Transcript for:
GCSE Biology Paper 2 Summary

hey everyone I'm Emma today I'm going to take you through the entire paper to biology for GCSE combined science if you study higher tier those parts are labeled like this and if you study foundation you'll know just to skip those of course this is just the content make sure you practice lots of questions if you watch my individual videos you'll have quick questions at the end and I've got other videos like maths and biology to help you talk about those skills too our first topic is homeostasis and response we're starting with number one Moyo stasis okay let's start with a definition homeostasis is regulation of the internal environments or conditions that just means keeping things constant this is both inside cells and inside whole organisms like this little fishy so it's important to keep these conditions constant so that enzymes work effectively these are inside cells and they're easily affected by changes in pH and temperature so we need to keep the conditions optimal which just means at their best so there are three conditions that you need to know in humans the first is the blood glucose concentration this second are the water levels and the third is body temperature which is around 37 degrees Celsius in humans these all need to be kept at a constant so a stimulus this is a trigger for the homeostatic processes in the body and it's just a change in the environment an example of this could be on a hot day the temperature rises and your body feels hot you need to detect that change and receptor cells are what do that detecting once you've got that information it needs to be passed on to a Coordination Center to be received and processed two examples of this are the brain and the pancreas these decide how to respond a factors then actually carry out the response and they restore the conditions back to the optimal level the two types you need to know are muscles and glands such as the pancreas do the human nervous system in the homeostasis video we learned that a stimulus is a change in the environment and that these changes are detected by receptor cells there are five main sense organs in the body pause and see if you can name them and what they detect all right so the eye detects light the nose detects chemicals this is by smell the tongue also detects chemicals but this time it's more by taste the ears detect both signs and balance basically being level and the skin detects pressure and temperature once the stimulus is detected by receptor cells nerves will carry this information to the central nervous system or the CNS this is made up of the brain and the spinal cord before we look at the journey through the nervous system you need to know what neurons are these are individual nerve cells here's a picture of one it's not very good but you'll see some in the next page if you have loads and then bundle together say hundreds or thousands then this is actually called a nerve so that's the difference a neuron is just one nerve cell ok now let's take a look at the path of the nervous system so a simulus occurs the first thing that happens is the receptor cell detects that stimulus that change in the environment and this causes an impulse to then be passed on to a sensory neuron this passes the impulse to a relay neuron and then to a motor neuron so we've got three neurons finally the motor neuron will then trigger the effector to carry out a response let's let's look at an example so here our stimulus is some cold ice cream dripping onto a finger this skin cells in the finger are going to detect that and they're going to trigger an chuckle impulse to be passed on the sensory neuron this fan passes on to the relay neuron which is in the central nervous system the spine and the brain the impulse passes through the motor neuron and then to the effector in this example the muscle and the finger would move away from the dripping ice cream in reality lots of other responses could also happen like saliva glands releasing saliva and preparation for licking the ice cream now just to point out that this is a one-way system and because it's happening through electrical impulses it is very very fast okay speaking of impulses we're gonna point out a little bug bearer we don't call them messages examiner's hate that we must call them impulses another tip is how you remember the relay neuron is like a relay race so if you think about it in a relay race you pass on a baton from one person to another so it's passing between different people a relay neurone also just passes an impulse between different neurons three reflect lectures although the nervous system is very fast there is something slowing it down sign APS's if you look very carefully you'll notice there is a tiny gap between these two neurons this is called a synapse here is a zoomed in version of a synapse as the electrical impulse reaches the end of one neuron it causes chemical messengers also known as neurotransmitters to be released and diffuse across the gap they attach to receptors on the next neuron this causes a new electrical impulse to be triggered and it will then travel across that neuron as well the diffusion of the chemical messengers is slower than the electrical impulse it's important to say that the chemical messengers diffuse not travel across the synapse and just a reminder we don't call the impulse a message we have to call it an electrical impulse in certain situations we need a very quick response here the person is holding their hand close to the fire because I've to close their hand will automatically pull away without them even realizing that they're doing it this is called a reflex action it happens automatically and rapidly it does not involve conscious parts of the brain but the main steps are the same as other nervous system responses pause and see if you can name each part in this sequence okay so we start with receptor cells then the sensory neuron they're really neuron the motor neuron the effectors and finally their response if you need to recap this go back to my nervous system video okay so let's look at this example the receptor cells here are going to trigger a response to the high temperature of the fire this travels along the green sensory neuron up to the spinal cord and then to the relay neurons but note that the relay neurons don't go all the way up to the brain they're going to come straight back and connect to a motor neuron and the effect is then that the muscles in the hand will contract pulling the hand away from the danger reflex actions are important because they help protect an organism from harm many basic body functions are also reflex actions like breathing if the brain were consciously involved in these actions you wouldn't be able to think about much else for the endocrine system we learned about the nervous system in a previous video and now we're learning about the second system the endocrine system this is composed of glands like the ones you see here gods secrete hormones into the bloodstream they travel through the blood to their target organ where an effect is actually purchased traveling through the blood is a lot slower than the electrical impulses of the nervous system but the effects are longer-lasting you need to know the names and positions of six glands in the human body pause and see if you can name any of these alright we've got the pituitary gland up here beside the brain then we've got the thyroid gland this is the pancreas these are the adrenal glands and in males we've got the testes and in females we've got the ovaries let's come back to the pituitary gland this is called the master gland this is because it releases several hormones that can travel to other glands and cause them to release hormones a tip to remember that it is the master gland is that it is fine beside the brain which is also like the master of the nervous system the word pituitary is a rather long fancy signing word which I think sounds a bit like an olden day master's name the next bit of info we're looking at is higher tier only so if you're studying foundation skip ahead to the questions okay so we're going to look at two glands and functions of the hormones that they produce so we'll look at the thyroid and the adrenal glands first up the thyroid gland makes the Ox seen this controls the basal metabolic rate in your body which is basically how quickly substances are built up and broken down it controls growth and development in children but in adults the levels of thyroxine stay pretty constant next is adrenaline produced by the adrenal glands what do you think it does to these body parts well this hormone increases the heart rate it also increases the amount of oxygen and glucose supplied to the brain and the moss and finally it increases your breathing rate these changes prepare you for the fight-or-flight response say you see a wild boar in the forest and it charges at you you might try to fight it or you might run away so adrenaline is produced in stressful situations when this situation is over the adrenaline levels naturally lower now we're going to look at something called negative feedback it controls different hormones and conditions to keep them at a constant level we're going to look at sigh rock scene so the pituitary gland makes something called TSH or thyroid stimulating hormone it makes the thyroid gland make more Thurrock Seng let's say that the thyroxine levels increase the response will be that the pituitary gland makes less TSH unless T SH means the thyroid gland makes less thyroxine this will bring the thyroxine levels back to the setpoint on the other hand if the thyroxine levels decrease then the pituitary gland will need to make more TSH more TSH means that the thyroid gland produces more thyroxine again bringing it back to the set point five control of blood glucose glucose is essential for ourselves the mitochondria in ourselves use it to respire this releases energy for essential functions like keeping warm moving and building larger molecules if we don't have enough glucose our cells will be able to respire if we have too much glucose it can damage organs like our eyes and our kidneys we need to keep blood glucose levels within a small range let's look at what happens when we eat a meal this bowl of spaghetti contains carbohydrates these are broken down by the enzyme amylase in our digestive system to make lots of glucose this glucose will then travel in our