A level Biology: Post your doubts here!

[Irfan1995]

What is the effect of changing the PH above/below the optimum PH?
what effect does it have on Rgroups in the active site?

I'll try to explain this without complicating things too much. But you have to know that the actual explanation goes much deeper.

A change in pH implies a change in the concentration of H+ ions. If the pH is too low (too acidic), there are too many H+ ions that form hydrogen bonds with the protein which affects the way it interacts with other chains.
If the pH is too low (too basic), there are too few H+ ions. This reduces the stability of the polypeptide, so some bonds will inevitably break.
Both cases will change the shape of the protein (hence denature it).

 

[Kinki Tiffany 12]

http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_w06_qp_1.pdf

can anyone explain to me abobut qns 18 and 27?
for qns 27, i thought capillaries have narrow lumen?

 

[Irfan1995]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w06_qp_1.pdf

can anyone explain to me abobut qns 18 and 27?
for qns 27, i thought capillaries have narrow lumen?

18) They tell you that the cell is at the late stages of prophase. When it enters the NEXT prophase, you'll have two cells with the same number of chromosomes.
27) Option 2 is wrong because arteries have narrow lumens and veins have wide lumens.

 

[Noor Ahmad]

question 32, isn't it the no.of men decreasing by 60% same as the percentage of smokers decreased by 60%?

http://papers.xtremepapers.com/CIE/Cambridge%20International%20A%20and%20AS%20Level/Biology%20(9700)/9700_w06_qp_1.pdf

 

[Noor Ahmad]

I'll try to explain this without complicating things too much. But you have to know that the actual explanation goes much deeper.

A change in pH implies a change in the concentration of H+ ions. If the pH is too low (too acidic), there are too many H+ ions that form hydrogen bonds with the protein which affects the way it interacts with other chains.
If the pH is too low (too basic), there are too few H+ ions. This reduces the stability of the polypeptide, so some bonds will inevitably break.
Both cases will change the shape of the protein (hence denature it).

Thank you so much!

 

[Kinki Tiffany 12]

http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_s07_qp_1.pdf
qns 15

http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_s08_qp_1.pdf
qns 28

 

[dornam]

Now I have a really interesting question here.

Check Q38 from here: http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w09_qp_11.pdf

Answer is C - the niche.

Check Q40 from here http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w12_qp_13.pdf

Answer is C - the ecosystem.

Now which is correct?

Anyone?

 

[geek101]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s07_qp_1.pdf
qns 15

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s08_qp_1.pdf
qns 28

for Q15 - you know that aerobic respiration (respiration in the presence of oxygen) must occur, inorder to produce ATP for active transport. when oxygen gas is bubbled, ATP is produced, so either of the 2 in the first picture could be taken up by active transport. In the second graph though, when there is no oxygen, and hence no ATP, the rate of uptake of the 6-carbon sugar is zero! Which shows that 6-carbon sugar molecules require ATP to be taken up (active transport)...also, the rate of the 3-carbon sugar is unaffected in the absence of oxygen, and requires no ATP, which shows that it is uptaken by diffusion...

Q28 - the timeline shows two complete cycles (because one cycle = AS + VS + diastole), now use direct proportion:
2 cycles > 1.5 seconds
x cycles > 60 seconds
x = ( 60 x 2 ) / 1.5 = 80 cycles in 1 minute

 

[Noor Ahmad]

Question 39 how is dust even responsible in the increase in nitrifying bacteria?

http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_w07_qp_1.pdf

 

[Irfan1995]

question 32, isn't it the no.of men decreasing by 60% same as the percentage of smokers decreased by 60%?

http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_w06_qp_1.pdf

If you look at the graph closely, you can see that approximately 80% of men used to smoke in 1980, but that fell to around 35%. This is a 45% decrease (not 60%)

 

[Irfan1995]

Question 39 how is dust even responsible in the increase in nitrifying bacteria?

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w07_qp_1.pdf

Volcanoes release a ton of nutrients into the soil. Although the lava initially kills all plants and animals, after it cools down, the nitrifying bacteria can thrive easily with the abundance of nutrients.

 

[Noor Ahmad]

Volcanoes release a ton of nutrients into the soil. Although the lava initially kills all plants and animals, after it cools down, the nitrifying bacteria can thrive easily with the abundance of nutrients.

So the nitrifying bacteria increase or decrease is not related to light intensity? I assumed that they increased since dust blocks light and hence no photosynthesis can take place.This reduces oxygen abundance and hence provides a suitable medium for growth of nitrifying bacteria. is that correct? do nitrifying bacteria grow better in oxygen deprived soil?

and thank you so much!

 

[strangerss]

Now I have a really interesting question here.

Check Q38 from here: http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w09_qp_11.pdf

Answer is C - the niche.

