AQA GCSE Biology Paper 1 Overview

Alright, 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, organisation, 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 organelles. 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. Eukaryotic cells have a nucleus in which their DNA is found. That's your plant and animal cells, for example. Prokaryotic cells don't have a nucleus, and their DNA is found in a ring called a plasmid. Both eukaryotic and prokaryotic cells contain similar organelles, or subcellular structures. The cell membrane keeps everything inside the cell, but they're also semi-permeable. So... 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 is 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 vacuole in which sap is stored. Just for triple, bacteria multiply by binary fission. We can do a practical on this by producing a culture on agar in a petri 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 sterilised equipment, we can either put a drop of bacteria culture in the middle, we'll 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 anaerobically. 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 pi r squared or pi d squared over 4 to calculate the area of the circles. Eukaryotic 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 haploid 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 doubled 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. 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 specialise depending on the function they need to fulfil. For example, nerve, muscle, root hair, xylem, phloem cells. Stem cells are those that haven't yet specialised. They're found in human and animal embryos and the meristem 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 specialise 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. 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 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 in 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 alveoli in your lungs, and Rue Haersals, for example, too. The practical on osmosis goes as follows. Cut equal size 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, damp the excess water off their surface and re-weigh. 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. It's when cells get organised 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 enzyme 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 your small intestine into the bloodstream to be transported to every part of your body for example Amylase 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, carbohydrates break down carbohydrates into simple sugars. Amylase 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, 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 op. optimum temperature, optimum meaning best. This is similar for pH as well except it can denature too high or too low pH. The practical on this involves mixing amylase 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 has been broken down. Calculate the time taken to do that, the amount of time it takes to make the mixture. 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, to yellow. Benedict's solution turns from blue to orange in the presence of sugars. Birouette'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 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 bronchi, then the bronchioles, and ends up in the alveoli, the air sacs where it diffuses into the blood vessels around it. like we said earlier, alveoli are lumpy, to have a large surface area, so this happens at a fast rate. The oxygen then binds to the haemoglobin 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, which 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 centre of the circulatory or circulatory system, the transport system of your body. We call it a... double circulatory system. Blood enters the heart twice every time it's pumped around the body. Deoxygenated blood from the body enters in the right side of your heart, by the way you always look at the heart as if it's yours, and it enters through the vena cava, the main vein, into the right atrium of the heart. The valve between the right atrium and the right ventricle stops backflow, just like all valves, to stop deoxygenated blood from going back into the body. The heart muscles contract and it goes through the pulmonary artery to the lungs to be oxygenated. It then comes back to the heart through the pulmonary vein into the left atrium Then it goes into the left ventricle, then out to the body through the aorta. The left side of the heart has thicker walls, as the left ventricle has to pump blood to the whole body, while the right ventricle only pumps to the lungs. A group of cells create electrical pulses that cause the heart muscles to contract, the heart to beat. If these aren't working properly, you can be given an artificial pacemaker to do the same job. Blood vessels that go away from the heart are always arteries, veins to walls. That means that arteries carry oxygenated blood, a apart from the pulmonary artery, and vice versa for veins. Arteries have thicker walls to withstand the higher pressure, so they have a thinner lumen, that's the hole in the middle. Veins have thinner walls due to the lower blood pressure, but have valves to stop 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 coronary artery. If these are blocked by the build-up of fatty deposits, a heart attack can occur. This is CHD, coronary heart disease. Stents 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 backflow 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. 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 ionising radiation. Cancer is a result of damaged cells dividing uncontrollably, leading to tumours. 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. 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 xylem. Roots are where water and mineral ions enter the plant. The meristem is where new cells are made, like we saw earlier. xylem 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 phloem are the conveyor belts of cells that transport sugars food and sap up and down the plant we call this translocation that's bidirectional the rate of transpiration can be increased by the following increasing the temperature decreasing the humidity and increasing the air movement all of these result in water evaporating from the leaves at a faster rate just for triple real quick the lack of nitrate ions you 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 mesophyll layer. Mesophyll just means a layer in the middle. These are chock full of chloroplasts so this is where the majority of photosynthesis takes place. Under that is the spongy mesophyll layer that has lots of gaps around the cells to increase the service area through which gas exchange can occur. Carbon dioxide diffuses into the cells while oxygen and water diffuse out. We also have the vascular bundle that includes the xylem and phloem. The lower epidermis is the bottom most 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 stoma 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 protists. These are single-celled 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? Measles is a virus that causes a rash and it can actually be pretty deadly too. It's 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 gonorrhoea, another STD that causes a yellow discharge from the genitalia. Yeah, fungi do something similar, like athlete's foot, while protists do all sorts of different things. For example, malaria is caused by a protist 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 discolouring 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 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 lymphocytes. 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. Phagocytes are then able to ingest them and destroy them. An antigen on a pathogen will have a specific shape so that means only an antibody that fits it will neutralize it. If pathogens are unknown to the immune system, lymphocytes will start making all different shapes until one fits. Miraculously, your immune system will then store a copy of this antibody 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 antibody without it infecting you. For example, the flu vaccine, you're injected with the virus that has been irradiated, so the DNA has been damaged inside, so it can't do the job. Incidentally, the COVID 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. Penicillin 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's 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, penicillin from a mould. Now, synthesising drugs is one of the biggest industries on the planet. They have to be trialled 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 analysing 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, monoclonal antibodies. They're made from clones of a cell which is able to produce a specific antibody to combat a disease. This is achieved by combining lymphocytes from mice to tumour cells and this makes a hybridoma cell. This is then cloned to produce a lot of antibodies ready to treat a patient. These monoclonal 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... die 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 Photosynthesis happens in chlorophyll and chloroplasts in plant cells to provide food for the plant. Here's the word and balanced chemical equation for it. And as energy is needed in the form of light to make this reaction happen, this is an endothermic reaction. The glucose made from photosynthesis is used for respiration or 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 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 pond weed in an inverted measuring cylinder. We measure the volume of oxygen made over time. We can instead count the bubbles, but it's less accurate. The independent variable could be the light intensity, and that's changed by varying the distance from the light source, for example a lamp. However, light intensity follows an inverse square relationship. In other words, if you double the distance... the light intensity quarters. Three times further, one ninth 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. Anaerobic respiration occurs when there's a lack of oxygen. Glucose is instead converted straight into lactic acid, which releases less energy. This is what you feel when your muscles ache during intense exercise. This poison can't stay in your body, so there is an oxygen debt built up. That means more oxygen is needed afterward to break it down in the liver, whereas turned back into glucose. Hence why your breathing rate and heart rate take some time to return to normal after exercise. Plantain yeast cells respire anaerobically 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 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 urea. 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. I'll see you in the next video. Best of luck.

