2026 Feb/March IGCSE Biology (0610) 0610/62/F/M/26 Paper [6] Dr. Hanaa Adel

追加: 2026-05-09

[00:00:09]Welcome to our biology lessons with Dr. Hana. Today we will solve with each other March 2026 paper six.

[00:00:19]Question one.

[00:00:21]Catalase is an enzyme that catalyzes the breakdown of hydrogen peroxide to form water and oxygen. So, we have here hydrogen peroxide breaks down into water and oxygen gas by the effect of catalase enzyme.

[00:00:54]The oxygen produced during the breakdown of hydrogen peroxide forms a foam.

[00:01:00]The height of the foam can be measured as a measure of the activity of the catalase.

[00:01:08]A student investigated how the surface area of potato tissue affects the activity of catalase.

[00:01:16]Now, we have to know that the surface area of potato tissue is independent variable.

[00:01:22]And then, what is the dependent variable here? So, you have to know that this is the activity of catalase and the dependent variable should be measurable.

[00:01:31]So, how can we measure the activity of catalase enzyme? They said that the height of the foam can be used to measure the activity of catalase. So, the height of the foam is dependent variable.

[00:01:47]The student um was provided with three cubes of potato tissue. Each a cube was 1 cm by 1 cm by 1 cm in size as shown in the figure. The total surface area of of the cube of potato was 6 cm squared.

[00:02:07]From where they get this is the total surface area. We have six faces of the cube.

[00:02:15]And the area of each cube we can get it by side by side.

[00:02:23]Each side of them with with one.

[00:02:28]You have six by one by one which is equal six cm squared.

[00:02:38]The student used this method.

[00:02:40]Label three test tube one, two, and eight.

[00:02:44]Put 10 cubic cm of hydrogen peroxide solution into each of the three test tube. So, we have controlled variable which is the volume of hydrogen peroxide solution.

[00:02:58]Step number three, put one of the cubes of potato into test tube one.

[00:03:03]Put one of the remaining cubes of potato onto the white tile. It looks like a ceramic piece. Use the ruler and scalpel to measure and cut the cube of potato as shown in the figure.

[00:03:19]This will make two equal size pieces.

[00:03:23]The total surface area of the two pieces 8 cm squared. So, we have the first one 6 cm squared and the second one uh 8 cm squared.

[00:03:37]Step number five, put both pieces of potato from step four into test tube two.

[00:03:45]Step number six, put the remaining cube on the potato onto the white tile again.

[00:03:52]Use the ruler and scalpel to measure and cut. This is a kind of safety hazard by using scalpel that cut.

[00:04:00]So, the cube of potato as shown in the figure 1.3, this will make eight equal-sized cubes. Each side of them 0.5 cm.

[00:04:13]Calculate the total surface area of the eight cubes of potato made in step six.

[00:04:18]So, how can we get uh again the uh the area of the total surface area of the eight cubes of potato made in step six?

[00:04:27]So, each cube has six sides, [clears throat] and the surface area of each cube six * S * S, which is the area of each side, and we have each side 0.5, 0.5, and 0.5 cm.

[00:04:46]So, we can get it. Each cube has six sides, and the surface area of each side six multiply the area of each side, which is 0.5 multiply 0.5 multiply the six side equal 1.5 cm squared. And finally, we have eight cubes. So, we have multiplied the 1.5 multiply eight, which is equal 12 cm squared.

[00:05:15]Put the eight cubes of potato into test tube eight and start the stop and wait for 5 minutes. So, we have also the same duration time, so this is controlled variable.

[00:05:29]After 5 minutes, place the ruler against the outside of test tube one and measure the distance from the top of the liquid to the top of the foam.

[00:05:40]And record the measurement in your table 1AII.

[00:05:44]Repeat step nine using test tube and eight.

[00:05:54]This figure this shows that the test tubes at the end of the investigation.

[00:05:59]We have test tube one, test tube two, and test tube eight.

