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A level Biology: Post your doubts here!

qwertypoiu

qwertypoiu

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My Name said:
View attachment 54806
The answer is D
Click to expand...
The egg is a haploid cell. After fertilisation, it fuses with another haploid cell to form a single diploid cell. The quantity of DNA has doubled.
The next doubling of DNA content occurs during the S phase of the cell cycle. The DNA undergoes semi-conservative replication. It may not be noticeable under a microscope until Prophase, when we see each chromosome consisting of two chromatids, but we know the chromatin form duplicates before during the S phase.
The reduction of DNA content next, which is what the question is asking about, happens at mitosis, when two new cells are formed from the diploid zygote, so the DNA material is shared. Each get one chromatid from the one chromosome.
This process of increase and decrease in DNA material will continue, each corresponding to S phase and mitosis.
All 4 options given in the question are a part of mitosis.
The point at which we consider the single cell to have truly split into two is when mitosis is complete.
This is at Telophase, after which cytokenesis will complete the separation.
 
qwertypoiu

qwertypoiu

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My Name said:
I dont get it. :/
What happens if they are squashed?
<I know that the number would be 5 so it can be either A or C >
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The cell was squashed, so the positioning of the chromosomes were altered.
Squashing changed the physical positions of them, but couldn't have split the chromatids.
So we conclude, given a choice between Metaphase and Anaphase, that it could only be Metaphase.
 
qwertypoiu

qwertypoiu

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My Name said:
View attachment 54807
The answer is A
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The poles of spindle have the centrosomes pulling at the centromere of the chromosomes. Over time, the distance between them decreases, since they're getting pulled closer by the microspindle tubules.
So this is represented by 1.
You might be wondering, (since I was), why the rate of decrease in distance between them suddenly increases in magnitude?
My suggestion is that perhaps the initial slow decrease is when the tubules are attempting to pull the chromatids apart, and then when it is finally torn apart, it's pulled much faster towards the poles, since energy is not wasted on breaking the bond.

Distance between centromeres of sister chromatids - this will initially be 0, when they are attached together and not separated yet.
Next, when the chromatids are finally separate, the distance increases between them. (see this happens at the 15th minute, corresponding to the time at which the rate I was talking about earlier suddenly increases).

Distance between poles of spindle remains relatively constant, maybe it decreases slightly at first because it pulls on the chromatids and gets pulled back or something. The increase later can be explained by the cells splitting and moving apart. The spindles may not be moving relative to their position in their new cell, but the forming cells probably are.
 
shinnyyy

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There's a question ie.
explain,using named example,how mutation can affect phenotype?? 7 marks
Can anyone ans me the question.
 
princess Anu

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shinnyyy said:
There's a question ie.
explain,using named example,how mutation can affect phenotype?? 7 marks
Can anyone ans me the question.
Click to expand...
Mutation--> altered nucleotide sequence of DNA( different genotype)---> different proteins made because this altered(new) DNA may form a different mRNA by transcription---->Different proteins with altered primary/ tertiary structure may led to a different physical feature(phenotype)..




^ somebody correct me if I'm wrong :)
 
shinnyyy

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can somebody please explain the epidemiological and experimental evidences linking cigarette smoking to disease and early death?
 
M

My Name

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shinnyyy said:
There's some error in papers section so I'll take a snap from my past papers booklet and will give u tomorrow okz???? :unsure:
:)
Click to expand...
I know I tried form maxpapers I didn't find the question. :p<That is why I asked >
:) Ohkay,sure thanks.
 
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shinnyyy

shinnyyy

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My Name said:
For a you are pointing at the thin one right? :3

Can you give me a sample answer please, with proper sentences.

Ty
Click to expand...

Then wait a sec, lemme take a photo from my copy otherwise it will take a lot of time to type in here from mob.
 
M

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shinnyyy said:
Then wait a sec, lemme take a photo from my copy otherwise it will take a lot of time to type in here from mob.
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Sure tysm!
The thing is I think I get the CO 2 transport part but I dislike this part of the chapter so if you could give me a sample answer Ill follow that. :)
 
shinnyyy

shinnyyy

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My Name said:
Sure tysm!
The thing is I think I get the CO 2 transport part but I dislike this part of the chapter so if you could give me a sample answer Ill follow that. :)
Click to expand...
No worries
just have a look on it and give a reading and then lemme know if you get it or not?
 
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