Mass Transport in Plants

Question 1

What is transpiration?

Answer 1

The evaporation of water from the leaves, through the stomata

Question 2

What is cohesion?

Answer 2

Water molecules stick together because they are polar

Question 3

What does the xylem do?

Answer 3

Transports water and minerals up the plant

Question 4

What is the structure of the xylem?

Answer 4

1. Hollow tube made of dead cells
2. No end cell walls

Question 5

Describe the cohesion - tension theory of water.

Answer 5

1. Transpiration of water through the stomata creates low pressure at the top of the xylem
2. Water in the xylem is pulled up creating tension
3. As the water molecules stick together via cohesion
4. Water molecules are sucked up to the leaves

Question 6

How does temperature affect Transpiration?

Answer 6

Higher temperatures increase the rate of transpiration as water evaporates quicker

Question 7

How does light affect the rate of transpiration?

Answer 7

More stomata open when there is more light and more water is used up

Question 8

How does humidity affect the rate of transpiration?

Answer 8

The higher the humidity the lower that rate as there is less of a conc gradient for the water to evaporate

Question 9

How does wind affect the transpiration rate?

Answer 9

Blows away the humid air around a plant away allowing for a steep conc gradient to be maintained thereby increasing rate

Question 10

What is the purpose of the phloem?

Answer 10

Transports Glucose and amino acids up and down the plant

Question 11

What is the structure of Phloem?

Answer 11

1. Sieve tube cells
2. Companion Cells

Question 12

What is the purpose of the companion cell?

Answer 12

1. Supports the sieve tube cell
2. Provides ATP as sieve tube cells have no mitochondria

Question 13

How would you use radioactive labelling to provide evidence for mass flow hypothesis?

Answer 13

1. Use radioactive C14 labelling
2. Grow plants in a C14 atmosphere
3. Measure C14 as it moves down the stem

Question 14

How would you use a ringing experiment to provide evidence for mass flow hypothesis?

Answer 14

1. Remove bark in a ring from the tree trunk
2. Solutes cant move up or down
3. Bulge forms above the ring
4. Fluid above the ring has more solutes than below - this is evidence that the solutes are moving down