Edexcel IGCSE 2024 Biology Paper 1 Walkthrough (4BI1/1B) [PART 1/2]

[0:03]All right. Hello everybody, welcome back to another Revise video. Today we have an IGCSE biology paper. This is a 4BI1B, this is paper one.

[0:13]So remember if you're a triple science and if you're a double science, you both have to complete this paper and it's worth a lot of marks so you better pay attention. So we're going to go through how to solve each of the questions in quite thorough detail, but try to do it as quickly as possible. So pay close attention and pause the video if you need some time to work on it. Let's get right into it. So the diagram shows part of a food web from an oak woodland and we have the food web here. Then it asks us, what is the producer in this food web? Well, we know the producer is going to be the first thing that we see at the bottom of the food web. It's going to be trophic level one and it's going to be usually a plant, which in this case is an oak tree. Now, it wants us to draw a food chain from this web that includes the mouse and contains four trophic levels. So we know that one food chain is one um, consequential sequence of these arrows, right? So this is a food chain and then the caterpillar, beetle, blue jay would be a food chain. Um, so yeah, I'm sure you know what a food chain is. But we know we need to include the mouse. So, how do we include the mouse? Well, we know we need to include the mouse with four trophic levels. Now, if we did the standard pathway of oak tree to mouse to tick, that would be three trophic levels, right? Because you can see that oak tree is trophic level one, and then it goes one arrow, then a our primary consumer mouse, and then our secondary consumer, which leads to three trophic levels. But if we want four, we have to take a different path. So we can take the path of the caterpillar. The caterpillar is at trophic level two, which then goes to the mouse, trophic level three, tick four. So, how do we write this? Well, when writing food chains, you want to write the name of the thing and then an arrow to indicate the direction that the energy is flowing. So it goes oak tree, caterpillar, mouse, tick. Which one of these organisms is in two different trophic levels in this food web? So when we get a question like this, we want to look for organisms that have two different paths, right? So two different arrows connecting to them, because that shows that they likely have two different trophic levels. And in this case, we see the mouse. The mouse has two arrows connected to it. So in this food chain of oak tree, mouse, to tick, mouse is at trophic level two. But if we take the one we just did, which is the caterpillar, mouse to tick, mouse is at trophic level three, so it has two different trophic levels. So our organism is the mouse. A tick is a small spider-like organism that bites and then takes in blood from the mammals as it feeds. This is a magnified image of a tick. The actual length of the tick, as shown by line A-B, is 3.5 mm. Calculate the magnification of the image of the tick. This is an easy question. So the first thing we have to do is measure the line. So we'll use our ruler here. We'll see our line is roughly 10.4 mm, uh, centimeters, right? So we have 10.4 cm as the actual as the measured one from the image, right? So the image length is 10.4 uh, cm. And then the actual length is 3.5 mm. To get the magnification, we need to do this number divided by this number. So, 10.4 divided by 3.5. But, you may notice that the units are actually different. So, what we have to do is we have to convert 10 uh, 10. uh, 104 uh, 10.4 cm to millimeters, which in this case, is 104 mm. So now we have 104 mm divided by 3.5 mm. That gives us 29.7 roughly, right? So we'll write 29.7. Usually you don't see magnification with decimal places. So this question, I believe allows you to write um, any answer from 29 to 30. But uh, I recommend just putting um, a good amount of decimal places, a reasonable amount, uh so that uh you can keep your answer accurate, you know what I mean? So uh, yeah. Next one. The tick absorbs substances from the mammal's blood it has taken in. Give the function of two substances absorbed by the tick. This is a bit of a confusing question because it's not really apparent what it wants you to talk about, right? Because you may say that you don't know anything about ticks, but in actuality it wants you to talk about a mammal's blood, right? Because you know lots about blood, and you know the tick is absorbing blood. So you just need to say the functions of two substances that are in mammal's blood. Easy way of breaking it down. So you can say loads of substances. Now, one substance that you may be aware of is glucose. Right? That's one we all know. And glucose, what does glucose do? Well, we know glucose is used for respiration.

