Water transport

Question 1

classic osmosis def:

Answer 1

Diffusion of water molecules from an area of high water potential to an area of low water potential across a partially permeable membrane down a water potential gradient.

Question 2

How is water drawn into the roots

Answer 2

Osmosis

Question 3

What are the 2 different pathways water travels through the roots into the xylem?

Answer 3

1) symplast

2) Apoplast

Question 4

Which pathway is living, and which is non-living?

And what are the living and non-living parts?

Answer 4

Symplast is LIVINNNNGGGGG cuz its simplistic so has nothing to worry bouttt. (CYTOPLASM)

Apoplast is non- living (CELL WALLS)

Question 5

Symplast pathway:

Answer 5

• The cytoplasm of neighbouring cells connect through plasmodesmata.
• water moves through the symplast pathway via osmosis.

Question 6

Apoplast pathway:

Answer 6

• The walls are very absorbent and water can simply diffuse through them, and even flow around.
• The water can carry solutes and move them from an area of HIGH hydrostatic pressure to an area of LOW hydrostatic pressure along a pressure gradient.

this is an example of mass flow.

Question 7

Which out of the 2 pathways are better?

Answer 7

Apoplast pathway as it provides the LEAST resistance.

Question 8

What is one thing to note about apoplast pathway ( to do with endodermis)

Answer 8

• Once the water in the apoplast pathway reaches the endodermis cells, the path is blocked by a casparian strip.
• which means the water has to take the symplast pathway

Question 9

Why is it good that water takes the symplast pathway after being blocked by the casparian strip?

Answer 9

So that water can travel through the cell membrane

which is better, as the cell membrane can control what substances from the water can get through.

after this barrier is passed the water moves into the xylem.

Question 10

By which pathway does water tend to leave the xylem and enter the leaf cells?

Answer 10

Apoplast pathway

• The water evaporates from the cell walls and moves into the spaces between the cells in the leaf.
• water diffuses out of the stomata down a water potential gradient.

Question 11

What 3 mechanisms play a big part in the transpiration stream?

Answer 11

1) cohesion
2) Tension
3) Adhesion

Question 12

Cohesion and Tension:

Answer 12

1) Water evaporates from the leaves at the top of the xylem
2) This creates tension and more water is drawn into the leaf

3) Water molecules are cohesive, which means they stick together so when water molecules are drawn into a leaf, others follow.
This means all the water in the xylem moves upwards.

Water enters the stem through the root cortex cells.

Question 13

What is adhesion?

Answer 13

When water molecules are attracted to the walls of the xylem vessels.

• helps the water to move up the xylem.