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

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What does all or nothing and refractory period mean anyoneee?

all or nothing is a term used to say...

that minimum amount of stimulus is required to start an action potential, the all or nothing effect is beneficial as it prevents a stimulus starting of the smallest of things happening

By summation effect and/or temporal

(edited 11 years ago)

Reply 4241

nadzzdan

Going into that paper tomorrow only to have done one past paper lol GOOD LUCK everyone!!!

Reply 4242

VRS

Original post by nadzzdan

Going into that paper tomorrow only to have done one past paper lol GOOD LUCK everyone!!!

lol do some more now!?

Reply 4243

Dentistry:)

Can anyone explain to me what exactly this learning outcome is asking:

LO 15, Topic 7: explain the principle of negative feedback in maintaining systems within narrow limits.

Reply 4244

PlatypusPigeon

Original post by Dentistry:)

Can anyone explain to me what exactly this learning outcome is asking:

LO 15, Topic 7: explain the principle of negative feedback in maintaining systems within narrow limits.

I'd suggest it just means negative feedback in terms of homeostasis. As for maintaining systems and it's limits it'll talk about high/low pH levels (too much CO2 in blood) or high/low blood pressure and how negative feedback restores the balance (so receptors to medulla oblongata to effector cells simply). Hope that helps!

Reply 4245

Dentistry:)

Original post by PlatypusPigeon

Ah i get it now. Cheers mate.

Hows your article prep?

Reply 4246

iesians

ok last min rev !!!
how does IAA cause cell elongation (5 marks)

Reply 4247

iesians

describe negative feedback mechanism (2 marks)

Reply 4248

HDchicky

some1 please explain to me how;
plants sensitivity is brought about in plants? when phytochromes red light Pr is converted into far-red light Pfr..?
to be honest the plant thingy...?

Reply 4249

ZTSR

OMG, Gene expression Paragraphs (43-48) fadskjfnhkdsj ??:s

I just dont understand what they're trying to get to in the Article Paragraphs (43-48).
I get everything else in the Article but this... :| . Someone care to explain please in a short summary, and what topics id have to read over for this bit

Thanks

Reply 4250

Waqar.

I've managed to confuse myself, can someone just clarifiy whether depolarised is being made positive or negative? And same with hyperpolarised. Thanks

Reply 4251

examtalk

depolarised is more positive and hyperpolarised is more negative

Reply 4252

Waqar.

Original post by iesians

describe negative feedback mechanism (2 marks)

I know it but it's hard to write/explain. I'd probably say something along the lines of a change results in the opposite event occuring to counteract the initial change.

Reply 4253

PlatypusPigeon

Original post by Dentistry:)

Ah i get it now. Cheers mate.

Hows your article prep?

****tt, I lost the article so am using an online copy with no synoptic highlights so am completely clueless. I'm just hoping the bio4 resit is still fresh in my head because that may help :P How about you?

Reply 4254

Kylewalker346234

Original post by iesians

ok last min rev !!!
how does IAA cause cell elongation (5 marks)

IAA is a Auxin that causes uneven growth in plants and controls the tropisms, Uneven growth is caused by uneven distrubution of the IAA.

In shoots it moves to the more shaded parts so that the shoot bends towards the light.

I may be utterly wrong here, but do we actually need to know about how the cells are actually elongated?! :colondollar:

Reply 4255

Kylewalker346234

Original post by iesians

describe negative feedback mechanism (2 marks)

a process of homoeostasis such as Vasolidation or Sweating which maintains constant internal temperature from small deviations in the external environment?

Reply 4256

PlatypusPigeon

Original post by ConnorB

IAA binds to receptor sites on cell surface membrane
Activates a pump, which pumps H+ out of the cytoplasm into the cell wall
Since the conc of H+ changes, pH drops, so the optimum pH for enzymes is reached. These enzymes break the bonds between the cellulose microfibrils
Cell wall becomes flexible, absorbs water (osmosis) and stretches (woooo elongation)

I think we need to know that :s-smilie:

Reply 4257

hetty123

Original post by platypuspigeon

iaa binds to receptor sites on cell surface membrane
activates a pump, which pumps h+ out of the cytoplasm into the cell wall
since the conc of h+ changes, ph drops, so the optimum ph for enzymes is reached. These enzymes break the bonds between the cellulose microfibrils
cell wall becomes flexible, absorbs water (osmosis) and stretches (woooo elongation)

i think we need to know that :s