okay OCR GCSE people let's see how fast we can cover everything you need to know for biology paper one or three or five or seven it's awfully confusing basically just the first paper you do for biology this video is good if you do higher and Foundation Tier double combined or triple or separate biology that's topics one to three cell level systems scaling up and organism level systems I'll tell you when something is just for triple but not for higher tier because there's not a huge difference to be honest we're going to be really moving here so pause the video if you need a bit more time to get your head around something you see on the screen let's go all life consists of cells we can see cells with a normal light microscope and maybe the nucleus but the subcellular structures won't really be visible using an electron microscope however allows us to see far finer details so we can see an image of the organel as such these microscopes have a better resolving power and a higher resolution we say we can calculate the actual size of a cell by knowing the magnification of the microscope magnification is equal to image size divided by object size therefore rearranging this we can measure the size of the image then divide by the magnification and that gives us the actual cell size eukaryotic cells have a nucleus in which their DNA is found that's your plant and animal cells for example procaryotic cells don't have a nucleus both eukaryotic and procaryotic cells contain similar organel or subcellular structures the cell membrane keeps everything inside the cell but they're also semi-permeable which means they allow certain substances to pass through plant cells and most bacteria have an extra cell wall made of cellulose providing a rigid structure for them cytoplasm is the liquid that makes up the cell in which most chemical reactions take place mitochondria is where respiration takes place releasing energy for the cell to function ribosomes are where proteins are assembled or synthesized plant cells also contain chloroplasts which contain chlorophyll with photosynthesis takes place plant cells also contain a permanent vacu in which sap is stored just for triple bacteria multiply by binary fision so the number doubles every say 10 minutes so if we started with one bacterium after an hour we'd have 2 to the power of 6 that's 64 after 6 hours that's 36 lots of 10 minutes so in theory we'd have 2 to the power of 36 that's in standard form 6.87 * 10 10 we can do a practical on this by producing a culture on agar in a Petra dish using aseptic technique that is making sure nothing else contaminates the culture we lift the lid of the dish towards a flame which causes other microbes in the air to move away and upwards from the dish and it destroys them too using sterilized equipment we can either put a drop of bacteria culture in the middle or spread it all around and put spots of different antibiotics on top instead we put a few bits of tape around the dish to hold the lid on but not all the way around otherwise air will not get in and the bacteria will respire anerobic we then incubate it at 25° once the culture has grown we can either calculate the size of the culture from an initial drop or the area in which bacteria did did not grow or were killed by an antibiotic to then compare with others in both cases we use PK r^ s or Pi D ^2 over 4 to calculate the area of the circles genome is the term given to all the genetic material in an organism this code is stored in DNA of course which is a two stranded polymer in a double helix shape a gene is a section of DNA that codes for a specific protein the Human Genome Project completed its initial goal in 2003 when scientists mapped out what every Gene is respons ible for coding this is powerful because it can help us identify what genes cause diseases or inherited disorders genotype is the term given to what code is stored in your DNA specifically well phenotype is how that code is expressed in your characteristics what proteins are made it affects your physiology for triple you need to know that the monomers between the two strands are called nucleotides and they're made from a sugar and phosphate group of which there are four types A T C and G you don't need to know what the names are but a and t always match to each other in the sequence as do C and G every three of these bases we can call them are a code for an amino acid the sequence is copied by mRNA this copy is then taken out of the nucleus to a ribosome in the cell where amino acids are connected in the order needed which makes a protein the shape of which affects His function they need to be folded as well first harmful mutations can change a gene so much that it results in a protein being synthesized that doesn't do the job it's supposed to we now know that some DNA however doesn't directly code for proteins but it influences how other genes are expressed this is the realm of epigenetics and it's changing the way that we view DNA quite drastically enzymes are biological catalysts some of which break down larger molecules into smaller ones that can then be absorbed by the Villi in your small intestine into the bloodstream to be transported to every part of your body for example amalay is the enzyme that breaks down starch into glucose is found in your small intestine and saliva enzymes are specific that is they only