Let's see how quickly we can cover the main ideas found in EDXL GCSE biology paper one. This is good for higher end foundation tier, double combined or triple separate. That's topics one to five. Key concepts cells and control genetics natural selection and genetic modification and health disease and medicines. It's a mouthful, isn't it? I'll tell you when some of the bigger concepts are just for triple but not for higher and foundation tier because there's not a lot of difference to be honest. We're going to be really moving here. So, pause the video if you need a bit more time to get your head around something you see. Let's go. All life consists of cells. We can see cells with a normal light microscope and maybe the nucleus, but the subcellular structures won't really be visible. Using an electron microscope, however, allows us to see far finer details. So, we can see an image of the organels. As such, these microscopes have a better resolving power and a higher resolution. We say we can calculate the actual size of a cell by knowing the magnification of the microscope. Magnification is equal to image size divided by object size. Therefore, rearranging this, we can measure the size of the image, then divide by the magnification, and that gives us the actual cell size. We put them into two main groups. Ukarotic cells have a nucleus in which their DNA is found. That's your plant and animal cells, for example. Proarotic cells don't have a nucleus. Both ukarotic and proarotic cells contain similar organels or subcellular structures. The cell membrane keeps everything inside the cell, but they're also semi-permeable, which means they allow certain substances to pass through. Plant cells and most bacteria have an extra cell wall made of cellulose providing a rigid structure for them. Cytoplasm is the liquid that makes up the cell in which most chemical reactions take place. Mitochondria where respiration takes place releasing energy for the cell to function. Ribosomes are where proteins are assembled or synthesized. Plant cells also contain chloroplasts which contain chlorophyll where photosynthesis takes place. Plant cells also contain a permanent vacule in which sap is stored. Enzymes are biological catalysts, some of which break down larger molecules into smaller ones that can then be absorbed by the villi in your small intestine into the bloodstream to be transported to every part of your body. For example, amalayise is the enzyme that breaks down starch into glucose. It's found in your small intestine and saliva. Enzymes are specific that is they only break down certain molecules. For example, carbohydrases break down carbohydrates into simple sugars. Ama is one of these. Proteases break down proteins into amino acids. And lipases break down lipids, that's fats, into glycerol and fatty acids. They're specific because they work in a lock and key principle. The substrate, for example, the starch, binds to the enzyme's active site. We then call this a complex. However, this can only happen if the substrate is the right shape in order to fit the active site. In reality, they're incredibly complex shapes. No pun intended. These shapes here are just to represent them. Much like a lock and key, it only works if they're the right shape for each other. The rate of enzyme activity increases with temperature due to the molecules having more energy. That is until the active site changes shape and so the substrate no longer binds. We say the enzyme has denatured. This maximum rate occurs at the optimum temperature. Optimum meaning best. This is similar for pH as well except it can denature at too high or too low pH. The practical on this involves mixing amalayise with starch at different temperatures or with different pH buffer solutions. Once mixed, we start timing. Then every 10 seconds, we remove a couple of drops and put in a spot in tile dimple with iodine in. To begin with, the iodine will turn black due to there still being starch present, but eventually will stay orange showing that all of the starch has been broken down. Calculate the time taken to do that. Then plot these times against pH or temperature. draw a curved line of best fit and the lowest point is where the starch would have taken the shortest time to be broken down. That's the optimum temperature or pH. However, in true biology fashion, we're technically not allowed to interpolate between points for some reason. So, we must only say that the optimum pH or temperature is between the two lowest points. Shrug. Food tests allow us to identify what nutrients are in our grub. Iodine turns from orange to black in the presence of starch, like we just saw. Benedict's solution turns from blue to orange in the presence of sugars. Bouet's reagent turns from blue to purple with proteins. Cold ethanol will go cloudy with lipids, that is fats. Diffusion is the movement of molecules or particles from an area of high concentration to an area of low concentration. We say they move down the concentration gradient. Like a ball just rolling down a hill, it'll do it by itself. This doesn't require any energy input. So, we say it's passive. This will happen across a semi-p permeable membrane if the holes are large enough for the molecules to move through. For example, water can pass through, but glucose will not, at least not by diffusion anyway. Osmosis is the name