biology paper 1 doubts

[athaan]

ah, no big deal. i'm quite interested in learning science, ^^ and since I keep getting C for paper 1 when I'm correcting my work! haha.

That makes sense, thank you again for explaining. you must've be really smart ~
i forgot about the presence of oxygen in air, and keep thinking it has to do something with the inert properties of nitrogen.. i guess i mixed myself up with chemistry, xD

 

[nelly trich]

The process of PRODUCING the eggs creates variation. They produce eggs through meiosis which involves independent assortment and crossing over (which leads to variation).

sperm cells are produced by mitosis ,mitosis doesn't involve independent assortment or crossing over ? mitosis produce genetically identical cells !!

 

[Irfan1995]

sperm cells are produced by mitosis ,mitosis doesn't involve independent assortment or crossing over ? mitosis produce genetically identical cells !!

Wait, that completely goes against almost everything I've learnt about this subject. In spermatogenesis, you start with a primary spermatocyte which is diploid. After passing through meiosis I and II (which results in halving the chromosome number), then you will have immature spermatids (which are all haploid). After metamorphosis and maturation, you get 4 sperms which are all haploid originating from one primary spermatocyte.

To make this a whole lot simpler, you have an initial cell (diploid) which undergoes reduction division (meiosis) to produce haploid cells. During meiosis, independent assortment and crossing over leads to variation.

Conclusion: sperm cells are NOT produced by mitosis. If they did, then we would double the chromosome number every generation. Then our whole body would be flooded with chromosomes.

 

[NouranAyman]

Guys Only one day is left!! How should we prepare for paper 1 biology??? ( what to do tomorrow??? im not really getting high marks after solving! should i revize or what ? jst a day is left

 

[Irfan1995]

Guys Only one day is left!! How should we prepare for paper 1 biology??? ( what to do tomorrow??? im not really getting high marks after solving! should i revize or what ? jst a day is left

I'm guessing you're not 100% confident about the material. I strongly suggest you quickly revise the book. If you can't do that, then at least find some notes online and look at them thoroughly. After that, solve just the last few past papers (2011-2012) and you should be good to go! Good luck

 

[xtremeforums]

is a 36-39 out of 40 a good grade at this stage?

 

[NouranAyman]

I'm guessing you're not 100% confident about the material. I strongly suggest you quickly revise the book. If you can't do that, then at least find some notes online and look at them thoroughly. After that, solve just the last few past papers (2011-2012) and you should be good to go! Good luck

Thank youu!!! I will try revizing from early morning any other tips

 

[NouranAyman]

is a 36-39 out of 40 a good grade at this stage?

]
Thats really gooddddd!!!!!!!! MashAllah! I get 30 or 29 did you revize?

 

[Irfan1995]

is a 36-39 out of 40 a good grade at this stage?

That's awesome! Now all you have to do is quickly revise the concepts which you got wrong most of the time

 

[hmlahori]

can anyone give me any link for the bio 9700 o/n 2011 examiner report? doesnt seem to be available here on xtremepapers.

 

[Irfan1995]

]
Thank youu!!! I will try revizing from early morning any other tips

Yeah, one more thing. Be 100% that you know exactly what the question is asking for. Believe me, I lost many marks in the first two papers for this. After realizing this mistake by the third past paper, I never got below a full mark from June '07 till June '11

 

[nelly trich]

Wait, that completely goes against almost everything I've learnt about this subject. In spermatogenesis, you start with a primary spermatocyte which is diploid. After passing through meiosis I and II (which results in halving the chromosome number), then you will have immature spermatids (which are all haploid). After metamorphosis and maturation, you get 4 sperms which are all haploid originating from one primary spermatocyte.

To make this a whole lot simpler, you have an initial cell (diploid) which undergoes reduction division (meiosis) to produce haploid cells. During meiosis, independent assortment and crossing over leads to variation.

Conclusion: sperm cells are NOT produced by mitosis. If they did, then we would double the chromosome number every generation. Then our whole body would be flooded with chromosomes.

what you are saying hapens in normal sexual reproduction ,this question is talking about an abnormal case not studied by you in either AS or A2, and if you check the question choice number2 sperm cells are produced by mitosis which is right ,please check the Question again check the choices and tell me do you agree with me that mitosis process produces genetically identical cells or not ?! okay thank you for your replies I appreciate it Good luck in your exam

 

[hmlahori]

hey people really need o/n 2011 examiner report...can someone upload it please?

 

[Irfan1995]

what you are saying hapens in normal sexual reproduction ,this question is talking about an abnormal case not studied by you in either AS or A2, and if you check the question choice number2 sperm cells are produced by mitosis which is right ,please check the Question again check the choices and tell me do you agree with me that mitosis process produces genetically identical cells or not ?! okay thank you for your replies I appreciate it Good luck in your exam

The case mentioned in the question is known as haplodiploidy (a form of parthenogenesis). It's a bit complicated to explain fully, and may seem extremely confusing.
But in the normal cases that we took, producing the unfertilized eggs (gametes) is a source of variation in itself.

To answer your question, all sperms are produced by mitosis and they are genetically identical. However, just because the sperms are identical doesn't mean that the offspring are. I know this is an extremely confusing topic, and I really don't know why they brought it up in an AS Biology exam.

 

[Jevin Sanoo]

Can someone please explain to me what is more negative and less negative in terms of water potential?

 

[railey]

Can someone please explain to me what is more negative and less negative in terms of water potential?

When you say the water potential is more negative it means there are more solutes, (solute potential is high), when you water potential is less negative it contains less solutes, (Lower solute potential). The water potential for Pure Water=0

 

[ZohaibAsad]

-Less negative means that water is proportionally greater than solute
-More negative means that the proportion of water is less than solute

Relative to another solution . . .

 

[Irfan1995]

Can someone please explain to me what is more negative and less negative in terms of water potential?

Water potential is generally negative.
The higher the water potential, the purer the water is.
The lower the water potential, the more solutes dissolved in it.
Water moves from an area of high water potential to an area of low water potential.
So if the water potential of A is less negative than B, then A has a higher water potential, and water will go from A to B.
If it helps, think of it as numbers, lets say A is -100 and B is -200. This implies that A is less negative (more positive) than B, so A has a higher water potential than B. So water moves from A to B.

 

[nelly trich]

Spermatogenesis starts in the germinal epithelium of the testis. Repeated mitotic division of these cells occurs producing spermatogonia. Then during the growth stage the diploid primary spermatocyte undergoes meiosis I to produce secondary spermatocyte. These then undergoes meiosis II to produce spermatids, which after differentiation becomes spermatozoon. The diploid initial cell u r referring to comes from mitotic divisions.

Did you check the Question ?? It doesn't refere to this process ,it referes to asexual reproduction ! can you please check the question in the begining and then answer me !

 

[nelly trich]

Spermatogenesis starts in the germinal epithelium of the testis. Repeated mitotic division of these cells occurs producing spermatogonia. Then during the growth stage the diploid primary spermatocyte undergoes meiosis I to produce secondary spermatocyte. These then undergoes meiosis II to produce spermatids, which after differentiation becomes spermatozoon. The diploid initial cell u r referring to comes from mitotic divisions.

This is the Question teh answer is C ! my question is why it's not D ??