Water Flow In Phleom

Question 1

Why is the name of water transport in phleom

Answer 1

Translocation

Question 2

What direction does the phloem transport wate r

Answer 2

Either direction

Question 3

What is the phloem transport

Answer 3

Sugars produced from photosynthesis

Question 4

What theory is used to describe transport in phloem

Answer 4

Mass flow theory

Question 5

What is the mass flow hypothesis for mechanisms of translocation

Answer 5

• in source sugars actively transported into phloem by companion cells
• lowers wp of sieve tube and water enter via osmosis
• increased pressure causes mass movement towards sink
• sugars used in roots for respiration for storage

Question 6

What 3 things that are a part of translocation

Answer 6

• companion cells
• sieve tubes
• sink

Question 7

Describe the sink

Answer 7

Part of the plant that uses sucrose eg respiring tissues

Question 8

Describe the source

Answer 8

Produces sucrose eg leaf

Question 9

Describe how sugar are transported from source to sink

Answer 9

1) Solutes, e.g. sucrose produced by the source diffuses into the companion cells by facilitated diffusion. In here, sucrose is actively transported into the sieve tube elements using ATP.
2) This decreases the water potential of the sieve tubes, causing water from the companion cells and the xylem to diffuse into the phloem by osmosis, increasing the hydrostatic pressure.
3) Near the sink, sucrose is either used up or converted to starch for storage. Either way, this decreases the water potential of the sink.
4) As a result, water diffuses from the sieve tubes into the sink by osmosis, decreasing the hydrostatic pressure in the phloem.
5) As a result, there is a high hydrostatic pressure gradient as there’s a high hydrostatic pressure near the companion cells and a low hydrostatic pressure near the sink. Therefore, we have a mass flow of solutes throughout the plant.

Question 10

How is a high hydrostatic pressure created in the leaves

Answer 10

• wp becomes lower a sugars enters phloem via osmosis

- increase volume of water increases the pressure

Question 11

How are companion cells adapted

Answer 11

Have many mitochondria release ATP for active transport

Question 12

How are sieve tubes adapted

Answer 12

Few organelles allows for more flow

Question 13

How does sucrose near the phloem

Answer 13

• Sucrose moves via facilities diffusion with H+ into the companion cell from the source cell
• H+ actively transported out
• sucrose moves into phloem sieve elements by facilitated diffusion

Question 14

Evidence against mass flow

Answer 14

• Sieve plates don’t make sense
• not always the sink with the lowest water potential
• organic molecules move at different speeds

Question 15

Evidence for mass flow

Answer 15

• ringing experiment
• tracer experiment
• metabolic experiment
• aphids

Question 16

Metabolic experiment

Answer 16

• inhibit respiration
• translocation doesn’t occur
• shows that ATP is required

Question 17

Tracer experiment

Question 18

Ringing experiment