9.4 Transloaction

Question 1

Where and how do plants transport organic compounds?

Answer 1

Plants transport organic compounds in the phloem from sources to sinks in a process called translocation

Question 2

Is translocation an active or passive process

Answer 2

Translocation is an active process that requires energy to take place so substances can be transported up and down the plant

Question 3

Assimilates

Answer 3

Products of photosynthesis

Question 4

What is sucrose

Answer 4

the main assimilate transported around the plant. it is mainly found in cell sap

Question 5

What are the main sources in the plant

Answer 5

-Green leaves and green stems
- Storage organs such as tubers and tap roots that are unloading their stores
- food stores in seeds when they germinate

Question 6

What are the main sinks in the plant

Answer 6

-Roots that are growing or absorbing mineral ions
- meristems that are dividing
-storage organs

Question 7

What route is used the most in active loading of the phloem

Answer 7

the apoplast route

Question 8

How does sucrose travel in the plant

Answer 8

Sucrose from the source travels through the cell walls and inter cell spaces to the companion cells and sieve elements through the apoplast route.

Question 9

How is sucrose moved into the cytoplasm or companion cells

Answer 9

Uses energy in an active process. H+ ions are actively pumped out the companion cell into the surrounding tissue using ATP. The hydrogen ions return to the companion cell down the concentration gradient via a co transport protein. Sucrose is co transported which increase the concentration of sucrose in the companion cells through the many plasmodesmata between the 2 cells.

Question 10

How do companion cells increase there surface area

Answer 10

Companion cells have many infolding to increase the SA for the active transport of sucrose into the cell cytoplasm.

Question 11

Why do companion cells have a lot of mitochondria

Answer 11

To supply the ATP needed for the transport pumps

Question 12

What causes water to move in to companion cells by osmosis?

Answer 12

The build up of sucrose in the companion cell causes water potential to drop so water moves in by osmosis. This causes a build up of turgor pressure

Question 13

Where does the water carrying the assimilates go?

Answer 13

Moves into the tubes of the sieve elements reducing the pressure in the companion cells. They then move up and down the plant by mass flow to sinks

Question 14

Where does phloem unloading occur

Answer 14

In the sinks for example a cell

Question 15

What is the main mechanism of phloem unloading

Answer 15

Diffusion of sucrose from the phloem into other cells by diffusion or converted into another substance for example glucose for respiration starch for storage. This maintains a concentration gradient of sucrose is maintained between contents of the phloem and surrounding cells

Question 16

What does the loss of solutes from the phloem lead to

Answer 16

A rise in the water potential of the phloem. Water moves out into surrounding cells via osmosis. Some water moves into the xylem