• We need your support!

    We are currently struggling to cover the operational costs of Xtremepapers, as a result we might have to shut this website down. Please donate if we have helped you and help make a difference in other students' lives!
    Click here to Donate Now (View Announcement)

A level Biology: Post your doubts here!

falcon678

falcon678

Messages
2,113
Reaction score
982
Points
123
Alice123 said:
on being attacked by antigens, the plasma cells secrete
  • antibodies that combine with the antigens to destroy them....they are short-lived....
  • and memory cells that remain in blood.... when the same antigen invades the body again, the memory cells divide into plasma cells and destroy the antibody...(its like the MEMORY CELLS remember the shape of the antigen, so when it attacks again, they recognise and destroy them)...
Hope i cud help
Click to expand...


oh yeah...thanks... :)
 
D

dornam

Messages
80
Reaction score
32
Points
18
Can anyone explain me these questions?

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

Question 24. The answer is C. Can anyone explain? I chose B, because I thought that the amount of glucose absorbed also depends on the cell surface area, because the higher the surface area, the more the transport proteins, so more glucose is absorbed.

Question 26. It may well be C, so what's the trick?
 
Student12

Student12

Messages
375
Reaction score
205
Points
53
http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_s09_qp_5.pdfhttp://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_s09_ms_5.pdf
Question 3 (iv) How do we find the degree of freedom for this question?


http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_w09_qp_52.pdfhttp://papers.xtremepapers.com/CIE/Cambridge%20International%20A%20and%20AS%20Level/Biology%20(9700)/9700_w09_ms_52.pdf
Question 2 (b)

http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_w08_qp_5.pdfhttp://papers.xtremepapers.com/CIE/Cambridge%20International%20A%20and%20AS%20Level/Biology%20(9700)/9700_w08_ms_5.pdf
Question 2 (ii) & (iii) How do we find 'n' for (ii) & the degree of freedom ?
 
Mishaa

Mishaa

Messages
15
Reaction score
6
Points
3
dornam said:
Can anyone explain me these questions?

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

Question 24. The answer is C. Can anyone explain? I chose B, because I thought that the amount of glucose absorbed also depends on the cell surface area, because the higher the surface area, the more the transport proteins, so more glucose is absorbed.

Question 26. It may well be C, so what's the trick?
Click to expand...


24. More glucose is absorbed, that is true corresponding to the surface area. But the hormones detected are in no way related to the volume of the cell, they too are dependant on the area. So B is incorrect. In C, both the colums are correct, greater are = more hormones detected on the surface, and more CO2 is produced by a larger cell.

26. The water potential of the xylem can never be zero due to dissolved mineral salts and other impurities. The only other option where xylem has a greater water potential is D, so that's the answer.

Hope I helped! :)
 
I

Irfan1995

Messages
274
Reaction score
277
Points
53
dornam said:
Can anyone explain me these questions?

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

Question 24. The answer is C. Can anyone explain? I chose B, because I thought that the amount of glucose absorbed also depends on the cell surface area, because the higher the surface area, the more the transport proteins, so more glucose is absorbed.

Question 26. It may well be C, so what's the trick?
Click to expand...

Question 24:
You're completely right about the glucose transport proteins being found on the cell membrane, but remember that hormone receptors are found there too.
So the number of hormone receptors is limited to the cell's surface area rather than its volume. This makes the second column wrong, hence the entire option is wrong.
(The last two sentences also explain the first column in option C)
A cell's activity depends on a number of things. But generally, the larger a cell is, the greater its energy demands are (for cell division, protein synthesis etc...). Energy demands obviously require ATP which is produced through respiration (which releases more carbon dioxide).
So the greater the cell's volume is, the greater the energy demands, hence the greater the carbon dioxide production is.

Question 26:
I'm not exactly sure what the problem is, so I'll explain all the options.
They tell you that the water outside is salty, so the water potential is definitely less than 0, so option A is wrong.
Also, they tell you that the land is unsuitable for growth. This implies that water flows from the xylem vessels outside (rather than the other way round). This means that the water potential of the xylem vessels should be greater than that of the soil. So option B is wrong.
We all know that xylem vessels transport water and salts. Since the water is not 100% pure, the water potential must be less than 0. So option C is wrong.
Option D pretty much gives the correct information (based on what I've said above).

I hope that made sense :)
 
I

Irfan1995

Messages
274
Reaction score
277
Points
53
Noor Ahmad said:
Can someone tell me what are the advantages of immobilized algae?
Click to expand...

Lets say you want to make lactose-free milk. Milk naturally contains lactase, so if you want lactose-free milk, you have to add an enzyme (lactase) to break lactose down to its constituent products (glucose and galactose).
But if you take a glass of milk and add some enzyme solution, you'll definitely get lactose-free milk, but the enzyme is still in the milk. This creates lots of problems:
a) the milk will taste terrible (believe me, enzymes taste like crap)
b) the (very expensive) enzyme is wasted since its consumed.

To fix these issues, we can immobilize them. This means putting them in beads where they can react without getting used up or contaminating the milk.
Advantages:
1) The enzyme can be reused (saves a lot of money)
2) The product isn't contaminated (since they remain in the beads rather than dissolving out to the solution)
3) Immobilized enzymes are more resistant to temperature and pH changes (since they have a fixed structure, it's kinda tough to denature them)

That's all I can think of for now.