[4:50]Right? Something as simple as that. Um, you don't need to overthink it, right? We just need a we need a name of a substance and then we need to give an explanation, a simple explanation. Okay? Now what could be another um a substance? Well, we know that amino acids are in blood. Right? And what is the function of amino acids? Well, they they are used in protein synthesis, right? They're the building blocks of proteins. Um, they're used in protein synthesis. Now, I'm sure you can see there's a very broad scope of what you can put for this question. So if you have anything in your head, um, water, cholesterol,

[5:33]any vitamin, name vitamin, there's going to be loads of things you can say, as long as you can justify it, um, yeah, as long as you can justify it, uh, write it down, but these are just the ones I thought of. Okay. Ticks can pass diseases between organisms. Suggest how ticks can pass diseases from one organism to another. Okay. Now, this is the question on the spread of a disease and it's quite a logical answer. So, the first thing that would happen, right, is the tick acquires the disease, right? Because it's passing from one organism to another, so how would it do it? Well, we know a tick takes blood as described in the previous question. So the tick takes in blood from an infected organism. That's the key word, infected organism, vital signs, right? An organism has this infection, the tick sucks up blood, and then the now the the infected blood is in the tick. So, what would happen next? We can say that a um, will be will be quite vague. We'll say a pathogen is in the blood. So now that we have a pathogen in the blood, the tick bites a new animal, the pathogen spreads. And uh, yeah, quite simple, just had to break it down into steps. Okay. The diagram shows a flower with some structures labeled. Which structure is the style? Well, we should know that the style is this thing. It's the long part that connects up to the stigma. So, we know that the style is part Q, which is B. Which structure releases pollen? We can quite clearly see which structure releases pollen, because we know pollen is in the anthers and then we know U is pointing to that. So, our next answer is going to be D. On which structure do the pollen grains germinate? This is an interesting question. So, if we look at the different ones, we should know that pollen grains germinate on the stigma, as the pollen grains land on the stigma and that's where they germinate and the whole process begins. So, which one points to the stigma? It's P. And P is A. Okay. This flower is insect-pollinated. Describe how structures P, R and T would be different in a wind-pollinated flower. Okay. So P, uh, our stigma. R, a petal. And T, being the filament. So, how would they how would they be different in a wind-pollinated flower? Okay. So P. So remember, in an insect-pollinated flower, the stigma is going to be different than a wind-pollinated flower, because in a wind-pollinated flower, our P, we want it to have a we want it to have a very feathery appearance, right?

[9:01]We want to increase the surface area so that more so it's so it's more exposed, right? Because in the insect-pollinated plant, it's going to be quite a precise event when the pollen is brought to touch the stigma. But in a wind-pollinated plant, the pollen is just flying throughout the air, and you just want to hope that you catch some pollen with your stigma. So, in this case, you want a larger surface area,