break down certain molecules for example carbohydrases break down carbohydrates into simple sugars amalay is one of these proteases break down proteins into amino acids and lipases break down lipids that's fats into glycerol and fatty acids they're specific because they work on a lock and key principle the substrate for example the starch binds to the enzyme's active sight we then call this a comp comp Lex however this can only happen if the substrate is the right shape in order to fit the active site in reality they're incredibly complex shapes no pun intended these shapes here are just to represent them much like a lock and key it only works if they're the right shape for each other the rate of enzyme activity increases with temperature due to the molecules having more energy that is until the active site changes shape and so the substrate no longer binds we say the enzyme has denatured this maximum rate occurs at the optimum temperature Optimum meaning best this is similar for pH as well except it can denat a too high or too low PH the Practical on this involves mixing amales with starch at different temperatures or with different pH buffer Solutions once mixed we start timing then every 10 seconds we remove a couple of drops and put in a spot in tile dimple with iodine in to begin with the iodine will turn black due to the still being starch present but eventually it will stay orange showing that all of the starch has been broken down calculate the time taken to do that then plot these times against pH temperature draw a curved line of best fit and the lowest point is where the starch would have taken the shortest time to be broken down that's the optimum temperature or pH however in true biology fashion we're technically not allowed to interpolate between points for some reason so we must only say that the optimum pH or temperature is between the two lowest points shrug every cell bar red blood cells has mitochondria which is where respiration takes place to provide energy for every organism for other chemical reactions to take place for movement and warmth they do this by making a molecule called ATP which transports energy to different organel that need it to carry out their various functions aerobic respiration means with oxygen here's the word and balanced chemical equation as respiration results in net energy being released this is an exothermic reaction during exercise your breathing rate and heart rate increase to increase the rate of oxygen delivered to cells for respiration anerobic respiration occurs when there's a lack of oxygen glucose is instead converted straight St into lactic acid which releases less energy this is what you feel when your muscles ache during intense exercise this poison can't stay in your body so there is an oxygen debt built up that means more oxygen is needed afterward to break it down in the liver where is turned back into glucose hence while your breathing rate and heart rate take some time to return to normal after exercise plant and yeast cells respire anerobic but slightly different instead glucose is turned into ethanol and carbon dioxide that's why yeast is added when baking the CO2 bubbles made cause the bread or the K to rise this can also be called fermentation it's also used to make alcoholic drinks as ethanol is produced grouping all of these together Metabolism is defined as the sum of all reactions in a cell or organism these can include respiration conversion of glucose into starch glycogen and cellulose glucose can also be built into cellulose which is used to make cell walls glucose and nitrates are used to make amino acids for protein synthesis fatty acids and glycerol are built up into lipids and also the breakdown of excess proteins this is turned into Ura more about that in paper to photosynthesis happens in chlorophyll and chlorop plus in plant cells to provide food for the plant here's the word and balanced chemical equation for it and as energy is needed in the form of light to make this reaction happen this is an endothermic reaction the glucose made from photosynthesis is used for respiration or it's turned into starch or fat as a store of energy cellulose is used to produce cell walls and amino acids are used for synthesizing proteins the rate of photosynthesis is increased with higher temperature unless it's so high that enzyme denaturing occurs increasing light intensity or increasing CO2 concentration any one of these can be a limiting factor by the way for example even if there's lots of CO2 and it's warm if there's not enough light the rate will be limited by this in other words it doesn't matter how much you increase the other two it won't get any faster a graph might look like this before the graph plateau levels out the variable on the x-axis has to be the limiting factor after it isn't it must be one of the other two instead if you have two lines for example different temperatures then temperature must be a limiting factor here's the Practical on this we can measure the rate of photosynthesis by submerging pondweed in an inverted measuring cylinder we measure the volume of oxygen made over time we can instead count the bubbles but it's less accurate the independent variable could be the light intensity and that's changed by varying the distance from the light source for example a lamp however light intensity follows an inverse Square