All of AQA BIOLOGY Paper 1 in 25 minutes - GCSE Science Revision

0:00 All right, let's see how quickly we can cover everything you need to know for AQA GCSE biology paper 1. This is good for higher and foundation tier, double combined trilogy and triple or separate biology that is cells, organization, infection and response and bioenergetics. I'll tell you when something is just for triple, but not when something's just for higher tier because there's not much difference to be honest. We're going to be 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. First up, everything about cells. 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.

0:47 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

1:34 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. Just for triple bacteria multiply by binary fision. We can do a practical on this by producing a culture on aar in a petetro 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

2:19 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 degrees. 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 r^ 2 or p d^² over 4 to calculate the area of the circles. 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

3:05 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. 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. By the way, AQA just say the nucleus divides, which isn't quite right, but you will get the mark if you put it. 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 shoot. Stem cells are made in your bone marrow throughout your life as well, but these ones can only specialize into blood cells. We can

3:50 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. 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-permeable membrane if the holes are large enough for the molecules to move through. For example, water can pass

4:36 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 equalsiz 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

5:22 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 time 100. If it's lighter than it was before, this must be a negative change in mass. We plot these percentages against sugar concentration and we draw a line of best fit. Where this crosses the x-axis is what concentration should result in no change in mass. So no osmosis. So this means this must be the same as the concentration inside the potato. Glucose and other nutrients and minerals can move through a membrane 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

6:09 cells. It's when cells get organized together that things get interesting, though. When similar cells are connected, we call this a tissue, say heart tissue. Tissues form organs, for example, your heart, and organs work together in an organ system, like your circulatory system. Your digestive system breaks down food you eat into useful nutrients for your body to use. Acid in your stomach breaks it down. Bile and enzymes work together in your small intestine to break it down further. Bile is made in the liver and stored in the gallbladder before being used. What it does is neutralize the acid from the stomach and also emulsifies fats to form droplets that increases their service area exposed to the enzymes so they're broken down faster. Enzymes are biological catalysts, some of which break down larger molecules into smaller ones that can then be absorbed by the villi in

6:54 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 on 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

7:39 shapes here are just to represent them. Much like a locking 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 it will stay orange, showing that all of the starch

8:25 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. Boruette's reagent turns from blue to purple with proteins. Cold ethanol will go cloudy with lipids, that is fats. Respiratory system. Next, all to do with

9:12 breathing and gas exchange. Breathing isn't respiration, but it does provide the necessary oxygen for respiration to happen in our cells. The air moves down the trachea into the bronchite, then the bronchioles, and ends up in the alvoli, the air sacks where it diffuses into the blood vessels around it. Like we said earlier, alvolia lumpy to have a large service area. So this happens at a fast rate. The oxygen then binds to the hemoglobin in your red blood cells. They then transport it to every cell in your body to be used for respiration. Carbon dioxide made from respiration is dissolved into the plasma of the blood where it diffuses into the lungs and is exhaled. Some water is also excreted this way too. As you know when you breathe on a cold mirror, the heart is at the center of the circulatory or circulatory system, the transport system of your body. We call it a double circulatory system. Blood enters the

9:58 heart twice every time it's pumped around the body. Deoxxygenated blood from the body enters in the right side of your heart. By the way, you always look at the heart as if it's yours. and it enters through the vennea the main vein into the right atrium of the heart. The valve between the right atrium and the right ventricle stops back flow just like all valves to stop deoxxygenated blood from going back into the body. The heart muscles contract and it goes through the pulmonary artery to the lungs to be oxygenated. It then comes back to the heart through the pulmonary vein into the left atrium. Then it goes into the left ventricle then out to the body through the aorta. The left side of the heart has thicker walls as the left ventricle has to pump blood to the whole body while the right ventricle only pumps to the lungs. The group of cells create electrical pulses that cause the

10:44 heart muscles to contract the heart to beat. If these aren't working properly, you can be given an artificial pacemaker to do the same job. Blood vessels that go away from the heart are always arteries veins towards. That means that arteries carry oxygenated blood apart from the pulmonary artery and vice versa for veins. Arteries have thicker walls to withstand a higher pressure. So they have a thinner lumen. That's the hole in the middle. Veins have thinner walls due to the lower blood pressure, but have valves to stop backflow. Like we said, arteries split and get smaller and smaller until they end up as tiny capillaries with one cell thick walls to allow the fast diffusion of molecules in and out of cells. The heart is a muscle, so it needs its own supply of oxygen and therefore blood to keep the muscle pumping. This is delivered by the

11:30 coronary artery. If these are blocked by the buildup of fatty deposits, a heart attack can occur. This is CHD, coronary heart disease. Stances are little tubes that are inserted into blood vessels to keep them open so blood can flow in this case. Statins are drugs that reduce cholesterol which in turn reduces the fatty deposits. Faulty heart valves result in back flow occurring. These can be replaced with artificial ones. Along with plasma and red blood cells, blood also carries white blood cells which combat infections. More on this later, and platelets, which clump together to clot wounds and stop bleeding. CBD, 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

12:16 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.

