exam questions Flashcards
1
Q
state and explain 4 adaptations of xerophytes (4)
A
- 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
2
Q
give 2 reasons which support translocation being an active process (2)
A
- translocation stops when stems are treated with a substance which inhibits respiration
- rate increases with temperature
3
Q
give 2 reasons which support translocation transporting sugars from source to sink (2)
A
- increase in sugar content of leaves is followed by similar change in stem
- roots, young leaves and growing fruits import sugars
4
Q
explain how mass flow of the phloem sap occurs in plants with a vascular system (3)
A
- 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
5
Q
describe a procedure for observing xylem vessels in celery stalks (2)
A
- cut transversely
- soak in dye
- place under microscope on lowest power
6
Q
give one way in which the walls of xylem would be different in a hydrophyte and xerophyte (2)
A
- hydrophyte would have little to no lignin
- xerophyte would have a lot more lignin
7
Q
state 1 similarity and 2 differences between the structure of xylem and phloem (3)
A
- 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
8
Q
what is meant by adhesion? (1)
A
attraction of water molecules to impermeable walls of xylem tissue
9
Q
summarise the process of how water enters xylem via symplast pathway (4)
A
- 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