[9:37]right? And you want a feathery part P. Now for R, which was the petal, right? Petals in wind-pollinated plants are quite redundant, because in insect-pollinated plants, petals have the major purpose of attracting pollinators. And attracting pollinators is not important for wind-pollinated plants because I mean, they're pollinated by the wind. So, usually in wind-pollinated plants, R is absent, right? We don't see petals, or we have petals that are small. They're not very visually attractive, they're often uh often green, um right, like the rest of the plant. So, yeah. Now, for T is interesting. T is our filament, which holds the anther. So, what would we want from our from our anther and filament? Well, we want it to be longer, right? We want it to be longer so it's more exposed to the air so that more yeah. You know the process of wind pollination. So we have a longer filament, longer, more exposed, right? That would be a key difference. Flowering plants can reproduce asexually. Give an example of a natural method of asexual reproduction in plants. Okay. Now, I want you to think of potatoes um and these these plants that are in the ground, right? And you must know of tubers, right? You've heard of tubers before. Um, very common form of asexual reproduction, probably the most famous one. Um, another famous one often taught in British schools is runners. Runners is common um, method of asexual reproduction. But uh, I this is again, just memorization, things that you should know. Um, so all possible answers, okay? And give an example of an artificial method of asexual reproduction. Well, you should instantly think of cuttings. Right? When we take a cutting of a plant and then that cutting um becomes the explant and essentially forms a new plant that is identical to the original plant. And that's a form of asexual reproduction, because it only involves one plant. But we're artificially doing it because we're causing this cutting, right? And this cutting kind of falls in the process of micro propagation, right? So that would be another answer as well, micro propagation and the whole idea of ex plant and so on and so forth. Give three differences between asexual and sexual reproduction. Okay. Very easy question. I'm sure you can think of more um, many of them. The things that instantly go into my head, right? So in asexual reproduction, the offspring are genetically identical to parent.

[12:05]Where a sexual shows variation. So we have variation in sexual reproduction, because we have assortment of gametes and then it leads to genetic variation, where the offspring is not genetically identical to the parent, right? What else what asexual? Asexual reproduction is very fast compared to sexual. That's why you see these asexually reproducing plants.

[12:38]They're making a lot a lot a ton of plants, a ton of clones. Whereas you sexually reproducing plants, it's a lot a lot less compared to sexual reproduction.

[12:53]Okay. Um, and no fertilization in asexual, whereas in in sexual, sorry, my handwriting's kind of disintegrating because I'm just trying to write fast, but uh, yeah, loads of things you can say here.

[13:18]Um, you can even talk about no gametes are required, right? No gametes produced in asexual reproduction. Um, no meiosis, right? There's there's a ton of things you can say, but these are just quite Okay. A farmer has two varieties of a plant species. One variety has a red flower color and no scent. The other variety has a white flower color and a perfumed scent. The farmer wants to produce a variety that has the red flower color and the perfumed scent. Explain how the farmer could achieve this. So the central idea here is that the farmer wants to undergo selective breeding of his plants, right? Selective breeding. Now, how did he go about this? Well, he should cross the two plants.

