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Today's Mammalian Physiology (OCR)

Hi coug thanks for the reply;

No, the reflective layer is so light can be absorbed a second time for sure. That argument of yours is useless because the cats can just close their pupils like you or eye in the day time - infact the question even states this was possible.

Fair do's about the last two points, I wrote them also.

But please tell me, I appreciate cats constrict their pupils during the daytime, my point however was that simply because at night when the pupil is dilated so much it is very dangerous to have intense light shone into it. The question was about the cat at night having a beam of light shone directly into its eyes, I think it is a protection mechanism as well. I appreciate your point, even if I don't understand the physics of it fully (only did GCSE), however surely it is also a protection for the cats eyes. Please re-read my earlier post I edited it just before you posted your reply, maybe my point was made more clearly. Not really worth all this for one mark, but I do think it should recieve credit.

Reply 41

kingpong

The rabbit mucus question was only 2 marks wasn't it? Lubrication would nab you one of them I'd have thought.

Reply 42

cougem

Tealer

Hi coug thanks for the reply;

Fair do's about the last two points, I wrote them also.

But please tell me, I appreciate cats constrict their pupils during the daytime, my point however was that simply because at night when the pupil is dilated so much it is very dangerous to have intense light shone into it. The question was about the cat at night having a beam of light shone directly into its eyes, I think it is a protection mechanism as well. I appreciate your point, even if I don't understand the physics of it fully (only did GCSE), however surely it is also a protection for the cats eyes. Please re-read my earlier post I edited it just before you posted your reply, maybe my point was made more clearly. Not really worth all this for one mark, but I do think it should recieve credit.

How could it protect the cats eyes if it BEHIND the retinas? The light would already have passed through them and so would have done any damage would it not?

Also, the question was about how cats are adapted to hunt at night, where
did you get 'The question was about the cat at night having a beam of light shone directly into its eyes' from?

Reply 43

Tealer

kingpong

Shine a torch at a cat or dog at night and you'll see what I mean. VERY reflective.

Hmm.. please re-read my post. I did not dispute that when intense light is shone in they reflect it, but in dim light when it is dark you do not see any reflection. I still say it is partially a protection mechanism. Like I say cover your eyes for 5 minutes with one of those things you get on planes for sleeping then get a friend to immediately shine a torch straight into your eyes when you take the blindfold off. Now if you think the cats pupils are about 5 times larger... it could do some serious damage to the sensitive parts of the eye.

Reply 44

adrian

cougem

Yeh that was tricky, I said maybe it happens in solution and that gasses formed passes up through the throat and out, but that was a guess

I put that oxygen combined with haemoglobin to mop up the O2. This is the same mechanism as what happens in plants whereby the legohaemoglobin mops up the O2 in the nodules making them anaerobic. Well that's what I put down anyway.

Reply 45

Tealer

cougem

How could it protect the cats eyes if it BEHIND the retinas? The light would already have passed through them and so would have done any damage would it not?

Also, the question was about how cats are adapted to hunt at night, where
did you get 'The question was about the cat at night having a beam of light shone directly into its eyes' from?

Heh, a good point, I did not read they were behind the retina :smile:

. I was kinda arguing that it was a protection mechanism which *allowed* it to dilate the pupils to such a great extent when hunting at night, without putting the eyesight of the cat at great risk. 1 mark lost - Oh no! :smile:

Reply 46

cougem

Tealer

Hmm.. please re-read my post. I did not dispute that when intense light is shone in they reflect it, but in dim light when it is dark you do not see any reflection. I still say it is partially a protection mechanism. Like I say cover your eyes for 5 minutes with one of those things you get on planes for sleeping then get a friend to immediately shine a torch straight into your eyes when you take the blindfold off. Now if you think the cats pupils are about 5 times larger... it could do some serious damage to the sensitive parts of the eye.

See what I said above, how the hell can the reflective layer help if it's BEHIND the retinas? It'll reflect the light and do MORE damage; it's definately so the cat can reabsorb photons that weren't absorbed the first time - ESPECIALLY since the question was about how cats can hunt at night, not how it's adapted so it doesn't go blind.

And I don't think cats usually sit there staring at the sun, and I don't think they evolved while having Maglites continually shone into their eyes either.

Reply 47

Tealer

I suggest you take a nice big batch of chill pills cougem.
Regards,
Tealer.

Reply 48

goliath

For the pin question I remembered something about Pacinian corpuscle cells in the skin which sense pressure (i think?), and just wrote about what happens with them to generate an action potential etc etc.

that was a description of the reflex arc as it showed the butterfly diagram so u put receptor sends ap 2 sensory neuorone-relay-motor-muscle that wud get the marks (with a small explanation)

actually i think i was over dramatising before i shud bad around 70/90 coz the other questions were fairly gd

Reply 49

adrian

kingpong

The rabbit mucus question was only 2 marks wasn't it? Lubrication would nab you one of them I'd have thought.

For the mucus one, I put that the mucus allowed easy ingestion with minimum friction and also that the mucus provided an airtight environment which would give the microorganisms the anaerobic environment needed to further digest the food particles. Long winded I know!

Reply 50

kingpong

Tealer

Regions of brain - picture is from beneath /below.
Cerebrum
pituitary I think. (I put hypothalmus d'oh!)
Cerebellum
Medulla oblongata.

Same answers as I put, except I put pituitary (phew!, that one was a little tricky) and parietal lobe rather than cerebrum.

Reply 51

zizou

yeah...
i wrote the same as u..thats the only things could think of....the enswers of this questions r summarised in the MP book in the blue boes where there is a diagram of the per synapticmembrane

Reply 52

shazerkhan

Yo blood u know i dun the same as u 4 qn 7, but not entirely sure on whether this is correct wat we wrote. i just sed a slight more bout ca2+ binding to troponin n causing filiment movementg of actin etc

Reply 53

cougem

Why, when it asked about how Ca2+ was released? I just said how the action potential was induced with the Na+ and K+ channels and depolarisation and hyperpolarisation etc, and T-tubules, propagation of action potential, and ion channels and ion pumps inside the sarcoplasmic reticulum.

Reply 54

kingpong

cougem

Why, when it asked about how Ca2+ was released? I just said how the action potential was induced with the Na+ and K+ channels and depolarisation and hyperpolarisation etc, and T-tubules, propagation of action potential, and ion channels and ion pumps inside the sarcoplasmic reticulum.

Just out of interest which MP book do you have? I sure my piece of crap didn't go into half the detail required for this process.

Reply 55

cougem

All the Na+ and K+ ion bits are from Module 4 central concepts text book, the Biology 2 Cambridge one.
All the T tubules and Sarcoplasmic reticulum with ion channels and pumps are from the Cambridge Mamallian Physio and Behaviour textbook.

Reply 56

goliath

wud i get 1 mark for saying the depolarisation of the sarcolemma causes the ca2+ to flood in?

Reply 57

cougem

Wasn't that sort of given in the question?

Reply 58

shazerkhan

Guess wat peeps, i hated enviro bio so much i decided to giv it up n teach my self physiology, its hard but much more interesting, i duno wat 2 make of dat exam cuz first time i did it. wat dya peeps tink of dat?

Reply 59

kingpong

shazerkhan

Guess wat peeps, i hated enviro bio so much i decided to giv it up n teach my self physiology, its hard but much more interesting, i duno wat 2 make of dat exam cuz first time i did it. wat dya peeps tink of dat?

English.

You speak it?

Today's Mammalian Physiology (OCR)

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