[00:06:05]How can we measure the height? So, we you have to know that the foam is uneven surface. So, how can we measure it? So, we have to put a line using pencil and ruler and then measure the height of the foam.

[00:06:25]Okay.

[00:06:26]But the problem here, the surface of the foam is uneven.

[00:06:30]But how can we improve it?

[00:06:32]Instead of measuring the height of the foam, we can measure the volume of gas produced using gas syringe.

[00:06:40]But now we have to prepare a table and record the student result. We have the test tube. So, we have one and two and eight.

[00:06:49]And also we have the surface area of potato.

[00:06:53]They give us two of them and we calculate the third one.

[00:06:58]And we measure the height of the foam in each test tube.

[00:07:02]So, the table by this way in test tube one, the total surface area we said that the 6 cm squared.

[00:07:10]And by measurement the height of test tube one, we can find 0.6 cm.

[00:07:19]And the second one, two test tube two, its total surface area he said that this 8 cm squared.

[00:07:27]And the by measurement the height of the foam was 1.3 cm.

[00:07:38]And the third one that we calculated the total surface area of potato in test tube eight. So, 12.

[00:07:47]And the height of the foam equals to centimeter.

[00:07:53]Let's concentrate in this table.

[00:07:57]You have to put in consideration that the measuring unit we put it in the heading of the table, not in the cell.

[00:08:06]So, no no one will make it like this. It is wrong. We have to put the measuring unit in the heading of the table.

[00:08:15]And we have another point here about also the height of the foam. The measuring unit you have you put it in the table, not inside the cell.

[00:08:25]So, this is wrong. You have to put it in the heading of the table.

[00:08:31]Third point here, you have to put uh 2.0. So, why we put it 2.0 by this way? Why we didn't put it two only?

[00:08:40]Because you have to put the values with the same decimal places, cuz we have uh 0.6, 1.3.

[00:08:48]And we have to use same decimal places when we put the values in the table.

[00:08:57]Next the question ask about the conclusion of the result of the uh the effect of the surface area on the activity of catalase enzyme. So, how can we write the conclusion?

[00:09:09]If you concentrate, we can find that in test tube one and two and three, the total surface area increases.

[00:09:17]And also we can find the height of the foam increases also.

[00:09:21]Okay? But the conclusion you have to to talk about the activity of enzyme.

[00:09:27]So, by increasing the the the surface area, so what happens to the activity of enzyme? So, it will increase. So, the greater the surface area, the greater the activity of catalase enzyme.

[00:09:43]Next question ask about the state two variables that were kept constant in this investigation.

[00:09:49]So, if you concentrate well, we have to return it back uh to the volume of hydrogen peroxide, which is equal 10 cubic centimeter, and the time left before measuring the foam, which is 5 minutes.

[00:10:06]And also the type of potato, and finally with the temperature. And in this question, they ask about two variables only. In the exam, you can write just two. But, here we can write all the possible answers.

[00:10:20]Next the question ask about to identify one safety hazard in this investigation.

[00:10:24]We have here two hazards. The first one using scalpel, which is sharp and could cut the hand, and also hydrogen peroxide is added.

[00:10:35]And also in the exam, you just write only one.

[00:10:41]Next the question identify two possible sources of error present in this investigation.

[00:10:46]We have more than two. So, we can We just explain one of them.

[00:10:52]While talking about this measurement, the height of the foam, the first one, the surface of the foam is uneven.

[00:10:58]So, it's a kind of error. How can we improve it? We can measure the volume of gas produced by using gas syringe instead of the height of the foam because the height of the foam or the surface of the foam is un even.

[00:11:15]We have another a source of error, which is there is no repetition in this investigation. So, we have to repeat it three times at least, and take an average.

[00:11:27]The third source of error, and if you concentrate well, we can find the temperature not maintained. So, we have to maintain it by using thermostatically controlled water bath.

[00:11:45]Next the question. Iodine solution can be used to show the potato tissue contain starch.

[00:11:51]State the result of positive test with iodine solution. So, who can remember what is the color of iodine solution before this experiment? So, it was brown or yellow brown or orange brown.

