12.13 Mass transport in plants

Question 1

Mass transport definition

Answer 1

The bulk movement of substances from one area of an organism to another area of the same/similar rate

Question 2

What tissue and what direction is the cohesion tension theory found in?

Answer 2

The xylem
Upwards, from the shoots to the leaves

Question 3

What tissue and in which direction is the mass flow hypothesis found in?

Answer 3

The phloem and in any direction, from source to sink

Question 4

How does water enter into the plant?

Answer 4

Through the root hair cells within the epidermis by osmosis

Question 5

How are root hair cells adapted?

Answer 5

• Hair like extensions which increases the surface area to increase the area of carrier and channel proteins
• Have thinner cellulose walls too decreases the diffusion distance
• Actively transport ions using energy from the hydrolysis of ATP via carrier proteins

Question 6

Describe the structure of the xylem tissue

Answer 6

• Dead cells that form hollow tubes with no cytoplasm
• End walls break down so xylem forms a continuous tube with no end walls
• Xylem pits
• Cells walls are strengthened with lignin

Question 7

Describe the function of the dead cells that form hollow tubes

Answer 7

Faster water flow with less resistance

Question 8

Describe the function of the end walls breaking down to form continuous tubes

Answer 8

A continuous column of water can form due to cohesion

Question 9

Describe the function of the cell walls being strengthened with lignin

Answer 9

This makes the xylem waterproof and rigid to provide support

Question 10

Describe the function of xylem pits

Answer 10

Little holes that allow water too move laterally between xylem vessels and to get around blocked vessels

Question 11

Describe the cohesion tension theory

Answer 11

1. Water evaporates from the leaves
2. This lowers the water potential in the leaf cells
3. Water replaced by the xylem
4. Water potential gradient creates tension
5. Hydrogen bonds/cohesion/adhesion maintain continuous column of water

Question 12

Describe transcription

Answer 12

1. Stomata open which causes water to diffuse from the air spaces act a higher water potential inside the leaf to a lower water potential of the air outside the leaf
2. The loss of water causes water to move down the water potential gradient from the mesophyll to the air spaces
3. This lowers the water potential of the mesophyll cells so water moves across from adjacent mesophyll cells
4. this sets up a water potential gradient across the leaf to the xylem vessels
5. Water from the xylem enters the leaf sonf causes water to be pulled up under tension through the xylem from the roots
6. Water forms a continuous column in the narrow xylem vessels
7. water form weak hydrogen bonds between them, so they stuck together
8. They are also attracted to the walls of the xylem (adhesion)
9. The column of water is under tension
10. The movement of water through the plant from the roots to the leaves is known was the transpiration stream

Question 13

Root pressure moves water through the xylem. Describe what causes root pressure

Answer 13

Active transport of the ions into the xylem by the endodermis. This lowers the water potential in the xylem. water enters by osmosis

Question 14

Describe how a high pressure is produced in the leaves

Answer 14

The water potential becomes more negative as sugar enters the phloem. Water enters phloem by osmosis.
This increases volume of water increases the pressure in the leaves

Question 15

What are the factors that affect the rate of transpiration?

Answer 15

Light intensity
Temperature
Humidity
Wind speed
Stomatal density