[14:07]Right? Now in genetics, when we say cross it means cross um in this case cross pollinate, but we're saying cross breed, right? So we have plants with two characteristics, right? Uh two different characteristics and we want some of the characteristics from each plant. So we're going to crossbreed the two plants, right? And then we're going to breed the offspring of the plant, right? Because we're going to get loads of offspring, we're not going to only breed them once, we're going to get loads of plant offspring for desired traits, right? Now in this case, our desired traits is red color and perfumed scent. And the whole idea is that we're going to repeat this breeding process. Keep breeding them, keep breeding them until we get a red flower color with a perfumed scent, because on the first try we might get a white color that has a that has a scent, but not a not a perfect scent. Um, and then yeah, you you keep on uh reproducing, keep on cross breeding your plants until you get the perfect plant. Um that you're looking for. So, yeah. This passage describes the process used to produce yogurt. Complete the passage by writing a suitable word or words in each blank space. Yogurt is made by heating milk to a high temperature. Milk is what we're missing here, okay? This heating process is known as pasteurization. I'm sure you've all heard of pasteurized milk before, unless you're one of those raw milk drinkers, which I don't don't advise. Don't drink raw milk, guys. It's not safe for you. Um, okay. This ensures that bacteria present in the liquid are killed, right? Which is why pasteurization is important. We want to kill the bacteria. The liquid is then cooled to between 40° C and 46° C. A type of bacteria called lactobacillus is then added. Right? Remember lactobacillus, lactose, right? Easy way to remember it. These bacteria use a sugar called lactose for a certain type of respiration. We should know is anaerobic respiration, right? But why is it anaerobic? Well, anaerobic respiration has a certain by-product that's useful because the pH of the yogurt decreases, right? We want it to decrease because the respiration produces a substance called lactic acid, right? So we want the pH to decrease, that's why you might see your yogurt is a bit sour sometimes, it's because of this lactic acid. A respirometer is a simple apparatus that can be used to measure the rate of respiration in small organisms. A student uses the respirometer to investigate the rate of respiration in some germinating seed. Okay, and then we have this apparatus here, so we have germinating seeds, a wire basket and soda lime to absorb the carbon dioxide, and then we have the respirometer. Very basic setup and then the colored liquid that's going to move across the scale. And it wants us to give the balanced chemical equation for aerobic respiration. Okay, aerobic respiration. We're going to have C6H12O6. Right? If you can't remember that, just think of 6, 12, 6, right? We know they're all multiples of six, so it's quite easy to remember. 6O2, right? Forms and then the products are going to be carbon dioxide and water, as we know from aerobic respiration. But what are the coefficients? Well, it's going to be 6CO2 plus 6H2O. So remember, six is very prominent in this equation. We have six, six, six, and then C6O6, and then the only thing that's 12 is the H12. So you just have to remember this equation. It's not too hard to remember. Yeah. The student uh, you can add state symbols as well, um, I just thought of it, but we don't need to, um, in this question. The student measures the rate of respiration of 10 g of germinating seeds at 20° C. They then repeat this with another sample of 10 g of germinating seeds at 30° C. The rate of respiration can be measured by recording the distance, in mm, the bubble of colored liquid moves across the scale in one minute. They measure the rate three times at each temperature. Explain why carbon dioxide needs to be absorbed by the soda lime when measuring the rate of aerobic respiration. Okay. Well, we know this is absorbing all the carbon dioxide um that is produced by the germinating seeds. So, why is it important? Because the seeds are going to be producing carbon dioxide, right? We see this in the equation.

[18:41]Now, if they're producing carbon dioxide and you're consuming oxygen, the carbon dioxide you produce is going to offset the oxygen. So, we want to measure how much oxygen is being taken up, right? By the seeds. But if we're producing a gas, what's going to happen is it's just going to counterbalance where we have minus oxygen from the system and plus carbon dioxide. So, the liquid is going to stay in the same place. So, the idea is we get use this to get rid of all the carbon dioxide. So, we're just losing oxygen, minus O2, minus O2. And that's going to move the colored liquid across the scale. Okay? So, how do we explain that? Well, um, it needs to be absorbed because otherwise the bubble wouldn't move. Bubble wouldn't move as the produced CO2 would offset the lost O2. There we go.

[19:43]State how the student could have changed the temperature in this investigation. Okay. Lots of things you can say, but the standard way to change temperature is to place whatever you're doing, whatever you have in a water bath, right? A temperature controlled water bath. Um, I think that's the easiest way to say it. Uh, because stuff like a heating block, it usually heats too high. I'm sure they would allow heating block or something like that, but usually you want water. You want um, you want something to do with water because it's good at um, transferring that energy across the system, um, to the seeds so that you have a uniform uh, heating of the seeds. Okay. The table shows the student's results. And it wants us to calculate the mean distance moved by the bubble at 30° C. So 30 degrees C is here and we need the mean. So we have 22, 25, 24. Okay. So 22 plus 25 times 24 is 71. And then we have three different measurements. So it's 71 divided by three and that equals to roughly 24. No, yeah, roughly 24. So we'll write 24 um millimeters as our answer. Yeah. Explain the effect of increasing the temperature on the movement of the bubble. Okay. So we know the bubble is going to move depending on how much oxygen is is lost, right? So essentially how much respiration. So, it's essentially asking us what increasing the temperature has a what the effect of increasing temperature is on respiration. Well, if we increase the temperature, we're going to have a higher kinetic energy, right? So that's right that down. So, increase temperature, increased temp means higher kinetic energy. I'm writing like this just for the sake of explaining it, but when you guys write it, make sure you write in paragraphs, okay? So, increase temperature means increased kinetic energy. Now, what does increased kinetic energy mean, right? Now, if we have a system that has particles, like enzymes, like um, just just uh particles like glucose and oxygen, right? If we increase the temperature, we're going to have more collisions, right? More frequent collisions. Okay? Now, more frequent collisions means that there're going to be more successful collisions, right? Because we're increasing energy, there's going to be faster moving particles and the molecules are going to be higher energy. So, we're going to have more successful collisions. And what does a successful collision do? Well, a successful collision leads to the formation of an enzyme substrate complex. Right? I'm sure you've heard of enzyme substrate complex, because enzyme substrate complexes allow the enzyme to have its function, right?

