7 - Plant Transport

Question 1

Describe the structural features of xylem vessels

Answer 1

Cell walls contain lignin
Cells are dead
Walls contain tiny holes called pits
No end walls

Question 2

Suggest advantages of xylem vessels being dead

Answer 2

Living cells have cell membranes and cytoplasm, water movement would be slower if it had to pass through these
Less resistance to water flow (no organelles, cytoplasm etc.) so faster rate of water movement

Question 3

Describe the cohesion tension theory

Answer 3

Evaporation of water from leaves pulls up more water from the xylem in the stem.
Water is dipolar
Cohesion between water molecules with H bonds
Adhesion between water molecules and xylem walls with H bonds

Question 4

Why is the trunk diameter lowest at noon?

Answer 4

Stomata are open, transpiration rates are high, increased tension, so water column pulled up xylem faster, so walls of xylem pulled in and xylem vessels decrease in diameter

Question 5

What are the xerophytic adaptations

Answer 5

Leaf rolled up
Thick waxy cuticle
Trapped him ait with high water potential
Hairs on lower epidermis of leaf
Stomata sunken in pits

Question 6

Describe the radioactive tracer experiment

Answer 6

Plant exposed to radioactively labelled CO2
Carbohydrates synthesised by photosynthesis contain the CO2
Cut thin sections of the plant and place photographic film over them