ALL CIE BIOLOGY DOUBTS HERE !!!

[Deadly_king]

Thank You, DK!
Oh, I was doing a past paper this morning and there were questions on drug tolerance and caffeine and what not? I don't think that's in the 2010 CIE syllabus, right?

Yeah it has been removed.

I guess you're doing old papers.

[Dania]

Yeah it has been removed.

I guess you're doing old papers.

Yes, it's a 2003 paper. I'll just skip it. Thanks

[Dania]

What role do the "papillary muscles" have in the initiation, coordination & the contraction of the heart.

[Deadly_king]

What role do the "papillary muscles" have in the initiation, coordination & the contraction of the heart.

Papillary muscle: Small muscles within the heart that anchor the heart valves.

Are you sure this is found in the syllabus

To tell the truth, i've never come across it.

[Dania]

I've never come across it either. But in some mark schemes they are some references to it so I was just wondering. Thank you, though. I'll look into it.

[Deadly_king]

I've never come across it either. But in some mark schemes they are some references to it so I was just wondering. Thank you, though. I'll look into it.

Ooh.........but i don't think we need to know about it.

Just focus on those in the syllabus.

[Arthur Bon Zavi]

Ooh.........but i don't think we need to know about it.

Just focus on those in the syllabus.

Do we only have to do, which is there in the syllabus ? You never know !

[Deadly_king]

Do we only have to do, which is there in the syllabus ? You never know !

That's true.

But it's highly improbable to get thing outside the syllabus.

I said to focus on the syllabus since the majority if not all of the questions for the exams comes from there.

[Arthur Bon Zavi]

That's true.

But it's highly improbable to get thing outside the syllabus.

I said to focus on the syllabus since the majority if not all of the questions for the exams comes from there.

That's right, take it as 99%, from the syllabus. When I sat CIE IGCSE Chemistry (0680), past May/June, there came a question about cyclo-alkene, of which topic was not present in syllabus, though answers were not related to that ! But for general, get doing extra things which are out of the syllabus, it will enable to catch questions comfortably.

[Deadly_king]

That's right, take it as 99%, from the syllabus. When I sat CIE IGCSE Chemistry (0680), past May/June, there came a question about cyclo-alkene, of which topic was not present in syllabus, though answers were not related to that ! But for general, get doing extra things which are out of the syllabus, it will enable to catch questions comfortably.

You should expanded your knowledge outside the syllabus during the whole year and not just before exams

Anyways even if something outside the syllabus comes out, it's usually easy for it's either general knowledge or they give you some notes about it before asking the questions in the paper itself.

[Arthur Bon Zavi]

You should expanded your knowledge outside the syllabus during the whole year and not just before exams

When did I tell, only before exams ?

Anyways even if something outside the syllabus comes out, it's usually easy for it's either general knowledge or they give you some notes about it before asking the questions in the paper itself.

Same what I said...But in a different manner.

[Deadly_king]

When did I tell, only before exams ?

Same what I said...But in a different manner.

That was not specifically for you. Rather for Dania since both her and i are on the eve of exams.

If you say so.

[Dania]

How do companion cells load sucrose into sieve tube elements?

[elemis]

How do companion cells load sucrose into sieve tube elements?

    * Sieve tube elements: These are living, tubular cells that are connected end to end. The end cell walls have perforations in them to make sieve plates. The cytoplasm is present but in small amounts and in a layer next to the cell wall. It lacks a nucleus and most organelles so there is more space for solutes to move. The cell walls are made of cellulose so solutes can move laterally a well as vertically. Next to each sieve tube element is a companion cell.
    * Companion cell: Since the sieve tube element lacks organelles, the companion cell with its nucleus, mitochondria, ribosomes, enzymes etc., controls the movement of solutes and provides ATP for active transport in the sieve tube element. Strands of cytoplasm called plasmodesmata connect the sieve tube element and companion cell.
    * Parenchyma: Provides support through turgidity.
    * Fibres: Provides support for the sieve tube elements.

http://en.wikipedia.org/wiki/Phloem

[Deadly_king]

How do companion cells load sucrose into sieve tube elements?

The sucrose id first loaded into the companion cell by active transport, using a protein molecule in the cell membrane as carrier or transporter. The latter pump out hydrogen ions actively. This creates a high concentration of H⁺ ions outside the companion cell.

Now the H⁺ ions diffuse back into the companion cell using a protein carrier down its concentration gradient. The latter move sucrose at the same time as the H⁺ ions. But the sucrose moves against its concentration gradient.

In other words, sucrose is being co-transported along with the H⁺ ions. The sucrose moves into the adjacent sieve tube elements through the plasmodesmata.

Hope it helps