let's see how quickly we can cover everything you need to know for AQA biology paper 2 this video is good for higher and Foundation Tier double combined Trilogy and triple or separate biology that is topics 5 to 7 that's homeostasis and response inheritance variation in evolution and ecology I'll tell you when something is just for triple but not when something's just for higher tier because there's not much difference to be honest we're going to be moving hecking fast so pause the video if you need a bit more time to get your head around something you see let's go homeo Asis 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 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 stimulus 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 sinapse 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 affector this is a reflex arc this of course is much faster than a conscious decision glands can also be effors 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 take mean average not too many times though as their nervous systems will start to get a bit better at reacting 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 equal half 80 squ but you'll never be expected to do that in this paper but it's something you could mention if you were as a six mark 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 onata 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 Titan they're both connected to the lens this results in the lens becoming thin and 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 ciliary 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 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 Styles 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 object 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 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 science goodness which is for everyone the endocrine system is a system of glands that produce or secrete hormones that travel to effectors 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 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 teses 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 one 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 reprodu if you 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 too little water however and they become flaccid didn't 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 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 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 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 pituary gland causes an egg to mature in the ovary this also causes the ovaries to produce estrogen which causes the uterous 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 pituitary 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 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 tide 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 injects 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 will 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' 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 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 the last triple content in B5 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 ethine induces ripening of fruits orins control chot 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 phototropism in 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 next big topic B6 that's inheritance variation and evolution in order to reproduce sexually gametes sex cells must be made this happens by meiosis for example in the testes to make sperm the chromosomes in a diploid cell that is 23 pairs for us are copied similar chromosomes then pair up and the genes are swapped between them the cell then divides to make two diploid cells which then divide again along with the chromosomes themselves to make four haid cells ready to fuse with another gamt which in this case would be an egg this is one way that variation occurs in Offspring the resulting diploid cell then starts to divide via mitosis which is covered in paper one plants do this with pollen and egg cells but they can also reproduce asexually but as it doesn't evolve gametes the daughter cells will be genetically identical so a clone of the parent is made by mitosis an advantage of sexual reproduction is that variation occurs which can result in organisms becoming better suited to their environment more in this in a bit so more likely to survive an advantage for asexual is that only one parent is needed so for example a plant on its Lonesome can still reproduce in order for the species to survive another thing that can do both is the parasite that causes malaria as can some fungi 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 responsible 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 while 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 nuclear es 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 back to double some characteristics are controlled by just one gene like color blindness these different types of the same gene are called alal usually characteristics are dependent on two or more genes though and them interacting dominant Al are those that result in a characteristic being expressed even if there is another alil present a recessive alil for example if you have the Al's Big B little B for I color Big B be brown little B be blue you will have brown eyes it's only when there's no dominant Al in this case that the recessive alil is expressed so me having blue eyes I must have the gene little be little be Big B Big B or little B little be are called homozygous as they only have one type of alil whereas Big B little B is what we call heterozygous we can use a punet square to predict the probability of a certain phenotype my parents have brown eyes but they both have heterozygous Al for eye color there are three different outcomes of these combining with a 25% chance of making me that's little be little be so I'm not so much one in a million more one in four my sister has brown eyes but her has blue eyes so she must be Big B little B eye color is by the by but some alals can result in disorders being inherited for example polya extra fingers or toes which is caused by a dominant alil or cystic vibrosis which is caused by a recessive Al even if two parents don't have cystic fibrosis they could still be carrying the recessive alal so their child could have the disorder human DNA is containing 23 pairs of chromosomes but only one pair determines sex if you have XX chromosomes you are female XY you're male the