[22:31]The enzyme the substrate binds to the enzyme active site and then we have this complex being formed, where then the enzyme breaks down the substrate, okay? So, if we have higher enzyme activity, right? So, we have higher enzyme activity, we have higher respiration, right? Because it's a process that is fueled by enzymes. We have many enzymes. So, more respiration means more oxygen consumed, right? Because remember, if we think back to our equation, in our reactants, we have oxygen. So, we're consuming more oxygen.

[23:12]More oxygen consumed means more movement of bubble. Okay? And remember, for the um, for the increasing temperature with the enzyme, the temperature will only increase the activity of the enzyme up to the optimum temperature, right?

[23:35]Once you reach this optimum temperature, the optimum temperature, there's after this there's going to be a sharp decrease where the enzyme denatures. But I'm sure you know that. Okay. And increased uh, so increased release of greenhouse gases are a threat to many ecosystems. Which of these are greenhouse gases? Okay. We should know that CFCs, chlorofluorocarbons, those are greenhouse gases. There used to be a big problem with ACs and refrigerators with CFCs, but they're not that much of a problem anymore. Um the world kind of came together with that and we we made it much less of a problem um to the atmosphere. A major problem nowadays is methane, right? Because of the amount of cattle rearing and everything. So, that's a problem. Oxygen is not really a problem and water vapor is a greenhouse gas. Yes. It's not a greenhouse gas that we're as familiar with because it's not one that we um, we associate. We usually associate carbon dioxide, methane as these greenhouse gases. But water vapor does have a greenhouse gas effect as well. So, one, two and four would be C. Explain what is meant by the term greenhouse effect. Okay. So we should know that the greenhouse effect is when we have this long-wave radiation that comes down to the earth and then comes back up, bounces off the earth.

[25:12]And then becomes long-wave, and then we have this long-wave infrared gets trapped, right? By these by these greenhouse gases that have a special property that allows them to trap infrared radiation, uh, in the long-wave form. So, it gets trapped by greenhouse gases.

[25:36]Right? And what does this do? Well, this leads to increased global temperature. It's important to note, though, the greenhouse effect, in and of itself, is not a bad thing, right?

[25:55]It's kind of what allows us to live on earth. Um, the greenhouse effect just like this is what keeps the earth warm enough for us to live here, right? If we didn't have any greenhouse gases, it would be very cold on the earth. Now, the issue that we have with global warming is the enhanced greenhouse effect, where the greenhouse effect is becoming too prominent, because we have too many greenhouse gases, and then that's causing problems. But the issue, we don't really have an issue with the greenhouse effect. We should actually be grateful for the greenhouse effect, which is something to think about. The graph shows the mass of greenhouse gases emitted from four sources in the United Kingdom from 1990 to 2020. Calculate the percentage of total greenhouse gases emitted, um, that came from energy production in 2020. So, 2020, and energy production is the small dotted lines. So, energy production in 2020 is here, uh, which seems to be 110 uh, million tons, 110 million tons.

[27:03]So, uh, energy production is 110 million tons. So, energy is 110. Right. Agriculture seems to be 50. Okay. Uh, what's this one? It was business. Business seems to be below 120. Uh, let's say 119, 118.

