A level Biology: Post your doubts here!

[kareem22010]

View attachment 59952 View attachment 59953 guys please help with this question
???

as you can see, affinity for oxygen has decreased so, this means that red blood cells are able to dissociate oxyhaemoglobin and release oxygen more easily in respiring tissues without having to be completely saturated. can you please refer to the markscheme? i answered this question once and it was correct but i don't remember my exact answer now.

 

[Eugene99]

can somebody help me with this confusing markscheme doubt?
The question says: Outline the differences between the apoplast and symplast pathways after the water has left the xylem?( 4 points)
My answer is: Apoplast:water moves through cell walls only and passes from one cell to another through adjacent cell walls or through airspaces between cells.
Symplast:water moves through cytoplasm and vacuole and passes from one cell to another via plasmodesta.
View attachment 59954
i think i should earn 2 marks for mentioning about plasmodesta and cell walls for apoplast somehow, the 2nd point of the markscheme says 'ref to only cytoplasmic/not including vacuoles' then at the 6th point it says '(includes) vacuolar pathway /(through) vacuoles' and according to my coursebook symplast pathway passes through both cytoplasm and vacuoles.i am confused.how many marks should i earn for mentioning both cytoplasm and vacuole in symplast?

R, in markschemes, means Reject and you answered perfectly well...They mean that if candidate mentioned only 'cytoplasmic' and did not include vacuoles then reject, but since you mentioned vacuoles as well, so you get the credit

 

[kareem22010]

R, in markschemes, means Reject and you answered perfectly well...They mean that if candidate mentioned only 'cytoplasmic' and did not include vacuoles then reject, but since you mentioned vacuoles as well, so you get the credit

oh,thank you so much, i was dying to know what the hell is going on with this markscheme.

 

[Eugene99]

oh,thank you so much, i was dying to know what the hell is going on with this markscheme.

lol, yes they are confusing sometimes

 

[Shah34]

Just wanted to ask what can we expect from the new syllabus topics, I mean enzyme constant Km, what type of questions ??
And also I am practicing plan diagram from google images. I just type the specimen and draw plan diagrams is it okay???

 

[mohmed ahmed soliman]

Explain, with examples, how the environment may affect the phenotype. (N’07 Q:11 b)


1. phenotypic variation results from interaction of genotype and environment / VP = VG

+ VE ;

2. environment may limit expression of gene(s) / AW ;

3. e.g. for size / mass / height ;

4. because, food / nutrients / ion, missing / malnutrition ;

5. named, nutrient / ion / mineral, missing ;

6. environment may, trigger / switch on, gene ;

7. ref. low temperature and change in animal colour ;

8. ref. high temperature and, curled wing in Drosophila / gender in crocodiles ;

9. ref. UV light and melanin production ;

10. ref. wavelength of light and, flowering / germination / fruit colour ;

11. other named trigger plus example ;

12. environment effect usually greater on polygenes / ora ;

13. environment may induce mutation affecting phenotype ;

i want help to score the following MS points
13. environment may induce mutation affecting phenotype ;



ref. low temperature and change in animal colour ;


8. ref. high temperature and, curled wing in Drosophila
10. ref. wavelength of light and, flowering / germination / fruit colour ;


11. other named trigger plus example ;
13. environment may induce mutation affecting phenotype ;

 

[mohmed ahmed soliman]

Explain, with examples, how environmental factors can act as stabilising or evolutionary forces of natural selection;
help

 

[kareem22010]

Explain, with examples, how environmental factors can act as stabilising or evolutionary forces of natural selection;
help

i found a question and answer very similar to yours but without examples:
(b) Coelacanth haemoglobin has a very high affinity for oxygen, suggesting that coelacanths,
which have been captured at depths of between 200 m and 400 m, live in water that has
a low concentration of oxygen.
Explain how an environmental factor, such as the low concentration of oxygen in deep
water, can act:
(i) as a stabilising force in natural selection
MS:
1. idea of, unchanging / constant, environment ;
2. oxygen concentration acts as a selective agent ;
3. organisms best adapted to these conditions survive ; ora
4. extreme (phenotypes) selected against ;
5. ref. narrow range of genetic variation / allele frequency maintained ;
6. sketch graph ;
7. ref. mutation ; [max 3]

somehow,when answering this question as an essay-type question,try to use examples like the one mentioned in the question,or examples like agouti rabbits or siamese cats. i hope i have helped.

 

[mohmed ahmed soliman]

i found a question and answer very similar to yours but without examples:
(b) Coelacanth haemoglobin has a very high affinity for oxygen, suggesting that coelacanths,
which have been captured at depths of between 200 m and 400 m, live in water that has
a low concentration of oxygen.
Explain how an environmental factor, such as the low concentration of oxygen in deep
water, can act:
(i) as a stabilising force in natural selection
MS:
1. idea of, unchanging / constant, environment ;
2. oxygen concentration acts as a selective agent ;
3. organisms best adapted to these conditions survive ; ora
4. extreme (phenotypes) selected against ;
5. ref. narrow range of genetic variation / allele frequency maintained ;
6. sketch graph ;
7. ref. mutation ; [max 3]

somehow,when answering this question as an essay-type question,try to use examples like the one mentioned in the question,or examples like agouti rabbits or siamese cats. i hope i have helped.

7. ref. mutation ;?? and the sketch like this also what should i write for this . ref. narrow range of genetic variation

 

[kareem22010]

7. ref. mutation ;?? and the sketch like thisView attachment 59969

Well,mutation can result in production of advantageous allele.
The sketch should look something close to that but you should replace the heading ' affinity of hb' with 'saturation of hb with oxygen '. Affinity means how easily oxygen can bind to haemoglobin but saturation refers to the amount of oxygen carried by hb.

 

[mohmed ahmed soliman]

Well,mutation can result in production of advantageous allele.
The sketch should look something close to that but you should replace the heading ' affinity of hb' with 'saturation of hb with oxygen '. Affinity means how easily oxygen can bind to haemoglobin but saturation refers to the amount of oxygen carried by hb.

lso what should i write for this . ref. narrow range of genetic variation and thanks

 

[kareem22010]

lso what should i write for this . ref. narrow range of genetic variation and thanks

You could write narrow range of alleles are selected and maintained by environmental selection pressure. You welcome

 

[Shah34]

QUESTION 17 HOW IS ANSWER D????

 

[Shah34]

Also this question. Much appreciated guys.

 

[Shah34]

Q29
ANS
A

 

[My Name]

View attachment 59979View attachment 59979 QUESTION 17 HOW IS ANSWER D????

Because it has the word ALWAYS 1 cannot be ever true.
UV radiation has increased no doubt but that doesnt mean everyone has skin cancer.

 

[mohmed ahmed soliman]

interbreeding means that offspring produced from two different species
inbreeding means two closely related organism produce an offspring
breed to produce an offspring (not just by mating) assisted reproduction can be used for breeding
ok am i right?

 

[Eugene99]

http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_s08_qp_32.pdf
Anyone solved this?

 

[mohmed ahmed soliman]

can anyone give me a video or notes(other than textbook) for random and systematic sampling

 

[mohmed ahmed soliman]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s08_qp_32.pdf
Anyone solved this?

are u taking both as and a2 in one session