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AS Biology P1 MCQs Preparation Thread

Jaf

Jaf

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Ashique said:
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.
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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?
 
oldfashionedgirl

oldfashionedgirl

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Jaf said:
Oops. Sorry*

I hate typing on phones!
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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.
 
Soldier313

Soldier313

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Ashique said:
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.
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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:
 
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rogue94

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Can Someone explain to me how Water Potential, Solute Potential and Pressure Potential are related?? (i mean which equation relates them??) :)
 
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rogue94

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Nibz said:
I don't know which graph are you talking about.
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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
 
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Nibz

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rogue94 said:
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
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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

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rogue94 said:
Can Someone explain to me how Water Potential, Solute Potential and Pressure Potential are related?? (i mean which equation relates them??) :)
Click to expand...

Its basically water potential = solute potential + pressure potential where solute potential is always NEgATIVE and pressure potential is always POSITIVE
 
Jaf

Jaf

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Soldier313 said:
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:
Click to expand...
Yes, that's how they are loaded at the source but the point is that the sources are the photosynthesising leaves, while the sinks are other parts of the plant, like the roots, storage organs. So, when the sugars are loaded into the sieve elements of the leaves, this means that there is more solute in the phloem sap. If you look at my answers above about solute potential is related to water potential, I have said solute potential is always negative, meaning more solute REDUCES/DECREASES water potential. The key here, to avoid confusion, is to understand that solute concentration is inversely proportional to water potential, and increasing it reduces water potential.
 
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sarahnafea

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During excercise tidal volume increases and this will decrease Inspiratory Reserve Volume (i.e. the volume of air which u could inhale but dont) - in this case, volume X. Same goes for volume Y. Thing of Reserve Volumes as a Bank of air. When u excercise u take loans of air from ur reserve and this loan is what increases ur tidal volume. Oh and thanks for ur reply up there :)
 
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