exam questions

Question 1

state and explain 4 adaptations of xerophytes (4)

Answer 1

• rolled leaves = traps moist air in enclosed space
• thick waxy cuticle = impermeable to water so minimises loss of water vapour from surface via transpiration
• hairs on leaf surface = reduces movement of air over leaf surface
• fewer air spaces in spongy mesophyll = reduced surface area for water to evaporate out

Question 2

give 2 reasons which support translocation being an active process (2)

Answer 2

• translocation stops when stems are treated with a substance which inhibits respiration
• rate increases with temperature

Question 3

give 2 reasons which support translocation transporting sugars from source to sink (2)

Answer 3

• increase in sugar content of leaves is followed by similar change in stem
• roots, young leaves and growing fruits import sugars

Question 4

explain how mass flow of the phloem sap occurs in plants with a vascular system (3)

Answer 4

• mass flow is assimilates moving into the sieve tubes
• water potential lowers
• water moves down concentration gradient
• hydrostatic pressure increases
• assimilates leave the sink and water potential increases
• water moves down the concentration gradient
• hydrostatic pressure decreases

Question 5

describe a procedure for observing xylem vessels in celery stalks (2)

Answer 5

• cut transversely
• soak in dye
• place under microscope on lowest power

Question 6

give one way in which the walls of xylem would be different in a hydrophyte and xerophyte (2)

Answer 6

• hydrophyte would have little to no lignin
• xerophyte would have a lot more lignin

Question 7

state 1 similarity and 2 differences between the structure of xylem and phloem (3)

Answer 7

• both tubes joined end to end
• xylem contains lignin phloem does not contain lignin
• phloem have companion cells and xylem do not have companion cells

Question 8

what is meant by adhesion? (1)

Answer 8

attraction of water molecules to impermeable walls of xylem tissue

Question 9

summarise the process of how water enters xylem via symplast pathway (4)

Answer 9

• water enters root hair cell by osmosis, creating a higher water potential than of the adjacent cell
• water moves between cell cytoplasms down water potential gradient until it reaches the endodermis
• mineral ions are actively transported into the xylem
• water enters xylem by osmosis