Hope that helps :)
 
I

Irfan1995

Messages
274
Reaction score
277
Points
53
Student12 said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s09_qp_5.pdfhttp://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s09_ms_5.pdf
Question 3 (iv) How do we find the degree of freedom for this question?


http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w09_qp_52.pdfhttp://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_w09_ms_52.pdf
Question 2 (b)

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w08_qp_5.pdfhttp://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_w08_ms_5.pdf
Question 2 (ii) & (iii) How do we find 'n' for (ii) & the degree of freedom ?
Click to expand...

1) When you're carrying out a t-test, you will have two different sets of readings.
The degrees of freedom is: (number of readings in the 1st set - 1) + (number of readings in the 2nd set - 1)
OR: (total number of readings - 2)
In the question above, they say that "The cultures were sampled at hourly intervals for 20 hours at each pH". This means that a reading was taken every hour, for 20 hours.
1st method:
number of readings in the 1st set = 20
number of readings in the 2nd set = 20
degrees of freedom = (20 - 1) + (20 - 1) = 38
2nd method:
total number of readings = 20 + 20 = 40
degrees of freedom = 40 - 2 = 38
Both methods are essentially the exact same thing. Use whichever one you prefer.

2) They tell you that air is being sucked out at 10 dm^3 per minute. That's equivalent to (10 x 60 = 600 dm^3) per hour. The question tells us that he has been doing this for 6 hours. So a total of 6 x 600 = 3,600 dm^3 of air was sucked in total. 3,600 dm^3 = 3.6 m^3

Also, they tell you that in 0.25 mm^2, there were 6 pollen. So in 1 mm^2, there are 6/0.25 = 24 pollen grains
The microscope slide has an area of 10mm x 42mm = 420 mm^2
If 1 mm^2 has 24 pollen grains, then 420 mm^2 has (24 x 420 = 10,080 pollen grains

10,080 pollen grains were found in 3.6 m^3, so 1 m^3 has 10,080/3.6 = 2,800 pollen grains

3) Question (ii) They tell you that there are 5 leaves and 4 strips. So that's a total of 20 readings. (so n = 20)
Question (iii) They tell you that they want the degrees of freedom for ONE epidermis (rather than both). So instead of taking the total number of readings (and subtract two), you only take the number of readings for one epidermis and subtract one.
So degrees of freedom = 20 - 1 = 19

Hope that helped :)
 
I

Irfan1995

Messages
274
Reaction score
277
Points
53
Noor Ahmad

Noor Ahmad

Messages
83
Reaction score
32
Points
28
Irfan1995 said:
I'm actually a bit confused here. A normal histogram is supposed to have an interval rather than specific values.
So I'm guessing here that they are asking for a bar graph (but the bars touch each other) with the number of beans plotted on the x-axis and the frequency on the y-axis.
Click to expand...


Yess,i was wondering as well!
but again how are we supposed to number the xaxis?
What will be the scale?
 
Noor Ahmad

Noor Ahmad

Messages
83
Reaction score
32
Points
28
Irfan1995 said:
Lets say you want to make lactose-free milk. Milk naturally contains lactase, so if you want lactose-free milk, you have to add an enzyme (lactase) to break lactose down to its constituent products (glucose and galactose).
But if you take a glass of milk and add some enzyme solution, you'll definitely get lactose-free milk, but the enzyme is still in the milk. This creates lots of problems:
a) the milk will taste terrible (believe me, enzymes taste like crap)
b) the (very expensive) enzyme is wasted since its consumed.

To fix these issues, we can immobilize them. This means putting them in beads where they can react without getting used up or contaminating the milk.
Advantages:
1) The enzyme can be reused (saves a lot of money)
2) The product isn't contaminated (since they remain in the beads rather than dissolving out to the solution)
3) Immobilized enzymes are more resistant to temperature and pH changes (since they have a fixed structure, it's kinda tough to denature them)

That's all I can think of for now.

Hope that helps :)
Click to expand...


Thanks a ton.But...
Immobilized ALGAE it is.Are they the same thing? D:
 
Alice123

Alice123

Messages
561
Reaction score
733
Points
103
Soldier313 said:
Aoa wr wb
For qn 2a of this paper, can we state radioactive phosphorus? or ?
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s11_qp_51.pdf
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s11_ms_51.pdf
Click to expand...

hope this helps:
  • the chromosomes need to be stained to view them under a microscope
  • fUsually, a suitable dye, such as Giemsa, is applied after cells have been arrested during cell division by a solution of colchicine. For humans, white blood cells are used most frequently because they are easily induced to divide and grow in tissue culture. Sometimes observations may be made on non-dividing (interphase)
 
Soldier313

Soldier313

Messages
958
Reaction score
3,499
Points
253
Alice123 said:
hope this helps:
  • the chromosomes need to be stained to view them under a microscope
  • fUsually, a suitable dye, such as Giemsa, is applied after cells have been arrested during cell division by a solution of colchicine. For humans, white blood cells are used most frequently because they are easily induced to divide and grow in tissue culture. Sometimes observations may be made on non-dividing (interphase)
Click to expand...
Yes it did help :) JazakAllah khair :)
 
You must log in or register to reply here.
Top