expression of these genes affects every cell in your body every aspect of your physiology we can also make a punet square for these as you can see there's a 50/50 chance of a child being male or female variation is a result of the genes inherited from an organism's parents and also environmental factors Charles Darwin's theory of evolution states that random variation in Offspring will result in some being better suited to their environment than others and so are more likely to survive and reproduce but like seeing we know that our DNA is able to respond to the environment in order to turn genes on and off depending on whether they're needed or not for example there were some blind translucent skin mackerel that were found in a dark cave when they were bred with normal mackerel in sunlight they regained fully working eyes and opaque skin within a few Generations John Baptist Lamar's Theory asserted that adaptation of variation is Guided by DNA in response to a changing environment this was scoffed at but we now know that there is some truth to this thanks to the discoveries made in epigenetics bacterial resistance is largely considered to be evidence of darwinian evolution bacteria divides mutations occur and inevitably a bacterium with an increased resistance to antibiotics will be produced that's why we only want to use them when absolutely necessary it also means you have to complete the whole course of antibiotics if you don't weaker bacteria will have been killed off but more resistant ones will still be there and then they'll reproduce and make you even more ill if organisms are able to produce fertile offspring we say they're of the same species tigers and lions have been known to make lier Offspring but as they're infertile we don't consider tigers and lions to be the same species we can selectively breed living things with desired characteristics to enhance these for example breeding dogs to produce breeds like labador colleagues and if you're into undesirable characteristics pugs too advancements in biology over the last few decades mean that we can also genetically modify organisms if we don't want to wait for selective breeding to do the job or when it can't actually achieve what we want it to for good or ill for example scientists have genetically modified bacteria to produce insulin which can be harvested and used to treat people with diabetes genetically modifying crops is one way of boosting their yields or nutritional value for example golden rice has a gene inserted into it that produces vitamin A it was developed to combat diets in certain areas that were lacking in this other GM crops have been modified to be more resistant to diseases for example the process of genetic engineering goes as follows a gene is chemically cut from the organism that has the desired characteristic this is done using enzymes for example the gene from a jellyfish that causes it to glow in the dark this is then inserted into a vector like a bacteria plasmid or virus that in turn inserts the gene into another organism say a bunny rabbit but it must be done in the early stage of its development say just after the YK has been fertilized as this is the only way you can be sure that the gene will be present in every cell of the bunny as it grows by the way I didn't make up this example this has actually been done fossils are the remains of organisms that died a very long time ago the classic fossils we think about are the bones that we dig up but they're not strictly speaking bones anymore in fact minerals have replaced the organic material to effectively leave Rock in exactly the same shape as the bone sometimes there can still be organic tissue Left Behind if the conditions for Decay are not present Footprints left in mud that have hardened over time for example are also considered fossils as well as any other trace of an organism it doesn't have to be the organism itself cloning is triple only making exact copies of plants is easy just take cuttings off a plant put them in the ground and that does the job you can also go the slightly harder route by cloning from a tissue culture that is cloning from a small group of cells this can be helpful for preserving some species from going extinct cloning animals is more difficult you can split embryo cells up just after fertilization than put them into surrogate mothers essentially you're forcing identical twins but you won't know exactly what you're getting until they've developed so if you have a fully grown animal that you want to clone you take the nucleus from one of its cells say in its skin then insert that into another's egg cell it's essentially now a fertilized egg shocking the egg jump starts the development process and it starts to divide it's then inserted into another female womb where it continues to develop classification caraus classified organisms into King om philm class order family genus and species a good pneumonic for this is King Philip came over for good soup the binomial a Latin name for an organism is just the genus and species combined as time went on it turned out that another level above kingdom was needed domain the three domains are ARA that's primitive bacteria normal or true bacteria and ukaria that's everything else of course with DNA and nucleus of the cells you should know about UK carotic cells from paper one ARA by the way are often found in extreme Environ on the earth they can therefore be called extremophiles final big topic ecology is a study of how lots of organisms interact in an ecosystem 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 the 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 carnivores or omnivores they prey on them and then we can have tery 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 fall 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 methane gas to be used as fuel back to double biodiversity is one of those Buzz words 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 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 pce also releases CO2 now going off piece 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 absorbed 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 eating 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 at the minute 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 there we go I hope you find that helpful leave a like if you did click on a card and it'll take you to the playlist for all six papers once you've done the exam come back here and tell us all how you did we'd love to know good luck