EX1 Q6&7

Question 1

What comprises the apoplasm?

Answer 1

-extracellular spaces (outside the cell walls)

Question 2

What comprises the symplasm?

Answer 2

-through the cell membranes via plasmodesmata

Question 3

Which route uses passive diffusion and which uses osmosis?

Answer 3

-apoplast: passive
-symplast: active

Question 4

What are the steps of the apoplastic pathway?

Answer 4

1. Root cell hairs absorb water from the soil through osmosis.
2. It diffuses along the permeable cell walls into the root cortex.
3. The filtered solution is released back into the apoplast on the other side of the Casparian strip by endodermal cells and living stele cells.
4. Water and minerals in the stele apoplast enter the xylem, where it flows by bulk flow up the roots.

Question 5

Which pathway is faster?

Answer 5

apoplast

Question 6

Which pathway goes only through non-living structures? (no protoplasts)

Answer 6

apoplast

Question 7

Casparian strip

Answer 7

A collection of endodermal cells which are impermeable to water.

Question 8

What are the steps of the symplastic pathway?

Answer 8

1. Water and minerals are immediately filtered as they cross a root hair cell’s cell membrane, entering the symplast.
2. The water and minerals move from cell to cell through plasmodesmata toward the stele cylinder.
3. Because these minerals and water are already in the symplast (and so already filtered by a membrane), they get to bypass the Casparian strip. Endodermal cells and living stele cells release the water and minerals out into the stele apoplast (the xylem).

Question 9

Why use symplastic movement?

Answer 9

Water cannot move through the casparian strip during apoplastic movement. It needs to switch to symplastic movement once it reaches the cortex.

Question 10

Cavitation

Answer 10

the formation of air bubbles or cavities within xylem vessels, which can interrupt the flow of water through the plant

Question 11

Explain in detail how water tension can lead to cavitation.

Answer 11

As plants transpire or experience high rates of evaporation, water is drawn up from the roots to the leaves through the xylem vessels. Cohesion and adhesion create tension, which creates negative pressure in the xylem. The extreme pressure causes vaporization of water molecules and therefore, air cavities.

Question 12

Are angiosperms or gymnosperms more prone to cavitation and why?

Answer 12

-Angiosperms
-The wider vessel elements provide greater surface area for air bubbles to form.

Question 13

What are some ways plants can negate cavitation?

Answer 13

-They can block off that section of vasculature
-They can increase the pressure on that portion of vasculature until the air bubble is reabsorbed into the water.