relationship in other words if you double the distance the light intensity quarters three times further 1 nth of the intensity next scaling up all about cells working together diffusion is the movement of molecules or particles from an area of high concentration to an area of low concentration we say they move down the concentration gradient like a ball just rolling down a hill it'll do it by itself this doesn't require any energy input so we say it's passive this will will happen across a semi-permeable membrane if the holes are large enough for the molecules to move through for example water can pass through but glucose will not at least not by diffusion anyway osmosis is the name specifically given to the diffusion of water across such a membrane for example if there is a higher concentration of glucose outside a cell the glucose cannot diffuse in to balance the concentration so instead the water moves out of the cell resulting in a decrease in its mass the rate of diffusion on osmosis can be increased by increasing the the difference in concentrations increasing the temperature or increasing the surface area this is why the Villi and your small intestinal lumpy as well as alveoli in your lungs and R hair cells for example too the Practical on osmosis goes as follows cut equal size cylinders from a potato or other vegetable weigh them and place in test tubes with varying concentration of sugar solution after a day or so we remove them dab the excess water off their surface and reway we calculate percentage change in mass by doing final Mass takeway initial mass divided by the initial mass time 100 if it's lighter than it was before this must be a negative change in mass we plot these percentages against sugar concentration and we draw a line of best fit where this crosses the x-axis is what concentration should result in no change in mass so no osmosis so this means this must be the same as the concentration inside the potato glucose and other nutrients and minerals can move through a membrane bya active transport where carrier proteins use energ energy to move substances through the membrane as there's energy used this can actually move them against a concentration gradient for example moving mineral ions into plant root hair cells eukaryotic cell nuclei contain DNA which is stored in several chromosomes humans have 23 pairs of these in every nucleus so we call them diploid cells that's not the case for gtes though they have half so just 23 not 23 pairs so therefore we call them haid cells new cells must constantly be made for growth and repair they do this by duplic by mitosis here's the process the mitosis process the genetic material is duplicated and the number of ribosomes in mitochondria is doubled as well the nucleus breaks down and one set of each chromosome pair is pulled to opposite sides of the cell a new nucleus forms in each of these to house the copied chromosomes and we now have two identical cells cells specialize depending on the function they need to fulfill for example nerve muscle root hair xylm flam cells stem cells are those that haven't yet specialized they're found in human and animal embryos and the merry stem of plants that's the top of the Chute stem cells are made in your bone marrow throughout your life as well but these ones can only specialize into blood cells we can use them cells to combat conditions like diabetes and paralysis in fact right out of the movie the island people are now getting clones of themselves made then harvesting the stem cells as these won't be rejected by the patient personally I think this is a dystopian man-made horror Beyond Comprehension you have to weigh up the ethical Arguments for yourself cloning plants can be used to prevent bur species from becoming extinct or produce crops with specific characteristics the heart is at the center of the circulatory or circulatory system the transport system of your body we call it a double circulatory system blood enters the heart twice every time it's pumped around the body deoxygenated blood from the body enters in the right side of your heart by the way you always look at the heart as if it's yours and it enters through the venina Cava the main vein into the right atrium of the heart the valve between the right atrium and the right ventricle stops back just like all valves to stop deoxygenated blood from going back into the body the heart muscles contract and it goes through the pulmonary artery to the lungs to be oxygenated it then comes back to the heart through the pulmonary vein into the left atrium then it goes into the left ventricle then out to the body through the aorta the left side of the heart has thicker walls as the left ventricle has to pump blood to the whole body while the right ventricle only pumps to the lungs a group of cells create electrical pulses that cause the heart muscles to contract the heart to beat if these aren't working properly you can be given an artificial pacemaker to do the same job blood vessels that go away from the heart are always arteries veins towards that means the arteries carry oxygenated blood apart from the pulmonary artery and vice versa for veins arteries have thicker walls to withstand the higher pressure so they have a thinner Lumen that's the hole in the middle veins have thinner walls due to the lower blood pressure but have valves to stop back flow