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A level Biology: Post your doubts here!

joanna omar

joanna omar

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H

hellangel1

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In Biology paper 5, when describing a procedure of an investigation, do we need to write the volumes of water and stock solution used to make up the concentrations?
 
ZaqZainab

ZaqZainab

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joanna omar said:
ZaqZainab roxylara oahmed64

Anyone please Explain me this and tell me a model answer ! Q6 (d) part


http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w10_qp_22.pdf
Click to expand...

To be honest i really suck at putting answer to words but lemme try
The exchange of O2 and CO2 occurs as a result of diffusion down a concentration gradient , gas molecules moving from an area of high concentration to low concentration.Across the lungs the pO2 in alveolar capillaries is lower than the pO2 in the alveoulus and so the oxygen diffuses from the alveoulus to the blood, the pCO2 in alveolar capillaries is higher than the pCO2 in the alveoulus and so the CO2 in the blood diffuses into the alveoulus from the blood.
Across the respiring tissue the pO2 in the tissue capillary is higher than the pO2 of the tissue and so the oxygen diffuses from the blood in the tissue capillary to the tissue, the pCO2 in the tissue capillary is lower than the pCO2 of the tissue and so the carbon dioxide diffuses from the tissue to the blood in the tissue capillary.

You can also mention figures to be on the safe side.
 
joanna omar

joanna omar

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ZaqZainab said:
To be honest i really suck at putting answer to words but lemme try
The exchange of O2 and CO2 occurs as a result of diffusion down a concentration gradient , gas molecules moving from an area of high concentration to low concentration.Across the lungs the pO2 in alveolar capillaries is lower than the pO2 in the alveoulus and so the oxygen diffuses from the alveoulus to the blood, the pCO2 in alveolar capillaries is higher than the pCO2 in the alveoulus and so the CO2 in the blood diffuses into the alveoulus from the blood.
Across the respiring tissue the pO2 in the tissue capillary is higher than the pO2 of the tissue and so the oxygen diffuses from the blood in the tissue capillary to the tissue, the pCO2 in the tissue capillary is lower than the pCO2 of the tissue and so the carbon dioxide diffuses from the tissue to the blood in the tissue capillary.

You can also mention figures to be on the safe side.
Click to expand...


Thiss is pretty good..thanks :) and yeaah exactly figures are must so yeah np I will include them :D
 
NaNinG

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Can sum1 explain briefly wot Promoters in Gene Technology actually r? as in proper definition.
 
mehria

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joanna omar said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s11_qp_12.pdf

Doubts....
Q10) why not B :/ ?
Q13 ....
Q14)...
Q17)....
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for Q10) cys-S-H + H-S-cys -> cys-S-S-cys, as you can see, a disulfide bond is created, but the cys and cys are not directly connected.
However, if cys-S-H + H-S-cys -> H-S-cys-cys-S-H, this way, the disulfide bond is not formed, but instead a peptide bond is formed (cys-cys). This is the answer for two Cysteine amino acids (cys).

Q13:- all enzymes have globular protein structure and all globular proteins are soluble in water..
Enzymes are also used for synthesizing a larger molecule from smaller ones to 2nd option is correct but not for all enzymes
Enzymes are not made up of Quaternary structure
So by excluding option 2 n 4 we get only one answer correct and that is C

Q14:- At P enzyme-substrate complex is formed by the formation of hydrogen bonds between them..

Q17:- As there is no change when it is placed in 0.35 mol dm–3 it means that the cells contain more solute potential..As we put it in a lower concentration 0.1 mol dm–3 (high water potential/hypotonic solution) then water will move inside the cell through osmosis and the cells become turgid. Here the high water potential is exerting pressure on cell wall.. that's why the pressure potential increases ( it will become more positive)
 
sudeep1097

sudeep1097

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roxylara said:
Can someone explain to me why phagocytes act only against the bacteria and not human cells?
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Been almost a year since i last gave as biology but i think it is because phagocytes have receptors in them which are specific to bacteria so they bind only to the bacteria and also chemicals secreted by bacterias may attract the phagocytes and they move by chemo taxis.
 
sudeep1097

sudeep1097

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Galactic said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s10_ms_51.pdf
Can anyone please help me with Question 2a (iii).
Thanks in advance.
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Test organism 1 and 2 both have antibodies for X. So there is precipitation that is one line each since the antibodies and antigens are complimentary hence draw one line each. But organism 2 has antibody for Y as well hence there is another line ( second line ) between Y and organism 2.
 
Galactic

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sudeep1097 said:
Test organism 1 and 2 both have antibodies for X. So there is precipitation that is one line each since the antibodies and antigens are complimentary hence draw one line each. But organism 2 has antibody for Y as well hence there is another line ( second line ) between Y and organism 2.
Click to expand...
Okay, but why is that line supposed to be smaller?
 
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