bloodstream the organ that detects any change in glucose is this one the pancreas if the blood glucose levels are too high it will release a hormone called insulin which also then travels in the bloodstream it allows glucose to move out of the blood and into ourselves where it is used for respiration if there is excess glucose that is not used it is stored as glycogen in both the liver and the muscles this question is insoluble which means it doesn't dissolve so it can be stored this restores the blood glucose levels back to normal and when the blood glucose levels are low the glycogen can be turned back into glucose if you're studying higher-tier watch on to find more about this if you are studying foundations here just skip ahead to the questions ok let's look at what happens when blood glucose levels drop this could happen to you to exercise because your cells are aspiring faster using up more glucose so let's imagine we have last glucose in the blood it is still going to be the pancreas that detects the fall in the blood glucose levels but this time it produces a different hormone we'll use bluem to illustrate it and this is called glucagon again glucagon travels in the blood but it travels to the liver that's its target organ and here it turns the stored glycogen back into glucose this is then released back into the blood increasing the blood glucose levels back to normal alright it's important that you learn these Spelling's glucose glycogen and glucagon it's really important to make sure you've got them clear in your head because if you spell them wrong or mix them up you're going to lose the marks one way to remember it what glucagon does is realizing that songs like glucose gone so it is a hormone produced when glucose is gone from the blood or at least it's in lower levels 6 treating diabetes [Music] there are two types of diabetes you need to be able to compare and contrast them we'll look at what the disorder is the causes and the treatments okay so in type 1 diabetes the pancreas doesn't actually produce any insulin this means that the blood glucose levels can rise to fatally high levels for the cause of it we know that it has a genetic element we also know that it tends to start in young children and teenagers the way we treat it is with insulin injections no they're not as big as it looks like in this picture ok these are given before meals so that insulin is in the blood ready to deal with increasing blood glucose levels at the moment there is no cure for type 1 diabetes so people with this disorder will have to take insulin injections for the rest of their lives but there are lots of new advances in high this insulin is administered ok let's look at type 2 diabetes this is when the pancreas does make insulin but the body cells just don't respond to the main risk factor for type 2 diabetes is obesity but other factors include old age and the lack of exercise treating it then seems a little obvious people with this disorder need to do more exercise they also need to eat a carbohydrate controlled diet remember carbohydrates are broken down into glucose so you need to regulate those to make sure the glucose levels don't rise too high these are the two main ways to regulate your blood glucose levels uncontrolled type 2 diabetes however if this isn't working doctors may resort to drugs these can influence the cells to be easier able to take up the insulin or for the pancreas to make more insulin but again if that really doesn't work they will resort to insulin injections as well seven reproductive hormones during puberty reproductive hormones cause secondary sex characteristics to develop in males the testes make the main reproductive hormone which is testosterone this stimulus sperm production other changes include a growth spurt and the development of underarm facial and pubic hair the voice will also break which just means that it gets a little bit deeper in females the ovaries stimulate the production of the hormone estrogen other changes involve a growth spurt the development of underarms and pubic hair and the breasts start to grow they'll also begin their menstrual cycle if you're studying higher-tier you're going to learn a lot more about the hormones in the menstrual cycle but everybody needs to know what they are and what they do so we're going to start with that and if you're doing higher-tier make sure to watch my menstrual cycle video let's start with seeing if you can label the parts of the brief the female reproductive system first up we've got the ovary which is joined to the oviduct or the fallopian tube this is a uterus this is a cervix and this is the vagina okay so there are four hormones you need to know about that control the menstrual cycle the first is FSH which stands for follicle stimulating hormone this causes one egg and ovary to mature every 28 days which is called ovulation here's our mature egg luteinizing hormone or LH stimulates the release of the mature egg up here we can see that it will travel out of the ovary and into the oviduct oestrogen and progesterone carry on is some other function they help to maintain the uterus lining which just means it stays thick ready for a fertilized egg to come along and implant into it's the menstrual cycle this is higher tier content so if you're sunning foundation skip to the contraception video first you'll need to know the stages of the menstrual cycle then we'll look at the hormones behind it it's a 28-day cycle and we'll start with the egg maturing in the ovaries just like you can see here the uterus lining also thickens in preparation for a fertilized egg on day 14 one egg is released from an ovary this is called ovulation and it passes into the oviduct uterus lining will remain sick for a few more days after this but if the egg doesn't get fertilized and implants then the lining will break down this is known as having a period when this happens blood will come out through the vagina and a girl will need to use some sanitary products to capture it she can use pads tampons or menstrual cups now let's look at the four hormones that control the menstrual cycle FSH or follicle stimulating hormone comes from the pituitary gland and travels down to the ovaries it causes eggs to mature it also stimulates estrogen production estrogen is secreted by the ovaries it causes the lining of the uterus to develop ready for a fertilized egg it inhibits or stops the production of FSH so eggs do not continue to mature it also stimulates the release of LH LH or luteinizing hormone causes ovulation this causes the mature egg to be released into thought finally progesterone is produced by the empty follicle in the ovary after ovulation it inhibits LH as you don't want more than one egg to be released it also inhibits FSH finally it maintains the lining of the uterus for around ten days keeping it thick and ready for a fertilized egg now in contraception methods of contraception can be split into hormonal and non hormonal we'll start with the hormonal methods and as you need to be able to evaluate the different types of contraception we'll look at advantages and disadvantages of each first up we've got the oral contraceptive pill this is taken every day and contains hormones that will stop the eggs and maturing do you remember which hormone normally mix the eggs mature yeah its FSH so the pill inhibits FSH which just means it stops the production of FSH the big advantage of the pill is that it's easy to use and if it's used properly it's highly effective the disadvantage is it can be really easy to forget to take it or if you vomit you can lose your pill for the day and it has some side effects like increased blood pressure and other things next methods are the patched the injection and the implant all of these use the hormone progesterone this inhibits eggs in the ovary from maturing or from getting released and they last progressively longer so this is a big advantage of these methods however they all need replacing and the injection in the implant require a nurse or a doctor to receive now we're going to look at the non hormonal methods of contraception first off we've got spermicides this is a chemical method that can kill or stop sperm from working the benefit of these are that they're readily available you can buy them from any pharmacy but the disadvantages they're not very effective and shouldn't be used on their own next up our barrier methods such as condoms for meals and diaphragms for females the good thing about these is that there are no side effects and they can prevent against some STDs the disadvantages they need to be fitted correctly and if they get damaged they can easily let sperm through increasing your risk of pregnancy here we've got an IUD or an intrauterine device this is inserted into uterus just like you can see over here it works by preventing early embryos from implanting into the uterus lining some of them will also continue progesterone the big advantage is is that it's very effective and once inserted it's obviously very long lasting however in the early days it can be uncomfortable and cause some period pians next up we've got surgical methods this is for meals in the sperm duct and in females the ovary these can be either cut or tied the big advantage is that it's permanent this is for people who know they don't want to conceive the disadvantage is that for women this procedure requires a general anaesthetic which carries a risk with it the final method is abstinence this is making sure that you don't have sexual intercourse when the egg is in the oviduct the advantage to this is that it's got no side effects whatsoever but the disadvantage is a big one it's really risky and you have a high risk of getting pregnant with this method 10 infertility treatments NHS states that as many as one in seven couples have difficulty conceiving or getting pregnant this is called infertility it can be caused by blocked or damaged OB dogs or a lack of ovulation in males a low sperm count or sperm defects like having a shortened teal also cause infertility being a base or anorexic and simply getting older all increase your risk of infertility if a woman doesn't naturally ovulate because her body isn't producing enough FSH or LH this can be treated with fertility drugs these contain the right doses of these hormones then she can try to conceive naturally IVF or in vitro fertilization is another treatment that can be used for women who