Plants adaptations

Question 1

who do different plant in different habitats have to adapt?

Answer 1

in order to cope with availability

Question 2

what are mesophytes?

Answer 2

plants adapted to a habitat with adequate water

Question 3

what are xerophytes?

Answer 3

plants adapted to a dry habitat (e.g. cacti/marram grass)

Question 4

what are halophytes?

Answer 4

plants adapted to a salty habitat

Question 5

what are hydrophytes?

Answer 5

plants adapted to a freshwater habitat

Question 6

name 10 adaptations of xerophytic plants

Answer 6

• rolled leaves
• sunken stomata
• low stomatal density
• stomata open at night and closed midday
• small leaves - reduced SA: volume ratio
• hair on leaves
• extensive roots -vascular system
• waxy cuticle

Question 7

which adaptations enable plant to reduce water potential gradient?

Answer 7

• rolled leaves - maintains humid air
• sunken stomata - traps moist air
• leaf hairs - traps air

Question 8

why do xerophytes have small leaves or shred leaves in dry season?

Answer 8

less area for evaporation so reduces water loss

Question 9

how does waxy cuticle help?

Answer 9

prevents uncontrolled evaporation

Question 10

what is transpiration?

Answer 10

evaporation of water from leaves causing water to move through plant

Question 11

what is cohesion-tension theory?

Answer 11

• water sticks together because of hydrogen bonding and form a continuous column
• as water evaporates from mesophyll cells the water is drawn up
• this transpiration pull puts xylem under negative pressure within xylem - hence tension

Question 12

what other pressure helps water move up?

Answer 12

root pressure from active transport of minerals and salts

• acts as a force pushing water up
• solar energy also helps because pressure increases with temperature

Question 13

describe the transpiration stream

Answer 13

• energy from sun causes water to evaporate from mesophyll cells and diffuse through stomata
• decrease in water potential in leaf - creates a gradient so water moves up the xylem and into leaf by osmosis
• since water is cohesive due to hydrogen bonding, a continuous column of water pulled up
• this creates a negative pressure on xylem which causes tension - hence the cohesion-tension theory
• a decrease in water potential in xylem causes water to be drawn up from root hair cells by osmosis
• decrease in water potential of root hair cells means that water can be drawn up from soil by osmosis

Question 14

what is symplast pathway?

Answer 14

cytoplasmic route

Question 15

what is apoplast pathway?

Answer 15

cell wall route - stops at endodermis because of casparian strip sealing cell walls

Question 16

why does diameter of tree trunk vary according to rate of transpiration?

Answer 16

• day - sun supples more energy - more tension in xylem and pulls wall of xylem vessels inwards so trunk shrinks in diameter
• night - no solar energy - less tension - larger trunk diameter`

Question 17

why will transpiration stream be broken if xylem vessel is broken?

Answer 17

• continuous column is broken because of break in cohesion

- xylem vessels have no end walls

Question 18

what factors affect transpiration?

Answer 18

• light
• wind
• humidity
• temperature

Question 19

what does phloem transport?

Answer 19

transports organic molecules - sugar/amino acids

Question 20

what is translocation?

Answer 20

movement of solutes in phloem

Question 21

what does mass flow theory explain?

Answer 21

how solutes are transported from source to sink by translocation

Question 22

how does mass flow theory work?

Answer 22

• sucrose made from glucose
• diffuses down concentration gradient by facilitated diffusion into companion cell
• co-transport of sucrose with hydrogen ions through protein carriers
• high solute potential so water moves in by osmosis
• this creates hydrostatic pressure at source end
• solutes are removed at sink end are used up or are used for storage
• high water potential creates gradient so water moves out and lowers pressure in sieve tube
• this creates a pressure gradient from source to sink so solutes are pushed to sink