Aqa a-level biology 7402 - paper 2 - unofficial mark scheme 13th June 2019

RAKH000

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Drop down any questions and answers from the test and I will produce an unofficial mark scheme based on most popular answers, thanks!

- Describe Succession-
How an ecosystem changes over time (change in species diversity and habitat diversity) – relies on environment being made less hostile by present species via death and decomposition leading to it being outcompeted and replaced by larger better adapted species.

- Percentage question (3sf)
- KJmy calculation question

-Hardy-Weinburg Calculation-
48%

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Zxr_

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That hardy weinberg q- Me and my mates got 32% but people got like 46% or something?

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RAKH000

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I also got 46% too.

(Original post by Zxr_)
That hardy weinberg q- Me and my mates got 32% but people got like 46% or something?

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ellathenerd

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0.61 for rf question.
0.155% first question
48%
3.2?

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RAKH000

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What did you get for the calculation for KJmy and the percentage question, it was two of the first few questions.

(Original post by Zxr_)
That hardy weinberg q- Me and my mates got 32% but people got like 46% or something?

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RAKH000

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How did you get 0.155 for the percentage?

(Original post by ellathenerd)
0.61 for rf question.
0.155% first question
48%
3.2?

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The Anarchist7

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(Original post by RAKH000)
I also got 46% too.

I got 48 percent

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ellathenerd

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I multiplied all the percentages together

(Original post by RAKH000)
How did you get 0.155 for the percentage?

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RAKH000

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(Original post by The Anarchist7)
I got 48 percent

Do you remember the percentage for the question after succession or the calculation for KJ m y question.

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1Secord

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(Original post by RAKH000)
How did you get 0.155 for the percentage?

I cant remember the percentages exactly but I think between the Sun and vegetation it was 2.1%, between vegetation and Zebra 12.7% and between the zebra and I cant remeber the next one, was it 58% something?.

I worked it out by dividing 2.1 by 100, then multiplying by 12.7 = 0.2667. Then dividing 0.2667 by 100 and multiplying by 58.

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mcsqaured

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I got the same as that but my Rf value was 0.60

(Original post by ellathenerd)
0.61 for rf question.
0.155% first question
48%
3.2?

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The Anarchist7

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0.36= q^2 or recessive
q= 0.6

P must be 0.4 so p^2 = 0.16 ( number of homozygous dominant)

Therefore, 2pq =
0.64 - 0.16 = 0.48

48 percent WAS the answer can’t see how 0.46 was right unless some one can explain otherwise

(Original post by The Anarchist7)
I got 48 percent

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namelessfeelsx

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(Original post by Zxr_)
That hardy weinberg q- Me and my mates got 32% but people got like 46% or something?

I got 32% as well... because dominant homozygous would be p^2 so p=0.8 (after square rooting 0.64), then 1-0.8=0.2, then 2pq= 2x0.8x0.2= 0.32

If it is wrong we would still get marks for multiplying 2 by two other numbers.

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RAKH000

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Yeah thats exactly what I did, think I got the final value confused. Must've been 48 percent if those values are correct.

(Original post by The Anarchist7)
0.36= q^2 or recessive
q= 0.6

P must be 0.4 so p^2 = 0.16 ( number of homozygous dominant)

Therefore, 2pq =
0.64 - 0.16 = 0.48

48 percent WAS the answer can’t see how 0.46 was right unless some one can explain otherwise

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The Anarchist7

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Probs not seeing as you didn’t have to multiple anything by 2 to work out the answer

(Original post by namelessfeelsx)
I got 32% as well... because dominant homozygous would be p^2 so p=0.8 (after square rooting 0.64), then 1-0.8=0.2, then 2pq= 2x0.8x0.2= 0.32

If it is wrong we would still get marks for multiplying 2 by two other numbers.

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RAKH000

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Did you the other percentage question where you had to put it to 3sf?

(Original post by The Anarchist7)
0.36= q^2 or recessive
q= 0.6

P must be 0.4 so p^2 = 0.16 ( number of homozygous dominant)

Therefore, 2pq =
0.64 - 0.16 = 0.48

48 percent WAS the answer can’t see how 0.46 was right unless some one can explain otherwise

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1Secord

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(Original post by The Anarchist7)
0.36= q^2 or recessive
q= 0.6

P must be 0.4 so p^2 = 0.16 ( number of homozygous dominant)

Therefore, 2pq =
0.64 - 0.16 = 0.48

48 percent WAS the answer can’t see how 0.46 was right unless some one can explain otherwise

I also got 48%. I think the question told you the percentage of Grey body was 64%. That percentage included GG or Gg.
I did 1-0.64 = 0.36 - So 36% must be black body, gg.
Square root of 0.36 = 0.6.
1 - 0.6 = 0.4 ( Since 1 = p + q )
The question asked for heterozygous - 2*p*q
2 * 0.6 * 0.4 = 0.48 = 48%

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The Anarchist7

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(Original post by mcsqaured)
I got the same as that but my Rf value was 0.60

(Original post by RAKH000)
How did you get 0.155 for the percentage?

(Original post by ellathenerd)
0.61 for rf question.
0.155% first question
48%
3.2?

3.24 micro meters or something but other than that think I got exactly what u got

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Anonymousegetit?

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If for the sampling questions i talked about both quadrats and transects would i get 0 marks, it didn’t say state one method?

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1Secord

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I remember there was a question asking about photoionisation. ( 2 marks?)
Another question about how to estimate the population of sundews, a type of insect eating plant, in a marshy bog area. ( 5 marks )
The second part to this question was asking why it is beneficial to the sundews to eat insects when there is a low concentration of nutrients in the soil ( 2 marks ?)

There was another question about calculating the volume of distilled water and the concentrated IAA solution to make 40cm^3 of the solution with a concentration of 10 parts per million? ( I really can't remember the question that well, I just know I struggled with it )

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