Lesson 12 - Water transport in plants

Question 1

Why is water transport in plants significant?

Answer 1

do not have a muscular heart beating to move fluids through the vessels of the xylem and phloem.

Question 2

Turgor pressure?

Answer 2

Hydrostatic pressure.

Question 3

What causes turgor pressure?

Answer 3

Osmosis in plant cell provides a hydrostatic skeleton to support the stems and leaves.

Question 4

What does turgor pressure cause?

Answer 4

Cell expansion. It is the force that enables the plant roots to force their way through tarmac and concrete.

Question 5

What is the purpose of water loss?

Answer 5

Keeps plants cool.

Question 6

How are mineral ions and the products of photosynthesis transported?

Answer 6

In aqueous solution.

Question 7

How is water used in photosynthesis?

Answer 7

Reactant.

Question 8

Where is water taken into the roots from the soil?

Answer 8

Root hair cells

Question 9

What is a root hair?

Answer 9

A long , thin extension from a root hair cell. Specialised epidermal cell found near growing root tip.

Question 10

What is a root hair cell?

Answer 10

Specialised cells responsible for the uptake of water and minerals from the soil. They have long hair-like extensions known as root hairs, which are adapted as exchange surfaces.

Question 11

Adaptations of root hairs?

Answer 11

• Microscopic size means that they can penetrate easily between soil particles.
• Each microscopic hair has a large SA:V and there are millions growing on each root tip.
• Thin surface layer through which diffusion and osmosis can take place quickly.
• Concentration of solutes in the cytoplasm of root hair cells maintains water potential gradient between the soil water and the cell.

Question 12

Soil water:

Answer 12

has a very low concentration of dissolved minerals so it has a very high water potential.

Question 13

Cytoplasm and vacuolar sap:

Answer 13

contains many different solvents, including sugars, mineral ions and amino acids so the water potential in the cell is lower.

Question 14

Transport to the xylem:

Answer 14

• apoplast pathway
• symplast pathway

Question 15

Symplast?

Answer 15

Continuous cytoplasm of the living plant cells that is connected through the plasmodesmata. Moves water through the cortex.

Question 16

How does water move through the symplast?

Answer 16

Osmosis

Question 17

Explain the movement of water through the symplast?

Answer 17

Root hair cell has a higher water potential than the next cell along. Water moves through a partially permeable membrane, down the water potential gradient, in a net movement, via osmosis.

Question 18

How is the water potential gradient maintained?

Answer 18

As water leaves the root hair cell by osmosis, the water potential in the root hair cell cytoplasm decreases. Water continues to move from the soil into the root hair cell.

Question 19

Why is the symplast pathway relatively slow?

Answer 19

Pathway for water in the cytoplasm is obstructed by cell organelles.

Question 20

Where does water move in the apoplast pathway?

Answer 20

Through cell walls and intercellular spaces.

Question 21

How does water move through the cell wall in the apoplast pathway?

Answer 21

Water fills spaces between loose, open network of fibres in cellulose cell wall.

Question 22

Movement of water through the apoplast pathway?

Answer 22

As water molecules are pulled into the xylem, more cell molecules are pulled through the apoplast pathway due to cohesive forces between water molecules.

Question 23

Resistance in cell wall? Why?

Answer 23

Little to no resistance.
This is due to cohesive forces between molecules that create tension causing continuous flow through open structure.

Question 24

Features of the endodermis?

Answer 24

• Layer of cells surrounding the vascular tissue (xylem and phloem) of the roots.
• Casparian strip

Question 25

Casparian strip:

Answer 25

Band of waxy material called suberin. Runs around each of the endodermal cells creating a waterproof layer.

Question 26

Result of the casparian strip?

Answer 26

• Water in the apoplast pathway is forced into the cytoplasm of the cell, joining water in the symplast pathway.

Question 27

Movement from apoplast to symplast pathway?

Answer 27

Water passes through selectively permeable cell surface membrane. This prevents any potentially-toxic material from reaching living tissues (membranes have no carrier proteins to admit them).

Question 28

Movement of water from symplast to xylem?

Answer 28

Solute concentration in the cytoplasm of endodermal cells is relatively dilute in comparison to the cells in the xylem.

Endodermal cells move mineral ions into the xylem by active transport.

Question 29

Result of mineral ions transported into the xylem?

Answer 29

Water potential in xylem cells is much lower than in endodermal cells.
This increases the rate of diffusion.

Question 30

What happens when water enters the vascular bundle?

Answer 30

Water returns to apoplast pathway until it reaches the xylem.

Question 31

What is the system that water enters xylem with?

Answer 31

Root pressure

(Not transpiration)

Question 32

Why is root pressure an active process?

Answer 32

Active transport used to transport mineral ions from the endodermis cells to xylem.

Question 33

Evidence for role of active transport in root pressure?
- Poisons that effect the rate of respiration

Answer 33

Cyanide - affect mitochondria and prevent production of ATP.
- When cyanide is applied to root hair cells then root pressure disappears. No energy supply.

Question 34

Evidence for role of active transport in root pressure?
- temperature

Answer 34

Root pressure increases when temperature increases.
Root pressure decreases when temperature decreases.
Suggests that chemical reactions are involved.

Question 35

Evidence for role of active transport in root pressure?
- Oxygen supply

Answer 35

• When levels of oxygen / respiratory substrates fall, root pressure decreases.

Question 36

Evidence for role of active transport in root pressure?
- Guttation

Answer 36

Xylem sap may exude from cut end of stems at certain times. In the natural world, sap is forced out of special pores at ends of leaves in some conditions (e.g. overnight when transpiration is low).