[00:12:04]If we have starch, so we can find the color of iodine solution change from brown to blue black.

[00:12:12]You can write it blue black or dark blue.

[00:12:19]Next the question.

[00:12:25]A student investigated the effect of copper sulfate concentration on the activity of catalase in potato tissue.

[00:12:34]You have to know that when we find the word of effect of, we can find the independent variable. So, if he ask about what is the independent variable or the changed variable, which is copper sulfate concentration. And you have to know on the activity of catalase potato tissue.

[00:12:52]When the small discs of potato are dropped into a hydrogen peroxide solution, they sink.

[00:12:59]The catalase in potato breaks down hydrogen peroxide solution producing bubbles of oxygen. The bubbles of oxygen cling on the disc of potato causing the discs of potato to rise back up to the surface of hydrogen peroxide. So, if you concentrate well here, we have, for example, this test the contains the discs of potato and put it in a copper sulfate concentration before we have different concentration of copper sulfate. And then we have to put this potato hydrogen peroxide, so we can find it the discs moves up.

[00:13:51]Place a small discs of potato in different concentration of copper or sulfate solution which is independent variable, the variable that we change it, and leaves them to soak for 10 minutes. So, we have here the soaking time which is 10 minutes. Drop the soaked disc of potato into hydrogen peroxide solution. Measure the time taken for the disc of potato to reach the surface of hydrogen peroxide.

[00:14:18]So, we have something here measurable that related to the activity of catalase enzyme. So, measure the time taken for the discs of potato to reach the surface of hydrogen peroxide solution. So, we have here dependent variable which is the time taken for the discs of potato to rise the surface.

[00:14:46]And also we have independent which is the if the the concentration of copper sulfate solution.

[00:14:55]Suggest a suitable control experiment for this investigation.

[00:15:01]We have to know that what is a control?

[00:15:05]So, there is a difference between the word of controlled variable, the variables that should kept constant, and the word of control only. What is a control? Something that compared the result.

[00:15:17]So, how can we use something that is no effect of it on this reaction to be used to compare the result. So, we can call it control. So, control experiment used to compare the other result. So, we can soak the potato desk instead of enzyme into distilled water with the same volume because the water does not affect of at the potato. So, soak the potato desks in same volume of distilled water instead of copper sulfate solution. So, there is no copper sulfate solution. We can put instead of the copper sulfate solution water, distilled water to eat to compare the effect of copper sulfate different concentration on a on the potato, on the activity of enzyme.

[00:16:22]In front of us, this table 1.1 shows the result of the investigation.

[00:16:29]You have to know that the concentration of copper sulfate solution mole per decimeter cube in the first column and the time taken for the desk of potato to rise in seconds. So, if you concentrate well, we can find also the measuring unit we can find in the heading of the table.

[00:16:48]When we have this table, the first column for independent variable and we have to put it on the X axis.

[00:17:00]And the second column for the dependent variable and we have we have to put it on the Y axis.

[00:17:08]Okay? The first column independent variable something that change it, the concentration of copper sulfate solution and something that measured which is dependent variable we have to put it on the Y axis.

[00:17:24]On the grid, use the data in the table to plot the line graph to show the result of this investigation.

[00:17:33]We have many points you have to put it in consideration. Firstly, if you concentrate well, we have six marks.

[00:17:44]How can we get six marks?

[00:17:46]The first mark for axis label.

[00:17:52]The second mark for scale.

[00:17:57]Third mark for plotting.

[00:18:01]The last mark for line drawing a line.

[00:18:07]You have to put in consideration the least value and the highest one.

[00:18:13]And also least value and the highest one.

[00:18:16]And to put on the the graph paper and try to cover as much as possible.

[00:18:24]So, at least 2/3 of the graph paper from above half or as much as possible to be covered the whole distance covered by all the data.

