let's see how quickly we can cover the main ideas found in edexel GCSE biology paper 2 this is good for higher and Foundation Tier double combined and triple or separate science that's topic 6 to9 plants coordination control and homeostasis exchange and transport and ecosystems in True edexel Form there's so much more random vague bitty content compared to the other boards it's mental if you C every little tidbit in this video we'd be here for hours so this is an overview of the key Concepts to save time I'll tell you when some of the bigger concepts are just for triple but not for high and Foundation tier as there's not a lot of difference to be honest we're going to be really moving so pause the video if you need a bit more time to get your head around something you see let's go 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 xylm roots are where water and mineral irons enter the plant the merry stem is where new cells are made like we saw earlier xylm are the long continuous tubes which water rises up we say it's unidirectional only go 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 transpiration can be increased by the following increasing the temperature decreasing the humidity and increasing the air movement all of these result in water evaporating from the leaves at a faster rate 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 chalk 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 flow 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 stomato at night to reduce the rate of water loss as less water is needed for photosynthesis photosynthesis happens in chlorophyll and chlorop plus in 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 intens dity 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 plateaus 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 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 call it also promotes flowering and increases the size of fruits Ethan induces ripening of fruits orins control shoot 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 side so the Chute bends toward the Sun or light source this is what we call photo tropism 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 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 homeostasis is the term given to an organism's ability to regulate internal conditions even when external conditions change 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 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 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 Vaso 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 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 testes 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 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' become turgid and burst to 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 your blood to absorb useful substances like glucose and some ions 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 thyroxin is another hormone that's secreted by the thyroid and it controls metabolic rate thyroxin levels are too low your 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 bit more detail about how the kidneys work then anti-diuretic 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 go 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 menstruation occurs in females after puberty eggs start to mature first FSH that's follicle stimulating hormone made by the pituary gland causes an 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 pidu gland to produce LH lutenizing hormone which causes the egg to be released and it starts to travel towards the uterus via the UCT 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 UCT 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 big issues this IVF in vitro fertilization eggs are harvested from the woman after inducing their release and are then fertiliz 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 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 flow 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 toward Wars that means that 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 fast diffusion 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 respiratory system next all to do with breathing and gas exchange breathing isn't respiration but it does provide the necessary oxygen for respiration to happen in our cells the air moves down the trachea into the bronchite then the bronchioles and ends up in the alvioli the air sax where it diffuses into the blood vessels around it like we said earlier alvia lumpy to have a large surface area so this happens at a far rate the oxygen then binds to the hemoglobin in your red blood cells they then transport it to every cell in your body to be used for respiration carbon dioxide made from respiration is dissolved into the plasma of the blood where it diffuses into the lungs and is exhaled some water is also excreted this way too as you know when you breathe on a cold mirror 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 aerobic resp oparation means with oxygen here's the word and balanced chemical equation as you can see it's just the opposite of photosynthesis during exercise your breathing rate and heart rate increased 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 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 to break it down in the liver where is turned back into glucose hence while you're breathing raising 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 two organisms generally compete for food water space and other things like CO2 and light for plants shelter and mates for Animals interdependence is the term given to the fact that organisms can rely on each other for these things and they can form a community abiotic factors in an ecosystem are the non-living aspects for example light temperature moisture soil PH CO2 and O2 levels in the air biotic factors are due to organisms and things like food that's available Predators prey around other organisms pathogens breeding behavior and more we can use quadrats to estimate the size of a population of an organism in a certain area by sampling around say 10% of the area taking a mean and