• 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)

AS Biology P1 MCQs Preparation Thread

Messages
960
Reaction score
3,500
Points
253
Can someone PLEASE answer me? Why are the 4 levels of protein structure involved in maintaing the specificity of an enzyme when an enzyme is limited to a tertiary structure?? Much appreciated.
an enzyme is a protein therefore it has all the levels of protein structure (although nt all enzymes have a quarternary structure)
therefore obviously 2 proteins (enzymes) which have diff primary structure will have diff specificity
2 proteins (enzymes) which have diff secondary structure (ie one may be alpha helix while the other beta pleated) will have diff specificity

and so on with tertiary n quaternary

in short u cant expect 2 enzymes with same tertiary structure while diff primary structure to have the same specificity

hope u understood:)
 
Messages
211
Reaction score
175
Points
53
Can someone please EXPLAIN The following questions (I have the marking schemes so I am not asking for answers but explanations):

May/June 2010, question 23
October/November 2010, Questions 39 and 40

I want someone to explain how you reach the answers.

Thanks! :)
which variant?
 
Messages
301
Reaction score
114
Points
53
Can someone please EXPLAIN The following questions (I have the marking schemes so I am not asking for answers but explanations):

May/June 2010, question 23
October/November 2010, Questions 39 and 40

I want someone to explain how you reach the answers.

Thanks! :)

I'm assuming you need the answers to the first of the three available variants.

For May/June 2010 question 23-
Changing even one nucleotide base can alter the entire structure of the polypeptide molecule. Hence answer is A.

For October/November 2010 question 39-
The question asks for percentage energy transfer between the tropic levels. You have to know about efficiency. We know that energy transfer from the sum to producers is the least efficient, hence answer has to be A or B. Again the transfer of energy between the secondary and primary consumers is the most efficient, so it has to be 80. The efficiency of energy transfer between the producers and the primary consumers is also very less, and is the least between the decomposers (after the energy transfer from the sun to producers, of course.) Hence answer is A.

40- Planting leguminous crops increase the nitrifying bacteria in the soil which would in turn increase the nitrogen fixing bacteria. The decomposers will also increase as the crops eventually die.
 
Messages
960
Reaction score
3,500
Points
253
people the ans fr this is B....i understand the second column, however for the first isn't it water potential increases? I mean isn't that how the hydrostatic pressure is built up..... bcoz of high water potential in sieve tube elements in leaves, which will allow the mass flow to occur?Screen shot 2012-06-12 at 10.35.12 PM.png
 
Messages
301
Reaction score
114
Points
53
people the ans fr this is B....i understand the second column, however for the first isn't it water potential increases? I mean isn't that how the hydrostatic pressure is built up..... bcoz of high water potential in sieve tube elements in leaves, which will allow the mass flow to occur?View attachment 12854

The water potential in the sieve tube elements decreases. The sucrose is loaded in the sieve tube element by active transport in the vascular bundles in the stem. That's where the water potential decreases, and the hydrostatic pressure builds up and it moves by mass flow.
 

Jaf

Messages
321
Reaction score
232
Points
53
I'm assuming you need the answers to the first of the three available variants.

For May/June 2010 question 23-
Changing even one nucleotide base can alter the entire structure of the polypeptide molecule. Hence answer is A.

For October/November 2010 question 39-
The question asks for percentage energy transfer between the tropic levels. You have to know about efficiency. We know that energy transfer from the sum to producers is the least efficient, hence answer has to be A or B. Again the transfer of energy between the secondary and primary consumers is the most efficient, so it has to be 80. The efficiency of energy transfer between the producers and the primary consumers is also very less, and is the least between the decomposers (after the energy transfer from the sun to producers, of course.) Hence answer is A.

40- Planting leguminous crops increase the nitrifying bacteria in the soil which would in turn increase the nitrogen fixing bacteria. The decomposers will also increase as the crops eventually die.

Thanks a lot :) As for 39, shouldn't the efficient for the decomposition of the producers and consumers be the highest because, after all, unlike feeding by animals, the decomposes take all the mass of the organism while animals may leave out parts such as fur, bark, roots or hooves?

On 40, I understood what you said but my confusion was on if there are more leguminous plants, there is is more nitrogen which is fixed, which should provide more sources of energy for the denitrifying bacteria as they get heir energy from that process. Since they have more "food", they should increase in number. That's what is confusing me.... Why don't the numbers of the denitrifying bacteria increase?
 
Messages
211
Reaction score
175
Points
53
Oops. Sorry*

I hate typing on phones!
The minimum number of nucleotides required to change to cause sickle cell anaemia IS one. That's more like a fact. Have you studied from Mary Jones? If yes, then you might remember that it's written in that book that to cause even the slightest of mutation, only a single nucleotide needs replacement. And right after that, the example of sickle cell anaemia is also given in the book.
 
Messages
960
Reaction score
3,500
Points
253
The water potential in the sieve tube elements decreases. The sucrose is loaded in the sieve tube element by active transport in the vascular bundles in the stem. That's where the water potential decreases, and the hydrostatic pressure builds up and it moves by mass flow.
isn't it loaded into the companion cell via active transport and then from the companion cell to sieve tube by via plasmodesmata by diffusion?
Or am i mixing up things here?:unsure:
 
Messages
135
Reaction score
85
Points
38
Can Someone explain to me how Water Potential, Solute Potential and Pressure Potential are related?? (i mean which equation relates them??) :)
 
Messages
135
Reaction score
85
Points
38
I don't know which graph are you talking about.
The graph in which volume of blood in left ventricle is on y-axis and time is on x-axis. (for one cardiac cycle) I Hope it does not come. ECG and pressure graphs are enough!:p
 

Nibz

XPRS Moderator
Messages
4,615
Reaction score
9,574
Points
523
The graph in which volume of blood in left ventricle is on y-axis and time is on x-axis. (for one cardiac cycle) I Hope it does not come. ECG and pressure graphs are enough!:p
This one:
2.png
*time on x-axis.

It's the easiest of all three.
Have a look at it, too. You never know!
 

Jaf

Messages
321
Reaction score
232
Points
53
Can Someone explain to me how Water Potential, Solute Potential and Pressure Potential are related?? (i mean which equation relates them??) :)

Its basically water potential = solute potential + pressure potential where solute potential is always NEgATIVE and pressure potential is always POSITIVE
 
Messages
301
Reaction score
114
Points
53
isn't it loaded into the companion cell via active transport and then from the companion cell to sieve tube by via plasmodesmata by diffusion?
Or am i mixing up things here?:unsure:

Yes, you are right. It is loaded in the companion cell by active transport. Either ways, the water potential of the LEAF decreases with the increasing production of sucrose. :) I'm sure they were referring to this. :)
 
Top