translocation

translocation (2)

The movement of assimilates in the phloem from the source to sink. It requires energy.

assimilates

Substances made by the plant, such as sucrose and amino acids, that are transported around the plant in the phloem

-name the most common sugar in translocation and why

-how is it produced

-sucrose bcs it is soluble→so is easily transported in phloem sap

-glucose is converted to sucrose

what does translocation require and why?

requires energy for active transport of assimilates into the phloem.

-what is a source? example?

-what is a sink? example? (2)

-part of the plant where assimilates are made

e.g. leaves

-part of the plant where assimilates are used or stored

e.g. roots and meristem

what does enzymes at the sink do?

maintains a concentration gradient from the source to the sink by converting sucrose into other substances. This lowers sucrose concentration in the sink.

theory that links to translocation and what does it explain

mass flow hypothesis

-explain how assimilates are transported in the phloem from the source to sink

note: mass flow→the movement of substances from an area of high pressure to an area of low pressure.

active loading

-Hydrogen ions (H⁺) are actively transported out of companion cells into surrounding cells using ATP

-this creates a concentration gradient with a high concentration of H⁺ ions outside the companion cell.

-H⁺ ions diffuse back into the companion cell down their concentration gradient through a cotransporter protein.

-Sucrose moves in with H⁺ ions by facilitated diffusion

-sucrose diffuses into the sieve tube through plasmodesmata

Movement of assimilates along phloem by mass flow

-assimilates enter the sieve tube at the source, lowering water potential in sieve tube

-Water enters sieve tube by osmosis, increasing hydrostatic pressure

-assimilates leave the sieve tube at the sink, increasing water potential in sieve tube

-Water leaves the sieve tube by osmosis, lowering hydrostatic pressure.

-This creates a pressure gradient, causing assimilates to move from source to sink by mass flow

What occurs at the source during translocation?

What occurs at the sink during translocation?

-assimilates are actively loaded into phloem

-assimilates are actively unloaded from phloem