[00:18:36]So, if you concentrate, we can find on the X axis concentration of copper sulfate solution /mol per dm cube. So, when we write the axis label, you should write all things that we can find it in the heading of the table with its measuring unit.

[00:18:54]On the other side, so we can find on the Y axis, we can write it with its measuring unit. So, don't forget to write it as it is.

[00:19:06]So, now we did axis label.

[00:19:09]Second one we have to know that the least and the highest value of the table to be distributed on all uh the the the boxes. We count how many big boxes and then distribute this value on the x-axis.

[00:19:25]And exactly the same that happened on the y-axis. So, now we have the scale.

[00:19:31]Next, we have to plot all the points using x.

[00:19:37]So, in front of you two option the options. So, we have x or dots with a circle.

[00:19:44]But, which one of them is better? So, it is better to use x.

[00:19:49]But, what about if we have two different data?

[00:19:53]You can use both. One of them, so if you have a key, so you can use x and also the dot with a circle.

[00:20:02]But, if we have only just one, so you can use x.

[00:20:08]After finishing the plot in all the data, we have to store it to make a line.

[00:20:14]It is It's okay if you can join all the points with each other from dot to dot.

[00:20:20]From dot to dot is accepted in biology to make this line.

[00:20:27]Next the question, use your graph to estimate the concentration of copper copper solution copper sulfate solution when a desk of potato took 80 seconds. So, if you concentrate when we have we want find it. This is 80.

[00:20:42]And then go to this line graph and then drop it to the x-axis to know the concentration of copper sulfate solution which is 0.006.

[00:21:00]You have to show how can we obtain this value on the graph.

[00:21:12]Question two.

[00:21:15]Figure 2.1 is a photograph of fruit from chili pepper.

[00:21:20]The chili pepper fruit has been cut in half.

[00:21:24]And then they measure it from P to Q and its magnification 1.7 times. Draw a large diagram of chili pepper fruit shown in figure 2.1.

[00:21:38]So, please concentrate about the part of drawing.

[00:21:43]If you concentrate well, we have to know what are uh the points we have to put it in consideration we will start to draw.

[00:21:51]Firstly, we have something like this.

[00:21:57]This is the first part.

[00:21:59]Okay?

[00:22:00]And then we have two Put your pencil on the drawing and move around.

[00:22:10]To just give the chance to be printed in your mind.

[00:22:13]Okay? And then we have here two chambers inside it.

[00:22:19]Like this.

[00:22:23]Have to draw it smooth line.

[00:22:30]Okay?

[00:22:32]And we have many seeds.

[00:22:48]And you have to put it in consideration you have to make it large in size.

[00:23:02]This is all details that we can find in the drawing.

[00:23:09]And this is my large drawing.

[00:23:20]Line PQ on the figure 2.1 represent the length of the chili pepper fruit. Measure the length of PQ in the figure.

[00:23:28]So, if you measure it, we can find it 7.4 cm.

[00:23:38]But, we have to convert centimeter into millimeter. So, 1 cm equals 10 mm. So, when we convert it, so we have the 7.4 multiply 10, which is equal 74 mm.

[00:24:02]So, we have the 74 mm.

[00:24:07]Next question, calculate the actual length of chili pepper fruit using the formula and your measurement. They give us the the rule, which is a magnification.

[00:24:16]The length of PQ in the figure and actual length of chili pepper. And also, we have the magic triangle.

[00:24:23]What is a magic triangle we have here?

[00:24:27]Magic triangle.

[00:24:30]Set I am [clears throat] I am And he asked you to measure the actual length.

[00:24:42]What about the image? So, we have the image 74 and the magnification 1.7.

[00:24:50]So, when we calculate it, so the actual equal I divided M 74 divided 1.7 We make it by this way. We can find the answer uh 43.529 but he wants you to to answer in three significant figures. So, this is 43.

[00:25:20]5 three significant figure.

[00:25:26]Chili pep- a chili pepper fruit contain reducing sugar and non-reducing sugar.

[00:25:35]A student test the sample of chili pepper fruit with a Benedict solution to show that they contain reducing sugar.