like we said arteries split and get smaller and smaller until they end up as Tiny capillaries with one cell thick walls to allow the faster Fusion of molecules in and out of cells the heart is a muscle so it needs its own supply of oxygen and therefore blood to keep the muscle pumping this is delivered by the coronary artery if these are blocked by the buildup of fatty deposits a heart attack can occur this is CHD coronary heart disease Sten are little tubes that are inserted into blood vessels to keep them open so blood can flow in this case statins are drugs that reduce cholesterol which in turn reduces the fatty deposits faulty heart valves result in back flow occurring these can be replaced with artificial ones along with plasma and red blood cells Blood also carries white blood cells which combat infections more on this later and platelets which Clump together to clot wounds and stop bleeding plants also have organs leaves are where photosynthesis takes place producing food for the plant water also leaves the plant through them allowing transpiration to take place the diffusing of water into roots and up the zym roots are where water and mineral irons enter the plant the merry stem is where new cells are made like we saw earlier xym are the long continuous tubes which water rises up we say it's unidirectional only goes in One Direction that's transporation like we said while flm are the conveyor belts of cells that transport sugars food and sap up and down the Plant we call this translocation that's bidirectional the rate of transporation can be increased by the following increasing the temperature decreasing the humidity and increasing the air movement all of these was result in water evaporating from the leaves at a faster rate just for triple real quick the lack of nitrate ions means the plant can't synthesize proteins effectively and that stunts growth chlorosis is the scientific term for the yellowing of leaves this can be due to magnesium deficiency as it's needed to make chlorophyll the cross-section of a leaf looks like this every layer has its own specific function at the top we have the waterproof waxy cuticle not to stop water from entering the leaf but to stop it from evaporating from the top and causing the leaf to dry out the upper epidermis epidermis just means outer layer consists of transparent cells that allow light to pass through to the palisade mesophyll layer mesophyll just means a layer in the middle these are chock full of chloroplasts so this is where the majority of photosynthesis takes place under that is the spongy mesophyll layer that has lots of gaps around the cells to increase the surface area through which gas exchange can occur carbon dioxide diffuses into the cells while oxygen and water diffuse out we also have the vascular bundle that includes the xylm and flm the lower epidermis is the bottommost layer of the leaf and it has holes in it called stamata which is how gases enter and exit the leaf the size of a sto is controlled by the guard cells that flank the hole they change size to control the rate at which gases enter and leave for example they close the stomat at night to reduce the rate of water loss as less water is needed for photosynthesis finally organism level systems homeostasis is the term given to an organism's ability to regulate internal conditions even when when external conditions changed this is important so that crucial chemical reactions involving enzymes can happen at an Optimum rate amongst other things our bodies work hard to regulate blood glucose concentration temperature and water levels for example one way that our body achieves this is with our nervous system it consists of the CNS that's central nervous system that's the brain and spinal cord and the pns peripheral nervous system the nerves that go through the rest of the body a receptor for example skin detects a change due to a stimul like a hot hob an electrical signal travels to the spine through sensory and relay neurons nerve cells the signal travels across the gap between these neurons called the syapse by a neurotransmitter chemical once at the spine the signal can go to the brain where you can make the conscious decision to act the signal then goes back to an affector like the muscle in your arm via relay and motor neurons so that you move your arm a reflex is when the signal bypasses the brain and goes straight through the spine to the effector this is a reflex arc this of course is much faster than a conscious decision glands can also be effectors which produce specific chemicals your body needs depending on the situation for example your salivary glands in your mouth making saliva when you eat food you can investigate into reaction Times by holding the bottom of a ruler between a person's finger and thumb and drop it without warning then you measure the distance it falls before they catch it do this multiple times and taking mean average not too many times though as their nervous systems will start to get a bit better at reac re acting to this you can introduce an independent variable like a stimulant for example coffee or a sugary drink or a depressant which will have the opposite effect although I can't think of any ones that are legal for you at the minute to see how they decrease or increase Reaction Time respectively you could calculate the reaction time from the distance