specifically given to the diffusion of water across such a membrane. For example, if there is a higher concentration of glucose outside a cell, the glucose cannot diffuse in to balance the concentration. So instead, the water moves out of the cell resulting in a decrease in its mass. The rate of diffusion and osmosis can be increased by increasing the difference in concentrations, increasing the temperature or increasing the surface area. This is why the villi in your small intestine are lumpy as well as alvioli in your lungs and root hair cells for example too. The practical on osmosis goes as follows. Cut equaliz cylinders from a potato or other vegetable. Weigh them and place in test tubes with varying concentration of sugar solution. After a day or so, we remove them, dab the excess water off their surface, and reweigh. We calculate percentage change in mass by doing final mass take away initial mass divided by the initial mass times 100. If it's lighter than it was before, this must be a negative change in mass. We plot these percentages against sugar concentration and we draw a line of best fit. Where this crosses the x-axis is what concentration should result in no change in mass. So, no osmosis. So this means this must be the same as the concentration inside the potato. Glucose and other nutrients and minerals can move through a membrane by active transport where carrier proteins use energy to move substances through the membrane. As there's energy used, this can actually move them against a concentration gradient. For example, moving mineral ions into plant root hair cells. Ukarotic cell nuclei contain DNA which is stored in several chromosomes. Humans have 23 pairs of these in every nucleus. So we call them diploid cells. That's not the case for gametes though. They have half so just 23 not 23 pairs. So therefore we call them hloid cells. New cells must constantly be made for growth and repair. They do this by duplicating by mitosis. Here's the process, the mitosis process. The genetic material is duplicated and the number of ribosomes and mitochondria is doubles as well. The nucleus breaks down and one set of each chromosome pair is pulled to opposite sides of the cell. A new nucleus forms in each of these to house the copied chromosomes. And we now have two identical cells. Cells specialize depending on the function they need to fulfill. For example, nerve, muscle, root hair, xyllem, phm cells. Stem cells are those that haven't yet specialized. They're found in human and animal embryos and the merry stem of plants. That's the top of the chute. Stem cells are made in your bone marrow throughout your life as well, but these ones can only specialize into blood cells. We can use stem cells to combat conditions like diabetes and paralysis. In fact, right out of the movie The Island, people are now getting clones of themselves made, then harvesting the stem cells, as these won't be rejected by the patient. Personally, I think this is a dystopian man-made horror beyond comprehension. You have to weigh up the ethical arguments for yourself. Cloning plants can be used to prevent species from becoming extinct or produce crops with specific characteristics. 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 aector 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 aector. This is a reflex arc. This of course is much faster than a conscious decision. Glands can also be aectors which produce specific chemicals your body needs depending on the situation. For example, your salivory 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 a 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 suvat s= 80^ squ but you'll never be expected to do that in this paper but it's something you could mention if you were asked a six marker on this. 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 gata 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 eyes 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 siliary muscles relax and the suspensory ligaments tighten. 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 siliary muscles contract. The suspensory ligaments slacken and the lens becomes fatter or thicker and so that means that it becomes more powerful actually. So light is refracted more which means that the light coming from the object still converges meets focuses on the retina. So you can see a clear image. The pupil, the hole in the iris can change size depending on the light intensity hitting the eye. The cornea is the transparent outer layer where light enters the eye. It has a slight lensing effect itself. While the white surface that covers the rest is called the scara. The light is focused then on the retina at the back of the eye which consists of rod and cone cells which respond to light. Rods can only detect light intensity so no color while there are three different types of cones which detect green, blue or red wavelengths of light. a mix of which will produce the colors we then perceive when the signal reaches our brain via the optic nerve. Myopia is the medical term for short-sightedness. You can't focus on far objects. Hyperopia is long-sightedness. Glasses or contact lenses are usually used to mitigate this by slightly converging or diverging the light before it enters the eye. Laser eye surgery aims to change the shape of the cornea to achieve the same effect. 