A level Biology: Post your doubts here!

[Saad (سعد)]

Persistent high blood pressure damages the lining of the arteries, in order to repair the damage cholesterol is deposited at the site of damage but this results in the build up of plague over time. The plague hardens the arteries and also causes narrowing. This process leads to atherosclerosis which eventually leads to coronary heart disease.

I think you mean 'plaque'... with a 'q'... don't write 'plague', its something entirely different.

 

[littlecloud11]

I think you mean 'plaque'... with a 'q'... don't write 'plague', its something entirely different.

Typo. I'm so sorry, missed that entirely.

 

[Soldier313]

i really need help for qn 3b in this paper....the ms doesn't make sense to me...it says water moves out of cell Q into cell Q, can someoneee pleeeeeeasee check it out....thanx a lot!
qn paper: http://www.xtremepapers.com/papers/...nd AS Level/Biology (9700)/9700_w11_qp_23.pdf
ms: http://www.xtremepapers.com/papers/...nd AS Level/Biology (9700)/9700_w11_ms_23.pdf
tx again..

 

[sumaiyarox:)]

(d) discuss the roles of social, economic and biological factors in the prevention and control of cholera,
measles, malaria, TB and HIV/AIDS (a detailed study of the life cycle of the malarial parasite is not
required);
(e) discuss the global patterns of distribution of malaria, TB and HIV/AIDS and assess the importance of
these diseases worldwide;
can nyone giv an ans for dis....found it in the syllubus

 

[Jaf]

Persistent high blood pressure damages the lining of the arteries, in order to repair the damage cholesterol is deposited at the site of damage but this results in the build up of plague over time. The plague hardens the arteries and also causes narrowing. This process leads to atherosclerosis which eventually leads to coronary heart disease.

Spell-check. Plague is the infectious disease spread by rodents. The word is plaque.

 

[littlecloud11]

Spell-check. Plague is the infectious disease spread by rodents. The word is plaque.

Yeah, that was an inexcusable mistake. I don't know how i overlooked that. Sorry.

 

[Soldier313]

i really need help for qn 3b in this paper....the ms doesn't make sense to me...it says water moves out of cell Q into cell Q, can someoneee pleeeeeeasee check it out....thanx a lot!
qn paper: http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w11_qp_23.pdf
ms: http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w11_ms_23.pdf
tx again..

qn solved......sorry for the bother

 

[shan5674]

Can someone please give me a detailed explanation on opsonisation? or links that explain it please it isn't in my text book but i keep coming across that word in past papers

Thankss

 

[Aarjit]

Phosphate heads are responsible for the orientation of the phospholipid bilayer. In questions related to how the structure of a phospholipid allows it to form a bilayer, you have to mention that the phosphate heads are hydrophilic and therefore, water attracting so they face outwards towards the aqueous environment (cytoplasm, or fluid around the cell).

Phosphate heads are only a small part of the bilayer, the fatty acid/hydrocarbon, tails form the major part of the bilayer, which is the hydrophobic interior. This hydrophobic interior acts as a barrier to ions and polar molecules such as water. So basically, polar molecules can reach till the phosphate heads, but cannot pass through the hydrophobic interior of the bilayer!

True, but molecules such as H20 (very polar) and CO2 (though it has nil overall polarity) are small enough and CAN RAPIDLY PASS/diffuse through the bilayer, down the potential/pressure gradient. It's only the LARGE polar molecules such as glucose, amino acids and ions which cannot diffuse through the phospholipid bilayer, hence they opt for facilitated diffusion through hydrophilic protein channels.

Small intricate details/exceptions do indeed make a significant difference in one's comprehension on even the very rudiments of Molecular Biology, don't they?..

 

[geek101]

i really need help for qn 3b in this paper....the ms doesn't make sense to me...it says water moves out of cell Q into cell Q, can someoneee pleeeeeeasee check it out....thanx a lot!
qn paper: http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w11_qp_23.pdf
ms: http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w11_ms_23.pdf
tx again..

The mark scheme says, (water) moves out of, cell / Q. This is true, the water potential inside cell Q is more than the empty space in the spongy mesophyll layer, a potential gradient is created, and water moves down the potential difference, via a cell membrane out of Cell Q and onto the cell wall of Q. From here water evaporates and turns to vapour, now present in the air spaces of the spongy mesophyll layer. The concentration of water vapour is high inside the air spaces and low outside the stomata, so water diffuses out via the stomata, and transpiration takes place.