using suat S = half a^2 but you'll never be expected to do that in this paper but it's something you could mention if you were ask a six marker on this quite a bit that's just for triple biology now that's the brain eye and Thermo regulation skip to hormones if you're doing combined Trilogy that is double science there are three parts of the brain you need to know the cerebral cortex is responsible for higher level functions like memory speech and problem solving the cerebellum is responsible for your motor skills movement balance and coordination the medulla onbl controls unconscious actions your body takes you don't think about them like your heart and breathing rates it's also what controls the release of adrenaline MRI scans magnetic resonance imaging are a way of seeing the activity in your brain safely if something goes wrong with your brain though it can be very difficult or impossible to treat without damaging important parts of it your eyes are the most mind-bogglingly designed cameras ever conceived of accommodation is the ey's ability to change the shape of the lens in order to focus light that comes from objects that are different distances away on the retina to focus light that comes from objects that are far away the ciliary muscles relax and the suspensory ligaments tighten they're both connected to the lens this results in the lens becoming thin and that that means that light is only refracted a little bit and that focuses the light on the retina to focus on near objects the opposite is true the silary muscles contract the suspensory ligaments slacken and the lens becomes fatter or thicker and so that means that it becomes more powerful actually so light is refracted more which means that the light coming from the object still converges meets focuses on the retina so you can see a clear image the pupil the hole in the iris can change size depending on the light intensity hitting the eye the cornea is the transparent outer layer where light enters the eye it has a slight lensing effect itself while the White surface that covers the rest is called the Scara the light is focused then on the retina at the back of the eye which consists of Rod and Cone cells which respond to light rods can only detect light intensity so no color while there are three different types of cones which detect green blue or red wavelengths of light a mix of which will produce the colors we then perceive when the signal reaches our brain via the optic nerve myopia is the medical term for shortsightedness you can't focus on Far objects hyperopia is long-sightedness glasses or contact lenses are usually used to mitigate this by slightly converging or diverging the light before it enters the eye laser eye surgery aims to change the shape of the cornea to achieve the same effect Thermo regulation is your body controlling its internal temperature by the brain sensing blood temperature then sending nervous and hormonal signals to various effectors around your body in order that your body loses heat to its Sur surroundings more slowly or quickly for example if you're too hot sweat glands in your skin cause water to cover the surface this evaporates taking heat away from your body quickly blood vessels also dilate widen we call this vasod dilation to increase blood flow to the skin to increase the rate of heat loss too cold we have Vaso constriction instead hence why you go pale you also shiver which causes your muscles to produce more heat okay back to double science goodness which is for everyone the endocrine system is a system of glands that produce use or secrete hormones that travel to affectors Via the blood this is of course slower than any signal carried by the nervous system the pituitary gland in your brain can be considered the main or Master gland as it produces hormones in response to stimuli that travel to other glands in your body in order that they start then producing certain chemicals the examples are the pancreas which produces insulin we'll talk more about that in a bit the thyroid controls all sorts of things like growth heart muscle and digestive function and more the adrenal glands produce adrenaline and the ovaries in testies release eggs or produce sperm depending on which you have speaking of the pancreas then it's involved in making sure that your blood glucose levels aren't too high or too low too high and the pancreas secretes insulin which causes glucose to move from the blood into your cells to be used for respiration any excess glucose can be converted into glycogen to store energy and that's done by the liver too low on the other hand and the pancreas produces another hormone called glucagon which causes the liver and muscles to turn glycogen back into glucose ready to be used type 1 diabetes is what you have when your pancreas can't produce enough insulin and you have to take insulin injections to do the job instead type two is when your cells no longer absorb the glucose as they should so you have to be careful with your diet and if you're overweight or obese you have a much higher risk of developing this water and nitrogen balance are triple only so skip to the next topic reproduction if you're just double your body loses water when you exhale sweat or urinate if your body has too much water let's say for example you drink too much your kidneys remove it from your blood at a faster rate where