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AS LEVEL BIOLOGY... discuss here AS students only :)

daredevil

daredevil

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shafayat said:
(iii) After circulating in the blood for a short time, the pathogen enters liver cells of the
newly infected person and then enters red blood cells.
why does it enter the liver cell ..?

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its just a place where they act like reproduce and mature and stuff: the liver cells and the red blood cells.
 
daredevil

daredevil

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xxfarhaxx said:
problem? Q6-b ..
why does the mark scheme say at the top of the food chain n last in da the food chain? arent those big animals suppose to be the one's to eat the plants, so they will surely have more eneregy ryt? the mark scheme is so confusing!
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w07_qp_2.pdf
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w07_ms_2.pdf
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look the energy is being wasted at each trophic level as the link is eaten by the link above them. the big animals need more food to sustain them and have to eat a huuggee amount already and with the energy being wasted along the way they need even more food. not all the big animals get their fair share of this much amount of food so the ones that don't get enough die and those which get it they survive. and there is a very small number which survive so the big fierce animals are rare. ii hope u get the concept now :) (y)
 
xxfarhaxx

xxfarhaxx

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daredevil said:
look the energy is being wasted at each trophic level as the link is eaten by the link above them. the big animals need more food to sustain them and have to eat a huuggee amount already and with the energy being wasted along the way they need even more food. not all the big animals get their fair share of this much amount of food so the ones that don't get enough die and those which get it they survive. and there is a very small number which survive so the big fierce animals are rare. ii hope u get the concept now :) (y)
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ya tnx fr da xplantion!!:cool:
 
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HongYue said:
How to answer 9700/21/O/N/11
Question 2c ? Mark scheme confuses me. :p
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see the enzyme are wat? proteins in nature ryt?? if enzymes are broken down and haveto be REPLACED then surely wat needs to be done is MAKE new enzymes [proteins]. and how do we make proteins? by transcription aand translation process of the DNA molecules where the chains are pulled apart and then copied onto the mRNA which then moves out of the nucleus to the RER and ribosomes attach to the chain and tRNA come with the amino acids and one by one the specific amino acids are joined together to make the polypeptide and furhtermore the protein that is an enzyme in this case
 
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ok people confusion here : wat makes the cholestrol able to make the plasma memberane fluid?? is it the double bonds?
 
HongYue

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daredevil said:
see the enzyme are wat? proteins in nature ryt?? if enzymes are broken down and haveto be REPLACED then surely wat needs to be done is MAKE new enzymes [proteins]. and how do we make proteins? by transcription aand translation process of the DNA molecules where the chains are pulled apart and then copied onto the mRNA which then moves out of the nucleus to the RER and ribosomes attach to the chain and tRNA come with the amino acids and one by one the specific amino acids are joined together to make the polypeptide and furhtermore the protein that is an enzyme in this case
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Thx a lot :)
 
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heyy guys can anyone explain facillitated diffusion to me like rEALLL good/??
 
shafayat

shafayat

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daredevil said:
heyy guys can anyone explain facillitated diffusion to me like rEALLL good/??
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I CAN TRY .....facilitated diffusion is the diffusion by help of carrier or channel protiens ! carrier protiens are only from high concentration gradient to low conc. gradient ( only diffusion ) but channel can also carry out active transport ! :p nothing else coming to mind right now :p
 
daredevil

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shafayat said:
I Cfacilitated diffusion is the diffusion by help of carrier or channel protiens !
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hahha that much book was given to me by my PAAthetic teahcer ,,, i need more detail like an explanation of some kind to help me understand u know
 
HubbaBubba

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daredevil said:
hahha that much book was given to me by my PAAthetic teahcer ,,, i need more detail like an explanation of some kind to help me understand u know
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Facilitated diffusion is the diffusion of ions and polar molecules (Such as glucose) through carrier/transport proteins down a concentration gradient without the use of ATP energy. It's basically diffusion, but through carrier proteins in the cell membrane. That's all you need to know :)
 
NouranAyman

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HubbaBubba said:
Can anyone help me ^_^ Somebody please explain to me how the plant transports sucrose from the source to the sink?
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First the triose phosphate produced by photosynthesis is converted to sucrose by enzyme sucrose phosphate synthetase then the loading mechanism =>
which starts by 1) active transport of hydrogen ions out of the companion cells of the phloem to the mesophyll cells where the sucrose and amino acids are present, the hydrogen ions then return back down their concentration gradient carrying sucrose and amino acids with them to let them pass through co transporter protien. This step is needed as sucrose and amino acids cannot simply go into the companion cells, active transport of H+ should occur to create a potential that lets sucrose and amino acids go into the companion cells. Then next is 2) the sucrose and amino acids diffuse from the companion cells into the sieve tube cells through the plasmodesmata. When sucrose and amino acids are in the sieve tubes this makes its water potential low, so water from surrounding cells enter into the sieve tube cells till it possess high hydrostatic pressure (due to presence of water) , so the sieve tube transports sucrose and amino acids to all the cells having lower hydrostatic pressure.
Nextt is The unloading mechanism => Nothing much is done here after the sucrose and amino acids are transported to cells having lower hydrostatic pressure and sucrose is converted by enzyme sucrase or invertase to glucose and fructose which are soluble and can easily be used.
Also know that this all happens side by side so during unloading sucrose and amino acid are finishing from the sieve tubes so loading happens in the companion cells. I Hope this helped :)
 
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