 

[Soldier313]

The mark scheme says, (water) moves out of, cell / Q. This is true, the water potential inside cell Q is more than the empty space in the spongy mesophyll layer, a potential gradient is created, and water moves down the potential difference, via a cell membrane out of Cell Q and onto the cell wall of Q. From here water evaporates and turns to vapour, now present in the air spaces of the spongy mesophyll layer. The concentration of water vapour is high inside the air spaces and low outside the stomata, so water diffuses out via the stomata, and transpiration takes place.

yup kay tx a lot...

 

[trgirl]

can someone explain this?
explain why the person is unlikely become ill if they are infected by the same pathogen some months later

 

[trgirl]

Phosphate heads are responsible for the orientation of the phospholipid bilayer. In questions related to how the structure of a phospholipid allows it to form a bilayer, you have to mention that the phosphate heads are hydrophilic and therefore, water attracting so they face outwards towards the aqueous environment (cytoplasm, or fluid around the cell).

Phosphate heads are only a small part of the bilayer, the fatty acid/hydrocarbon, tails form the major part of the bilayer, which is the hydrophobic interior. This hydrophobic interior acts as a barrier to ions and polar molecules such as water. So basically, polar molecules can reach till the phosphate heads, but cannot pass through the hydrophobic interior of the bilayer!

which year is this?

 

[eyamwir]

what is the role of the companion cell? anyone?

 

[Jaf]

can someone explain this?
explain why the person is unlikely become ill if they are infected by the same pathogen some months later

Because the person has memory B lymphocytes in his bloodstream. When a pathogen with the same/similar antigen invades the body a secondary immune response will be triggered and the B lymphocytes will undergo mitosis to form plasma cells. These plasma cells will then produce antibodies specific to the antigen which will then destroy the invading cells.

 

[littlecloud11]

what is the role of the companion cell? anyone?

Companion cells are responsible for the active loading of sucrose. They use active transport to pump out H+ into surrounding mesophyll cells. After sufficient ions have been pumped out they move back into the companion cell by diffusion down the concentration gradient, carrying sucrose along with it through the co-transporter. The sucrose then diffuses from the companion cell into the sieve tube cell through the plasmodesmata.

 

[KurayamiKimmi]

for example the making of polypeptides by DNA. where peptide bonds are built up that is a primary structure?

yes

 

[rogue94]

True, but molecules such as H20 (very polar) and CO2 (though it has nil overall polarity) are small enough and CAN RAPIDLY PASS/diffuse through the bilayer, down the potential/pressure gradient. It's only the LARGE polar molecules such as glucose, amino acids and ions which cannot diffuse through the phospholipid bilayer, hence they opt for facilitated diffusion through hydrophilic protein channels.

Small intricate details/exceptions do indeed make a significant difference in one's comprehension on even the very rudiments of Molecular Biology, don't they?..

True! However, most cells have membrane protein channels called aquaporins, which allow quicker (facilitated) diffusion of water, but that i guess it is not in AS level, so in general at AS level they tell us that phospholipid bilayer acts as a barrier to water and CIE also uses this general statement in their mark schemes. Still, one's concepts should always be clear! The non-polar molecules such as CO2 and O2 can pass through the bilayer as well as fat solube vitamins such as vitamin A! small polar molecules can leak through the bilayer, but cholestrol prevents that to some extent and also facilitated diffusion of these small polar molecules is a faster process than passive diffusion! The intricacies are indeed of the utmost importance, but i guess at AS level more general concepts with suffice unless ofcourse one is aiming for a distinction :|

 

[sumaiyarox:)]

can someone explain this?
explain why the person is unlikely become ill if they are infected by the same pathogen some months later

memory cells r formd in the first immune response which retain the ability to divide rapidly and develop into active b or t cells on a secnd exposur to the same antigen/pathogen and threfore the respnse will be quicker and the body will be able to get rid of the pathogen bfre it infects the body.

 

[KurayamiKimmi]

Can someone please give me a detailed explanation on opsonisation? or links that explain it please it isn't in my text book but i keep coming across that word in past papers

Thankss

An opsonin is any molecule that targets an antigen for an immune response. However, the term is usually used in reference to molecules that act as a binding enhancer for the process of phagocytosis, especially antibodies, which coat the negatively-charged molecules on the membrane.
which pastpaper did you see this in ?