A level Biology: Post your doubts here!

[6Astarstudent]

Help in question
http://olevel.sourceforge.net/papers/9700/9700_s13_qp_11.pdf

Q27, 32, 33, 34, 39.

Answer is
27B
32D
33A
34A
39A (I dont understand why is nitrogen fixation is aerobic, I thought it has nitrogenase, why need anaerobic condition?)

#27
uhm you kind of have to read this yourself, specify your question abit more and I might be able to help you.
#32
haemoglobin only binds with O2, CO, H+, does not bind with HCO3-, so #4 is immediately wrong.
the affinity is CO>H+>O2. so CO and H+ will displace O2 from oxyhaemoglobin.
#33
COPD is irreversible so answer is A.
There is no way you can replace the elastic bands on alveoli, no way you can clean your lung, no way you can replace the tissue in your trachea.
#34
coronary bypass is when a coronary artery is blocked, so you place a vein between the blocked area of the coronary artery to allow alternate pathway for the blood.
It is not to divert the blood, because the blood does not path through the blocked coronary artery at all anymore.
#39
nitrogen fixation is N2 into NH4+ or NH3, no oxygen is required, hence anaerobic

 

[Jinosupreme]

#27
uhm you kind of have to read this yourself, specify your question abit more and I might be able to help you.
#32
haemoglobin only binds with O2, CO, H+, does not bind with HCO3-, so #4 is immediately wrong.
the affinity is CO>H+>O2. so CO and H+ will displace O2 from oxyhaemoglobin.
#33
COPD is irreversible so answer is A.
There is no way you can replace the elastic bands on alveoli, no way you can clean your lung, no way you can replace the tissue in your trachea.
#34
coronary bypass is when a coronary artery is blocked, so you place a vein between the blocked area of the coronary artery to allow alternate pathway for the blood.
It is not to divert the blood, because the blood does not path through the blocked coronary artery at all anymore.
#39
nitrogen fixation is N2 into NH4+ or NH3, no oxygen is required, hence anaerobic

Thanks a lot. But for q39 right, maybe u see wrong, the answer say is aerobic instead of anaerobic?

 

[6Astarstudent]

Thanks a lot. But for q39 right, maybe u see wrong, the answer say is aerobic instead of anaerobic?

that is very weird, I just double checked with CIE endorsed textbook 2013 third edition as well as the encyclopedia
nitrogen fixation in soil requires
supply of hydrogen, supply of ATP, anaerobic conditions

ONLY nitrogen fixation in the atmosphere which is caused by lightning which directly converts N2 to NO2/NO skipping NH3 requires aerobic condition.

the question stated conditions under soil so I'm quite shocked as well..

 

[Jinosupreme]

that is very weird, I just double checked with CIE endorsed textbook 2013 third edition as well as the encyclopedia
nitrogen fixation in soil requires
supply of hydrogen, supply of ATP, anaerobic conditions

ONLY nitrogen fixation in the atmosphere which is caused by lightning which directly converts N2 to NO2/NO skipping NH3 requires aerobic condition.

the question stated conditions under soil so I'm quite shocked as well..

Alright then, still thanks a lot

 

[Jinosupreme]

question 38, http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_w09_qp_11.pdf

Same as question 40
http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_w12_qp_13.pdf

But answer different, one is niche, another is ecosystem. :/ why?

 

[6Astarstudent]

question 38, http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w09_qp_11.pdf

Same as question 40
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w12_qp_13.pdf

But answer different, one is niche, another is ecosystem. :/ why?

its a niche, because all of these applies to the roles of the tree.
yeah this is ******* stupid, but from my definition its a niche.
I'll give you a direct quote from the 2013 CIE endorsed textbook. I'll colour label the same facts

textbook: The niche of an organism is its role in the ecosystem. The niche of an oak tree is as a producer of carbohydrates and other organic substances which provide food for otehr organisms in the ecosystem. It takes carbon dioxide form the air and returns oxygen to it. Its roots penetrate deeply into the soil, where they take up water and minerals. Water vapour diffuses from its leaves into the air. These leaves provide habitats for myriads of insects and other animals.

and here is the question:
A tree carries out photosynthesis and provides organic compounds for other organisms in a
forest.
It takes carbon dioxide from and returns oxygen to the atmosphere.
It takes water from the soil into its roots and its leaves lose water to the atmosphere.
Many other organisms live in the tree.

 

[Jinosupreme]

http://olevel.sourceforge.net/papers/9700/9700_s13_qp_13.pdf

Need help in Q12, 13, 15, 21, 39
12B
13B
15C
21D
39D

 

[6Astarstudent]

#12

http://olevel.sourceforge.net/papers/9700/9700_s13_qp_13.pdf

Need help in Q12, 13, 15, 21, 39
12B
13B
15C
21D
39D

#12
change in pH changes H+ ion concentration
H+ ion concentration only affects ionic and hydrogen bonds.
alpha helix secondary structure is held by hydrgoen bonds
so all correct except fact 1

#13
3 is wrong because warm water does not dissolve more oxygen
this is A2 chem so you kinda have to remember this, the enthalpy of solution is negative ie. exothermic

2 is correct because it gives a chance for algae that float on the pond, or animals that live closer to the top more minerals for growth.