it's mixed with Ura to become urine Ura is made from ammonia which is produced from excess proteins broken down into amino acids by the liver if that wasn't the case too much water builds up in your body and too much water would go into your cells by osmosis and then they'd become turgid and burst too little water however and they become flaccid and stop working kidneys do a good job of keeping the water balance just right kidneys also filter to your blood to absorb useful substances like glucose and some ions bit more detail about how the kidneys work then antidiuretic hormone or ADH is produced in the pituitary gland which travels to the kidneys and it causes the tubules in the kidney to reabsorb more water into the bloodstream so less then goes to the bladder the water level is too high less ADH is produced so the kidneys cause more water to be lost in urine in both cases the water level returns to normal we call this negative feedback the term negative feedback might sound like it's bad but all it means is that the body responds in such a way as to return things to normal if your kidneys aren't working properly dialysis is required essentially your blood is sent through a machine that does the same job as your kidneys if this doesn't happen the buildup of Ura will poison you okay reproduction is for everybody well you know what I mean menstruation occurs in females after puberty eggs start to mature first FSH that's follicle stimulating hormone made by the pituitary gland causes an egg to mature in the ovary this also causes the ovaries to produce estrogen which causes the uterus lining to thicken it also inhibits or stops the production of FSH so that no more eggs mature in that cycle very clever it also causes the patory gland to produce LH lutenizing hormone which causes the egg to be released and it starts to travel towards the uterus via the oviduct over several days finally progesterone is also produced by the ovaries which maintains the uterus lining this is great news if you're looking to get pregnant if not you need to find some way of stopping a sperm cell meeting an egg cell contraception options include pills that inhibit FSH production so no eggs mature progesterone injections that stop any eggs being released you can also have an implant that slowly releases this over months or years if needed condoms for men and diaphragms for women are simple barriers to stop sperm from reaching an egg an IUD or intrauterine device like a copper coil prevents a fertilized egg from implanting in the lining you could quite simply just avoid sex for some time after the egg has been released as that's when it travels slowly down the UCT where a sperm can meet it clamping the OV duct sometimes refer to having your tubes tied or cutting the sperm ducts either of these will obviously stop the cells meeting some couples however would love to have children but can't due to infertility sometimes it's something fairly simple like not enough FSH or LH produced which injections can fix the most expensive solution to bigger issues is IVF in vitro fertilization eggs are harvested from the woman after inducing their release and are then fertilize in the lab with the prospective father's sperm any embryos that develop are inserted back into the uterus where they will hopefully embed in the lining and grow normally the success rate however is very low but there is also the risk that there could be more than one baby born which might not be desirable we've already mentioned it adrenaline is the hormone that increases heart and breathing rate in stressful situations to prepare the body for fight or flight th oxin is another hormone that's secreted by the thyroid and it controls metabolic rate if thyroxin levels are too low the hypothalamus in your brain releases a hormone called TR you don't need to know the full name and that causes the pituitary gland to produce another hormone called TSH so the thyroid releases more thyroxin this again is an example of negative feedback plants also have their own hormones which we can utilize when growing plants gibberellins cause seed germination to occur which we can add to seeds to give them a wakeup core it also promotes flowering and increases the size of fruits Ethan induces ripening of fruits orins control choot and root growth it's destroyed by sunlight so it gathers on the Shaded side of a chute causing more growth and elongation of cells on the Shaded s so the Chute bends toward the Sun or light source this is what we call phototropism in Roots however orins inhibit growth the hormone gathers on the bottom of a root and so that means the top side grows more quickly causing the root to to grow downwards this is called geotropism we can also use orins as weed killers rooting powders and for promoting growth in tissue cultures we can do a mini investigation we can put some seeds on damp cotton wool in a Petri dish for example stand the petri dish on its side leave for a few days then turn 90° and you should see that the roots have bent in that time proving that geotropism is true for roots so I hope you found that helpful leave a like if you did and pop any questions or comments below and hey after you've done the exam come back here and tell us all how you found it we'd love to know click on a card to go to the playlist for all six papers I'll see you in the next video best of luck