A level Biology: Post your doubts here!

[Gehad Mohamed]

Hello! Can someone please explain why ans 5 b ii is not about enzyme activity with pH instead of collision with substrate
http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_s11_ms_22.pdf
http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_s11_qp_22.pdf

 

[not.maria]

Hello! Can someone please explain why ans 5 b ii is not about enzyme activity with pH instead of collision with substrate
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s11_ms_22.pdf
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s11_qp_22.pdf

it is about both the mark scheme says
"ref. presence of hydrogen ions, partial denaturation (less steep) / denaturation (plateau);"

this means that the enzymes structure is affected by change in ph so that it does not work fully.
Also as the number of substrate molecules will decrease over time the number of collisions with the enzyme would decrease and the rate of reaction would decrease
i hope that clears it up

 

[Gehad Mohamed]

it is about both the mark scheme says
"ref. presence of hydrogen ions, partial denaturation (less steep) / denaturation (plateau);"

this means that the enzymes structure is affected by change in ph so that it does not work fully.
Also as the number of substrate molecules will decrease over time the number of collisions with the enzyme would decrease and the rate of reaction would decrease
i hope that clears it up

Yes clear thnx alot

 

[Gehad Mohamed]

Hi !! Can someone please explain why in Q 2 F is partially permeable and G is fully permeable , shouldn't it be reverse as the outer on is always the cell wall !!
http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_s12_qp_21.pdf
http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_s12_ms_21.pdf

 

[ZaqZainab]

Hi !! Can someone please explain why in Q 2 F is partially permeable and G is fully permeable , shouldn't it be reverse as the outer on is always the cell wall !!
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s12_qp_21.pdf
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s12_ms_21.pdf

My Bad refer to mohammad saliks post

 

[Alazne Diamond]

well the reason is obvious that Chloroplast and mitochondria have internal membranes but it seemed like you need a reason why do they have internal membranes

i was askin abt nucleus not choroplast nor mitochondria

 

[Alazne Diamond]

View attachment 36770
in the question:-
"State three features of the leaf, visible in Fig. 3.1, which show that it has developed in
a sunny position."
the markscjeme mentions
>smaller air spaces
>thick leaf

I dont understand how smaller air spaces are an adaptive feature.
Nor do I undertsnad how we are supposed to know if the leaf is thick or thin because for me 450micrometres in THIN.

Can anyone please explain?

THANKS!

sunny position means high temperature n hence transpiration rate is more.......if ther would be larger air space then it wil b easy for water to evaporate.....so to reduce loss of water air space iz small.........n m nt sure abt the thickness

 

[ZaqZainab]

i was askin abt nucleus not choroplast nor mitochondria

To me it looks like you where talking about chloroplast and mitochondria

 

[Mohammed salik]

@
ZaqZainab

Hi !! Can someone please explain why in Q 2 F is partially permeable and G is fully permeable , shouldn't it be reverse as the outer on is always the cell wall !!
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s12_qp_21.pdf
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s12_ms_21.pdf

Cell walls Is Not F and It is Never Partially Permeable!
F is cell Membrane Which is Partially Permeable Phos-pholipid Bilayer
G is Cell Wall which is completely Permeable Because of Gaps between Cellulose Fibers, hence allows free Movement Of Water or other substances!
Hope That answers Your Question!

 

[ZaqZainab]

@
ZaqZainab



Cell walls Is Not F and It is Never Partially Permeable!
F is cell Membrane Which is Partially Permeable Phos-pholipid Bilayer
G is Cell Wall which is completely Permeable Because of Gaps between Cellulose Fibers, hence allows free Movement Of Water or other substances!
Hope That answers Your Question!

Cell walls are semi permeable
btw isn't the cell wall always the one on the outside? <--that's what my teacher has taught me

 

[MÁťT PŭמҚ]

what is oxidative phosphorylation? :/

 

[6Astarstudent]

what is oxidative phosphorylation? :/

It is the process when ADP is phosphorylated to ATP at the inner mitochondrial membrane via energy from the ETC

 

[MÁťT PŭמҚ]

It is the process when ADP is phosphorylated to ATP at the inner mitochondrial membrane via energy from the ETC

can u explain in more detail abt electron transport chain?

 

[6Astarstudent]

can u explain in more detail abt electron transport chain?

Reduced NAD/FAD passed to ETC, where they released the hydrogen (which gets split into H+ and e-).
The electrons are passed through a series of e- carriers down energy gradient in the inter-membrane space.
Energy released from this is used to move H+ from matrix to inter-membrane space.
The protons builds up a concentration gradient, so the protons pass back to the matrix through ATP synthase.
The proton motive force (electrical potential energy) synthesizes ATP from ADP + Pi (This is chemiosmosis)
Lastly in the matrix, H+ and e- combine with O2 to form H2O.

 

[Alazne Diamond]

To me it looks like you where talking about chloroplast and mitochondria

if u misunderstand i hav nothing to do...........anywayz y r we wastin tym by tokin abt dis........jst stop it nw -_-

 

[Mohammed salik]

Cell walls are semi permeable
btw isn't the cell wall always the one on the outside? <--that's what my teacher has taught me

You Could rephrase Your Sentence to :- The first membrane or (the membrane closest) to Cell organelles is Cell membrane and Second one is Cell wall. If we talk about this Electron Micro-graph Of two Adjacent cells.
If You look Closely The first Membrane to organelles is F so that is Cell Membrane And second one is G which is cell wall!
Hope that Answers You Question!

 

[joanna omar]

What are the advantages and disadvantages of captive breeding ?

 

[joanna omar]

june 11 p11 q14 can someone please explain it ?

Yeah I wonder its C ,there was some other ame Q in another year but it was B

 

[sara kamal]

PLEASSEEEEE ! Explain, using examples, how the environment may affect the phenotype of an
organism. [8] (I need brief detailed explanation) its a pastpaper Q's

 

[ZaqZainab]

PLEASSEEEEE ! Explain, using examples, how the environment may affect the phenotype of an
organism. [8] (I need brief detailed explanation) its a pastpaper Q's

Refer to this post hope it will help

I guess i can help with the first one..
Variations are of two types-phenotypic and genotypic..
Genotypic variations are influenced by genes only whereas phenotypic variations are influenced by both environment and their genes.
Simple examples include eating habits which are responsible for a person's growth..Lets say the person has a gene for tallness but only if the person acquires the required protein will he able to grow tall..Similarly obesity can also result this way as we choose it for us- by eating fatty foods..( i mean the environment is wat has an effect on the phenotype)
Phenotypic variations can also be due to selection pressures..
Here we can take the peppered moth biston betularia as an example..(given in bio text book)
Initial stages all people cud find was moths with pale wings and dark markings giving a speckled appearance.
In the 19th century once industrialisation started growing rapidly in certain areas the numbers of black moths started appearing..
The selection pressure here was the predation of birds coz in areas of industrialization there was polluted air which often covered the tree branches with soot and black moths seem to be better camouflaged than the speckled ones. These selection pressures gives rise to variations enabling "survival of fittest" where organisms with best adapted variations suited to that environment survive.Overtime this causes a genetic drift and change in allele frequency resulting in the ''birth'' of black peppered moths..(This is like an elaborated example)..
So u can go on with more examples as given in the text...
Hope this helped!!