9.2 water transport in multicellular plants

Question 1

What’s the function of transport systems

Answer 1

SUPPLY useful molecules to cells
REMOVE waste from cells

Question 2

How does water and dissolved minerals move into the roots

Answer 2

Root hair cell has lower ψ than soil (high solute concentration)
water + dissolved mineral ions move in by OSMOSIS

Question 3

Adaptions of root hair cells

Answer 3

LONG PROJECTION - increase SA
MICROSCOPIC SIZE - penetrate between soil particles
THIN SURFACE LAYER - short diffusion distance
CONTAINS SOLUTE - amino acids, mineral ions&raquo_space; low ψ

Question 4

How does water move across the root via the symplast pathway

Answer 4

Root hair cell has HIGHER ψ than neighbouring cell
Water moves by OSMOSIS from root hair cell ⟶ neighbouring cell.
next cell along always has lower ψ
∵ H2O has left root hair cell ψ DROPS, maintaining steep ψ gradient.
Continues until ENDODERMIS reached.

Question 5

Where is the apoplast pathway

Answer 5

Cell walls + intercellular spaces of living plant cells

Question 6

Whats the symplast pathway and how does H2O move

Answer 6

Symplast - continous cytoplasm of living plant cells that are connected through plasmodesmata
Water moves by osmosis down the water potential gradient from cell to cell, starting at the root hair cell until the xylem

Question 7

Describe the movement of water into the xylem

Answer 7

After water move by symplast and apoplast it reaches the endodermis (layer of cells surrounding xylem and phloem)
The Casparian Strip a Band of waxy material (suberin) that surrounds endodermal cells forming a water proof layer.
It stops water from entering via the apoplast pathway, it is forced into the symplast pathway
For water to enter the symplast pathway from apoplast, it must pass the selectively permeable membrane which stops toxic solutes from entering from the soil as there are no carrier proteins to admit them

Question 8

Evidence for the role of active transport in root pressure

Answer 8

Some poisons affect mitochondria and prevent production of ATP and root pressure then disappears
Root pressure increase with a rise in temp and decreases with a fall this suggests chemical reactions are involved
If oxygen or respiratory substrate levels fall root pressure falls
Xylem sap is forced out of pores in certain conditions

Question 9

What causes root pressure

Answer 9

The active pumping of mineral into the xylem to produce movement of water by osmosis results in root pressure