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Edexcel A2 Biology Unit 5 (6BIO5) - 22/06/2011- OFFICIAL THREAD ! watch
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- 20-06-2012 12:52
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- 20-06-2012 12:56
(Original post by ghogho)
ur welcome
but there is something to correct!!!
natural daylight contain mainly RED light!!! -
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- 20-06-2012 12:56
(Original post by i Pav i)
Explain how the structure of the axon cell membrane is related to the conduction of nerve impulses?! (3 marks)
help?! aha.
it is also impermeable to na + ions ( i think)
due to the phospholipid nature not allowing charged molecules to pass directly thry them !
xcant think of anything else. -
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- 3724
- 20-06-2012 12:57
what snynoptic topics do we need to know for this exam??
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- 20-06-2012 12:58
(Original post by d_94)
.
'explain the principle of negative feedback in maintaining systems within narrow limits' -
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- 20-06-2012 12:59
(Original post by Cleoleo)
wait so in the daylight Pfr is converted to Pr and in the dark, Pfr to Pr right? -
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- 20-06-2012 13:17
(Original post by iesians)
.(Original post by ghogho)
r(Original post by d_94)
](Original post by This Honest)
o
how can genes be switched on and off using DNA transcription factors including hormones??Last edited by wam-bam; 20-06-2012 at 13:18. -
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- 20-06-2012 13:22
(Original post by ghogho)
red light is abosorbed by PR and converted to PFR -
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- 20-06-2012 13:22
(Original post by Cleoleo)
In the daylight? -
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- 20-06-2012 13:25
(Original post by wam-bam)
how can genes be switched on and off using DNA transcription factors including hormones??
Although, I'm probs wrong somewhere. -
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- 20-06-2012 13:28
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bertiejess
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- 20-06-2012 13:29
(Original post by i Pav i)
Explain how the structure of the axon cell membrane is related to the conduction of nerve impulses?! (3 marks)
help?! aha.
These protein channels span the whole of the membrane and without them, ions cannot travel through the membrane due to the phospholipid bilayer being immpermeable. -
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- 3733
- 20-06-2012 13:35
(Original post by Cleoleo)
kk so Pr to Pfr in daylight and Pfr back to Pr at night, and then there's short day and long day plants, short day require all the Pfr to be converted back to Pr to cause germination (uninterrupted darkness must be more than 12 hours) and long day require some Pfr for flowering (uninterrupted darkness must be less than 12 hours), that's basically all i know about Pfr and Pr, is there anything missing?
for the shortday plants the PFr inhibits flowering so these plants flower in winter ie short days and long nights ie low level of PFR (long nights allow PFR made during the day to be converted to PR
for the longday plants : PFR stimulates flowering so these plants flower in summer ie short nights and long day ie hih level of PFR (nights are too short to change all the PFR back to PR.......
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- 20-06-2012 13:36
(Original post by wam-bam)
what do we need to know for this point on the spec,
'explain the principle of negative feedback in maintaining systems within narrow limits'
Then know what mechanisms the body uses when the external temp is too cold or too hot. So too hot, means sweat glands are active and when sweat evaporates, it cools you down. Liver lowers metabolic rate, skeletal muscles relax, hair erector muslces relax, vasodilation ... I'm not sure whether it's in the spec to know about shunt vessels but they basically contrict when you're hot, so increased blood flow to the surface. Oh, and the hypothalamus being the thermoregulatory centre and skin receptors detecting change.
Opposite for when temperature drops + shivering which increases respiration so more heat generated.
Please quote me if I've forgotten to add detailsLast edited by Cleoleo; 20-06-2012 at 13:39. -
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- 20-06-2012 13:38
(Original post by bertiejess)
Contains an Na-K protein channel, which allows the movement (diffusion) of ions from outside membrane inside and vice versa.
These protein channels span the whole of the membrane and without them, ions cannot travel through the membrane due to the phospholipid bilayer being immpermeable. -
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- 3736
- 20-06-2012 13:41
(Original post by wam-bam)
how can genes be switched on and off using DNA transcription factors including hormones??
this either INCREASES or DECREASES the rate of transciption of a particular gene.
if it increases then the transcription factor was an activator
if it decreases then it was a repressor. -
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- 20-06-2012 13:43
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- 20-06-2012 13:45
(Original post by iesians)
hormones initiate transcription factors in the cell to bind to a promoter region on DNA
this either INCREASES or DECREASES the rate of transciption of a particular gene.
if it increases then the transcription factor was an activator
if it decreases then it was a repressor.
so hormones can either turn transcription on or off? -
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- 3739
- 20-06-2012 13:46
(Original post by iesians)
its permeable to carbon dioxide and oxygen kinda stuff ! anything which is not charged and isnt too big.
what synoptic stuff do we need to know? -
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- 20-06-2012 13:50
(Original post by Cleoleo)
I thought repressor molecules were comoletely differerent things which could attach to the promoter region or the transcription factors themselves, inhibiting transcription?
so hormones can either turn transcription on or off?
its in CGP guide page 67.
and hormones ACTIVATE THE TRANSCRIPTION FACTORS which then act as either represoor or activator ans determine the transcription rate.
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