Qualification > Sciences
ALL CIE BIOLOGY DOUBTS HERE !!!
Arthur Bon Zavi:
--- Quote from: Deadly_king on November 14, 2010, 10:40:23 am ---You should expanded your knowledge outside the syllabus during the whole year and not just before exams ;D
--- End quote ---
When did I tell, only before exams ? :P
--- Quote ---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. ;)
--- End quote ---
Same what I said...But in a different manner. :D
Deadly_king:
--- Quote from: Ancestor on November 14, 2010, 10:48:11 am ---When did I tell, only before exams ? :P
Same what I said...But in a different manner. :D
--- End quote ---
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:
--- Quote from: Dania on November 15, 2010, 04:34:37 pm ---How do companion cells load sucrose into sieve tube elements?
--- End quote ---
--- Quote --- * 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.
--- End quote ---
http://en.wikipedia.org/wiki/Phloem
Deadly_king:
--- Quote from: Dania on November 15, 2010, 04:34:37 pm ---How do companion cells load sucrose into sieve tube elements?
--- End quote ---
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 :)
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version