as equal as possible Mass we use a paper tow in this experiment and we use some scales what we do step one we add about 30 cm cubed of a 0.8 moles per decim Cub solution to a boiling tube that's an example of a concentration you might use we repeat this step with equal volumes of 0.6 0.4 and 0.2 mes per decim Cub this sugar solution we then use water to give a concentration of 0 moles per decim cubed we cut out our five ERS of potato of equal size using a cork borer and we dry them remember it doesn't have to be potato it can be other plant tissue for example carrot we dry them so that the water on the surface doesn't affect the mass of the potato before we take the mass we then take the mass of each potato cylinder and place one in each tube we remove the potato cylinders from the solution after 24 hours if possible or at least after a few hours we dry each potato cylinder so that the solution on the surface doesn't affect the mass of the potato and we do that with a paper towel and then we reway the potato cylinders we have control variables in other words variables that we try and keep the same that's the temperature the type of potato so we don't switch potatoes or switch plant tissue and the age of the potato here are a set of results we've got the concentrations of the solutions we've got the mass before the mass after the change in mass and quite importantly the percent change in mass the percent change in mass is there to take into account the fact that we have slightly different size masses of potatoes at the start of the experiment we can then plot these results on a graph here are our axes we will plot the concentration of su Sugar solution versus the percent change in mass so we can put our labels on our graph percent change in mass goes on the y-axis concentration on the x-axis we can put in our numbers remember we've got some negative numbers there with the potato has lost Mass here are here are our concentrations we can plot these points on our graph very carefully and then we can draw a line of best fit this one follows a curve of best fit you will be in this case able ble to draw a straight line or a curve cuz it could be either for this example but there's our line the point where the line crosses the x-axis is where the potato neither lost nor gained Mass there was no net movement of water so the concentration inside and outside the potato tissue must be equal and that point there is 0.24 moles per decim cubed why does the potato lose Mass this is very commonly asked in exam questions the solution outside the potato is more concentrated than inside that's one marking Point therefore the water moves out of the potato that's the second marking point and mentioning osmosis is the third marking Point why does the potato gain Mass that's because the solution inside the potato is more concentrated than outside the potato water moves in by osmosis so that's it the whole of unit one for AQA gcsc biology if you found this useful be awesome if you could give a like and or a subscribe but other than that that's us done for today thank you for watching and I'll see you real soon