2025 October/November V2 IGCSE Biology (0610)-0610/62/O/N/25 Paper [6] Dr. Hanaa Adel

Añadido: 2026-05-11

[00:00:03]Welcome to our biology lessons with Dr. Hanik. Today we will solve with each other November 2025 variant 2 paper 6.

[00:00:17]Question one. A student investigated the rate of respiration in yeast using different concentrations of glucose.

[00:00:26]They used a 5% of glucose solution to make 1% of glucose solution and 4% the glucose solution.

[00:00:34]So from the first sentence who can tell me what is the independent variable? We know that the independent variable or the changed variable. So we will use different concentrations of glucose. So this is independent variable or changed variable. We want to know the its effect on the rate of this virus. Okay. The student used this method. Label two small test tubes 1% and 4%. Use a syringe to put 1 cm of 5% of glucose glucose solution into small test tube labeled 1%.

[00:01:17]and put 4 cubic cm of 5% of glucose solution into small test tube label 4%.

[00:01:25]Use a clean syringe. So why he use here a clean syringe not the same one to prevent the contamination or can change the concentration that is needed. So use a clean syringe to put 4 cubic cm of distilled water into small tested tubes label one and 1 cubic cm of a distilled water to the small tested tube label form.

[00:01:51]Pour east suspension into small test tube labeled 1% until it completely full. Keep the small test tube upright and carefully place a large test tube over the top of the small test tube label 1% and push the small test tube up like the figure again. So in front of us this the small testy tube containing yeast suspension and glucose solution and put it in an opposite way with a large test tube in an opposite way and just depress with your finger to hold the small test tube in its position and then you have to eat to invert this test tube to be like uh it exist in B and then we will put it in water bath containing warm water.

[00:02:55]Put the large test tube and small test tube labeled 1% into the warm water bath. So we have a source of error here.

[00:03:07]They they didn't mention the value of the temperature of the water bath and he didn't maintain this temperature. So how can we maintain the temperature? By using thermostatically controlled water bath, start the stop clock and wait for five minutes.

[00:03:26]This is controlled V.

[00:03:32]After 5 minutes, stop the stop clock and use the ruler to measure the height of the yeast suspension in the large testitute.

[00:03:43]This is the height that's needed to be measured.

[00:03:50]Remove the tested tube from the warm water bath and discard them. Pour the yeast suspension into small tested tube and label 4% until it's completely full.

[00:04:02]The same steps that we did it before for 1% we will make it for 4%.

[00:04:12]Figure 1.3 is a diagram of the water bath in step 8 and 11. So one of them for the glucose 1% and the other for the 4% of glucose solution. So we have two different concentration.

[00:04:26]Measure the height of the suspension in each of the large test tube. So we will measure this height of 1% of glucose solution and this height for 4% of glucose solution. So measure the height of the yeast suspension in yeast the in each of the large tested tubes shown in the figure.

[00:04:51]Prepare a table for the result and record your measurement. So what are the data that we needed to make or to prepare the table? So we have two different concentrations. So 1% and 4% and also the height of heat suspension by meter we have 1% and 4% and just measure the height of yeast suspension using meter.

[00:05:23]Sometimes your measurement is not exactly the same values that can find it in the mark scheme because the printed copy is totally different from the paper exam. So no problem if you find the difference between them your measurement is correct.

[00:05:43]State the conclusion for the result. So we have to know that when we start to write the conclusion we have to return back to the objective of the experiment.

[00:05:56]So we have to know that the different concentration of glucose solution. So this is the independent variable. You have to know its effect on the rate of respiration. Return back to the original objective.

[00:06:10]This one.

[00:06:14]So when we start to write the conclusion we have to refer to the concentration of glucose by increasing or by decreasing so whatever and its effect on the rate of respiration. So how can we write it?

[00:06:35]The higher the concentration of glucose, the higher the concentration of glucose solution, the greater the rate of respiration in yeast.

[00:06:47]Next, the question state the independent and dependent variable in this investigation. We just we get the independent variable from the first sentence. So about this is the concentration of glucose. So we have different concentrations of glucose and we just measure we just measure the height of the yeast suspension. So this is dependent variable to know that the rate of respiration.

[00:07:18]So the dependent variable the height feeds suspense describe how the temperature of the water bath could be maintained that we set it when we explain this investigation. So we said it by using theatically controlled water bath. Next the question you asked about why a clean syringe was used in step three. We said that if we have or if we use the same syringe that we put it uh the glucose volume and the same one we put the distilled water. So we will change the concentration. So it's called contamination. So we we use a clean syringe to avoid or to prevent the contamination.

[00:08:06]A student extended the investigation by using more concentration of glucose solution. Calculate the volumes of 5% of glucose solution and distilled water that are needed to make 5 cm of 3% of glucose solution.

[00:08:23]So we know that the 5% if we have the original concentration of the glucose solution I just get it from it 5 cm it's a concentration of 5%.