have full tob ducts or when there's no obvious cause for infertility the first stage is exactly the same she's given fertility drugs this causes her eggs to mature and these are then removed from the ovaries like this then the eggs are mixed with sperm in the lab so that fertilization happens if the infertility was caused by the man not producing enough sperm individual sperm can be ejected into the egg microscopy can then be used to monitor that fertilization has actually happened and to check that the fertilized eggs develop into the embryos which are just tiny little balls of cells one or two embryos are placed into the mother's uterus bypassing the faulty oviducts hopefully at least one baby will grow and be born although fertility treatment gives a woman the chance to have a baby on her own it is very emotionally and physically stressful placing two embryos in the uterus can also lead to multiple births which is a higher risk to the babies and the mother finally the success rates are not high and these decreased with age now we're on to topic six inheritance variation and evolution and we're starting with one sexual and asexual reproduction there are two types of reproduction sexual and asexual let's start with sexual this involves fertilization which is a fusion of the male and female gametes in animals the male gamete is a sperm cell and the female gamete is egg cell but in flowering plants the male gamete is actually pulling but the female gamete is still in Excel when the gametes fuse together there's mixing of genetic information from the meal on the females this leads to variation or variety in the offspring can you spot some differences in these three little hedgehogs now let's look at asexual reproduction asexual reproduction involves one parent only the parent cells reproduce by mitosis to make the offspring so there is no fusion of gametes or no fertilization since there's no fertilization there's no mixing of genetic information so the new offspring like this little runner coming off the strawberry plant is genetically identical to the other runner because of this we call them clones they are all the same do meiosis in the previous video we learned that sexual reproduction involves a fusion of gummies annika meats are made by the process of meiosis we're going to learn what meiosis is in this video okay first up you need to know the humans have got 46 chromosomes in their body cells these are arranged in 23 pairs or we say they have two sets of chromosomes in gametes like the egg cell and a sperm cell they have 23 chromosomes they're not arranged in pairs we say they have one set of chromosomes - is hi gametes are made let's look at the definition meiosis is a type of cell division that happens in the reproductive organs - half the number of chromosomes making Gummy's so it happens in a TAS T's and the ovaries let's take a look at the actual process of meiosis here we've got a body cell so we'll give it some chromosomes the first stage is the same as mitosis the genetic information doubles or copies so we get twice the number of chromosomes the next stage is the same as well we have a division so this cell splits in two and the genetic information is split between them okay here's where meiosis differs from mitosis it has a second division so we're going to end up with four cells each one is a gamete and each one has got half as many chromosomes as the parent cell or the body cell let's look at this in terms of humans in the body cell you've got 46 chromosomes so when the genetic information is copied you end up with 92 then in the first division where the cell splits in two you're going to go back to having 46 chromosomes in each cell and in the second division when each cell divides into again he'll get 23 chromosomes in each gummy okay let's look at what happens when the gametes fertilized the egg and the sperm each of 23 chromosomes so when they fuse together you're going to get the full 46 chromosomes in the fertilized egg cell the fertilized egg cell will then divide this time using mitosis it does as many times to form the early embryo and each cell of the early embryo will contain the 46 chromosomes as the embryo develops the cells on embryo differentiate this just means that they become specialized for a particular function like detecting light in the eyes eventually all the cells are specialized and you have a baby the last thing to mention is that meiosis makes every gamete unique so every offspring is different 3 DNA and the genome inside ourselves the nucleus contains chromosomes in the meiosis video we learned that our body cells have 46 chromosomes every chromosome is made up of DNA and DNA is made up with lots of small units so we can call it a polymer it is made from two strands that form a double helix this is a definition you need to learn now let's look at genes a gene is a small section of DNA that codes for a specific sequence of amino acids and these make a specific protein for example the pigment that color's your eyes you'll learn a lot more about how genes work in the next video as I mentioned at the start scientists have sequenced the human genome for what is a genome well it is simply the entire genetic material of an organism this includes all the DNA inside the nucleus and the DNA fine inside the mitochondria understanding the human genome is an important area of research scientists are using it in three ways number one they're using it to improve their understanding of inherited disorders and hard to treat them better this includes looking at cystic fibrosis and sickle cell anemia number two they're using it to search for genes linked to disease this includes diseases like heart disease and type 2 diabetes to do this they're looking for patterns in the genomes and trying to spot any similarities and finally number three they're using genomes to trace past human migration patterns to look at hi we moved across the world for inheritance keywords in the DNA video we learned the genes or sections of DNA the code for proteins some characteristics are controlled by a single gene such as fur color and mice and red-green color blindness in humans but most characteristics are as a result of multiple genes interacting rather than a single gene for example height in humans some genes have different forms we call these alleles for example the gene for fur color in mice has got both a brown fur allele and a black fur allele as well as some others alleles operate at a molecular level to develop characteristics we call these physical characteristics phenotypes so it's just the appearance of the organism here's a hint use the pH to help you remember that phenotype is physical characteristics genotype is then just the alleles that an organism has inside it remember an allele is just a different form of a gene so the genome part of the word just means a leo's let's take a look at how aliens work we'll look at the example of fur color in mice looking at these alleles and the word homozygous can you work out with homozygous actually means pulse have a think and press play when you're ready homozygous means having two of the same alias here's a hint you might have heard the word homosexual when a person is attracted to the same gender as themselves so homo simply means same what then do you think heterozygous might mean heterozygous means having two different alleles and by the same token being heterosexual means a person is attracted to a different gender than themselves so hetero just means different and you can see these are different but what fur color or phenotype will the mines have we need to know more about the alleles there are two types of alleles dominant alleles are always expressed or shown whereas recessive alleles are only expressed or shown if there are two copies of that allele ie both of the alleles are the seen we represent dominant alleles with capital letters whereas recessive alleles are shown by lowercase letters you'll get told which allele is dominant and which is recessive so you don't need to memorize that in this case black fur is the dominant allele so it gets the big B I'm borrowing for excessive so it gets a small B so let's look at the genotype of this mice it's got the Big B for the black fur and then it has a little B for the brown fur note that the capital always goes first since the dominant allele is for black fur the mice will have a phenotype of black fur if we look over here we can practice our genotypes this mice has two dominant alleles so we write it as Big B Big B and the phenotype is black fur but this mice has two recessive alleles so we write it as little B little B and the phenotype is brown fur we can call the genotypes homozygous dominant if there are two dominant alleles and homozygous recessive if there are two recessive alleles five inheritance punnett squares in the last video we learned a lot of the key words needed to understand inheritance now we know how alleles work we can use them to predict the genotypes and phenotypes of children or offspring let's look at eye-color in these parents the moms phenotype or physical characteristic is blue eyes and the dads phenotype is brown eyes for the genotype we need to know which allele is dominant and which is recessive remember you'll be told this or we'll be able to work it out from the information given in this situation the blue eye allele is recessive so we're going to label it with a lowercase letter a little B and so the mums genotype is little B little B the dad has dominant allele which gets a capital B so his genotype is Big B little B but if they have a child how do we know what genotype and phenotype it can have well to do this we're going to use punnett squares this is just a genetic diagram and to start off it looks a little bit like a knots and crosses great we'll start by splitting up the mums alleles because a child only gets half of its genes from its mother so we split up the little B on the next little B we'll do the same for the dad for the same reason that the child gets half its DNA from his dad as well so we split up the Big B little B now we work out the combinations by reading down and across and we get Big B little B in the next box we get another Big B little B why not pause and see if you can work out the remaining two boxes in this one we get little B little B and it's the same in the last box great so now we have all the genotypes we'll work out the probability of each