9. PLANT BIOLOGY

Question 1

Explain how a plant replaces the water it loses in transpiration

Answer 1

transpiration/evaporation of water causes suction/tension

b. water sucked/drawn out of xylem «in leaf»

c. water moves up in xylem

d. due to suction/tension/pulling forces

e. cohesion of water/hydrogen bonds between water molecules

f. movement from roots to leaves

g. water enters root by osmosis/due to higher solute concentration inside root

Question 2

Describe the role of shoot apex in plant growth.

Answer 2

• shoot apex has undifferentiated cells
• those meristems divide by mitosis
• cells elongate in the shoot apex and the stem grows
• auxin is produced which elongates the stem

Question 3

Outline how the hormone auxin controls phototropism in plant shoots.

Answer 3

• auxin efflux pumps transport auxin to the shaded side of the stem
• it promotes elongation by binding to auxin receptors and promoting gene expression for H+ pumping into the cell wall
• loosening of cellulose, cell elongation in the direction of light