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## #1 2007-06-05 19:23:11

Daniel123
Member
Registered: 2007-05-23
Posts: 663

### Biology

Any biologists here?

I have my biology gcse today and there are a few things I'm not too sure about.

1) In the nephron, how does the glucose move from the kidney tubule back into the blood (the book I have here says by active transport, but that can't be right - as active transport is against the concentration gradient, but there is no glucose in the blood at this point?)

2) What is an antigen and a pathogen?

3) Is chlorophyll an enzyme (because it is destroyed at around 45°C, so I thought maybe it could be?)

4) When particles diffuse through a cell membrane, do they move in both directions but have a net movement (as in osmosis), or do they just move in one direction?

5) I remember reading tht the upper epidermis in a leaf is semi-transparent. Is that right?

If anyone could help with any of these that would be great.

Thanks.

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## #2 2007-06-05 20:13:18

Identity
Member
Registered: 2007-04-18
Posts: 934

### Re: Biology

Say you have a high concentration of oxygen inside a cellulose bag, and a lower concentration outside. The net movement will be from inside to outside, but some particles from outside will still by chance happen to come in (remember that particle movement is based on probability, brownian motion - there is a higher probability that something will go out than come in)

Last edited by Identity (2007-06-05 20:15:13)

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## #3 2007-06-05 20:28:54

JaneFairfax
Member
Registered: 2007-02-23
Posts: 6,868

### Re: Biology

#1 Yes, active transport does take place in the nephron. The reabsorption of glucose and salts from the renal filtrate into the blood occurs at the distal convoluted tubule or the ascending limb of the loop of Henle  or both, cant quite remember exactly which. I dont remember either where the energy for the active transport comes from (but I do know that active transport does take place there).

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## #4 2007-06-05 20:31:43

Daniel123
Member
Registered: 2007-05-23
Posts: 663

### Re: Biology

Oh right ok thanks. I'm think the energy for active transport comes from respiration in the mitochondria of the cells of the kidney tubule... not 100% though. Biology is definitely my worst subject.

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## #5 2007-06-05 22:35:00

George,Y
Member
Registered: 2006-03-12
Posts: 1,320

### Re: Biology

Biology is of course hard. But it's hard to everyone so don't give up.

X'(y-Xβ)=0

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## #6 2007-06-05 22:41:38

Daniel123
Member
Registered: 2007-05-23
Posts: 663

### Re: Biology

. The way I see it - I do double science, so I get two GCSEs out of it. So I'm aiming to get an A in the biology paper, as I know I will get near enough full marks in the physics and chemistry, so it will average out to give me two A*s. Hopefully.

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## #7 2007-06-06 01:08:42

JaneFairfax
Member
Registered: 2007-02-23
Posts: 6,868

### Re: Biology

Daniel123 wrote:

Oh right ok thanks. I'm think the energy for active transport comes from respiration in the mitochondria of the cells of the kidney tubule... not 100% though. Biology is definitely my worst subject.

I found my old biology textbook and read up on the topic. You are right: the energy for active transport in the nephron can come from mitochondrial respiration. Another part of my textbook says that the active reabsorption of some substances from the renal filtrate is controlled by hormones. I dont know if this applies to glucose; if it does, then Id guess insulin might have a part to play.

In any case, biology is not my strongest subject either.

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## #8 2007-06-06 06:04:42

Daniel123
Member
Registered: 2007-05-23
Posts: 663

### Re: Biology

Aah right thanks! I have to say, that exam was the hardest exam I have ever done. I revised the nitrogen cycle thoroughly but the last question on it was really difficult. However the only thing in the exam that I did't actually have the knowledge for was a question that asked "apart from the lens, what other part of the eye bends the light". I had no idea, I know the parts of the eye but I wasn't aware any other part bent the light? So I just said ciliary muscles, which alter the shape of the lens and actually control the extent to which the light is bent.
Hopefully I have got a mid-to-high A though.

Last edited by Daniel123 (2007-06-06 06:05:39)

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## #9 2007-06-06 06:14:02

luca-deltodesco
Member
Registered: 2006-05-05
Posts: 1,470

### Re: Biology

i had a biology exam today, but i do single sciences and this was just the core paper, i have the extension paper next week with the more advanced biology stuff on. i get 6 exams in total for the 3 gcses, two in each science

The Beginning Of All Things To End.
The End Of All Things To Come.

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## #10 2007-06-06 06:16:09

Daniel123
Member
Registered: 2007-05-23
Posts: 663

### Re: Biology

Biology itself is not that difficult to understand, but explaining it and applying the knowledge to questions is more difficult.

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## #11 2007-06-06 07:33:35

JaneFairfax
Member
Registered: 2007-02-23
Posts: 6,868

### Re: Biology

Daniel123 wrote:

"apart from the lens, what other part of the eye bends the light"

The aqueous and/or vitreous humour. I remember learning about this long ago, so Im fairly sure thats the answer. In fact, the function of the lens is more to adjust the focal length of the eye (so as to focus light on the retina) than to bend light; light is actually refracted more by the vitreous/aqueous humour than by the lens itself.

Good luck on your getting an A in the paper. I also hope you did well in all your other papers (sorry I didnt wish you good luck before your papers  it was rather mean of me; I do apologize).

Last edited by JaneFairfax (2007-06-07 04:52:31)

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## #12 2007-06-07 06:21:47

Daniel123
Member
Registered: 2007-05-23
Posts: 663

### Re: Biology

Quite alright! I'm on track to reach my overall targets... I hope! I had my second English language exam today. It did not go well. English is one of my best subjects, but my mind completely froze - so I made up the biggest load of rubbish. I ended up reading back over it and crossing all 3 pages out and starting again, leaving me with 10 minutes for the last essay which, to my horror, was "analyse the extent to which the older generation are respected in your community, and how this may change in the future". I'm sorry, but I am not writing an essay on that. And they also expect us to write an A* essay in 30 minutes! If we had 2 hours, my essay would be the best in the year, but in 30 minutes it is very hard to make it stand out. Urgh.

Last edited by Daniel123 (2007-06-07 06:32:55)

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## #13 2007-06-07 06:44:13

luca-deltodesco
Member
Registered: 2006-05-05
Posts: 1,470

### Re: Biology

lol you care too much, seriously

on another note:

thank god i never have to touch English the subject again, im so glad (had my last exam today for english), i really HATE it as a subject.

The Beginning Of All Things To End.
The End Of All Things To Come.

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## #14 2007-06-07 21:12:15

Daniel123
Member
Registered: 2007-05-23
Posts: 663

### Re: Biology

lol I love english! well the literature part anyway. I'm probably doing it for A level... what are you taking?

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