you could be asked to give this as a fraction or a percentage so we'll do both okay so you can see we've got two big beep little beasts and two little B little B's that means we've got 50% of each or a half so we write the letters aren't Big B little B and we do the same for the little B little B not will right the phenotypes for each genotype you need to write them below in the same order or beside the genotype so it's very obvious exam questions will normally structure this for you so the Big B little B will give you brown eyes as the brown eye allele is dominant the little B little B will give you blue eyes because you have two recessive alleles lastly you can be asked to give the expected ratio this is one of the math skills you're required to know for your exam since is both 50% as a ratio this is one to one again you write it in the same order as you've given the phenotypes if you're studying higher-tier you need to be able to make the punnett squares yourself if you're studying foundation you need to be able to complete one and the questions will be more structured I recommend you watch this either way as it's good practice okay let's read the question to smooth paint plants are crossed they are both heterozygous record the proportions and ratios of the genotypes and phenotypes for this cross cross stress means they're reproducing together pause and grab some paper and try and work it out yourself then press play when you're ready to go through it okay so let's start with the parent genotypes they're both heterozygous which means they have different alleles two alleles we've got our smooth is dominant and wrinkled is recessive we'll use the letter S dominant one gets a capital and the wrinkled one gets a lowercase it doesn't matter what letter you use because we haven't been given it so both parents genotypes because they're heterozygous will be big s little s now we're going to do our cross so we start by splitting up each parents genotype into big s little s then we work out the different combinations if you didn't get to this point pause anyway and try and fill out the combinations okay so this box will be big s big s this is big s little s another big-ass little s unto little asses notice how I'm really emphasizing the size of the letters that's important okay now that's right I would offspring genotypes we have we can see we've got one big s big s which is 25% we've got two big-ass little asses which gives us 50% and we've got one little s little s which is 25% the question has asked us for the ratios of the genotypes so if we work it out we've got 1 2 2 2 1 if you wrote your genotypes in a different order you may have your ratio in a different order just check carefully next we'll work out the offspring phenotypes every offspring that has a dominant allele or a big s is going to be smooth but every offspring that has two little asses is going to be wrinkled we can see that we've got three offspring that have got the big dominant s so 75% are going to be smooth and that leaves 25% will be wrinkled finally we have to give this as a ratio and we compare 75 to 25 that's 3 to 1 the last thing we're going to look at is sex inheritance this person's phenotype is female and this person's is meal sex is controlled by an entire chromosome as opposed to one or multiple genes in females the sex chromosomes are X X and Emile's they are X Y we can construct a Punnett square to show the offspring probabilities doing this very quickly we can see that we end up with 2x X offspring and 2 XY offspring so the probability is 50% female and 50% meal you have to memorize the sex chromosomes for females and meals one tip I use to help me remember this is that my female friends tend to send me a little kiss kiss like an X X at the end of messages more than my male friends do 6 cystic fibrosis and polydactyly people who have the genetic disorder polydactyly will have extra fingers or toes part of the word poly octi means many like a polygon is a many-sided shape it is caused by a dominant allele this means people only need to have one allele to get the disorder cystic fibrosis is a disorder of the cell membranes the cell membranes struggle to move substances around which leads to thick mucus building up in places like the lungs it is caused by a recessive allele which means you need two recessive alleles to have the disorder if a person just has one of the recessive alleles they don't have the disorder but we call them carriers you may be asked to use punnett squares to work out the probabilities of offspring inheriting these disorders we'll start with a parent that has got polydactyly because they've got the dominant allele for it will then have them crossing with another parent that doesn't have polydactyly because they don't have the dominant allele let's do our combinations by reading dine and across and then we'll work out what genotypes we've got so we can see that we've got 50% big D little B and we've got another 50% of little D little D phenotypes are the physical characteristics are then 50% polydactyly because they've got the capital dominant allele and 50% normal and as a ratio this is one-to-one now let's look at a cystic fibrosis example let's start with a person that hasn't got cystic fibrosis and they have no cystic fibrosis alleles then we'll have another parent who does have cystic fibrosis when we do our combinations we can see that for our genotypes all of the offspring would have Big C little C a hundred percent probability a big C little C has a normal dominant allele they are 100% normal or non cystic fibrosis couples with a history of a genetic disorder in their family may be offered genetic screening this is when cells from the embryos are taken and screened or tested for specific disorders if the tests show that the embryo has a genetic disorder the parents will make a decision whether or not to keep the baby or whether to terminate the pregnancy there are of course many complex issues with this you need to be able to make judgments using information given so don't worry too much by memorizing these first of all with economic issues if that screening is very expensive and currently only offered to those with a family history of disorders some people think every couple should be offered it while others think the money could be better spent somewhere else however supporting a family with a child affected by a genetic disorder is also very expensive now we'll look at the ethical issues collecting cells from an embryo can increase the risk of a miscarriage whether or not the baby has the disorder and occasionally the tests can give a false positive saying the baby has a disorder when it hasn't it can also be a false negative saying the baby doesn't have the disorder but when it is born it does and of course once a couple has a screening done they face their own ethical decisions on whether or not to have an abortion finally social issues affect us all people are concerned that genetic screening could create a demand for designer babies which is when they're chosen for their certain characteristics seven family trees family trees are used to show inheritance this is often used whenever there is a family history of a genetic disorder like cystic fibrosis you will be given a key to use to figure out some answers here's an example males and females will be given different shapes shading is then used to indicate if the person has got the disorder okay so here we've got a man and a woman when they're joined by a horizontal line this means that they are parents a vertical line with branching other symbols means that they have got children so you can see these parents have three children if they're adult children they may have a partner of their own and form parents together the best way to understand family trees is to give some questions ago so pause and try them and then press play when you're ready to go through them so always start by looking at the key okay number one what is the genotype of an affected meal well this is a cystic fibrosis family tree and as we learned in the last video cystic fibrosis is caused by recessive alleles so we need two recessive alleles to have the disorder Lizzie and Amir have a healthy daughter Eva what symbol would she have on the family tree the key here is she is a healthy daughter so we're looking for an unaffected female so we're going to give her a blank circle and if you can use it black okay what is Eva's genotype genotype just means what allele she has so we already know that she's unaffected which means she has a normal dominant allele which she got from her dad but her other allele will have come from her mother who has got cystic fibrosis and therefore she can only pass on a little C to Eva so Eva's genotype is Big C little C for what is Sarah's genotype and explain how you know this so let's find Sarah here she is and she's also an unaffected female so because he's unaffected she must also have a Big C or dominant allele but how do we know what the other allele is well we need to look at her children to see what she and Tom have passed on one of her children has cystic fibrosis one allele killed from Tom but the other must have come from Sarah this means that Sarah must have a recessive allele herself as she passed it on to Lizzy try to use names in your answers if they've helped you work out the answer so she's Big C little C and finally Kari and Alex are both carriers of cystic fibrosis how does a family tree provide evidence for this so just a reminder carrier means they've got one recessive allele and one normal allele so they're both big C little C but how do we have evidence for this well we can see that they've got children that are affected or have cystic fibrosis but if we look at them we can see that they haven't got the disorder themselves which means they must be just carriers all right how did you do in the questions it's variation variation is to find us the differences in characteristics of individuals in a population this is a definition you should learn so for example poodles have got curly fur while Maltese have long straight fur Saint Bernards have floppy ears while German shepherds have ears that go really pointy and upright these are all examples of variation within dog populations can you think of any examples of human variation now we're going to look at what causes variation first up are genetic factors this just means that the genes you inherit