Check Q40 from here http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w12_qp_13.pdf

Answer is C - the ecosystem.

Now which is correct?

I would go for niche ,because they say it carries out photosynthesis and they're only talking about the tree's role in the environment and they say many organisms live in it , so it shows that it has a role of being a habitat..http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_w02_qp_1.pdf in question 5 , the answer is B , where as in in http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_s05_qp_1.pdf the answer A what do you think?

 

[bawlssohigh]

http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_s11_qp_12.pdf

question 1 anyone ?

 

[Kinki Tiffany 12]

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

qns 25 why the ans is c but not b?
qns 26
qns 31 why exocytotic vesicles?
qns 39 why the ans is a and not c?

 

[Irfan1995]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s11_qp_12.pdf

question 1 anyone ?

0.005 mm x 3.5 units = 0.0175 mm = 17.5 micrometers which is approximately equal to 18 micrometers

 

[Irfan1995]

So the nitrifying bacteria increase or decrease is not related to light intensity? I assumed that they increased since dust blocks light and hence no photosynthesis can take place.This reduces oxygen abundance and hence provides a suitable medium for growth of nitrifying bacteria. is that correct? do nitrifying bacteria grow better in oxygen deprived soil?

and thank you so much!

If there is no light, then I agree that no photosynthesis can take place. The levels of oxygen should remain unchanged, because one small area will have a very little effect on the entire atmosphere. For example, if one person died, we can't really say that the concentration of carbon dioxide in the entire world would decrease, because the effect of one person is almost nothing.
Actually, nitrifying bacteria respire aerobically, so they need oxygen to do their job. So I don't think your explanation would be accurate.

 

[Irfan1995]

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

qns 25 why the ans is c but not b?
qns 26
qns 31 why exocytotic vesicles?
qns 39 why the ans is a and not c?

25) Xylem doesn't have any cytoplasm. It is also found to the inside of vascular bundles (closer to the centre of the stem).
26) Solute potential is always negative, and pressure potential is always positive. The water potential is a sum of the two 'potentials', so it would be found somewhere in between. For example, if you add 5 and -3, you would get +2 (which is somewhere in between 5 and -3)
31) There are goblet cells which secrete mucus through exocytosis.
39) The first bag has large (7mm) pores, so everything available could eat it. The second bag has only 3mm pores, so earthworms and beetles (relatively larger animals) can't fit through to eat the leaf. The last bag has extremely tiny pores (0.03 mm), so only microorganisms could fit through and eat it.
So, the first bag can be eaten by: earthworms, beetles, small invertebrates and microorganisms
The second bag can be eaten by: small invertebrates and microorganisms
The third bag can be eaten by: microorganisms only
Looking at the last column tells us that microorganisms don't even eat the leaves at all.
The second bag is only eaten by small invertebrates. They eat (100 - 61) = 39% of the leaf. I just implied that 100% - amount eaten by small vertebrates = percentage of leaf remaining. The percentage remaining is 61% (given in the table).
The first bag is eaten by earthworms, beetles, and small invertebrates. To find out how much earthworms and beetles eat, use the simple equation:
100% - amount eaten by earthworms and beetles - amount eaten by small invertebrates = percentage of leaf remaining.
The table tells us that the percentage remaining is only 9% and we already calculated the amount eaten by small invertebrates (39%).
So: 100% - amount eaten by earthworms and beetles - 39% = 9%
amount eaten by earthworms and beetles = 52%
Comparing this to the amount eaten by invertebrates (39%), you can clearly see that earthworms and beetles are more important in breaking down leaves.

 

[Irfan1995]

I would go for niche ,because they say it carries out photosynthesis and they're only talking about the tree's role in the environment and they say many organisms live in it , so it shows that it has a role of being a habitat..http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w02_qp_1.pdf in question 5 , the answer is B , where as in in http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s05_qp_1.pdf the answer A what do you think?

Next year, you'll see that the cristae of mitochondria contains the enzyme ATP synthase which obviously makes ATP (that's what we use for energy). A high surface area means more ATP synthase molecules can be placed within the membrane.
So in Oct/Nov '02, "enzyme reactions" would be the correct answer for Q5.
In May/June '05, the answer for Q6 is still "enzyme reactions".

I don't really get your point here...

 

[strangerss]

Next year, you'll see that the cristae of mitochondria contains the enzyme ATP synthase which obviously makes ATP (that's what we use for energy). A high surface area means more ATP synthase molecules can be placed within the membrane.
So in Oct/Nov '02, "enzyme reactions" would be the correct answer for Q5.
In May/June '05, the answer for Q6 is still "enzyme reactions".

I don't really get your point here...

yeah I figured out it should be enzyme reaction because there's no radiation of energy in a mitochondrion just production of packets of energy you don't get what point?