IGCSE Biology May June 2015 Paper 62 Doubts

[XxChampXx]

Guys I have a few doubts with the following questions and would like to know what you wrote as your answer as well:-
1) For the enzyme control, what did you write?
2) When you had to count the number of cells, what was your answer?
3) For the two differences between cell A and cell B, what were your answers?
4) Finally, for the last answer where you had to write two differences between sides X and Y of the lung, what did you write?

 

[rachlord]

1) Enzyme control can be denatured leaves, or using paper instead of leaves.
The controlled variable is the usage of same H2O2 conc and volume. Another controlled variable is the size of the dead leaves/paper should be same as that of the live leaf pieces used.

2) It seems as if any answer from 45-55 is acceptable.
3) Difference 1- In cell B the chromosomes are visible, and not visible in cell A
Difference 2- In cell B there is no nucleus, but there is nucleus in Cell A

4) 1- There is a tumour in Area Y. Like there was a ball of cells that seemed out of place
2- Uncontrolled division of epidermal cells. The epidermal cells were the darker coloured ones. There were too many of them.

 

[XxChampXx]

1) Enzyme control can be denatured leaves, or using paper instead of leaves.
The controlled variable is the usage of same H2O2 conc and volume. Another controlled variable is the size of the dead leaves/paper should be same as that of the live leaf pieces used.

2) It seems as if any answer from 45-55 is acceptable.
3) Difference 1- In cell B the chromosomes are visible, and not visible in cell A
Difference 2- In cell B there is no nucleus, but there is nucleus in Cell A

4) 1- There is a tumour in Area Y. Like there was a ball of cells that seemed out of place
2- Uncontrolled division of epidermal cells. The epidermal cells were the darker coloured ones. There were too many of them.

Can the controlled variable be temperature as a fluctuation in temperature can result in a change in the activity of the enzyme. And is 56 cells acceptable?

 

[The_Boss]

1) A boiled leaf with same dimension as the set of leaves being tested. Can be achieved by heating a leaf in a water bath.
Thebcontrolled variable was the specie of plants and source of error was the conc of H2O2 solution.
2) 55 anything from 40 to 60 is acceptable here as some previous year question had a large range
3)"A" had more chromosomes visible while "B" had a nucleus with no obvious visible chromosomes due to being at a different in stages of mitosis
"A" had thread like shapes chromosomes while B had circular nucleus.
4) Healthy region had a more uniform distribution of cells while unhealthy region had lumps of cancerous cells
Healthy region had more tissues visible while unhealthy region had a single tissue layer(outermost) with many cells

 

[rachlord]

Can the controlled variable be temperature as a fluctuation in temperature can result in a change in the activity of the enzyme. And is 56 cells acceptable?

Yes it can be a controlled variable. But you will have to state that the experiment will be carried out in a water bath.
As for 56, yes it seems that the range is going to be high. The good students at my school seemed to get 45-55. But 40-60 should be alright.

 

[Mursalin15]

what could possible answers for the precautions and also can around 64 cells may be right? what was the magnification btw?

 

[XxChampXx]

what could possible answers for the precautions and also can around 64 cells may be right? what was the magnification btw?

I wrote precaution can be maintaining the temperature(a change in temperature might fluctuate the activity of the enzyme, which might lead to inaccuracy and unreliability)

 

[rachlord]

what could possible answers for the precautions and also can around 64 cells may be right? what was the magnification btw?

What do you mean by magnification?

As for the number of cells, you have to hope that marking scheme gives you credit. 40-60 looks to be the narrowest range.

Precautions- Same dimensions of strips. Same temp, same pH. Same conc and volume of peroxide. Using same amount of metal for wiring. There's many of them

 

[The_Boss]

Well the magnification asked for the real size for the cell. I got 0.275mm.

