The EXACT method to plan ANY IGCSE Biology investigation (Paper 6) – Apply in your 2026 exams

Added: 2026-05-08

[00:00:00]Now, that six marks question, you either easily get four, five, up to the entire marks here, or you pose and not get anything. But, it's super easy. Don't get overwhelmed with the details of something you haven't heard before. You can get those six marks with minimum minimum effort. How do you always get it? First, you just check the question and you see what has been changed. They said, "Eggs contain protein. It's called albumin." You may not heard of albumin, it's fine.

[00:00:32]This albumin will turn from cloudy to clear when it's digested [music] with a protease. "Plan investigation determine the effect of pH."

[00:00:42]You see this on? Two letters help you a lot. How? Because what comes before the on is your independent variable. That's the factor you're changing. And what comes after it is what you're measuring.

[00:00:57]Okay? So, now I know what I'm supposed to change. So, if I just write a sentence, I say, "I'll be changing the pH values."

[00:01:06]>> [music] >> That's worth one mark. And for the dependent, "I'll measure the digestion of the protein, the egg white, the albumin they've been talking about here." But, how do I measure it? You're not going to invent it. You're not going to make anything up. That's written here. You're going to time, you're going to find how long it takes to turn something from cloudy to clear. So, like the egg white is cloudy when it's not digested. As it gets digested, it turns clear. So, now I have the independent dependent That's like the most challenging thing. Once you do this, everything else is just a cliche. I'll going to control variables. Find two things, at least two, keep constant. And with enzymes, you can't go wrong. If you're changing the pH, the independent, [music] then I control the temperature. And whenever you have solutions, whenever you have like enzyme substrate, one very easy thing you can control and get all the marks, the [music] volume. So, take the same volume, take the same concentration of the enzyme and substrate. Lastly, tell them I'll be wearing gloves, mask, goggles, and tell them I'll be repeating several times, five times, and I'll take the average time it takes to digest. So, let me show you how I'm planning to design or planning this investigation. I have several water baths. Each has the same volume of enzyme and substrate. So, one test tube here is enzyme, one test tube is substrate. I keep them separate first. I let them both have the same temperature, the water bath, and I 5 minutes later, I mix, start the timer, and I keep looking. I wait until it becomes clear, until that cloudy color they've been talking about, until it comes clear. The temperature here is being controlled by water bath. I have a pH buffer. What's this for? It's just a solution to adjust the pH. To make sure that the pH stays constant throughout my investigation. I'll say, "Prepare five test tubes. Each is set at different pH." So, starting with pH four here on top, and this one here to seven, nine, and 11. I mean, I have a series of pH values. Does it have to be those values?

[00:03:23]Does it have to be these? No. You may write just any series. They just want you to change the pH. Then, I'll be adding fixed volume of pepsin, the enzyme, and I'll keep the temperature constant with a thermostatically controlled water bath. I'll place another test tube with substrate, the protein. I'll let them separate. That's essential. Whenever you have an enzyme experiment, you don't start the experiment until both your enzyme and substrate have the same temperature. So, let them equilibrate.

[00:03:55]>> [music] >> And then, 5 minutes later, time how long it takes for the solution cloudy color to turn clear. How you going to do this?

[00:04:02]You're going to be using this using a colorimeter. What's this colorimeter for? It's just a way to find the endpoint, to find the color change.