A level Biology: Post your doubts here!

[strangerss]

als alum allaykom
http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_w10_qp_11.pdf in question 39 , WHY THERE'S A PERCENTAGE OF ENERGY TRANSER OF 80? and 20? isn't always 10% between the trophic levels? and 1% between sun and producer?

 

[Irfan1995]

als alum allaykom
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w10_qp_11.pdf in question 39 , WHY THERE'S A PERCENTAGE OF ENERGY TRANSER OF 80? and 20? isn't always 10% between the trophic levels? and 1% between sun and producer?

It's definitely not only 10% between trophic levels.
As you go deeper in the chain, the efficiency increases greatly. This allows maximum absorption of a low quantity of energy at higher levels. If this did not happen, then every food chain would only have two or three trophic levels.

 

[Noor Ahmad]

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.

Oh yes,well thank you so much.
which bacteria respires anaerobically? is it only dentrifying bacteria?

 

[strangerss]

It's definitely not only 10% between trophic levels.
As you go deeper in the chain, the efficiency increases greatly. This allows maximum absorption of a low quantity of energy at higher levels. If this did not happen, then every food chain would only have two or three trophic levels.

But that's what I've studied ,it's in the book it's written in the book that: the overall efficiency of energy transfer from producer to consumer is rarely greater than 10% similar losses occur at each trophic level.so as energy is passes along a food chain , less and less energy si available at each successive trophic level. food chanins rarely have more than four or five trophic levels . they always ask why food chains are short and the answer is always because of the inefficiency of energy transfer

 

[Kinki Tiffany 12]

http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_s10_qp_11.pdf
for qns 8 why can't it be b?
qns 33
qns 38

 

[dornam]

Can you explain me question 25? http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_w05_qp_1.pdf

I chose B, because in the symplast pathway water does move through the partially permeable plasma membranes. D is for apoplast pathway whilst A and C in my opinion are incomplete because none of them shows water moving through partially permeable plasma membranes.

 

[Kinki Tiffany 12]

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.

the table 1 percentage remaining isn't it 6? or 9?

 

[Noor Ahmad]

Question 16 and 40 could anyone explain?

http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_w11_qp_11.pdf

 

[HubbaBubba]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s10_qp_11.pdf
for qns 8 why can't it be b?
qns 33
qns 38

q8 - It cannot be B because it's not describing anything about the structure and it's function. The correct answer is D because they are insoluble to not affect osmotic properties of the cell.

q33 - This one is supposed to confuse the candidates. It's not asking if the tidal volume increases. It's asking what happens to the lines X and Y. In moderate exercise the lines X and Y will obviously decrease because the person is inhaling and exhaling more air. Answer would be A.

q38 - It's mentioned that there should be a 10% efficiency rate. (1300 * 10% * 10%) would equal to 13 which is 1.3 * 10^1. If you want to find energy for the tuna just multiply (13 * 10% * 10% once again) which gives you 0.13 or 1.3 * 10^-1. Answer is A

 

[HubbaBubba]

Can you explain me question 25? http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w05_qp_1.pdf

I chose B, because in the symplast pathway water does move through the partially permeable plasma membranes. D is for apoplast pathway whilst A and C in my opinion are incomplete because none of them shows water moving through partially permeable plasma membranes.

Water does not necessarily have to pass through the plasma membrane itself. It can pass through the pores of the cell membrane as well and still be counted as a symplast pathway. It's not B or C because they are not complete symplast pathways. Any water that passes through the vacuole of a cell is considered the vacuolar pathway. A would be the most appropriate answer as it does not pass through the vacuoles at all.

I hope this helped!

 

[HubbaBubba]

Question 16 and 40 could anyone explain?

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w11_qp_11.pdf

q16 - Statement 4 is completely wrong, osmosis only involves water molecules. Therefore the correct answer would be C.

q40 - It cannot be B, because that is the intensity of light. You can tell, because it increases in summer, but decreases in winter, it's highest peak in the middle of summer, and lowest is in the middle of winter. C are the producers, because it reaches a high peak in between Winter and Summer, which is Spring (Where all plants begin to grow). Primary consumers would definitely start increasing when producers start increasing so D is a possible answer. This is confirmed because if you look at A, it's very high when D is very low, and very low when D is very high. This means that nutrients are high in quantity when there's no consumers around, and low when consumers begin to increase in population. D is the correct answer.

 

[Irfan1995]

the table 1 percentage remaining isn't it 6? or 9?

It's supposed to be 6%. Sorry!

 

[strangerss]

q8 - It cannot be B because it's not describing anything about the structure and it's function. The correct answer is D because they are insoluble to not affect osmotic properties of the cell.

q33 - This one is supposed to confuse the candidates. It's not asking if the tidal volume increases. It's asking what happens to the lines X and Y. In moderate exercise the lines X and Y will obviously decrease because the person is inhaling and exhaling more air. Answer would be A.

q38 - It's mentioned that there should be a 10% efficiency rate. (1300 * 10% * 10%) would equal to 13 which is 1.3 * 10^1. If you want to find energy for the tuna just multiply (13 * 10% * 10% once again) which gives you 0.13 or 1.3 * 10^-1. Answer is A

if the person is inhaling more air wouldn't the lines becoming higher like the curves peak becomes higher?:/ doesn't X and Y represent the tidal volume?