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 organelles. 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. Eukaryotic cells have a nucleus in which their DNA is found. That's your plant and animal cells, for example. Prokaryotic cells don't have a nucleus, and their DNA is found in a ring called a plasmid.

Both eukaryotic and prokaryotic cells contain similar organelles, or subcellular structures. The cell membrane keeps everything inside the cell, but they're also semi-permeable. So...

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 is 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 vacuole in which sap is stored. Just for triple, bacteria multiply by binary fission. We can do a practical on this by producing a culture on agar in a petri 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 sterilised equipment, we can either put a drop of bacteria culture in the middle, we'll 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 anaerobically. 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 pi r squared or pi d squared over 4 to calculate the area of the circles. Eukaryotic 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 haploid 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 doubled 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. 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 specialise depending on the function they need to fulfil. For example, nerve, muscle, root hair, xylem, phloem cells.

Stem cells are those that haven't yet specialised. They're found in human and animal embryos and the meristem 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 specialise 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. 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 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 in 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 alveoli in your lungs, and Rue Haersals, for example, too. The practical on osmosis goes as follows.

Cut equal size 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, damp the excess water off their surface and re-weigh. 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. It's when cells get organised 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 enzyme 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 your small intestine into the bloodstream to be transported to every part of your body for example Amylase 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, carbohydrates break down carbohydrates into simple sugars. Amylase 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, 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 op. optimum temperature, optimum meaning best. This is similar for pH as well except it can denature too high or too low pH. The practical on this involves mixing amylase 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 has been broken down. Calculate the time taken to do that, the amount of time it takes to make the mixture. 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, to yellow.

Benedict's solution turns from blue to orange in the presence of sugars. Birouette'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 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 bronchi, then the bronchioles, and ends up in the alveoli, the air sacs where it diffuses into the blood vessels around it.

like we said earlier, alveoli are lumpy, to have a large surface area, so this happens at a fast rate. The oxygen then binds to the haemoglobin 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, which 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 centre of the circulatory or circulatory system, the transport system of your body.

We call it a... double circulatory system. Blood enters the heart twice every time it's pumped around the body.

Deoxygenated blood from the body enters in the right side of your heart, by the way you always look at the heart as if it's yours, and it enters through the vena cava, the main vein, into the right atrium of the heart. The valve between the right atrium and the right ventricle stops backflow, just like all valves, to stop deoxygenated blood from going back into the body. The heart muscles contract and it goes through the pulmonary artery to the lungs to be oxygenated.

