Plants adaptations Flashcards
who do different plant in different habitats have to adapt?
in order to cope with availability
what are mesophytes?
plants adapted to a habitat with adequate water
what are xerophytes?
plants adapted to a dry habitat (e.g. cacti/marram grass)
what are halophytes?
plants adapted to a salty habitat
what are hydrophytes?
plants adapted to a freshwater habitat
name 10 adaptations of xerophytic plants
- 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
which adaptations enable plant to reduce water potential gradient?
- rolled leaves - maintains humid air
- sunken stomata - traps moist air
- leaf hairs - traps air
why do xerophytes have small leaves or shred leaves in dry season?
less area for evaporation so reduces water loss
how does waxy cuticle help?
prevents uncontrolled evaporation
what is transpiration?
evaporation of water from leaves causing water to move through plant
what is cohesion-tension theory?
- 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
what other pressure helps water move up?
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
describe the transpiration stream
- 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
what is symplast pathway?
cytoplasmic route
what is apoplast pathway?
cell wall route - stops at endodermis because of casparian strip sealing cell walls
why does diameter of tree trunk vary according to rate of transpiration?
- 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`
why will transpiration stream be broken if xylem vessel is broken?
- continuous column is broken because of break in cohesion
- xylem vessels have no end walls
what factors affect transpiration?
- light
- wind
- humidity
- temperature
what does phloem transport?
transports organic molecules - sugar/amino acids
what is translocation?
movement of solutes in phloem
what does mass flow theory explain?
how solutes are transported from source to sink by translocation
how does mass flow theory work?
- 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
