Osmosis and Plant Transport

Question 1

Define Osmosis

Answer 1

Osmosis is the diffusion of water molecules from a dilute solution to a more concentrated solution, through a selectively permeable membrane.

Question 2

Turgor support

Answer 2

When a plant cell is placed in a more dilute solution:
-water enters the cell by osmosis;
-the vacuole expands, pushing the cell membrane against the cell wall;
-turgor support occurs;
-the cell wall provides resistance for the further uptake of water.

Question 3

Plasmolysis

Answer 3

When a plant cell is placed in a more concentrated solution:
-water diffuses out of the cell by osmosis;
-the cell loses its turgor and the cell membrane detaches from the cell wall as the vacuole shrinks;
-flaccid cell as a result of plasmolysis.

Question 4

Cell wall role

Answer 4

The cell wall prevents the membrane expanding too far to cause damage and therefore limits the uptake of water.

Question 5

Transpiration (1)

Answer 5

Transpiration is the evaporation of water from the aerial parts of the plant.

Question 6

Transpiration (3)

Answer 6

Water moves by osmosis from the xylem to the spongy mesophyll cells.
Water evaporates from the surface of the spongy mesophyll cells to the intercellular airspaces.
Water vapor diffuses from the intercellular airspaces through the stomata into the atmosphere.

Question 7

Factors that affect the rate of Transpiration

Answer 7

Increased Transpiration rate:
-High wind speed
-High light intensity
-Low humidity (moisture in the air)

Decreased Transpiration rate:
-Low wind speed
-Low light intensity
-High humidity (moisture in the air)

Question 8

What affect does light intensity have on Transpiration rate?

Answer 8

At high light intensities, the rate of photosynthesis is greater. Hence, guard cells will be open to increase the intake of carbon dioxide.
As these guard cells are open, a greater volume of water vapor can escape, increasing the rate of transpiration.

Question 9

How does leaf surface area affect the rate of Transpiration?

Answer 9

Larger leaves will have more stomata, through which water can evaporate and diffuse.

Question 10

Uses of water in plants

Answer 10

-Photosynthesis
-Transpiration
-Transport of minerals and ions
-Turgor support