 

[AnonymousX9]

For source of error, I wrote scissors, use sharper scissors to cut the leaves so all leaves would have same dimensions. As for the describe the results of the graph, I wrote specie x/y/z has highest amount of catalase (in the graph) and specie x/y/z has lowest amount of catalase (in the graph). Each specie has different amount of catalase, it is a normal distribution. For the last question, I wrote the cells in area Y are deformed (stretched) while the cells in area X are normal in shape AND the cells in area Y are dividing rapidly by mitosis so they are a lot more in number than compared to cells in X.

Are these correct? :/

 

[rachlord]

For source of error, I wrote scissors, use sharper scissors to cut the leaves so all leaves would have same dimensions. As for the describe the results of the graph, I wrote specie x/y/z has highest amount of catalase (in the graph) and specie x/y/z has lowest amount of catalase (in the graph). Each specie has different amount of catalase, it is a normal distribution. For the last question, I wrote the cells in area Y are deformed (stretched) while the cells in area X are normal in shape AND the cells in area Y are dividing rapidly by mitosis so they are a lot more in number than compared to cells in X.

Are these correct? :/

Source of error is scissor. That is true. A better reasoning of fixing the error is to use scalpel. A scalpel is used for cutting up stuff. But sharper scissors should score you a mark.
The answer you got for the results of the graph is perfect.
Even your answer regarding the Area X and Area Y is correct. I feel you should have just added that cancer cells are larger in size than normal cells. However your usage of the word 'deformed' may actually help you get the mark. And the idea about rapid division is perfectly alright

 

[AnonymousX9]

Thanks man, although I think I made a mistake in magnification. I used 3cm/800, it should have been 30mm/800. How many marks do you think I'll lose?

 

[XxChampXx]

For source of error, I wrote scissors, use sharper scissors to cut the leaves so all leaves would have same dimensions. As for the describe the results of the graph, I wrote specie x/y/z has highest amount of catalase (in the graph) and specie x/y/z has lowest amount of catalase (in the graph). Each specie has different amount of catalase, it is a normal distribution. For the last question, I wrote the cells in area Y are deformed (stretched) while the cells in area X are normal in shape AND the cells in area Y are dividing rapidly by mitosis so they are a lot more in number than compared to cells in X.

Are these correct? :/

Woah my answers are almost the same as yours but my last answer was a bit different and the scissors part I wrote use a more accurate cutter(it was in the 2014 paper 32 marking scheme). My magnification was 0.045 is that correct?

 

[rachlord]

Thanks man, although I think I made a mistake in magnification. I used 3cm/800, it should have been 30mm/800. How many marks do you think I'll lose?

If you wrote the Magnification formula, then you will get 1 mark. You will lose the 2nd mark since the answer was wrong
Edit- I don't remember the question well, so it depends on the unit that the paper asked for. If there was no unit specified and you wrote in cm, you should get the mark


The actual length should range from 0.035-0.05 mm

 

[Raduwan]

Does anyone have the 2015 igcse papers ( any paper is fine), if u have it please give it to me at [email protected], I need it urgently please!!! :'(

 

[rachlord]

Does anyone have the 2015 igcse papers ( any paper is fine), if u have it please give it to me at [email protected], I need it urgently please!!! :'(

If you mean that you want a leaked paper, you ain't getting it. You are not allowed to see the paper before the exam.
If you mean that you want to look at a paper that has been done, we are not allowed to distribute it. Lol, the students are unlikely to have any paper with them. The teacher may have a paper with them.

 

[Mursalin15]

the precaution was asked to prevent any hazard to the student,thus mentioning about enzymes and temp and such will that reward any marks? i gave v 62 btw

 

[XxChampXx]

the precaution was asked to prevent any hazard to the student,thus mentioning about enzymes and temp and such will that reward any marks? i gave v 62 btw

I think they asked both precaution and hazard. I am not sure though

 

[XxChampXx]

the precaution was asked to prevent any hazard to the student,thus mentioning about enzymes and temp and such will that reward any marks? i gave v 62 btw

What did you write for hazard.....I wrote hydrogen peroxide might spill and lab coats and eye goggles should be worn

 

[Mursalin15]

What did you write for hazard.....I wrote hydrogen peroxide might spill and lab coats and eye goggles should be worn

me too (Y)