from your parents can determine some of your characteristics like natural eye color there is a lot of genetic variation within a population this is caused by mutations mutations are changes to your DNA and they're happening all the time but it's very rare that they actually lead to any physical change but when they do you get a new variant variation can also be caused by your environment this means any external influences that are changing your characteristics for example just dyeing your hair this changes the color of it another example are hydrangea flowers if the plant is in acidic soil the flowers will be blue but if it's put in alkaline soil the flowers change to pink and finally there can be combined causes of variation and this is where variation is caused by both your genetics and the environment interacting together for example skin color you naturally inherit this from your parents but if you were to spend all day sunbathing your skin with darken most variation is caused by both your genetics and your environment other examples include height and width 9 evolution by natural selection evolution is a change in the inherited characteristics of a population over time for example these plants have purple flowers at the start but over many years they may evolve to have blue flowers instead evolution happens by the process of natural selection this theory states that all species of living things have evolved from simple life forms that first developed over three billion years ago that's nine zeros it's a long time but remember this is making every species ok so you need to know the stages of natural selection so let's break it down it starts with mutations these are changes in the DNA that cause variation in a population most of the time mutations don't do anything and just go unnoticed but very rarely they can cause a new phenotype or a new characteristic for example a mutation could cause this caterpillar to be brown rather than green like the rest of the population this might be bad news because he stands out to predators but maybe there's a change in the environment for example if there was droit the leaves might be Brian as well suddenly being Brian's looking pretty good as he's really camouflaged so if this new characteristic is beneficial the individuals are more likely to survive and breed when this happens they're going to pass on that beneficial allele to their offspring this will happen again and again until all of the population possesses the beneficial allele we say that the population has evolved if two populations from the same species become so different in their phenotype that they can no longer breathe successfully to produce fertile offspring like the green and the brown population of caterpillars we say we've got a new species ten selective breeding selective breeding is the process by which humans breed animals and plants for particular genetic characteristics there are four examples in the specification to learn first we've got disease resistance in crops animals which produce more meat or milk domestic dogs with gentle nature's and large or unusual flowers that will sell well the first cases of selective breeding where thousands of years ago when humans first bred food crops from wild plants and these domesticated animals to do selective breeding there are a few stages first of all you must select the parents that have the desired characteristics for example maybe floppy eared bunnies or more popular pets so you would select two parents that have floppy ears the second step is to them freed them together they will produce lots of offspring some of which will have the floppy ears this is because allele fur the characteristic is not always passed on to every offspring just some the third step is then to select the offspring that do have the desired characteristic ie the floppy ears and then you breed them together you repeat this for many generations and eventually all of the offspring will have the desired characteristic there are some problems with selective breeding it can lead to inbreeding this is when some breeds have an increased risk of disease or inheriting genetic defects for example pugs are known to have an increased risk of eye diseases and they often have breathing problems eleven genetic engineering in the last video we looked at selective breeding this is a slow process that takes many generations of reproduction to change characteristics genetic engineering is a lot faster but it is more complicated and requires more regulation in this process genes from the chromosomes of one organism are cut out for example the glow-in-the-dark gene these are then transferred to another organism's genome like a cat genome this can then be used to make a new organism that will have the desired characteristic in this case a glow-in-the-dark kitten genetic engineering is more commonly done in plants we call the genetically modified plants GM crops they are modified in a number of ways such as being more resistant to both disease and insect attacks increasing yield so that more of the same plant is grown in the same space like here you can see more Tomatoes have being purchased inside the same fire pot they can be modified for producing bigger and better fruits like these massive apples and they can be modified to become herbicide resistant which means that the weeds are killed but the crops are fine genetic engineering can also be done in bacteria for example putting the human gene for insulin into bacteria this means the bacteria can then make insulin that's used to treat diabetes if you study higher tier you'll need to know the steps of how genetic engineering is done so we'll look at those now but if you're studying foundation skip forward to the benefits and risks of genetic engineering first of all the desired gene is selected and cut out from an organism's genome using enzymes you can think of enzymes as a pair of scissors then a vector will be used to transfer the gene vectors can be bacterial plasmids or viruses in this case it'll be a plasmid which is just a loop of DNA the plasmid will be removed from the bacterial cell and then it will also need to be caught open again using enzymes the desired gene which in this case is insulin is then inserted into the vector the vector then transfers the gene into the new organism in this case the new organism is another bacterial cell when it reproduces all of the offspring will have the desired characteristic so all of these bacterial cells will be able to produce insulin this is then harvested and used to treat diabetes please note that if a gene is transferred into an organism like an animal or a plant it needs to happen at a very early stage of its development ie when it's still a very early embryo you've seen a lot of benefits of genetic engineering for example we saw lots of GM crops that had really good characteristics one more possible benefit is being explored by modern medical research they're hoping to cure genetic disorders for example replacing cystic fibrosis alleles with healthy alleles this would be a huge benefit however there are some risks on objections to genetic engineering some people are concerned that the effects of eating GM crops on our human health hasn't been fully explored there's also a risk of the modified genes spreading to other wild plants and flyers some GM crops were initially created to be infertile so it would have a huge impact if these genes managed to spread but so far this hasn't happened and some people worry there's a desire to manipulate the genes of future children in order to change how they look overall scientists agree that genetic engineering has had huge benefits but it's important to continue to regulate its practice 12 fossils and extinction fossils are the remains of organisms from millions of years ago that can be find in rocks it's important that you do say millions of years ago when you define it you need to know the different ways that fossils can be formed the first is when the conditions for decay are absent for example warmth and oxygen this insect is trapped in amber so we'll have no oxygen secondly hard parts of the organism like the skeleton and teeth are replaced with minerals as they decay and thirdly fossils can be preserved traces of organisms rather than the organism itself such as footprints burrows and rootlets races which gives evidence of plants we can learn from fossils how much or how little different organisms have changed as life developed an earth but the record is incomplete let's look at why it's incomplete well first of all most organisms that die don't actually become fossils then early fossils have actually been lost by geological activity for example when the crust moves and is pushed down into the mantle the fossils get destroyed then we think that there are lots of fossils still to be find finally early forms of life were soft-bodied which means they left few or no traces behind as soft parts decay and cannot be replaced by minerals this is why we cannot be certain about how life began on earth now we're going to look at extinction extinction occurs when there are no remaining individuals of a species still alive there are loads of examples of this but the most commonly known ones are the dinosaur species you need to know how extinction can occur so let's look at the five methods first of all is an introduction of new predators if a new species of predator appears it can quickly cause extinction of its prey species this happened when humans introduced predators on the island of Dodos secondly introducing new diseases can quickly cause extinction the species have no immunity to it next up there can be new more successful competitors if the new species competes for the same resources such as food or space then the old one made i-ight in this case the new plant gets all of the sunlight and all of the water and so the old plant will instead die now we'll look at some physical changes there can be changes to the environment over geological time this just means a really long period like millions and billions of years for example an ice age could cause the extinction of species that live in really warm climates and finally single catastrophic events like an asteroid collision or a volcanic eruption could cause a mass extinction this is one theory for how dinosaurs died 13 antibiotic resistance bacteria can evolve rapidly because they reproduce at such a fast rate some