translocation- transport in plants

Question 1

define translocation

Answer 1

• the process where plants transport organic compounds from source to sink
• is an active process in many plants
• the products of photosynthesis which are transported are called assimilates, the main one transported around the plant is sucrose

Question 2

main sources in plants

Answer 2

• green leaves and green stems
• storage organs e,g tubers
• food stores in seeds where they need to germinate

Question 3

main sinks in plants

Answer 3

• roots that are growing or actively absorbing mineral ions
• meristems that are actively dividing
• developing seeds, fruits or storage organs

Question 4

2 main routes in which plant load assimilates into the phloem

Answer 4

• apoplast route

- symplast route

Question 5

symplast route

Answer 5

• largly passive route
• the sucrose moves through the cytoplasm of the mesophyll cells and on into the sieve tubes by diffusion through the plasmodesmata
• the sucrose ends up in the sieve elements and water follows by osmosis. This creates a pressure of water that moves sucrose through the phloem by mass flow

Question 6

apoplast route

Answer 6

• active route
• sucrose from source travels through the cell walls and intercellular spaces to the companion cells and sieve elements by diffusion
• in the companion cells sucrose is moved into the cytoplasm across the cell membrane
• hydrogen ions are actively pumped out of the companion cell into the surrounding tissue
• the hydrogen ions return to the companion cell down a conc gradient via a co transport protein
• this increases the sucrose conc in companion cells and sieve elements
• as a result of the build upof sucrose, water moves in= a build up of turgor pressure
• the water moves into the tubes of the sieve elements, reducing pressure and moves up and down plant by mass floe

Question 7

phloem unloading

Answer 7

• sucrose diffuses from phloem into surrounding cells and is converted into another substance e.g glucose or starch so the conc gradient of sucrose is maintained
• the loss of the solutes from the phloem lead to a rise in the water potential of the phloem. water moves out into surrounding cells by osmosis