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A level Biology: Post your doubts here!

qwertypoiu

qwertypoiu

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shingiechingz@8 said:
guys where can l find some old biology past exam papers like from 1995-1998
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Sorry I can't answer your question, but I'm just interested, why insist on doing old papers?
Wouldn't new papers be more relevant as it would resemble the actual papers we'll do more?
 
shingiechingz@8

shingiechingz@8

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qwertypoiu said:
Sorry I can't answer your question, but I'm just interested, why insist on doing old papers?
Wouldn't new papers be more relevant as it would resemble the actual papers we'll do more?
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in my country we are based on the old papers [CIE SYLLABUS] 1998
 
M

My Name

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Can anyone tell me what are the main/repeated questions that come from the nervous system chapter for A2?
 
M

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upload_2015-12-17_22-14-4.png
What is the reason that it goes a little below the resting potential?
Is the reason needed?
 
Bhaijan

Bhaijan

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Hey there,
Is endodermis found only in roots;
if it is found in stems also then where are they located?
 
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zeejay

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Salam everyone,
I have a query to solve regarding microscopic resolution. I know that resolution is the ability to distinguish between two points close together. But what are those two points??? example, for a light microscope the resolving power is 200nm and it is not possible to see a ribosome under it but what are the two points they mean in the definition? Two opposite points on the diameter of the ribosome or a point on the ribosome diameter and the cytoplasm?? or do they mean that the distance between two points( two organelles ) should be greater than 200nm for them to be visible? Anybody please help me with this query for I'm really confused with a concise and acceptable explanation.... I would be really grateful :)
 
phanttasy

phanttasy

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Bhaijan said:
Hey there,
Is endodermis found only in roots;
if it is found in stems also then where are they located?
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In many seedless vascular plants, the endodermis is a distinctly visible layer of cells immediately outside the vascular cylinder (stele) in roots and shoots. In most seed plants, especially woody types, an endodermis is absent from the stems but is present in roots.
 
techgeek

techgeek

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zeejay said:
Salam everyone,
I have a query to solve regarding microscopic resolution. I know that resolution is the ability to distinguish between two points close together. But what are those two points??? example, for a light microscope the resolving power is 200nm and it is not possible to see a ribosome under it but what are the two points they mean in the definition? Two opposite points on the diameter of the ribosome or a point on the ribosome diameter and the cytoplasm?? or do they mean that the distance between two points( two organelles ) should be greater than 200nm for them to be visible? Anybody please help me with this query for I'm really confused with a concise and acceptable explanation.... I would be really grateful :)
Click to expand...
By the resolution of light microscope being 200 nm means that if two objects are closer together than 200 nm, they wouldn't be distinguishable as two, under the light microscope. Why we are unable to see a ribosome under a light microscope is because, it's diameter being 22 nm, is far less than half the wavelength of the light radiation. Since the light has wavelength of 400 nm, anything smaller than 200 nm (half the wavelength of the radiation used to view the specimen) can't be seen by light.
 
Z

zeejay

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techgeek said:
By the resolution of light microscope being 200 nm means that if two objects are closer together than 200 nm, they wouldn't be distinguishable as two, under the light microscope. Why we are unable to see a ribosome under a light microscope is because, it's diameter being 22 nm, is far less than half the wavelength of the light radiation. Since the light has wavelength of 400 nm, anything smaller than 200 nm (half the wavelength of the radiation used to view the specimen) can't be seen by light.
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Thanks :)... but part of my question still remains unanswered.(n)
 
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