bacteria are pathogens which means they cause disease while others are harmless to humans mutations of pathogens can produce new strains of disease some of these strains are resistant to antibiotics and so when antibiotics are used they don't get killed instead they survive and reproduce the population of the resistant strain will increase and the new strain will then spread this is because people have no immunity to it it's a brand new disease there is no effective treatment for these resistant pathogens mr sa is an example of a resistant bacteria that you need to know about the M R means methicillin-resistant which is a type of antibiotic it's resistant to and this super bug can commonly be find in hospitals it's really important that we prevent the rise of antibiotic resistant bacteria or we may live in a world where we cannot treat infections but you might ask why not just make new antibiotics well the antibiotics are very expensive and very slow to develop it can take many years and they're unlikely to keep up with the emergence of new strains so we need to prevent them here are three ways hi first of all dr. should not prescribe antibiotics if they're not necessary ie if your illness is caused by a virus in which case antibiotics don't work or if it's not a serious illness secondly if you are prescribed antibiotics it's your duty as a patient to make sure that you complete the full course so that all the bacteria are killed and none survive to mutate and form resistant strains this is really important as some people think they feel better and stop taking them but actually they've still got pathogens in their bodies and thirdly antibiotics should not be used in agriculture some farmers use antibiotics to prevent their animals getting sick in the first place but this greatly increases the risk of resistant strains developing 14 evolutionary trees evolutionary trees are made using current classification data for living organisms and fossil data for extinct organisms you need to know how to interpret them the species name are put along the top of the diagram I've used letters here to keep it simple the time frame will be given usually in millions of years and you read across from it until you reach the branches where two branches meet it shows the last common ancestor between two species where the branches split is where speciation occurred species a and B and all of the other species evolved through natural selection branches that split recently are closely related species like B and C whereas branches it's but a long time ago are distantly related species like a and D you can be asked to collect data from evolutionary trees for example when did species D evolve just find the species on the diagram read dine until the branch splits and across and you'll get your answer and species D was about seven point five million years ago if there is a species whose line doesn't or up to the top or to the zero million years mark like species II then this shows us that that species went extinct in the case of species II we can read across and work out that it went extinct 2.5 million years ago 15 classification [Music] in the 18th century Carl Linnaeus developed a classification system that is still being used today it groups living things based on their structure and characteristics he came up with these levels of hierarchy with the highest and biggest at the top it goes kingdom phylum class order family genus and species this is something you need to know in the correct order so let's make a mnemonic for it you should try making your own with something that's really personal to you you just take the first letter of each word and make it into a silly sentence here's an example keep palms clean or frogs get sick no in the exam you just write your letters out again and then revert them back to the scientific words the last two levels of classification make up the binomial classification of a species which is just its two-part name remember by means two so if you're asked for the species name or binomial name you always give the genus and the species part for example humans are Homo sapiens and wolves are Canis lupus you'll be given the information needed to work the site notice that the words are written in italics and the genus name always starts with a capital letter there is now a new level of classification developed by an American scientist called carl woese this new level is called due means and it is above kingdoms so we could modify our mnemonic to say definitely keep ponds clean or frogs get sick he and his team came up with this new classification due to improvements in biology first of all microscopes have really improved a lot over the years and we can now see a lot more of the internal structures of cells secondly our understanding of biochemical processes that happen in living things has also really progressed since the 18th century domains can be split into three different grips and you need to know the names of them first of all we've got the archaea these are primitive forms of bacteria that live in extreme environments eg hot vent bacteria that can survive really high temperatures the next domain we've got are bacteria also known as the true bacteria the third domain is eukaryota you'll have learned by eukaryotic cells in the first topic of biology and hopefully you remember the four kingdoms fungi protists animals and plants and if you want to read about the prokaryotes which you also learned by in that topic then archaea and bacteria both encompass these type of cells finally I've got a little tip for you to remember what's his name we can split it up maybe he was woeful which means sad when he first saw Linnaeus his classification system and realized something was wrong and now he's saying see look I fixed it maybe it'll help now we're on the last topic which is ecology number one communities ecosystems are complex they are made up of communities of living things interacting with each other and the nonliving parts of their environment some examples of ecosystems include grassland desert and tropical rainforests to survive and reproduce organisms require a supply of materials from their surroundings and from the other living things there for example cars need grass and plants need sunlight water and nutrients as well as other things if one species is removed it can affect the entire community for example if Penguins were removed then a number of sales would decrease which in turn would affect the numbers of polar bears and killer whales we'll look at food genes in more detail in a later video because species survival depends on other species we say that they are interdependent inter just means between so interdependent is dependence between species if species are imbalanced with each other and environmental factors are also imbalance then we call it a stable community in this community the population size remains fairly constant because of all of the balance do biotic and abiotic factors abiotic factors are the nonliving factors which can affect a community there are lots in this diagram I want you to take a moment to pause the video and see how many you can spot ready first up is light intensity plants require light for photosynthesis so where it is dark plant growth is limited which of course will affect the rest of the community next is moisture levels these are really important for all organisms as all life needs water to survive the desert is really dry as it doesn't rain very often so there are much fewer organisms living there some insects like slugs for example need really moist environments - wind intensity and direction can affect the ability of plants to grow and anchor their roots as well as affecting smaller organisms did you spot this one carbon dioxide levels affect plants as it's a reactant for photosynthesis and occasionally it can affect animals like mosquitoes that detect their prey by high carbon dioxide levels maybe you spotted this one - oxygen levels affect aquatic animals like fish that use it to respire the pH of soil and its mineral content affects plants some plants don't survive in very acidic or alkaline environments and of course all plants need minerals to survive temperature affects many organisms as most live within a small range of temperatures this is why climate change is having such a severe and drastic effect on species all around the world now I will look at biotic factors these are the living factors that affect communities why not do the same thing and pause the video and see how many biotic factors you can ice Popp ready here we've got a new predator these can really disrupt a community and they can even cause extinction availability of food is also really important as without adequate food populations can starve to death new pathogens can also devastate populations if they have no immunity - and finally one species are competing another can cause numbers to decrease to the point where they are no longer sufficient to breathe you can see this bird has got loads of worms while this bird has none notice that three of these biotic factors are the same as three of the five reasons for species extinction can you remember the other two I recommend making a mnemonic to learn all of the biotic and abiotic factors that affect communities this is a really good way to help you revise three competition there are many organisms in any given community and they all require resources for example food or territory these things are limited so competition takes place when each individual attempts to secure the resources it needs competition can take place between different species for example different tree species in a forest competing for light it can also take place within a species this is often more intense competition as the individuals require exactly the same resources let's look at animal competition first of all animals compete for food here you can see seagulls fighting over some chips this is a really common form of competition secondly animals compete for territory which is just space lions are very territorial and there is usually just one adult meal in each pride pet cats are territorial too and most cat fights are as a result of overlapping territories thirdly animals compete for mates or sexual partners there are lots of adaptations in the animal kingdom to win myths including the amazing meal Peacock's feathers males will often fight each other as well for access to