• We need your support!

    We are currently struggling to cover the operational costs of Xtremepapers, as a result we might have to shut this website down. Please donate if we have helped you and help make a difference in other students' lives!
    Click here to Donate Now (View Announcement)

A level Biology: Post your doubts here!

shingiechingz@8

shingiechingz@8

Messages
112
Reaction score
24
Points
28
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?
Click to expand...
in my country we are based on the old papers [CIE SYLLABUS] 1998
 
M

My Name

Messages
4,988
Reaction score
23,955
Points
523
Can anyone tell me what are the main/repeated questions that come from the nervous system chapter for A2?
 
M

My Name

Messages
4,988
Reaction score
23,955
Points
523
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

Messages
46
Reaction score
49
Points
28
Hey there,
Is endodermis found only in roots;
if it is found in stems also then where are they located?
 
Z

zeejay

Messages
47
Reaction score
7
Points
18
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

Messages
38
Reaction score
22
Points
18
Bhaijan said:
Hey there,
Is endodermis found only in roots;
if it is found in stems also then where are they located?
Click to expand...
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

Messages
187
Reaction score
976
Points
103
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

Messages
47
Reaction score
7
Points
18
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.
Click to expand...
Thanks :)... but part of my question still remains unanswered.(n)
 
You must log in or register to reply here.
Top