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a level biology

Hi, I have a question:

So during translocation, is the sucrose activaly transported or co-transported into the sieve-tube element. I thought it was co-transported by H+ ions from the companion cell to the sieve-tube but the mark scheme im looking at says its actively transported?
Original post by jivinion
Hi, I have a question:
So during translocation, is the sucrose activaly transported or co-transported into the sieve-tube element. I thought it was co-transported by H+ ions from the companion cell to the sieve-tube but the mark scheme im looking at says its actively transported?

ATP is used first, to pump H+ out of the companion cell (its the reason why companion cell has many mitochondria, to produce ATP for energy) as well as a folded membrane (increase surface area, so more carrier proteins).

Although a carrier protein co-transports H+ and sucrose into the companion cell, the concentration gradient for H+ required for this is maintained by active transport.

Active transport is used to create a concentration gradient for __. Then, it passively diffuses with another substance (x). Although x passively diffuses, this needs the previous active transport step.

It is co-transport. Co-transport is active transport coupled by facilitated diffusion.
(edited 10 months ago)
Reply 2
Original post by BankaiGintoki
ATP is used first, to pump H+ out of the companion cell (its the reason why companion cell has many mitochondria, to produce ATP for energy) as well as a folded membrane (increase surface area, so more carrier proteins).
Although a carrier protein co-transports H+ and sucrose into the companion cell, the concentration gradient for H+ required for this is maintained by active transport.
Active transport is used to create a concentration gradient for __. Then, it passively diffuses with another substance (x). Although x passively diffuses, this needs the previous active transport step.
It is co-transport. Co-transport is active transport coupled by facilitated diffusion.

ohh ok, thank you so much!

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