AS LEVEL BIOLOGY... discuss here AS students only :)

[Mariam Mohamed SX132]

Can anyone help me ^_^ Somebody please explain to me how the plant transports sucrose from the source to the sink?

Mechanism of loading:
1) Hydrogen ions are actively transported outside companion cells to reach mesophyll cells.
2) Hydrogen ions return back down their concentration gradient forcing sucrose with them through co-transporter proteins.
3) Sucrose diffuses through plasmodesmata from companion cells to sieve tube as its concentration in companion cell is higher.
4) Sucrose in phloem causes it be of lower water potential, therefore water enters by osmosis from the surrounding cells creating high hydrostatic pressure in phloem at region of loading so water with sucrose and amino acids flow to region of low hydrostatic pressure (this is known as mass flow).
I studied this from a study guide I got!It was really helpful hope it helps you too! Good luck <3

 

[deane26]

Can anyone help me ^_^ Somebody please explain to me how the plant transports sucrose from the source to the sink?

Presence of sucrose in the sieve tube element at (source) lowers the water potential. Therefore water moves down conc gradient from xylem to sieve tube cell via osmosis. Entry of water increases volume, hence high hydrostatic pressure. At (sink) sucrose is removed from sieve tube element into surrounding cells (they need it for energy or respiration). At this point the loss of sucrose means now it has higher water potential. Water moves out down conc gradient via osmosis, hence lower hydrostatic pressure. This differences in pressure causes solutes(sucrose) move from high pressure to low pressure.

 

[ankemol]

How do you guys get a good grade in biology? I understand the whole concept but still get an U (resitting the bio unit 1 and 2)
so heartbroken. because bio is my favourite subject. What should I do any help please?

 

[Irfan1995]

Guys could you help me what happens during closing of stoma in reference to the K+ ion and water potential. Thanks.

When guard cells are turgid (full of water), they are open, and when they're flaccid (no water), they're closed.

K+ ions are actively transported out of guard cells
This decreases the water potential outside
Water leaves from the guard cells to outside by osmosis
The guard cells become flaccid
The stomata will close

I think that's all the details you need to know for AS.

 

[deane26]

How do you guys get a good grade in biology? I understand the whole concept but still get an U (resitting the bio unit 1 and 2)
so heartbroken. because bio is my favourite subject. What should I do any help please?

I got a C for AS and retaking.

 

[Jinkglex]

I got a C for AS and retaking.

your chromosome graph might be wrong, the sister chromatids are the side-by-side long chains, not the above and below chains, atleast thats what it looks like you drew

 

[deane26]

your chromosome graph might be wrong, the sister chromatids are the side-by-side long chains, not the above and below chains, atleast thats what it looks like you drew

Thanks but I already mentioned that one chromosome contains two sister chromatids not four hehehe.

 

[Mariam Mohamed SX132]

Can someone please explain the mutalistic relationship in the ecology unit?

 

[MÁťT PŭמҚ]

can some1 explain me the interpretation of Meselsohn-Stahl experiments on semi-conservative replication of DNA..!!

 

[daredevil]

Can someone please explain the mutalistic relationship in the ecology unit?

uhh come again?? :O wats that?? not sure i heard of it in AS :O

 

[Jinkglex]

I think he means where the parasite and host both benefit from each other like rhizobium and a few trees which need nitrogen in nitrogen-scarce areas....but i dont think that relationship is part of AS or even A2.

 

[Irfan1995]

Can someone please explain the mutalistic relationship in the ecology unit?

A mutualistic relationship is when both parties benefit from each other.
For example, in legumes, you have nitrifying bacteria that can fix nitrogen (make nitrogen gas in the atmosphere to nitrate ions which plants can use), but they can't make their own food.
Also, legumes can make their own food, but they can't get any nitrogen (required to synthesize proteins)
So nitrifying bacteria (e.g. Rhizobium) house themselves in nodules in legumes. The nitrifying bacteria get food from the plant, and in return, they provide the plant with usable nitrogen.

 

[daredevil]

I think he means where the parasite and host both benefit from each other like rhizobium and a few trees which need nitrogen in nitrogen-scarce areas....but i dont think that relationship is part of AS or even A2.

A mutualistic relationship is when both parties benefit from each other.
For example, in legumes, you have nitrifying bacteria that can fix nitrogen (make nitrogen gas in the atmosphere to nitrate ions which plants can use), but they can't make their own food.
Also, legumes can make their own food, but they can't get any nitrogen (required to synthesize proteins)
So nitrifying bacteria (e.g. Rhizobium) house themselves in nodules in legumes. The nitrifying bacteria get food from the plant, and in return, they provide the plant with usable nitrogen.

soo r we required to know that by name... well actually now i come to think of it the name was pretty self explanatoyr but still is there a need for us to know it??