[00:25:42]State the positive uh result of this test. So, we know that the positive result or uh the test of Benedict which is brick red.

[00:25:57]So, it was blue and becomes brick red.

[00:26:02]The sugar content of chili pepper fruit increases as the fruit ripens. Scien- Scientists have found that the domain sugar content of chili pepper fruit increases from 19.6 g per kilogram in unripe chili pepper fruit to 36.1 g per kilogram in ripe chili pepper fruit. Calculate the percentage increase.

[00:26:30]How can we calculate the percentage increase? So, we have the rule said that final minus initial divided initial multiply 100.

[00:26:43]This is the final one and initial one divided the initial and when we calculated they wanted in two the value into decimal places.

[00:26:55]So the answer would be the final minus initial divided initial multiply 100. So 36.1 minus 19.6 divided 19.6 multiply 100 give us 84.

[00:27:08]183 and two decimal places so we have to write it by this way.

[00:27:16]Because three is less than five. If this more than five you can add it so it will be 19 but it's not.

[00:27:27]Next the question ask about to plan an investigation.

[00:27:33]To determine the effect of wind speed on the rate of uh transpiration.

[00:27:42]So when we want to know the effect of wind speed so this is independent variable the something that we will change.

[00:27:52]So the rate of transpiration how can we measure the rate of transpiration? Uh if you remember that we have a device called potometer and inside the potometer there is a bubble gas and after movement this bubble gas we will measure the distance traveled by the distance traveled by the bubble to know that the the uptake of water so we will know that this is the rate of transpiration so we will use poto meter to measure the distance traveled by the bubble.

[00:28:35]How can we start the investigation?

[00:28:37]Firstly we have to know that what are the factors affecting the rate of transpiration.

[00:28:44]We have four factors affecting rate of transpiration.

[00:28:50]So, our uh the first factor temperature and light intensity and wind speed and the last one humidity.

[00:29:24]If you choose one of them, which is wind the speed as uh independent variable, so we have to keep all other factors to be controlled variable. We have to keep them the same.

[00:29:40]So, we will start the investigation with each other. So, we have to cut three leafy shoot of the same type and same size and same number of leaves with the same surface area because this is one of the factor that affect the rate of transpiration and we have to just to change the wind speed.

[00:30:02]And then we have to connect this leafy shoot with a potometer that we set it now.

[00:30:07]And keep the potometer with a leafy shoot at the same uh same light intensity, same temperature, and same humidity level.

[00:30:17]So, how can we control the temperature? How can we maintain it? So, we have to use a thermostatically controlled water bath to maintain the temperature.

[00:30:32]So, all of these data, which is controlled variable, where is the independent variable?

[00:30:41]All right, start now to change the wind speed. But how can we change the wind speed using a fan? [clears throat] We know that the fans we can change their wind speed by we have low, medium, and high.

[00:30:53]So, we have different speeds of the fan.

[00:30:56]So, change wind speed by using a fan with different speeds, low, medium, and high.

[00:31:02]And then, we have to leave the experiment 5 minutes for equilibrium.

[00:31:07]What's meant by equilibrium? We have to let all the components of the experiment to start to react with each other. And then, make it a period of time to uh to start the reaction and leave it for 30 minutes.

[00:31:25]So, now we have many controlled variable, and we have an independent variable. So, where is the dependent variable?

[00:31:36]So, we have to measure the distance traveled by the bubble in the potometer.

[00:31:40]Okay? And then, calculate the rate of water uptake.

[00:31:48]And finally, we have to repeat this three times and take an average.

[00:31:55]Three times for each wind speed, so we have three for the medium, three for the low, three for the high speed. And take an average. And finally, we have to make the safety precaution by wearing gloves, goggles, use tongs, and cut the shoot away from hands using cutting board.

[00:32:20]Now, we have finished uh the exam. And don't forget to like and share and subscribe because all of the new exams will reach to you. Thank you, and goodbye.

[00:32:40]>> Mhm.