then multiplying up for the whole area using a Quadra with a transect allows us to observe how population distribution changes over a distance food chain shows the direction that biomass and therefore energy Flows In an ecosystem from one organism to another producers are any organism that uses sunlight to produce biomass that's usually plants or algae primary consumers eat the producers herbivores that eat only plants or omnivores that eat both meat and plants then Predators known as secondary consumers that could be Carnival or omnivores they prey on them and then we can have tertiary consumers as well apex predators are those at the top of the food chain they have no natural predator above them these levels are called trophic levels by the way the population numbers of all of these will fluctuate in an ecosystem over time by the way this food chain is possible I looked it up bears do eat foxes all life is carbon based which means that when an organisms die the carbon is recycled which ultimately can be used to make more organisms one way of course is when CO2 is produced which plants then used to grow bacteria also release CO2 when an organism undergoes decomposition water follows a cycle rain falls then runs into rivers into the sea then it's evaporated and the cycle continues for triple you need to know that farmers utilize decomposition to produce natural fertilizers that can then be used on crops it can also be used to produce mean gas to be used as fuel if you're like me you probably take clean drinking water for granted but many people around the world don't have that potable water is what we call water that has low enough levels of salt and microbes that it's safe to drink in most countries water is taken from a fresh water source so little salt is dissolved in it is passed through filter beds to remove large insoluble particles then sterilized to kill microbes usually using chlorine but we can also use ozone or UV light in some countries there are few or no freshwat sour es so they must get sea water and remove the salt this is called desalination which can be done through distillation but also by using special membranes that imploy reverse osmosis however both of these require a huge amount of energy potable water isn't pure water of course in fact Pure or distilled water is dangerous to drink in large amounts as there being nothing dissolved in it water will move into your cells due to osmosis and then become turgid nitrogen also moves in a cycle nitrogen gas in the atmosphere N2 is converted into nitrates by nitrogen fixing bacteria found in the soil or root nodules of some plants other bacteria and some fungi convert proteins into ammonia during decomposition of urine feces or dead organisms this ammonia is converted into nitrates by nitrifying bacteria now that we have nitrates they can enter plants through the roots and be used by them for growth nitrates are turned back into nitrogen gas by denitrifying bacteria cost there's a bacterium for everything man-made fertilizers contain nitrates to help crops grow of course if too much is used water say from rain can cause it to run off into ponds and lakes where the water is still this causes algae on the surface to bloom causing a barrier that stops light from reaching underwater plants these then die and respiring bacteria feeding on this dead plant material use it more oxygen in the water starving fish and other creatures of it and they die this is urif foration biodiversity is one of those buzzword that's very much in Vogue at the minute basically it means how many different types of organisms you have in an ecosystem High biodiversity generally makes for a stable ecosystem as organisms don't have to depend on one species for a resource for example sadly human development usually results in lower biodiversity this development also poses problems when it comes to waste we're having to find more ways of disposing of sewage fertilizers toxic chemicals atmospheric pollution and more to reduce our impact on the environment one factor is the land that we need for building quarrying farming and disposing of waste an example of this is the destruction of Peete bogs to make compost which affects the habitat of many organisms and microorganisms burning Pete also releases CO2 now going off peace for a second for your exams you need to say that carbon dioxide and methane contribute to global warming deforestation bad on a big scale flattening forests reduces biodiversity and it's often done to create Farmland the Pyramid of biomass is a food chain that shows us how much mass enters the next trophic level relatively you need to be able to draw one on graph paper using numbers supplied in the question and also calculate the percentage absorb by the next level as per usual percentage is equal to the bit divided by the lot time 100 of course this shows that biomass is lost at each level because it's not just a rectangle as not all biomass is absorbed or consumed into the next organism some is lost due to the organisms living for some time before being eaten by a predator for example it's also lost as water Ura and CO2 food security is a big thing especially in these uncertain days food is becoming more scarce due to increasing world population changing diets food being transported around the world which requires huge amounts of energy changing growing environments the cost of farming that's a big one of the and conflicts for example around 40% of the world's wheat comes from Ukraine or at least it used to farmers are constantly trying to find more efficient ways of farming largely by maximizing biomass input to crops and animals while also reducing biomass lost by them fishing sustainably is also important if a species is fished at a greater rate than its breeding then its population can disappear in those areas one way of sustainably fishing is by having Nets with holes in that catch adult fish but are big enough to let the little ons out if young fish aren't caught then they go on to breed 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 click on the card to go to the playlist for all six papers I'll see you in the next video best of luck