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 hloid cells ready to fuse with another gamet which in this case would be an egg. This is one way that variation occurs in offspring. Plants do this with pollen and egg cells, but they can also reproduce asexually. But as it doesn't involve 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 on 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. 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 nucleotides, and they're made from a sugar and phosphate group, of which there are four types, A, T, C, and G. You don't need to know what the names are, but A and T always match to each other in the sequence, as do C, and G. Every three of these bases, we can call them, are a code for an amino acid. The sequence is copied by mRNA. This copy is then taken out of the nucleus to a ribosome in the cell where amino acids are connected in the order needed which makes a protein the shape of which affects its 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 alals. Usually characteristics are dependent on two or more genes though and them interacting. Dominant alals are those that result in a characteristic being expressed even if there is another alil present, a recessive al. For example, if you have the alals big B, little B for eye color, big B being brown, little B being blue, you will have brown eyes. It's only when there's no dominant alil in this case that the recessive alil is expressed. So me having blue eyes, I must have the gene little B little B. Big B big B or little B little B are called homozygous as they only have one type of alil. Whereas big B little B is what we call hetererozygous. We can use a punit square to predict the probability of a certain phenotype. My parents have brown eyes, but they both have hetererozygous alals for eye color. There are three different outcomes of these combining with a 25% chance of making me. That's little B, little B. So, I'm not so much one in a million, more one in four. My sister has brown eyes, but her son 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, polactylene, extra fingers or toes, which is caused by a dominant alil, or cystic fibrosis, which is caused by a recessive alil. Even if two parents don't have cystic fibrosis, they could still be carrying the recessive alil. So, their child could have the disorder. Human DNA is contained in 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 punit 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 the environment than others and so are more likely to survive and reproduce. But like we've seen, 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. Jean Baptiste 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 divide, 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 like 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 Labrador's colleagues. And if you're into undesirable characteristics, pugs, too. Just for triple, Johan Mendel was one of the first people to assert their characteristics were determined by units that are passed on to offspring. Due to the discovery of genes and chromosomes, he was proven largely correct. 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 egg 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. CVD, cardiovascular disease, is an example of a non-communicable disease as the cause of it comes from inside your body. Other examples of such diseases include autoimmune conditions like allergic reactions and cancer. A communicable disease must be caused by a pathogen that enters your body that will cause a viral, bacterial, or fungal infection. Again, more on these in a bit. Back to non-communicable diseases. Obesity and too much sugar can cause type 2 diabetes. A bad diet, smoking, and lack of exercise can affect the risk of heart disease. Alcohol can cause liver diseases. Smoking, lung disease, or cancer. A carcinogen is the name given to anything that increases the risk of cancer, for example, ionizing radiation. Cancer is a result of damaged cells dividing uncontrollably, leading to tumors. Benign cancers don't spread through the body, and they're relatively easy to treat. However, malignant cancers are when these cancerous cells spread through your body, much worse. BMI stands for body mass index. It's an indication of whether or not somebody has a healthy weight or not relative to their height. The equation is this. BMI is equal to weight. Well, mass we know, don't we? Divided by height squared. And whatever number you have will put you into certain bands will determine whether or not you're a healthy BMI, overweight, obese, etc. As mentioned just now, communicable diseases are caused by pathogens. That can be viruses, bacteria, fungi, or protests. These are single-sellled parasites. They all reproduce in your body and cause damage. But viruses can't reproduce by themselves. A virus is in fact just a protein casing that surrounds genetic code that it injects into a cell, which causes the cell to produce more copies of the virus. The cell explodes, and the virus goes on to infect more cells. Creepy, isn't it? HIV is an STD or STI, sexually transmitted disease or infection that compromises your immune system. This is also called AIDS for short. It can also be spread by people sharing needles. Bacteria on the other hand release toxins that damage your body's cells. Fungi do something similar like athletes foot while protest