Edexcel A2 Biology Unit 5 (6BIO5) - 22/06/2011- OFFICIAL THREAD !

the chemoreceptors are resposible for the ventilation rate not the heart rate when it detect that there is an increase in the co2 and decrease in the ph it sends to the inspiratory center in the medulla

You're pretty much bang on Though i'm nitpicking a bit here, where are the chemoreceptors located which detect the lower Ph caused by the increase in Co2?

Thanks
aortic bodies, carotid bodies and medulla...i'm 100% it's the first two

you're getting confused with breathing rate dear.
stretch receoptors and diapragm are stimulated when inhaling

inspiratory centre is also related to breathing rate, not heart rate

more co2 produced
chemoreceptors detect increase in co2 and send nerve impulses to medulla
medulla sends nerve impulses to heart via sympathetic nervous system to depolarise SAN
depolarisation of SAN increases which increases the heart rate
???

.

You Sir, are ready for this exam

my teachers notes say that the main stimulus that controls breathing rate is the concentration of carbon dioxide in the blood
blood concentration is detected by the chemoreceptors present in the carotid arteries they are sensitive to co2 conc and PH of the blood.
while what controls the heart rate he wrote:
stretch receptors in the walls of the aorta send nerve impulses to the cardiovascular center when changes in the blood pressure occur then the cardiovacular center in the brain either send sympathatic or parasympathatic nerve impulses to the SAN

Literally just seen this question on an oldish paper, a few things I reckon could be added to make sure you get all the marks:
State the obvious: aerobic respiration increases during exercise (I know it sounds stupid but they do often give one mark for that)
State the location of the chemoreceptors.
And in the markscheme I looked at, it said 'increases the frequency of impulses down the sympathetic nerve to the sinoatrial node' The heart is myogenic so no impulses would be sent from medulla to the SAN, but I think I'd add that little extra phrase to be on the safe side.

Hope that helps!

heart muscle is myogenic, what is meant by myogenic (3 marks)

i feel like this is a really stupid question but can someone explain phytochromes to me please? There was a question on how plants use photoreceptors and i had absolutely no idea

i feel like this is a really stupid question but can someone explain phytochromes to me please? There was a question on how plants use photoreceptors and i had absolutely no idea

Phytochrome

Phytochrome is a pale-blue pigment which is important in plant growth and development. It exists in two interconvertible forms. P660 has a maximum light absorption peak in the red end at 660 nm, whereas P730 has maximum absorption in the far red at 730 nm. When P660 is exposed to light at 660 nm, it is converted to P730. When P730 is exposed to light at 730 nm, it is converted to P660, and it slowly decays to P660 in the absence of light. Thus during daylight the plant accumulates P730 since daylight contains more red light. P730 is believed to be enzymatically active and influences a number of light-related processes, for example, photoperiodism, leaf lamina unfolding and seed germination. During the night the P730 slowly converts back to P660, which is then ready to respond to the daylight again.

Thus, in summary:
· Red light is absorbed by P660 which converts it to P730.
· Far red light is absorbed by P730 which converts it to P660.
· P730 in the dark slowly converts to P660 and it is this slow conversion

That is the ‘clock’ by which the plant measures night length.

Flowering in long day plants (henbane, snapdragon, cabbage, spring wheat and barley) is stimulated only if the level of P730 stays above a critical value. Flowering in short day plants (cocklebur, chrysanthemum, soya bean, strawberry and tobacco) is stimulated only if the level of P730 falls below a critical value. The levels of P730 are governed by the duration of dark periods (night).

u r wrong over there
natural sunlight contains a lot of RED light ! which is absorbed by Pr which then changes into Pfr.

thankyouuu :d