• 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!

F

fizzah96

Messages
13
Reaction score
14
Points
13
Irfan1995 said:
A primary structure of a protein is held by peptide bonds only. So there are no hydrostatic forces of attraction at all. This makes option A wrong.
There are no ionic bonds in a secondary structure, only hydrogen bonds (responsible for the alpha-helix and beta-plated sheet). This makes option B wrong.
Everything is correct with option C.
There are definitely hydrogen bonds holding a quaternary structure together. There are also no peptide bonds linking two different polypeptide chains.

One more point I'd like to clarify, When I say that a quaternary structure doesn't have any peptide bonds, I don't mean that there are no peptide bonds at all. All I'm saying is that it's not responsible for forming and maintaining a quaternary structure.
Click to expand...
oh i get it...thankyou very much :)
 
D

dornam

Messages
80
Reaction score
32
Points
18
Irfan1995 said:
The answer is A. How is it D?
Diffusion evens out the concentrations; it tries to attain equilibrium. For example, if solution A is 1M sucrose, and solution B is 3M sucrose, when the particles diffuse, both solutions would be of 2M sucrose.
Active transport does the opposite: it tries to widen the concentration gradient. For example, if solution A is 1M sucrose, and solution B is 3M sucrose, when a pump is placed, solution A would be 0.5M sucrose, and solution B would be 3.5M sucrose after a while.

Active transport makes something concentrated even more concentrated. Inside the cell, there is a high concentration of potassium. Active transport tries to make it even more concentrated, so it transports potassium inside the cell (that is, process number 2).

The same holds true for the other three processes.

EDIT: Your problem may be that you didn't differentiate between the outside and inside parts of the cell. From the diagram, you can clearly see that the inside of the cell is up and the outside of the cell is down. So processes 1 and 2 point towards the inside of the cell and processes 3 and 4 point towards the outside of the cell.
Click to expand...


Really, really stupid of me
 
Aries_95

Aries_95

Messages
134
Reaction score
117
Points
28
Ikram Khaliq said:
is bulk transport an active process?
Click to expand...

Active transport is when molecules that are small, but not lipid soluble go through the carrier proteins in the cell membrane.
Bulk transport is when the membrane surrounds large molecules to big to go through the lipid bilayer, to form a vesicle inside which then travels through the cytoplasm.
 
Ikram Khaliq

Ikram Khaliq

Messages
187
Reaction score
77
Points
38
Aries_95 said:
Active transport is when molecules that are small, but not lipid soluble go through the carrier proteins in the cell membrane.
Bulk transport is when the membrane surrounds large molecules to big to go through the lipid bilayer, to form a vesicle inside which then travels through the cytoplasm.
Click to expand...

I know what they are. I just want to know if its active or passive. does it use energy?
 
Shreeram

Shreeram

Messages
23
Reaction score
6
Points
13
Can anyone please help me with how to measure the microscopy stuff in paper 1 please.
Thanks in advance
 
I

Irfan1995

Messages
274
Reaction score
277
Points
53
selena said:
s03 may/june P1 q20,22,23,30
Thankyou
Click to expand...

20) The answer is C. Normally, we make RNA out of DNA (using the enzyme DNA Polymerase). Viruses have a way of making DNA from RNA (the opposite) using an enzyme called reverse transcriptase. This piece of information is required at the A2 level only, not AS.
22) Remember that the pressure in the pulmonary vessels is much lower than the aorta. This is because a small pressure is required to pump blood through the lungs only (compared to pumping throughout the rest of the body). Also, remember that the pulmonary ARTERY carries deoxygenated blood. So a range of 2 - 6 kPa seems appropriate (option B).
23) The pressure of the ventricle is rising, so it's definitely contracting. That's because when it contracts, the pressure rises so that it pumps out the blood.
When the blood pressure in the ventricle is higher than that of the aorta, the semilunar valve open to let the blood flow from the ventricle to the aorta. This corresponds to option B.
30) The rate of aerobic respiration is limited by the quantity of oxygen that can reach the muscles. All four options definitely have an effect, but the MAIN factor would be option D. Under standard conditions, options A and B are relatively constant (and high), so they have little effect on limiting the rate of aerobic respiration. The volume of blood that flows through the lungs is important, but in the end, it depends on how much oxygen is reaching the muscles. So ultimately, it is rate of blood flow through the muscles that contribute the most.
 
I

Irfan1995

Messages
274
Reaction score
277
Points
53
dornam said:
Why is denitrification increased in soils with little oxygen?
Click to expand...

I'm not sure if you're supposed to know this, but denitrifying bacteria are obligate anaerobes. This means that they die when oxygen is present, so if such bacteria were to populate a region, that region must have a very low oxygen content.
 
Noor Ahmad

Noor Ahmad

Messages
83
Reaction score
32
Points
28
What is the effect of changing the PH above/below the optimum PH?
what effect does it have on Rgroups in the active site?
 
You must log in or register to reply here.
Top