females now let's look at plant competition plants compete for light growing as quickly as possible vertically to reach the sunlight or having large thin leaves to increase the surface area and maximize light absorption plants also compete for space often they're very crowded so they spread their roots stems and branches and when they disperse their seeds they try and get the seeds as far away as possible from the parent plants this means that the seeds will have enough space of their own to grow in this example you can see that the dandelion is using wind to spread its seeds but water an animal dispersal or other methods and finally plants compete for both water and minerals from the soil their roots absorb both of these and so the roots will spread as much as possible to absorb what the plant needs for adaptations adaptations are features that allow organisms to survive in the conditions in which they normally live a simple example is that fish live underwater so they need gills to take in oxygen from the water adaptations can be structural behavioral or functional we're going to take a look at some examples of each so that you understand what these words mean but you don't need to memorize the examples as a specification says you'll be given appropriate information to allow you to explain how organisms are adopted structural adaptations are physical characteristics for example polar bears have fur to insulate them in a cool environment another example is that cacti have spines instead of leaves to reduce the surface area so less water is lost in a hot and dry desert environment behavioral adaptations are higher organism behaves for example a lizard basking in the hot Sun on a rock to raise its body temperature another example is that birds migrate to warmer countries in the winter functional adaptations are about how something works or functions for example some fish and frogs living in very cool environments have got antifreeze in their cells so that they don't freeze to death and some animals only give birth in a certain season to maximize their offsprings survival there is one group of organisms that you need to know about in slightly more detail these are called extremophiles these organisms live in very extreme environmental conditions for example they may live in high temperatures high pressure or high salt concentrations bacteria that live in deep-sea vents are called extremophiles and these are an example you need to know five fit jeans fit jeans are simple ways of showing the feeding relationships within a community they always start with a producer a producer is an organism that can use light to carry out photosynthesis to make oxygen and glucose producers are green plants algae like seaweed and phytoplankton primary consumers eat producers here the field mice will eat the grass secondary consumers then eats the primary consumers this weasel will hunt and eat the mice because it kills other organisms to feed from we call it a predator we then call the mice the prey tertiary consumers eat secondary consumers these are often top predators or apex predators that aren't hunted and eaten by anything else for example polar bears or killer wheels there can be levels above this but this doesn't happen too often as energy gets lost as you go up through each different level you'll learn more about this when you study pyramids of biomass now let's look in more detail at predator prey feeding cycles if the prey like this mice has access to lots of food then his numbers will rise as more individuals survive and reproduce we'll use green to represent prey but if the predator now has a larger food source it will be more successful too so its population will increase as well and we'll use red for the predator of course NARR there are more predators to eat the prey so the prey numbers will start to drop again and they'll drop back to roughly where they started but as the prey numbers drop so will the Predators as there are too many to get enough food so some won't survive to adulthood to reproduce this cycle will continue with fewer predators meaning the prey population can start to increase again and so on and so on the cycle will constantly repeat itself if it's in a stable community six sampling transics and quadrats sampling is done by ecologists to find the abundance of organisms that means how many there are and to see the distribution of organisms which means where they are fond we're going to look at two methods that are used these are both part of a required practical so it's important to make sure that you understand them firstly you can use quadrats these are square frames that are laid in the ground they may or may not have a grid inside them you can then count the number of plants or slow-moving organisms inside them for obvious reasons they can't be used for large or quickly moving organisms how many flowers can you count inside this quadrat well we can clearly see that there are five that are inside the quadrat and one that's part in in part it actually doesn't matter which way you count it it could be five or six as long as you use the same method for every quadrats ample that you do it's also important to take as many samples as possible let's make sure that your data is followed which means that it shows what is actually happening you also need to do quadrat sampling at random you can do this by blindfolding yourself and spinning before throwing closing your eyes or a better way is to split your sample area up into a grid and then use a random number generator to pick your sample sites if this Quadra were representative of a community how many flowers would you expect to find in one meter squared well first of all let's take a look at the size of this Quadra we've been given the length of it as 0.25 meters we want to know the area as its meter squared and as it's a square we're just going to multiply that number by itself this will give us on a calculator which you are allowed to use 0.0625 meters squared now we need to see how many times smaller this is than one meter squared so we do 1 divided by 0.0625 and that comes out at 16 so this quadrat is 16 times smaller than a 1 meter squared quadrat let's say we took our coin to be 5 we would nine just do 5 times 16 to see how many you get in one meter squared and it comes out at 80 flowers per meter squared now let's say you took seven samples with your quadrats and these are the results that you got you could be asked to process the data to give any one of these two let's take a look at what each one means and work it on the mean is just the average so to do this all you do is add up all of the numbers and divide by how many values you have so in this case we had seven samples so we divide by seven and this would give us four point two eight five seven questions will specify if they want it to two decimal points or two significant places etc in this case we'll do it to two decimal points and the five makes the eight round up to give us four point two nine the median is the middle value so we need to write all of our numbers out from smallest to largest and then we just check which number is in the middle and is five the mode is the most common value in this case it's 6 as we have three of those and finally the range is the highest value minus or dig away the lowest value which in this case is 6 minus 1 gives you 5 the second method of sampling is a transect we're going to look at line trans x this is just a measuring tape that is stretched between two points with quadrats placed along it at regular intervals like every 5 meters it allows you to see the effects of an abiotic factor on the organism distribution and you can also measure this factor along the transact for example light intensity reducing from a grassland into a woodland and you might predict that there'll be a big change in the distribution and variety of organisms find as there'll be different amounts of photosynthesis able to take place in each area seven water decay and carbon cycles the water cycle is all around you you see this being cycled all the time in the form of rain water is evaporated from the Earth's surface to become water vapour as it rises in the atmosphere it cools dawn will eventually condense then it falls as precipitation in the form of rain snow or heel and then the cycle starts all over again next up is a decay cycle decomposers are really important these are microorganisms which include the groups of bacteria and fungi decomposers feed and break down dead organisms as they do this they release carbon dioxide back into the atmosphere because they are aspiring decomposers also release mineral ions back into the soil for new plant growth the job of decomposers is really important if we didn't have them all of the materials would be locked inside dead organisms and eventually no new life would be able to form now let's look at the carbon cycle pause the video take a look at the pictures and see how much of it you can already describe then press play to learn more about it we'll start off with feeding which is just when one organism takes in the organic material of another which contains carbon all living things will eventually die plants and animals do this but of course ponds don't have skeletons when an organism is dead if it's left in the right conditions for millions of years it will fossilized into coal oil or gas the alternative is that it will be broken down in the decay process which we just learned is done by decomposers as they do this the decomposers release carbon dioxide back into the atmosphere this is just showing that as some of the carbon dioxide may dissolve into the waters and oceans of our earth here's a little dawn cross diagram to test your links in chemistry okay so going back to fossilization we can burn the fossil fuels in the process of combustion and this releases energy but also carbon dioxide all living things carry out the process of respiration to release energy for their cells but also releases carbon dioxide into the atmosphere when is aerobic respiration finally the process of photosynthesis is a big process that removes carbon dioxide from the atmosphere this is really important as you'll soon learn in the climate change video you'll have learned more about photosynthesis in the bioenergetics topic it biodiversity and land use biodiversity is a variety of all the different species of organisms on earth or within an ecosystem the rainforest