do all sorts of different things. For example, malaria is caused by a protest that burrows into red blood cells to multiply then burst out destroying the red blood cell in the process. It's spread by mosquitoes. So, we say mosquitoes are the vector for the disease. Our bodies are excellent at protecting us from these pathogens, though, thank goodness. Skin is the first barrier to them entering. And if they do enter your nose and trachea, they can be trapped by mucus. Acid and enzymes in your digestive system will destroy them, too. If they still manage to enter the bloodstream, though, white blood cells are ready to combat them. One type of these are called lymphosytes. They produce antitoxins to neutralize the poisons pathogens produce and also they make antibodies which stick to the antigen on a pathogen and this stops them from being able to infect more cells and it makes them clump together. Fagasites are then able to ingest them and destroy them. An antigen on a pathogen will have a specific shape. So that means only an antibbody that fits it will neutralize it. If pathogens are unknown to the immune system, lymphosytes will start making all different shapes until one fits. Miraculously, your immune system will then store a copy of this antibbody next to a copy of the antigen, so it's ready to stop it from causing an infection next time you're exposed to it. You now have immunity. A vaccine is a dead or inert version of a pathogen, usually a virus, that exposes your immune system to the pathogen so it can produce the antibbody without it infecting you. For example, the flu vaccine, you're injected with the virus that has been irdiated, so the DNA has been damaged inside, so it can't do the job. Incidentally, the co jab, however, was intended to work differently. Instead, you're injected with the DNA, technically mRNA, needed to trick your cells into synthesizing part of the virus, including the antigen. It was the first widely used jab that used this mRNA technology. Just for triple, bacteria multiply by binary fision. So, the number doubles every, say, 10 minutes. So, if we started with one bacterium, after an hour, we'd have 2 ^ of 6, that's 64. After 6 hours that's 36 lots of 10 minutes. So in theory we'd have 2 ^ of 36. That's in standard form 6.87 * 10. We can do a practical on this by producing a culture on agar in a petra dish using aseptic technique. That is making sure nothing else contaminates the culture. We lift the lid of the dish towards a flame which causes other microbes in the air to move away and upwards from the dish and it destroys them too. Using sterilized equipment, we can either put a drop of bacteria culture in the middle or spread it all around and put spots of different antibiotics on top instead. We put a few bits of tape around the dish to hold the lid on, but not all the way around, otherwise air will not get in and the bacteria will respire anorobically. We then incubate it at 25°. Once the culture has grown, we can either calculate the size of the culture from an initial drop or the area in which bacteria did not grow or were killed by an antibiotic to then compare with others. In both cases, we use p<unk> r^ squ or p<unk> d^2 over 4 to calculate the area of the circles. Antibiotics kill bacteria. They don't kill viruses. Penicellin was the first one. There are good bacteria in our bodies. So, antibiotics are designed to be as specific as possible because you don't want to damage those or your body cells either. Problem is, as bacteria mutate, they can become resistant to them. So, the more you use them, the less effective they become. Drugs used to be extracted from plants and other organisms. For example, aspirin comes from willow trees, penicellin from a mold. Now synthesizing drugs is one of the biggest industries on the planet. They have to be trial to see how effective they are and to check for side effects. First, we do lab trials on cell tissue, then trials on animals. Next, human trials. We give the drug to a group of people, but we also give a placebo to a control group without telling them. Say a pill that's just sugar, not the actual drug. This is what we call a blind trial because the test subjects don't know what they're taking. A double blind trial is when even those analyzing the results from the tests aren't aware of which group is which. And that's to eliminate any bias. Just for triple, this is a crazy one. Monocclonal antibodies. They're made from clones of a cell which is able to produce a specific antibbody to combat a disease. This is achieved by combining lymphosytes from mice to tumor cells and this makes a hybrid cell. This is then cloned to produce a lot of antibodies ready to treat a patient. These monoconal antibodies can also be used for medical diagnosis, pathogen detection in a lab, or even just identifying molecules in tissue by binding them to a dye so they glow when grouped together because they'll be designed to bind to a specific molecule. The downside to these is that the side effects are turning out to be worse than scientists expected. So, I hope you found that helpful. Leave a like if you did and pop any questions or comments below. And hey, after you've done the exam, come back here and tell us all how you found it. We'd love to know. Click on the card to go to the playlist for all six papers, and I'll see you in the next video.