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

Original post by ghogho

ur welcome :smile:

but there is something to correct!!!
natural daylight contain mainly RED light!!! :colondollar:

wait so in the daylight Pfr is converted to Pr and in the dark, Pfr to Pr right?

Reply 3722

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.

umm it has sodium pumps and potassium pumps to transfer na and K ions respectively owing to the need of depolarisation or repolarisation
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.

Reply 3723

what snynoptic topics do we need to know for this exam??

Reply 3724

wam-bam

Original post by This Honest

Original post by d_94

.

what do we need to know for this point on the spec,

'explain the principle of negative feedback in maintaining systems within narrow limits'

Reply 3725

ghogho

Original post by Cleoleo

wait so in the daylight Pfr is converted to Pr and in the dark, Pfr to Pr right?

red light is abosorbed by PR and converted to PFR

Reply 3726

wam-bam

Original post by iesians

.

Original post by ghogho

r

Original post by d_94

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Original post by This Honest

o

how can genes be switched on and off using DNA transcription factors including hormones??

(edited 11 years ago)

Reply 3727

Original post by ghogho

red light is abosorbed by PR and converted to PFR

In the daylight?

Reply 3728

ghogho

Original post by Cleoleo

In the daylight?

yup

Reply 3729

Original post by wam-bam

how can genes be switched on and off using DNA transcription factors including hormones??

with this q, don't you talk about hormones like anabolic and peptide hormones, with peptide they bind to a receptor on the outside of the cell surface membrane and then this initiates a second messenger which initiates transcription because it causes the RNA polymerase and the transcription factors to form a complex and then bind to the promotor region. While anabolic hormones like testosterone bind to the receptor in the cell directly rather than through a second messenger and has the same effect of intiating transcription.

Although, I'm probs wrong somewhere.

Reply 3730

Original post by ghogho

yup

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?

Reply 3731

bertiejess

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.

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.

Reply 3732

ghogho

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.......

Reply 3733

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'

I think you just need to know that when there's a change from the norm/set point, then the body counteracts the change in the opposite direction and restores it back to this narrow limit (think of it as wave, where if there's a rise from the base line, the body counteracts the change by bringing it back down (in the opposite direction) which is basically what negative feedback is.

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 details

(edited 11 years ago)

Reply 3734

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.

what is the phospholipid bilayer permeable to again? :smile:

Reply 3735

Original post by wam-bam

how can genes be switched on and off using DNA transcription factors including hormones??

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.

Reply 3736

Original post by Cleoleo

what is the phospholipid bilayer permeable to again? :smile:

its permeable to carbon dioxide and oxygen kinda stuff ! anything which is not charged and isnt too big.

Reply 3737

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.

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?

Reply 3738

Original post by iesians

its permeable to carbon dioxide and oxygen kinda stuff ! anything which is not charged and isnt too big.

ahh kk thank you :smile:

what synoptic stuff do we need to know?

Reply 3739