AQA AS Biology Unit 2 - 1 June 2015

Any predictions for the 6 mark question in this years paper?

I have a feeling that it's going to be from one of the topics below:
Meiosis
Adaptions of chloroplast/mitochondria
Gas exchange in insects
Gas exchange in fish
Structure of starch/cellulose/glycogen
Factors that affect genetic diversity
Selective breeding

What do you guys think?

Yeah
Partial pressure basically means 'want'
The haemoglobin has a lower want I.e. Partial pressure for oxygen at the respiring tissues


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Meiosis ensures that the haploid cells produced have variation in thier alleles so that genetic diversity is increased

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Thanks so if this was an exam question would it be wrong if i mentioned the chromosome number?

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I reckon water transport in plants. Does anyone have any good notes on water transport for 6 markers? Thanks in advance

Yeah I think these are really good, maybe causes of variation, or describe how water moves through the apoplast/symplast pathways


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Not exactly, but tbh it depends on the question but where applicable, I would write that meiosis;
-has two nuclear divisions m1 and m2. --In m1, two daughter cells are produced which divides again (m2)
-independent segregation ensures that in m2, four genetically unique daughter cells are produced, two from each of the previous two daughter cells that were produced in m1
-meiosis produces gametes (sperm and egg cells) so these daughter cells must be haploid meaning that they contain 23 chromosomes, half that of cells derived from miotic divisions as they must fuse with another gamete during sexual reproduction

Hope this helps and as far as writing about the chromosome number, if u write 'haploid' then I'm sure u will gain the mark

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Thanks so if this was an exam question would it be wrong if i mentioned the chromosome number?

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Okaay thanks for helping me understand it do you know how many points you would write for independant assortment? Sorry random question but i get confused on how the concept of independant assortment works

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Independent segregation occurs in the original parent cell BEFORE the first nuclear division, m1, actually takes place and it happens as follows;

-during metapahse, each chromosome pairs up with its homologous partner at the vertical equator and the order of which each pair arranges itself is totally random and now the cell with spindles fibres attach to the centromeres of each chromosome
-in anaphase, these spindles contract and when they do so, due to the random arrangement of these pairs, the pair that is passed into each daughter cell is also random
-therefore this process is called independent segregation(assortment)

And now, in telophase, the physical cell division m1 occurs

Hope this helps

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Okay, in some notes it says in anaphase homologous pairs of chromosomes seperate so chromatids seperate and this assortment produces a mix of alleles in independant assortment? So does the process definitely happen in metaphase or could it be anaphase?

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According to the nelson thrones aqa book, pg 168, it stars that
- interpahse is when the DNA replicates
- prophase is when the DNA becomes visible and the nuclear envelope disappears
- metapahse is when the chromosomes arrange themselves in the cell centre and spindles form
- anaphase is when these spindles contract
- telophase is when the nuclear envelope reforms and the cell divides

Going by this book, it only mentions independent segregation which occurs at the metapahse stage of the cell cycle in m1

I am not sure what independent assortment is :/ unless it's the same thing

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Finding meiosis hard, need help

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with what parts, the process or application?

According to the nelson thrones aqa book, pg 168, it stars that
- interpahse is when the DNA replicates
- prophase is when the DNA becomes visible and the nuclear envelope disappears
- metapahse is when the chromosomes arrange themselves in the cell centre and spindles form
- anaphase is when these spindles contract
- telophase is when the nuclear envelope reforms and the cell divides

Going by this book, it only mentions independent segregation which occurs at the metapahse stage of the cell cycle in m1

I am not sure what independent assortment is :/ unless it's the same thing

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Yeah, essentially it states that the way in which a homologous pair of chromosomes line up (forming a bivalent) is independent of the way in which all of the others line up.
To show it with some numbers, it's 2^23 (over 8 million). Think of 23 lines labelled 1 through 23, and then 23 other lines labelled A through W. Now. You could have 1A,1B,1C etc to 1W. Then 2A, 2B etc.. and this amount of combinations is huge!!
Nevermind crossover which is about 2^30000 (to the power of the number of genes), which is the same as 1 with 9000 zeros!! Coupled to 2^23 and you just cry at how amazing cells are!