 

[HubbaBubba]

if the person is inhaling more air wouldn't the lines becoming higher like the curves peak becomes higher?:/ doesn't X and Y represent the tidal volume?

Nahh you misunderstood me. See as he inhales more, the line x gets shorter, and as he exhales more, the line y also gets shorter.

 

[SalmaXXXX]

Hey guyss !! Please I need Help !! After solving almost all of the pastpapers, I got shocked when I answered November 2012 V12. Questions 16, 24 and 33 !!! Please Help me my exam is in a couple of days. In question 16, The cholestrol decreases the fluidity of the membrane not increases it, right?? Question 24,I don't understand it at all. Question 33, How come the deposition of fatty materials in ARTERIES and veins does not contribute to heart failure??

http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_w12_qp_12.pdf
Please Please pLease Reply

 

[Noor Ahmad]

Question 21
Isn't it mRNA is transcribed from the anti-sense strand? how is the answer B,isn't it supposed to be D?

and question 34
isn't it bacteria can be transferred directly too? Why not cholera then?


http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_w02_qp_1.pdf

 

[Irfan1995]

Hey guyss !! Please I need Help !! After solving almost all of the pastpapers, I got shocked when I answered November 2012 V12. Questions 16, 24 and 33 !!! Please Help me my exam is in a couple of days. In question 16, The cholestrol decreases the fluidity of the membrane not increases it, right?? Question 24,I don't understand it at all. Question 33, How come the deposition of fatty materials in ARTERIES and veins does not contribute to heart failure??

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w12_qp_12.pdf
Please Please pLease Reply

16) As far as I know, cholesterol keeps a balance of fluidity. At low temperatures, the phospholipids should crystallize (become like a solid). Cholesterol has an irregular shape, so it doesn't fit perfectly in the membrane. This prevents phospholipids from going too close to each other, so the presence of cholesterol prevents membrane crystallization.

24) If you just read option 3, you can immediately point out that it's wrong. When water travels through the plasmodesmata (junction between two cells), that is considered as the symplast pathway (not the apoplast). When you eliminate option 3, choice A is the only option available.
Option 1 is true, as water passes by the root through osmosis (down a concentration gradient). It can travel either through the apoplast pathway or the symplast pathway.
Option 2 is wrong because water passes up the xylem through capillary pull.

33) Option 1: high blood pressure could damage artery walls leading to atheromae (which leads to blood clots)
Option 2: deposits of fatty materials in arteries definitely results in heart failure. But fatty deposits in VEINS do not. The option implies that fatty deposits in both arteries AND veins contribute to heart failure, which is wrong.
Option 3: The cardiac muscle is simply the heart. If it can't receive enough oxygen, it can't receive any energy necessary for contraction.
Option 4: If a blood clot occurs near the coronary artery, it will cut off blood supply to the heart. The heart can't receive any glucose nor oxygen (this results to the same situation as that in option 3)

Good luck

 

[Irfan1995]

Question 21
Isn't it mRNA is transcribed from the anti-sense strand? how is the answer B,isn't it supposed to be D?

and question 34
isn't it bacteria can be transferred directly too? Why not cholera then?


http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w02_qp_1.pdf

21) I'm just as confused as you are. I believe the answer should be D as well.

34) You're right. But that's not what the question's asking.
They asked for the disease which is least likely to be passed from parent to child.
A: you already mentioned it
B: HIV can be passed through the placenta (the connection between the mother and the baby in the womb)
C: Malaria must pass through a vector (the female Anopheles mosquito)
D: Sickle-cell anaemia is a genetic disease, so it can definitely pass from parent to child.

 

[Kinki Tiffany 12]

http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_w10_qp_12.pdf

qns 1
qns 4
qns 16 why the ans not c
qns 27 is statement 4 correct?
qns 35

 

[h4rriet]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w10_qp_12.pdf

qns 1
qns 4
qns 16 why the ans not c
qns 27 is statement 4 correct?
qns 35

1. Option A is unnecessary because the xylem is measured in millimetres, not micrometres. Option 2 is unnecessary too because 4 tells you that the eyepiece graticule is already calibrated.
4. All you have to do is cross multiply. If 1.5x(10^1) micrometers = 1 cell, then 1x(10^-4) micrometres will = x cells. Take care of the units.
16. DNA replication occurs during interphase, which is not part of nuclear division.
27. Water does move out of cell 3, but it doesn't move out so much as to plasmolyse it. The difference is water potential between cell 3 and the surroundings is very slight.
35. For a person to have absorbed the most O2, he must have had the highest breathing rate, the largest tidal volume and the largest total lung volume. Multiply the 3 columns.