13:01 Plants also have organs. Leaves are where photosynthesis takes place, producing food for the plant. Water also leaves the plant through them, allowing transpiration to take place, the diffusing of water into roots and up the xyllem. Roots are where water and mineral ions enter the plant. The merry stem is where new cells are made. Like we saw earlier, xyllem are the long continuous tubes which water rises up. We say it's unidirectional, only goes in one direction. That's transpiration like we said. Well, phem are the conveyor belts of cells that transport sugars, food and sap up and down the plant. We call this transllocation. That's birectional. The rate of transpiration can be increased by the following. Increasing the temperature, decreasing the humidity, and increasing the air movement. All of these result in water evaporating from the leaves at a faster rate. Just for triple real quick, the

13:47 lack of nitrate ions means the plant can't synthesize proteins effectively and that stunts growth. Chlorosis is the scientific term for the yellowing of leaves. This can be due to magnesium deficiency as it's needed to make chlorophyll. The cross-section of a leaf looks like this. Every layer has its own specific function. At the top, we have the waterproof waxy cuticle. Not to stop water from entering the leaf, but to stop it from evaporating from the top and causing the leaf to dry out. The upper epidermis, epidermis just means outer layer, consists of transparent cells that allow light to pass through to the palisade meaphil layer. Mesophil just means a layer in the middle. These are chalk full of chloroplasts. So this is where the majority of photosynthesis takes place. Under that is the spongy messil layer that has lots of gaps around the cells to increase the surface area through which gas exchange can

14:33 occur. Carbon dioxide diffuses into the cells while oxygen and water diffuse out. We also have the vascular bundle that includes the xyllem and phim. The lower epidermis is the bottommost layer of the leaf and it has holes in it called stomata which is how gases enter and exit the leaf. The size of a stor is controlled by the guard cells that flank the hole. They change size to control the rate at which gases enter and leave. For example, they close the stomata at night to reduce the rate of water loss as less water is needed for photosynthesis. Next big topic, infection and response. 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

15:18 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? Measles is a virus that causes a rash and it can actually be pretty deadly, too. It spread by droplets from sneezes or coughs. 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 like salmonella in undercooked food or gonorrhea, another STD that causes a yellow discharge from

16:04 the genitalia. Yeah, 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. Not only animals, though, plants are particularly susceptible to fungal infections like rose black spot. Purple black spots appear on the leaves and then they fall off. Such infections can be treated with fungicides. Tobacco mosaic virus affects plants by discoloring leaves due to inhibiting chlorophyll production. Less photosynthesis occurs and that causes stunted growth. Our bodies are excellent at protecting us from these pathogens though. Thank goodness. Skin is the

16:49 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

17:35 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. Antibiotics kill bacteria. They don't kill viruses.

18:22 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

19:07 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, monoconal 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

19:53 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. Photosynthesis happens in chlorophyll and chloroplast in plant cells to provide food for the plant. Here's the wood and balanced chemical equation for it. And as energy is needed in the form of light to make this reaction happen, this is an endothermic reaction. The glucose made from photosynthesis is used for respiration or is turned into starch or fat as a store of energy. Cellulose is used to produce cell walls and amino acids are used for synthesizing proteins. The rate of photosynthesis is increased with higher temperature unless it's so high that enzyme denaturing occurs, increasing light intensity or increasing CO2 concentration. Any one of these can be a limiting factor. By the

20:39 way, for example, even if there's lots of CO2 and it's warm, if there's not enough light, the rate will be limited by this. In other words, it doesn't matter how much you increase the other two, it won't get any faster. A graph might look like this. Before the graph plateaus, levels out, the variable on the x-axis has to be the limiting factor. After it isn't, it must be one of the other two instead. If you have two lines, for example, different temperatures, then temperature must be a limiting factor. Here's the practical on this. We can measure the rate of photosynthesis by submerging pondweed in an inverted measuring cylinder. We measure the volume of oxygen made over time. We can instead count the bubbles, but it's less accurate. The independent variable could be the light intensity, and that's changed by varying the distance from the light source. For example, a lamp. However, light

21:24 intensity follows an inverse square relationship. In other words, if you double the distance, the light intensity quarters, three times further, 1 nth of the intensity. Every cell bar red blood cells has mitochondria which is where respiration takes place to provide energy for every organism for other chemical reactions to take place for movement and warmth. Aerobic respiration means with oxygen. Here's the word and balanced chemical equation. As you can see, it's just the opposite of photosynthesis. During exercise, your breathing rate and heart rate increase to increase the rate of oxygen delivered to cells for respiration. Anorobic respiration occurs when there's a lack of oxygen. Glucose is instead converted straight into lactic acid which releases less energy. This is what you feel when your muscles ache during intense exercise. This poison can't stay in your

22:10 body. So there is an oxygen debt built up. That means more oxygen is needed afterward to break it down in the liver where is turned back into glucose. Hence why your breathing rate and heart rate take some time to return to normal after exercise. Plant and yeast cells respire anorobically but slightly different. Instead, glucose is turned into ethanol and carbon dioxide. That's why yeast is added when baking. The CO2 bubbles made cause the bread or the cake to rise. This can also be called fermentation. It's also used to make alcoholic drinks as ethanol is produced. Grouping all of these together, metabolism is defined as the sum of all reactions in a cell or organism. These can include respiration, conversion of glucose into starch, glycogen, and cellulose. Glucose can also be built into cellulose which is used to make cell walls. Glucose and

22:57 nitrates are used to make amino acids for protein synthesis. Fatty acids and glycerol are built up into lipids and also the breakdown of excess proteins. This is turned into ura. More about that in paper two. 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.