OFFICIAL OCR A2 Biology - F214 Thread

i predict questions on: thermoregulation, osmoregulation, singals and messages(e.g. outline the siginificance of the frequency of impusle transmission), cAMP, nature of hormones e.g. protein/steroid, regulation of blood glucose, regulation of insulin levels e.g. outline how insulin secretion is controlled, deamination, structure of liver, hairpin countercurrent mulitplier,calvin cycle, structure and function of mitochondria, krebs/link reaction and evidence for chemiomosis

are you suree? how do you know?

lol what happend to everyone? where are the questions?

Don't really want to trawl through 3000 posts so could someone please summarise the pregnancy testing bit. Much obliged!

is this right about ADH and water potential?

when there is a low water potential in the blood, osmoreceptors in the hyptothalmus detects this and lose water by osmosis causing them to shrink. They then stimulate neurosecretory cells which send an action potential down its axon to the posterior pituitary gland which releases more ADH into the blood.

this ADH causes more aquaporins to appear in the walls of the collecting duct and the collecting duct becomes more permeable. more water leaves the collecting duct and into the blood by osmosis so more water is re absorbed. As a result less urine is produced and it is more concentrated.

Ok. Water reabsorption:

From the PCT, Ions(Sodium and chloride) and water and urea flow down.

During the descent down the descending limb, water diffuses out, due to a very low tissue fluid potential. At the same time, ions diffuse into the descending limb?

This means that the descending limb has a high conc. or ions and urea, but little water.


At the base of the loop, ions diffuse out and then are actively transported out at the thick ascending limb BUT NOT WATER CAUSE ITS IMPERMEABLE(Musnt forget)?

This means that the "balance" is restored as ions have been taken out as well as water. This leave conc. urine/urea.

Then the DCT and collecting duct?

When water diffuses out of the descending limb, does it mix with the tissue fluid or is it absorbed by the capillaries?

it mixes up with the tissue fluid

Thanks, You are a big help!

Also, the conc of the medulla increases as you go down the medulla, because:

less water is diffusing out by osmosis as you do down the descending limb, and easy diffusion of ions out of the ascending limb at the bottom, possibly allows more ions to leave, the the actively transporting of the ions at the top of the ascending limb?

Non cylic is when photosystems 1 and 2 are involved, whereas cyclic only involves photosystem 1. For cylic photophosphorylation, the excited electrons (once they have gone through the electron transported thingymebob and generated the ATP) are passed back to the pigment. In contrast, in non-cyclic photophosphorylation, both photosystems are involved and will emit electrons, but this time PSI absorbs the electrons emitted from PSII to replace the ones it lost when it's hit by the light, and PSII regains the electrons it loses via the photolysis of water. The hydrogen ions also produced in the photolysis of water are used to reduce NADP to form reduced NADP, and the oxygen left is released as a waste product.

So the main differences are:
*Cyclic only uses PSI, whereas non-cyclic uses both
* The product of CPP is ATP, and the products of NCPP are ATP, reduced NADP and oxygen

So in what you said, you've got all the details of cyclic photophosphorylation spot on

I hope this helped

Don't really want to trawl through 3000 posts so could someone please summarise the pregnancy testing bit. Much obliged!