 

[daredevil]

ok me gonna go now... gud nyt....
we will hopefully continue this convo tomorrow

 

[MÁťT PŭמҚ]

Can someone please explain the mutalistic relationship in the ecology unit?

THE plant supplies living space, and the conditions required for bacteria to fix nitrogen . the bacteria supply the plant with fixed nitrogen . this is an example of mutualism , in which two organisms of different species live very closely together each meeting some of the other's need..

 

[Irfan1995]

can some1 explain me the interpretation of Meselsohn-Stahl experiments on semi-conservative replication of DNA..!!

This is kinda hard to explain, so please bear with me.
1) You get a colony of bacteria to grow for many generations in a petri dish full of N15. So all the bacteria will have DNA that's made from N15.
2) For the next generation, breed those bacteria in a culture of N14. Remember that DNA has two strands, and when they divide, the strands break up and new nucleic acids add to them. So the two N15 strands break up and an N14 strand is added to each of them. Now, all bacteria would have DNA with one strand made up of N15 and the other from N14.
3) Continue to culture the bacteria in an N14 solution. Here's what will happen:

• You will have a strand of DNA (made from N15-N14) and this will break up.
• N14 strands will be built up on each of them.
• So you'll have one strand that's N15-N14 and another strand which is N14-N14
• So 50% of the DNA will be N15-N14 and 50% will be pure N14

4) Continue the same process:

• You have two strands of DNA. One of them is N15-N14, the other is N14-N14
• Both helixes will break up and N14 will add to all of them.
• So you're left with N15-N14, N14-N14, N14-N14, N14-N14.
• So 25% of the DNA will be N15-N14, and 75% will be pure N14.

5) When you look at them using the test-tube method, remember that the mass of N15-N15>N15-N14>N14-N14
Also, the heavier one will be found lower, and the lighter one will be found higher.
So if you look at the Mary Jones book (in the blue box, can't remember the page), you will see how it started purely from N15-N15 (really low), then the next generation is purely N15-N14 (the sector shifted up), then 50% of each (so it splits in two), and then 75%-25% (so more from the lower region goes to the higher region, so the lower region is thinner and the higher region is thicker).
Sorry for the long post, but I hope that makes sense

 

[MÁťT PŭמҚ]

This is kinda hard to explain, so please bear with me.
1) You get a colony of bacteria to grow for many generations in a petri dish full of N15. So all the bacteria will have DNA that's made from N15.
2) For the next generation, breed those bacteria in a culture of N14. Remember that DNA has two strands, and when they divide, the strands break up and new nucleic acids add to them. So the two N15 strands break up and an N14 strand is added to each of them. Now, all bacteria would have DNA with one strand made up of N15 and the other from N14.
3) Continue to culture the bacteria in an N14 solution. Here's what will happen:

• You will have a strand of DNA (made from N15-N14) and this will break up.
• N14 strands will be built up on each of them.
• So you'll have one strand that's N15-N14 and another strand which is N14-N14
• So 50% of the DNA will be N15-N14 and 50% will be pure N14

4) Continue the same process:

• You have two strands of DNA. One of them is N15-N14, the other is N14-N14
• Both helixes will break up and N14 will add to all of them.
• So you're left with N15-N14, N14-N14, N14-N14, N14-N14.
• So 25% of the DNA will be N15-N14, and 75% will be pure N14.

5) When you look at them using the test-tube method, remember that the mass of N15-N15>N15-N14>N14-N14

Also, the heavier one will be found lower, and the lighter one will be found higher.
So if you look at the Mary Jones book (in the blue box, can't remember the page), you will see how it started purely from N15-N15 (really low), then the next generation is purely N15-N14 (the sector shifted up), then 50% of each (so it splits in two), and then 75%-25% (so more from the lower region goes to the higher region, so the lower region is thinner and the higher region is thicker).
Sorry for the long post, but I hope that makes sense

gr8..!! Thnkxx dude..

 

[Mariam Mohamed SX132]

Thank you guys! Well I remember taking something called a mutualistic relationship but i forgot to write notes about it and didnt find it in my study guide!

 

[shafayat]

(iii) After circulating in the blood for a short time, the pathogen enters liver cells of the
newly infected person and then enters red blood cells.
why does it enter the liver cell ..?

.

 

[shafayat]

how to identify the different cells in immune system ! like b plasma , neutrophil , macrophage etc