[00:08:38]So how much uh cubic cm needed to make it three%.

[00:08:45]So we will make it a cross multiplication. So 3 * 5 / 5 which is equal 3 cm of glucose solution and we have to then add it to be five.

[00:08:58]So we will add 2 cm of distilled water.

[00:09:05]Sports drink often contain glucose which is a reducing sugar. State how you could test the sample of sport drink for reducing sugar. So we have the Benedict reagent or Benedict solution and then apply heat using water bath at 80° Celsius. If the blue color of Benedict solution change it from blue to green or yellow or orange or brick. So this solution contains reducing sugar. Why we have all of these uh colors? Because this investigation or this test used to test the concentration also of the reducing sugar. So the most concentrated glucose or reducing sugar. So it will give us break red and the least one give us green.

[00:09:57]If emulsion test can be used to show that the sample of food contains fat.

[00:10:04]State the result of a positive test. So the positive test of emulsion when we test the presence of oil or fat or lipid so it will give us white emulsion or cloudy emulsion. So just one safety precaution that should be followed when using ethanol. We know that ethanol is flammable and volatile.

[00:10:28]So uh we have to keep ethanol away from flame because ethanol is flammable and we have to cover ethanol container to prevent evaporation and also you have to wear goggles. So we have the priority first for the flammable. So we have to keep it away from the flame. If you just added more points, so you have to cover it or wear gloves.

[00:10:58]Next, the question to plan an investigation to determine the effect of exercise intensity on the heart rate in human. In this investigation have to know that the exercise intensity is independent variable. So we can change it by ask the people for walking, for running, for jogging. So different intenses of exercise on the heart rate. How can we measure the heart rate? How can we convert the heart rate into dependent variable? So we can using heart monitor or ECG or counting the heartbeats at a certain time. So in front of you many options to to write it as a dependent value.

[00:11:47]Firstly uh this exercise or this investigation for people. So when we ask people to do an exercise or to do the activity so they have uh should have the same age, same math, same gender and fitness level or activity level.

[00:12:10]And then we have to measure their heart rate at rest at the beginning of this investigation using ECG. What is ECG?

[00:12:19]This is called electroc cardiogram that used to monitor the heart rate or also can count the heart the number of heartbeats in a certain time and then ask them to walk for 5 minutes with the same intensity of walking and same environment environmental temperature to not affect on their heart rate. After that we have to measure their heart rate directly after walking using again ECG.

[00:12:56]After doing this walking ask them to rest for 5 minutes or 10 minutes to return back to their normal heart rate.

[00:13:06]After that we have to repeat all of these steps above uh once for running and other for jumping.

[00:13:17]Okay, repeat this uh activities or this uh investigation three times for each exercise intensity and take an average. And people should be well hydrated, wearing comfortable shoes, comfortable sports wear and not suffering from any health issues.

[00:13:55]Next, the question. The figure 3.1 is a photograph of a necklace starfish.

[00:14:01]Okay. He ask you to draw a large diagram of a necklace starfish like this. So please you have to put in your mind the main important points and analysis for this diagram. So how many arms for this starfish? Okay. And you can do it by this way.

[00:14:27]This we have an arm here and then another one.

[00:14:36]The third four in one straight line. If you have a problem with the drawing, so no problem to erase it and redraw it again. But don't press on your pencil. It is preferable to use a pencil with the HB.

[00:14:59]This is the uh um degree of graphite.

[00:15:04]Okay. Not more dark or not lighter. So it it is in the middle. And then if you concentrate well we can find them five arms and some of the arms this dark and the other is light. So we can make any shadowed area to be separated from each other. And then we have a central desk in the middle just like that. So if you find this any problem with the drawing and I think this is fully a mistake you can erase it and make it where there is no intersection.

[00:15:40]So when we start to draw like this no it is not preferable to do it like this.

[00:15:45]So, what we're going to do like this and be careful and be slowly to join them together.

[00:15:56]And this is my drawing.

[00:16:04]Line PQ in figure 3.1 represent the diameter of the necklace starfish.

[00:16:10]Measure the length of PQ in the figure.

[00:16:12]So you have to bring your ruler and measure from P to Q. I I know that you use your ruler in cm but you have to convert it into me and also you can find your answer is totally different from the value in the mark scheme. So no problem because the printed copy is totally different from the paper exam. So your measurement is correct but you have to convert it into mill.

[00:16:42]So my answer is 93 mm. So calculate the actual diameter of the necklace starfish. They give us the rule but I like my magic triangle that said I am this is magic triangle for the magnification. So I represent the image, A represent this actual length and L M represent magnification. So just circle that the part that you needed and this one means divide and in between it means multiply. So when we need actual length so image divided magnification from where we can get the magnification so we can find it 0.32.

[00:17:28]So 93 over 0.32. So it will give us 290,625 and he wants this two significant figure. So 290.