1 is correct because it allows circulation of pond water, ie. more constant temperature, circulation of minerals, transport of waterborne seeds

#15
you only read to nearest seconds
hundreds is too small, big uncertainty. ie. You take couple hundreds of a second to click start and stop of stop watch, eye hand lag, neuron transmissionalg

#21
p53 suppress tumours, and RAD51 repairs any mutated gene
BRCA mutation cause tumor
so you need all 3 to mutate, so cancer cell produced, not repaired by RAD51 and P53 does not repair cell.

#39
1 correct because there are more non woody producers in X, more woody producers in Y
2 correct because X smaller temperature fluctuation, Y great fluctuation. water generally smaller fluctuation due to greater heat capacity
3 correct because X more trophic levels, so probably less energy loss to be able to maintain more trophic levels
4. correct because more trophic level, more energy needed to maintain, so more producers, more green plants leads to higher rate of photosynthesis

 

[7865]

Did anyone find topic wise paper 1s for biology?

 

[Jinosupreme]

In many freshwater ecosystems, the availability of inorganic nitrogen compounds is a limiting factor for growth. This means that producers cannot grow as quickly as they could even though no other factor is limiting.
Which statements about these ecosystems are correct?
1 Transfer of energy to higher trophic levels is also limited by availability of these nitrogen compounds.
2 Addition of excess nitrate compounds will benefit all organisms in the ecosystem.
3 The percentage of energy lost between trophic levels will be the same whether nitrogen compounds are limiting or not.
4 Addition of ammonium compounds will cause an increase in the numbers of nitrifying bacteria.
A 1,3and4only
B 1and3only
C 2,3and4only
D 2and4only

Answer is A why?

 

[6Astarstudent]

In many freshwater ecosystems, the availability of inorganic nitrogen compounds is a limiting factor for growth. This means that producers cannot grow as quickly as they could even though no other factor is limiting.
Which statements about these ecosystems are correct?
1 Transfer of energy to higher trophic levels is also limited by availability of these nitrogen compounds.
2 Addition of excess nitrate compounds will benefit all organisms in the ecosystem.
3 The percentage of energy lost between trophic levels will be the same whether nitrogen compounds are limiting or not.
4 Addition of ammonium compounds will cause an increase in the numbers of nitrifying bacteria.
A 1,3and4only
B 1and3only
C 2,3and4only
D 2and4only

Answer is A why?

1. is correct because limited nitrogen compound = limited number of producers = limited number of energy available to consumers
2. is wrong, it's never good to change an ecosystem with external factors. If you add excess nitrate compounds, this will cause eutrophication causing algae bloom (overgrowth of the producers) depleting oxygen for other animals such as fish.
3. its % energy loss, this is a ratio so won't be affected.
4. more ammonium compound means more nitrifying bacteria, you can think of NH4+ as food to them, more NH4+ for them to convert to NO3-, number increases.

 

[Sarah kh]

Please help in question 4 http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_w08_qp_1.pdf
Answer is B
And I have a question
Is the solute potential of the cells of the phloem sieve tube low or high?

 

[6Astarstudent]

Please help in question 4 http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_w08_qp_1.pdf
Answer is B
And I have a question
Is the solute potential of the cells of the phloem sieve tube low or high?

you measure the closest distance from the inner alveolar wall to the membrane of the red blood cell, which is roughly 6-8mm depending on where you measure
magnification is x2500 so 6mm or 8mm divide by 2500 = 2.4 or 3.2 micrometers
so answer is B

and solute potential of cells in phloem sieve tube is generally low

 

[Jinosupreme]

A graft of tissue, such as skin, from a different person is usually rejected by the body.
Which statement about graft rejection is correct?
A The graft is rejected by B-lymphocytes because they make and release antibodies which react with the surface antigens on the graft cells.
B The graft is rejected by B-lymphocytes because T-lymphocytes are not stimulated to produce antibodies.
C The graft is rejected by T-lymphocytes because the graft tissue causes T-lymphocytes to release antibodies.
D The graft is rejected by T-lymphocytes because they circulate in the blood and can gather at the graft site.

Answer is D why?

 

[6Astarstudent]

A graft of tissue, such as skin, from a different person is usually rejected by the body.
Which statement about graft rejection is correct?
A The graft is rejected by B-lymphocytes because they make and release antibodies which react with the surface antigens on the graft cells.
B The graft is rejected by B-lymphocytes because T-lymphocytes are not stimulated to produce antibodies.
C The graft is rejected by T-lymphocytes because the graft tissue causes T-lymphocytes to release antibodies.
D The graft is rejected by T-lymphocytes because they circulate in the blood and can gather at the graft site.

Answer is D why?

T-lymphocytes is the only one that reacts to organ transplants, and they flow freely around the body. so D correct
C is wrong because T cells do not release antibodies, even T helper cells only aid B cells on antibody production
B is wrong because T cells do not release antibodies.
A is wrong because B lymphocytes never leave the lymph nodes, only the antibody they secreted can move. This is only activated by T cells, it is the T cells that rejct them.

Just remember its mainly killer T that react to these things

 

[hassankhan]

Can anyone tell me in photosynthesis when the light intensity is low why should the temperature be kept low too??

 

[hassankhan]

What are 3 factors affecting glomerular filtration rate??

 

[Mohamed Nossier]

i want 1990-2000 Exams please , AS Biology

 

[Mohamed Nossier]

I Want As Biology Exams 1990-2000

 

[$$AK$$]

hey,
how are u all?
can u please tell me how to prepare for an exam in biology paper 1 AS?? like which topics are most important ( i know that i should study everything )??
thnx