It then comes back to the heart through the pulmonary vein into the left atrium Then it goes into the left ventricle, then out to the body through the aorta. The left side of the heart has thicker walls, as the left ventricle has to pump blood to the whole body, while the right ventricle only pumps to the lungs. A group of cells create electrical pulses that cause the heart muscles to contract, the heart to beat. If these aren't working properly, you can be given an artificial pacemaker to do the same job. Blood vessels that go away from the heart are always arteries, veins to walls.

That means that arteries carry oxygenated blood, a apart from the pulmonary artery, and vice versa for veins. Arteries have thicker walls to withstand the higher pressure, so they have a thinner lumen, that's the hole in the middle. Veins have thinner walls due to the lower blood pressure, but have valves to stop 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 coronary artery.

If these are blocked by the build-up of fatty deposits, a heart attack can occur. This is CHD, coronary heart disease. Stents 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 backflow 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. 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 ionising radiation. Cancer is a result of damaged cells dividing uncontrollably, leading to tumours.

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. 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 xylem. Roots are where water and mineral ions enter the plant. The meristem is where new cells are made, like we saw earlier. xylem 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 phloem are the conveyor belts of cells that transport sugars food and sap up and down the plant we call this translocation that's bidirectional the rate of transpiration can be increased by the following increasing the temperature decreasing the humidity and increasing the air movement all of these result in water evaporating from the leaves at a faster rate just for triple real quick the lack of nitrate ions you 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 mesophyll layer. Mesophyll just means a layer in the middle. These are chock full of chloroplasts so this is where the majority of photosynthesis takes place.

Under that is the spongy mesophyll layer that has lots of gaps around the cells to increase the service area through which gas exchange can occur. Carbon dioxide diffuses into the cells while oxygen and water diffuse out. We also have the vascular bundle that includes the xylem and phloem. The lower epidermis is the bottom most 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 stoma 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 protists.

These are single-celled 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? Measles is a virus that causes a rash and it can actually be pretty deadly too.

It's 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 gonorrhoea, another STD that causes a yellow discharge from the genitalia. Yeah, fungi do something similar, like athlete's foot, while protists do all sorts of different things.

For example, malaria is caused by a protist 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 discolouring 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 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 lymphocytes. 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. Phagocytes are then able to ingest them and destroy them. An antigen on a pathogen will have a specific shape so that means only an antibody that fits it will neutralize it. If pathogens are unknown to the immune system, lymphocytes will start making all different shapes until one fits.

Miraculously, your immune system will then store a copy of this antibody 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 antibody without it infecting you. For example, the flu vaccine, you're injected with the virus that has been irradiated, so the DNA has been damaged inside, so it can't do the job. Incidentally, the COVID 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. Penicillin 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's 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, penicillin from a mould. Now, synthesising drugs is one of the biggest industries on the planet. They have to be trialled 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 analysing 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, monoclonal antibodies. They're made from clones of a cell which is able to produce a specific antibody to combat a disease. This is achieved by combining lymphocytes from mice to tumour cells and this makes a hybridoma cell. This is then cloned to produce a lot of antibodies ready to treat a patient.

These monoclonal 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... die 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 Photosynthesis happens in chlorophyll and chloroplasts in plant cells to provide food for the plant. Here's the word and balanced chemical equation for it.

And as energy is needed in the form of light to make this reaction happen, this is an endothermic reaction. The glucose made from photosynthesis is used for respiration or 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 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 pond weed in an inverted measuring cylinder. We measure the volume of oxygen made over time.

We can instead count the bubbles, but it's less accurate. The independent variable could be the light intensity, and that's changed by varying the distance from the light source, for example a lamp. However, light intensity follows an inverse square relationship. In other words, if you double the distance...

the light intensity quarters. Three times further, one ninth 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. Anaerobic respiration occurs when there's a lack of oxygen.

Glucose is instead converted straight into lactic acid, which releases less energy. This is what you feel when your muscles ache during intense exercise. This poison can't stay in your body, so there is an oxygen debt built up.

That means more oxygen is needed afterward to break it down in the liver, whereas turned back into glucose. Hence why your breathing rate and heart rate take some time to return to normal after exercise. Plantain yeast cells respire anaerobically 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 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 urea. 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.

I'll see you in the next video. Best of luck.

Transcript for:AQA GCSE Biology Paper 1 Overview

Transcript for:
AQA GCSE Biology Paper 1 Overview