[00:17:49]Figure 3.2 is a photograph of spiny starfish and necklace starfish.

[00:17:57]State two spiny state two ways the spiny starfish differ from the necklace starfish and one way is similar. So they ask us to write the similarities and differences are just two differences and one uh similarity. So we can find here this rough surface or spiny surface on this one but this one is smooth. So spiny starfish has spines or rough surface while the necklace starfish is smooth or does not have spines.

[00:18:35]So we can find the central desk or the central part here is lighter than necklace starfish.

[00:18:43]Okay. The book can tell me similarities between them. Both have five arms. So one two three four five one two three four five. So both have five arms and they have circle in the middle. So whatever this is light or dark the circle in the middle. Okay. So whatever this is the point of differences this is dark or and light and the similarities both have this circle. This is called the central dust and they have radial symmetry. So what's irradial symmetry? This radial it means that it looks like the radius. So we have this is equal to each other. This is radial symmetry both. Okay. From the center 1 2 3 4. So they have radial symmetry. Also saved armed starfish live in the sea.

[00:19:46]Scientists investigated the distribution of seven armed starfish [clears throat] in one region in one region. So this is very photograph of 20 m² area of seabed were taken at different depth. So this is the same area same size of area or same area which is 20 m²ared. The depth in the water in each area was measured when the water at its height.

[00:20:16]Okay.

[00:20:18]The number of seven armed starfish in each photograph were counted. All photographs were taken on the same day in July. Also this is control variable.

[00:20:30]So we have control variable control variable control bin. State two ways that the method used by the scientist ensured that the number of seven armed starfish counted at different depth different depth this is independent one could be compared because it just have only one different but all the other factors exactly the same. So when we have an experiment we just we have to change only one variable to know its effect not more than one variable should be changed because we never know which one of them that affect the result. It just we have different depth in the same region at the same area at the same highest level of uh water or at high tide and the same day in July. So just only one factor there change it which is different depth.

[00:21:29]So the answer as we just said now the same area the same size of area which is 20 m²ared and same day the same tide of same time of tight.

[00:21:42]The result of the investigation are shown in the table.

[00:21:47]They give us the depth by meter and we can find that if you concentrate well we can find it uh it's in a range form is in the range it's a range range we know that if we find any range so we have to draw histogram or frequency diagram what is a histogram or frequency diagram this is diagram this is uh we can use it in a boys touch each other there is no gaps between them. So it's a range by using the depth and uh so we will put the depth in on the xaxis.

[00:22:29]Okay, because this is independent value something that only change it here which is independent variable and we have to put it on the x-axis and then we have to count the number of seven armed starfish in this area.

[00:22:46]So the question is plot a histogram. I just say the histogram exactly the same idea if they ask about the frequency diagram. Exactly the same on the grid on the data. So I draw it by this way.

[00:23:07]Depth.

[00:23:12]Okay. depth we just make it try to make it large as much as possible. So we have the depth in millimeter and the number of seven armed uh starfish counted and then we have to put below each column its identification or its range from 0 to 9.9. Next column from 10 to 19.9 next column because each data below it this is was labeling for this column. Okay.

[00:23:48]So the first column it's the range from 0 to 9.9. The second column from 10 to 19. So this is give us it looks like a label. Okay. Don't make it this arrow just show you to to just understand it.

[00:24:06]But don't draw this arrow.

[00:24:10]And then we have to make the column.

[00:24:13]This column should be equal in the width.

[00:24:18]So the width this width should be equal to each other.

[00:24:33]This all of them. No one is greater than the other should be equal. All of them should be equal to each other and there is no gaps between the bars because this type of histogram or frequency diagrams.

[00:24:50]So including a range. So we have here a range.

[00:24:55]So we have to draw it by this way.

[00:25:02]State the depth range in table 3.1 at which post seven armed starfish were found. So which one of them is the highest? Which one of them? Yes. From 10 to 19.9 this is the highest value.

[00:25:18]So we have to write it also in the form of range.

[00:25:26]Using the information in the table 3.1 calculate the total number of seven armed starfish. The total number that were photographed at all depths use this value to calculate the percentage of starfish that were photographed in this area. So at the beginning we have to calculate the total. So total sum of all starfish that exist in an area and we have to know the percentage of the range from 0 to 9.9.

[00:25:59]So firstly we have to make the total this total sum of all of them which is equal 3,428 and then how can we get the percentage?

[00:26:09]So the value of uh from 0 to 9.9 where is it 337 divided the total multiply 100 which is the percentage of the starfish in this area.

[00:26:28]it give us this 9.83 and just becomes uh the nearest whole number which is equals 10.

[00:26:44]Now we reach to the last part of the exam. I hope that you enjoy it and waiting for more and more exam. Thank you and goodbye. Don't forget to like, share, and subscribe to uh find all the new exams. Thank you and goodbye.