has a really high biodiversity because there are lots of different species there while the desert has a much lower biodiversity as last species live there the future of the human species on earth relies on us maintaining a good level of biodiversity let's recall the definition for a stable community this is one in which there's a fairly constant population size but why well having a higher level of biodiversity means that species are less dependent on just one other single species for their survival like for shelter or food for example monkeys might live in trees that's their habitat but let's say a tree gets a disease and that species is wiped out well if it's a high level of biodiversity the monkeys can just find other trees to live in as those will be there too let's say there's a species of bird in a desert that relies on a scorpion when the scorpion dies the birds will also die as that's their only source of food as there's a very low biodiversity so biodiversity is important for species survival but humans unfortunately have been doing activities that reduce biodiversity and is only recently that we've recognized this and tried to stop it let's look at three main ways in which humans have reduced biodiversity first of all is building we clear huge amounts of land of animals and plants to make way for our buildings secondly is quarrying this uses explosives to blow up parts of the earth to get the materials that we want from it of course this is really destructive to vegetation and animals living there and thirdly is landfill these horrible mines of rubbish unfortunately ruin habitats and can even be toxic 9 pollution and waste management humans have lived in this planet for thousands of years but in relatively small numbers in the early 1800s our population passed the 1 billion mark for the first time in the last 200 years it has skyrocketed to over 7 billion people and the United Nations predicts there will be nearly 10 billion people by 2050 in addition to this huge number of people our standard of living is definitely increasing this means that we are using more and more resources and producing more and more waste and if this waste isn't handled properly it can cause serious pollution which is reducing biodiversity by killing animals and plants there are three types of pollution that you need to know about the first is land pollution in the previous video you saw that landfill sites destroy natural habitats and the household waste can spread toxic chemicals from the waste into the soil pesticides and herbicides are one example they can get into food chains when plants covered in the toxic chemical are eaten the further up the chain you go the more toxic chemical accumulates which can end up poisoning top predators the second type of pollution is air pollution when we burn things the smoke that comes off it contains tiny solid particles that can hang around in our atmosphere humans and animals breathe them in causing damage to the lungs acidic gases like sulfur dioxide are also formed when fossil fuels are burned this sand dissolves into rainwater forming acid rain which can kill animals and plants in lakes and thirdly we've got water pollution this includes pesticides herbicides sewage and fertilizer all of these can get into our waterways but the last to continue nitrates when they're washed into the water it can cause algae to grow very rapidly but it will then die and when this happens microorganisms break it down but they use lots of oxygen out of the water to respire and this low oxygen level means that aquatic organisms like fish died one tip to remember these three types of pollution is law land air water and the link is that perhaps we need more laws to protect our environment from this pollution if we don't biodiversity will continue to drop and drop 10 deforestation on peat bog destruction peat bogs take thousands of years to form from dead plants they're very acidic and so they provide a unique ecosystem for lots of organisms that depend on it for example Finas flytraps peat can be taken from the peat bogs and used as fuel but when it burns it releases carbon dioxide it can also be used as garden compost by leaving it to decay but as it decays it also releases carbon dioxide destroying peat bog reduces biodiversity as species lose this unique habitat deforestation is also reducing biodiversity which is when land is cleared of its trees this is happening particularly in tropical areas like rainforests it's cleared for a few different reasons first of all to make room for cattle and also for rice fields and the third reason is to make room for crops that are used to make biofuel species like orangutans are now facing extinction as their habitats are taken from them there's another impact and it's to do with carbon dioxide pause the video and see if you can make the link between deforestation and carbon dioxide okaywell deforestation increases carbon dioxide levels normally trees absorb carbon dioxide during photosynthesis the last trees mean there's less absorption of carbon dioxide during this process if the cut time trees are burned they'll also release more carbon dioxide into the air you'll learn more about the impact of this gas in the next video eleven global warming global warming is the increase of the Earth's average temperature it's caused by two gases carbon dioxide and methane in the previous video we learned that the burning and decay of peat releases carbon dioxide and we saw that deforestation also causes an increase in the levels of this gas burning fossil fuels is another huge contributor to these increasing levels but methane is also on the rise cattle release methane as they digest grass and rice fields release it as they grow both carbon dioxide and methane caused global warming by creating a greenhouse effect this is when solar radiation from the Sun is prevented from escaping our atmosphere by the blanket of greenhouse gases instead it gets reread eiated back to the earth increasing the surface temperature it's important to know the difference between global warming and climate change as I mentioned at the start global warming is the Earth's average temperature but climate change is more severe weather patterns if you're given one particular freeze in an exam question you should use that same phrase in your answer global warming and climate change will have biological consequences there are four you need to know first of all is a loss of habitat when the sea levels rise it will cause flooding and coastal habitats will disappear this will cause a change in distribution of organisms as well for example grizzly bears will be able to spread further north as a gas warmer but polar bears range will shrink as they lose the ice caps global warming will also cause changes in migration patterns many species of birds insects and some mammals move around the world with the seasons but this may change as the climate changes and finally it will cause reduced biodiversity climate change will cause the extinction of many species as they are unable to survive in a changing environment I have one final thing to mention that is slightly hidden in the specification that is that there is scientific consensus which means agreement that global warming is happening and climate change will occur as a result this is based on systematic reviews of thousands of peer-reviewed publications to sum it up there is a huge amount of evidence that global warming is happening 12 maintaining biodiversity scientists and concerned citizens have put in place programs to reduce the negative effects of humans on ecosystems and biodiversity these include breeding programs for endangered species like this goal in lion tamarin which can be pretty hard as some species take a long time to reproduce and it's important to prevent inbreeding even if it is successful often the species natural habitat has been destroyed so there's no where to safely release them another method is the protection and regeneration of rare habitats this will secure a home for the species that live there these habitats include wetlands and coral reef thirdly when farmers grow only one type of crop in a field they've been encouraged to reintroduce hedgerows which are these bushes and shrubs at separate fields and field margins which are unfarmed areas around the crop this will allow wildflowers and other species like insects and birds to live there and this is the theme for hedgerows they provide a home for lots of countryside animals ok there's two more methods you need to know this is the reduction of deforestation and carbon dioxide emissions but this is only by some governments unfortunately it's not being done worldwide and some countries refuse to acknowledge the level of threat that we're facing from climate change and finally five recycling resources rather than dumping waste and landfill this will help to reduce the toxic waste entering our soils and weighs and reduced the consumption of new materials okay well this topic is likely to come up as a six mark question so it's important that you do learn all of these methods a good idea to help you remember them would be to come up with a mnemonic well come up with 1 9 so let's just recap what each letter stands for B is for breeding endangered species pH is protection of habitats FMH is field margins and hedgerows d c o is reducing deforestation and carbon dioxide emissions and r is for recycling so these are our five methods of maintaining biodiversity now I will go through and make a mnemonic which is a silly sentence to help you remember these letters you can learn more about this in my mnemonic video but here's one that I have come up with big pandas have frequent madness however doctors can only record so I'm imagining a grumpy panda and a doctor standing nearby looking at them and recording their observations time to check so can you remember what the mnemonic is pause or just say it alright light and maybe this silly illustration will help here it is big pandas have frequent madness however doctors can only record non pause the video and see if you can say the five methods of maintaining biodiversity using these letters here they are let me know how many did you get right you can leave a comment below saying how many you got out of five sherry is Gary you can also support me by buying me a virtual coffee on coffee calm the links below and thank you again so much for watching my videos [Music]