Mass Transport In Plants

Question 1

Compare the similarities and differences of the xylem and phloem?

Answer 1

Differences
Xylem is unidirectional (only moves substances up) phloem is bidirectional (moves substances up and down)
Xylem transports water phloem transports food and other organic substances
Xylem made of dead cells phloem made of living cells
Phloem contains sieve tubes xylem does not
Similarities
Both made of cells
Both involved in movement of substances

Question 2

Define translocation

Answer 2

The process used to transport dissolved products in the phloem, from areas of excess to an area where it is needed

Question 3

Explain the mass flow hypothesis

Answer 3

States that mass flow of solutes takes place in the phloem
Sucrose is actively transported into the phloem lowering the water potential so water moves into phloem by osmosis from xylem

Question 4

Phloem pressure is reduced during the hottest part of the day. Explain why

Answer 4

High rate of transpiration so water is lost through stomata
This means there is less water movement from xylem to phloem

Question 5

Define transpiration

Answer 5

The loss of water vapour from plant leaves by evaporation of water on the surface of cells and the diffusion of water vapour through the stomata

Question 6

What is the cohesion tension theory ?

Answer 6

Due to the dipolar nature of water, hydrogen bonds are formed between water molecules, creating cohesion. This results in water forming a continuous column in the plant stem. Tension is created when water evaporates out of the stomata

Question 7

What is the cohesion tension theory ?

Answer 7

Due to the dipolar nature of water, hydrogen bonds are formed between water molecules, creating cohesion. This results in water forming a continuous column in the plant stem. Tension is created when water evaporates out of the stomata