Mass Transport In Plants

Question 1

Explain how water enters the xylem from the endodermis in the root and then is transported to the leaves.

Answer 1

Casparian slip blocks the apoplasm pathway allowing the symplasm pathway
Active transport by endodermis
Ions into xyloem
Lowers water potential in xylem
Water moves in by osmosis
Evaporation
Hydrogen bonds between water molecules(cohesion)
Water molecules bind to xylem walls(adhesion)
Forms continues column of water

Question 2

Root pressure moves water through the xylem. Describe what causes root pressure.

Answer 2

Active transport by endodermis
Ions into xylem
Lowers water potential
Water moves into xylem

Question 3

Name a factor that can affect transpiration

Answer 3

Light intensity
Temperature
Humidity
Air movement

Question 4

Give two precautions the students should have taken when setting up the potometer to obtain reliable measurements of water uptake by the plant shoot

Answer 4

Cut shoot at a slant
Keep leaves dry
Cut shoot in water
Seal joints
Ensure no air bubbles are present

Question 5

Describe mass flow hypothesis for the mechanism of translocation in plants. 5points

Answer 5

In the source sugars enter phloem by active transport
By companion cells
Lowers water potential of sieve cell so water enters by osmosis
Increase in pressure causes mass movement toward sink
Sugars used in root for respiration

Question 6

Describe how co2 in the air outside a leaf reaches mesophyll cells inside the leaf. 4 points

Answer 6

Stomata opens
By guard cells
Co2 diffuses into air spaces
Down concentration gradient of co2

Question 7

Explain why plants grown in soil with very little water grow only slowly

Answer 7

Stomata closes
Less co2 for photosynthesis

Question 8

Describe how high pressure is produced in the leaves.

Answer 8

Low water potential in leaves
Increased osmosis into phloem
Increased volume of water increased pressure

Question 9

How is the xylem cells adapted to its function

Answer 9

Long tube with no end walls so allows continuous column of water
Dead cells form hollow cells so allows easier water flow
Cells walls contain lignin so is water proof and rigid so withstand tension
Xylem pits so water can move laterally between xylem vessels