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A2 Biology OCR June 2015 Revision Thread

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What's the difference between kineses and taxes? I know it's non directional stimulus and directional stimulus respectively but any examples? don't really know what those stimuli terms mean. thankyou

I did a practical on kinesis. We were given maggots and a tray. Half of the tray was shaded and half of the tray was illuminated. We placed the maggots on the illuminated side, that is, in unfavourable conditions. They increase their rate of movement (in any random direction) until they reach the shaded side. When they're in the shade their rate of movement decreases because they're in favourable conditions.
I found an example of taxis in another thread which is probably better than the ones in the textbook.

Original post by charlie15432

Examples of a positive phototaxis would be something like the golden jellyfish in Jellyfish Lake in Palau that follow the arc of the sun during the day so that their symbiotic algae can photosynthesise

Reply 421

saikhan

Hi guys,
Has anyone done the evaluative on peas and the quantitative task that involves field work? I literally need all the help I can get ☺️
Thanks xo

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Reply 422

sophieholgate

Hi, I'm revising the liver and none of the text books are giving me the answer to this question; 'describe how liver structure ensures that blood flows past as many liver cells as possible'. Does anyone have a suitable answer?

Reply 423

RagaZ

Original post by sophieholgate

I think... Liver cells are arranged in a cylindrical lobule and within the lobule the hepatocytes surround regions called sinusoids this is where blood from both the hepatic portal vein and hepatic artery mix, the close proximity between the blood and cells allows substance to diffuse into and out of the hepatocytes. I think. I could equally be wrong, but that's what I'd put in an exam.

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Reply 424

SarahWatson96

I'm so confused on epistasis, like I get what it is but when I get to the questions like "describe how the genes at the loci interact" I get so confused and deriving the relationship from the ratios.
Anyone got any useful tips or hints for tackling these questions

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Reply 425

ChoccyPhilly

Is synaptic convergence a kind of spatial summation?

they seem to be identical in my revision guide

(edited 9 years ago)

Reply 426

rd1234567

Original post by mariamaisabelle

I only have a copy of the F214 paper, but I've written on it as it was my mock exam..
I could ask my teacher to email it to me if you'd like?

yes please if possible
thanks in advance

Reply 427

username1850327

Original post by Hilton184

If stimulatory, neurotransmitter binds to complementary receptors on postsynaptic membrane and this causes depolarisation - action potential generated (standard synapse: Na+ channels open, Na+ diffuses into neurone, threshold potential reached hence action potential generated).

If inhibitory, neurotransmitter binds to complementary receptors on postsynaptic membrane and this causes hyperpolarisation - not depolarisation I believe. Ie may cause chloride ions to diffuse into postsynaptic knob to make membrane potential even more negative than it already is, hence making it harder to reach threshold potential from anything stimulatory.

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i'm confused where does this come up about stimulatory and inhibitor action potentials?

Reply 428

96akhan

Original post by frozo123

What's the difference between kineses and taxes? I know it's non directional stimulus and directional stimulus respectively but any examples? don't really know what those stimuli terms mean. thankyou

As you said, kineses is non-directional and taxes is directional. They are both types of innate behaviour;

With kineses, the rate of movement increases when the animal is in unfavourable conditions.

With taxes, the direction of movement is in response to the stimulus that triggers it, so a positive response = organism moves towards stimulus, a negative response = organism moves away from stimulus

Examples:
Kineses - woodlice moving rapidly in the light
Taxes - (not quite sure, sorry!)

Reply 429

Hilton184

Original post by phoebc

i'm confused where does this come up about stimulatory and inhibitor action potentials?

Don't say inhibitor action potential. An inhibitor synapse would be inhibiting action potentials by making the membrane potential more negative and hence making it harder to reach threshold potential (because more Na+ would need to enter in order to reach threshold potential).

It doesn't talk about it much in the textbook. It says in the synapses section that synapses can be excitatory or inhibitory. So that post was just talking about how a inhibitory synapse might work.

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Reply 430

vincentjack

Original post by phoebc

i'm confused where does this come up about stimulatory and inhibitor action potentials?

don't worry about it, it was just mentioned in the revision book in a table comparing synapses to neuromuscular junctions. the revision book has some really weird points tbh

Reply 431

frozo123

Original post by vincentjack

don't worry about it, it was just mentioned in the revision book in a table comparing synapses to neuromuscular junctions. the revision book has some really weird points tbh

Which revision book?

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Reply 432

AnnekaChan173

Original post by frozo123

Which revision book?

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The endorsed revision guide, I think.

Reply 433

Zippyzazu

Hey guys

Please can someone help me, would we ever be asked to draw/ describe the structure of the co-enzymes used in respiration?

Thanks :smile:

Reply 434

Cara_rose

Original post by Zippyzazu

Hey guys

Please can someone help me, would we ever be asked to draw/ describe the structure of the co-enzymes used in respiration?

Thanks :smile:

You may be asked for examples and their uses. But the structure of them is not in the specification. Also, it has not been mentioned by my old teacher (now tutor) who has been teaching this stuff for years and is very good at teaching what you need and nothing more.