Miss Lee - Water Transport

Question 1

Why is water needed in the plant

Answer 1

• Mineral ions and sugars are transported in aqueous solution
• Water is a raw material of photosynthesis
• Cooling effect (by transpiration)
• Turgor pressure –hydrostatic skeleton

Question 2

What is water potential

Answer 2

• Water potential is the term used to describe the tendency for water molecules to move within and between cells.
• A net movement of water will occur from one region to another as a result of a difference in water potential.
• Water will move from a region of higher water potential to a region of lower water potential.

Question 3

What are the adaptations for root hair cells

Answer 3

• Very thin cellulose walls, that are readily permeable to water and dissolved mineral ions.
• Microscopic in size
• LargeSA:Vratio
• Concentration of solutes in the cytoplasm of root hair cells maintains a water potential gradient between the soil water and the cell.

Question 4

What are the 3 different ways water can enter the plant

Answer 4

• Symplast Pathway (through cytoplasm)
• Vacuolar Pathway (through vacuoles)
• Apoplast Pathway (through cell walls)

Question 5

How does water move

Answer 5

Water moves through the roots cells and into the xylem tube by three pathways

Question 6

Vacuolar Pathway - Vacuoles

Answer 6

• Vacuolar pathway is the same as the symplast pathway when the water moves through the cells vacuoles in addition to the cytoplasm
• This is the slowest route

Question 7

Symplast Pathway - Cytoplasm

Answer 7

1. Water enters the cytoplasm across the partially permeable plasma membrane
   2.What can move into the SAP in the vacuole, through the tonoplast
2. Water may move from cell to cell through the plasmodesmata
3. Water may move from cell to cell through adjacent plasma membranes and cell walls
   -This is the movement of water through the living spaces of the cell – cytoplasm
   • Enters cells through the plasmodesmata
   • Each cell further away from the roots has a lower water potential so water is drawn through the plant

Question 8

The apoplast pathway - cell wall

Answer 8

1. Water enters the cell wall
2. Water moves through the cell wall
3. What a memory from cell to cell, across the intercellular spaces
4. Water may move directly from cell wall to cell wall
   • Thisisthe movement of water though the cell wall and intracellular spaces
   • Cohesiveand tension forces acting on the cell walls pulls the water up the plant
   • Thisisthefastest movement of water

Question 9

What is the casparian strip

Answer 9

The casparian strip is a impermeable layer of suberin – a waxy material.

Question 10

What does the casparian strip do

Answer 10

• When water reaches the endodermis of the root, it’s path is blocked.
• The endodermis has a waterproof, impenetrable layer called the Casparian strip in its walls. This is because of the waxy layer of suberin in the walls of endodermal cells.
• In order to cross the endodermis, the water that has been moving through the cell walls (in the apoplast pathway) must now move through the cell surface membrane & into the cytoplasm (forced into the symplast pathway).
• In this way the selectively permeable plasma membrane of the cells can control what enters the xylem tissue.
• This is important as the cell surface membrane can remove any toxic solutes from the soil, and only allow necessary water molecules and mineral ions to enter.