A2 Biology OCR June 2015 Revision Thread

Hi, just wondering if someone can clarify this question about neurones to me. http://biogishumerus.com/2013/04/25/f214-homeostasis-past-papers/ Just click the link and click on nerves and hormones, scroll down and it's the pacinian corpuscle question from 2008.

I don't really understand how a change in p.d is caused in the sensory neurone at light and medium pressures? surely the voltage gated sodium ion channels in the sensory neurone membrane don't open until the threshold value is reached? So are there other sodium ion channels that open in response to the generator potentials in the sensory receptor cell membrane? Just one final thing, do receptor cells contain voltage gated sodium ion channels, or do they only contain sodium ion channels that respond to changes in energy level i.e. pressure? The action potential doesn't occur in the receptor cell, right? :s-smilie:

The book isn't really that clear on it, neither is the mark scheme :| and I just can't seem to make sense of it.

Thank you :smile:

The strength of the pressure doesn't change the size of the action potential, instead it changes the frequency. A light pressure would mean the action potential is less frequent but strong pressure would result in so many action potentials forming. As for your second question, yeah I think they have both sodium ion channels to maintain the resting potential and voltage gated sodium ion channels for when there is a stimulus. An action potential has to occur in the receptor cell for it to actual transmit the message.
Correct me if i'm wrong please.

Reply 1601

Hilton184

9

Original post by Zoze

Hi, just wondering if someone can clarify this question about neurones to me. http://biogishumerus.com/2013/04/25/f214-homeostasis-past-papers/ Just click the link and click on nerves and hormones, scroll down and it's the pacinian corpuscle question from 2008.

I don't really understand how a change in p.d is caused in the sensory neurone at light and medium pressures? surely the voltage gated sodium ion channels in the sensory neurone membrane don't open until the threshold value is reached? So are there other sodium ion channels that open in response to the generator potentials in the sensory receptor cell membrane? Just one final thing, do receptor cells contain voltage gated sodium ion channels, or do they only contain sodium ion channels that respond to changes in energy level i.e. pressure? The action potential doesn't occur in the receptor cell, right? :s-smilie:

The book isn't really that clear on it, neither is the mark scheme :| and I just can't seem to make sense of it.

Thank you :smile:

From what I understand, the sensory receptor will have pressure gated Na+ channels (or ____ gated, whatever the stimulus is).
Hence when pressure is applied to the cell, pressure gated Na+ channels open, Na+ diffuses in and threshold potential is reached, causing voltage gated Na+ channels to open, generating an action potential.😊

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Reply 1602

brooklyniona

what's the pathway of gluconeogenesis in the liver to make glucose from other molecules?
Like amino acids or lipids... what's the pathway to them forming glucose? thanks

(edited 8 years ago)

Reply 1603

domcandrews

2

Could anyone be able to explain how to calculate the net gain of ATP in the question on Page 97 of the textbook and Page 20 of this pdf: http://www.pearsonschoolsandfecolleges.co.uk/AssetsLibrary/SECTORS/Secondary/PDFs/Science/HeinemannScience/OCRALevelSampleLessons/OCRA2Biology_StudentBook9780435691905_Unit1Module4.pdf
thanks in advance

Reply 1604

cinderella25

11

I'm scared!

Any predictions? I have a feeling a lot about photosynthesis and respiration will come up :/

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(edited 8 years ago)

Reply 1605

maisie__x

2

Original post by cinderella25

I'm scared!

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I second that!!

Reply 1606

thequackingduck

4

What are the grade boundaries like over the past few years for F214? Aiming for an A!

Reply 1607

tewas

2

Plants that live in the Arctic have a relatively short growing season in which the light intensity is always relatively low. Many species growing in these conditions have a high level of anthocyanin pigments in their leaves. The combined effect of these red pigments with the green chlorophyll makes the leaves appear dark purple or black.
Suggest why this adaptation is useful in increasing photosynthetic rates.

How do you answer this?

Reply 1608

Molly_xox

16

Original post by tewas

Plants that live in the Arctic have a relatively short growing season in which the light intensity is always relatively low. Many species growing in these conditions have a high level of anthocyanin pigments in their leaves. The combined effect of these red pigments with the green chlorophyll makes the leaves appear dark purple or black.
Suggest why this adaptation is useful in increasing photosynthetic rates.

How do you answer this?

I'm pretty sure it's going to have something to do with how different photosynthetic pigments absorb light of different wavelengths. How many marks is it?

Reply 1609

EllieTaorps

5

Original post by tewas

Plants that live in the Arctic have a relatively short growing season in which the light intensity is always relatively low. Many species growing in these conditions have a high level of anthocyanin pigments in their leaves. The combined effect of these red pigments with the green chlorophyll makes the leaves appear dark purple or black.
Suggest why this adaptation is useful in increasing photosynthetic rates.

How do you answer this?

It'll be something along the lines of they absorb a greater range of light wavelengths and reflect less, this means they can maximise the amount of light they absorb and thus the rate of photosynthesis in low light intensities.

Reply 1610

MeeraP07

7

Original post by Beni24

Glycolysis,links and krebs cycle occurs twice for every glucose molecule? why does this happen again? :smile:

Glycolysis only occurs once per glucose molecule but the link reaction and krebs cycle occurs twice per glucose because 2 pyruvate is produced at the end of glycolysis.

Reply 1611

tewas

2

Original post by EllieTaorps

It'll be something along the lines of they absorb a greater range of light wavelengths and reflect less, this means they can maximise the amount of light they absorb and thus the rate of photosynthesis in low light intensities.

yes that is right but could you explain how you worked that out from the info given in the question? thanks

Reply 1612

ChoccyPhilly

13

Just had a dream I missed the exam and failed it. Lol the pressure is getting to me

Reply 1613

domcandrews

2

Original post by domcandrews

Could anyone be able to explain how to calculate the net gain of ATP in the question on Page 97 of the textbook and Page 20 of this pdf: http://www.pearsonschoolsandfecolleges.co.uk/AssetsLibrary/SECTORS/Secondary/PDFs/Science/HeinemannScience/OCRALevelSampleLessons/OCRA2Biology_StudentBook9780435691905_Unit1Module4.pdf
thanks in advance

Can anyone do this? So confused as to how to do it, They always put some sort of calculation in, and this is the hardest one I've seen! Any help? :frown:

Reply 1614

cinderella25

11

Original post by ChoccyPhilly

Just had a dream I missed the exam and failed it. Lol the pressure is getting to me

Same here. This unit is the worst!

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Reply 1615

LA_95

1

Guys what is photorespiration? its mentioned in the revision guide that increasing temperature will make the rate of photorespiration greater than rate of photosynthesis but it doesn't actually say what it is???

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