[27:48]Um and transport that looks to be around 175. Um, right, up there.

[28:03]Okay. So then we have all of these, we have to add them together, right? If we add them together, we get a value of 453. And then we want us to say how much that came from energy production. So, we do 110 divided by 453. And then to make it a percentage, we have to times that by 100. Okay? So, this gives us something that's around 24%. Okay? But if you write anything between 23.9 to 24.9, you'll be okay. But we'll go with 24%.

[28:38]Comment on the changes in the four sources of greenhouse gases from 1990 to 2020. Use information in the graph and your own knowledge to support your answer. Okay, five marks. We have a lot of things to say here. How do we go with this? Well, let's go with them. Let's let's let's let's go with general trends first and then kind of zero in on the on a single one. Well, for every single one of them, the emissions has decreased, right? So the overall the overall mass has decreased from 1990 to 2020. Okay?

[29:26]Now, what else can we say? Well, we can talk about which were the leading causes back then and which were the leading causes now. Well, if we look at 1990, we can see that the leading causes was uh energy production.

[29:40]We have a really high number of, really high mass of greenhouse gas produced. But now, energy production has dropped a lot, and now the leading the leading um one is uh transport. So, In 1990, energy production was top. Now, transport leads in mass of greenhouse gas. Uh, like I said, again, I'm running in like half sentences just for the sake of time, but please write in proper sentences in your actual exam. Okay.

[30:30]Now, what else can we say? Well, we can also notice that the difference, uh the disparity between the between the um different sources was a lot higher in 1990 compared to 2020. In 2020, they're a lot closer together but in 1990 they were quite far. So that's another thing to say that the disparity between sources in 1990 was far greater than in 2020. Right?

[31:02]The disparity I'm talking about the difference from there to there. And here I'm talking about the difference from here to here, right? We can see the disparity decreased. Okay. Now, now we can think about um using information using our own knowledge, right? So, why do we think that we would see such a decrease in um in everything, right? Especially energy, right? Let's let's zero in energy because we know a lot about renewable energy, right? So, decrease in energy is the largest, right? We saw that it's the largest decreased and can be explained by now we can talk about the new innovations that we have in in renewable energy, right?

[31:51]So, wind power, solar power, um hydro hydro hydro electric dams, right? Uh thermal uh vents, right? Uh geothermal vents, right? We're using those. So, there's just so many things you can say, okay? What else can we say? We've we've said quite a lot, um, okay.

[32:23]Think about it this way, I've only really commented on um energy production. You could do it for all of them. But we've already got roughly five marks, so I'll just throw in another one. Uh, I feel like the easy one to do is agriculture, right? Why do you think we would see a decrease in agriculture? Because I mean, it's not a large drop but it is a drop. So, agriculture drops, why? Well, compared to 1990 to now, we're rearing um, the the data is trying to make us say that we're we're farming less cattle. Um, in the UK this is likely true, right? I was going to say in the world, I mean, I wouldn't know if that's true, but in the UK it's likely true that uh the UK is shifted from the primary sector more to these tertiary, quaternary sectors. But agriculture drops because less cattle reared, right? But I guess you could even make the argument that it's not dropping by very much, because agriculture is a stable industry. It's I wouldn't write it right now, because it's just we've already gotten enough marks, but it's something to think about, the agriculture not dropping. Uh, for transport, you can talk about like public transport, the rise in um, uh public transportation being so ubiquitous. The fact that less people are buying cars because cities are becoming more walkable. All those help with with um, with that. Um, yeah. Well, I'm talking about this drop in transport here. But we actually saw an increase in transport up to 2010. I guess that makes sense, because from 1990 to 2010, we had more cars. So, here we have the increase of cars and then we're like, oh, there's too many cars. So, let's get public transport. And then we got really good at public transport. Here. So, yeah. There we go.