plants Flashcards
root hairs
- long and very thin: increase SA to vol
- hypersonic so osmosis moves water into the roots
Water moves from hypotonic to hypertonic
photosynthesis
- transforms sunlight energy into chemical energy
factors affecting transpiration
light intensity:stimulates guard cells to take in water and open to allow CO2 diffuse in for photosynthesis, increasing photosynthesis and transpiration
temp: hotter increases photosynthesis and transpiration, water evaporates and diffuses quicker as temp rises
humidity: when the surrounding air is dry diffusion out of leaf is faster increasing diffusion gradient and water loss
wind: in still air the air surrounding the stomata becomes more humid thus reducing the rate of transpiration, when a breeze is present the humid air is carried away and replaced by dry
soil water: plants cant keep transpiring rapidly if water lost is not replaced from the soil, this reduces transpiration and photosynthesis
waxy cuticle
forms a waterproof layer to limit loss of water
upper epidermis
layer of cells covered by a thick waxy cuticle prevents water loss from the upper surface
palisade mesophyll
contains many chloroplasts which contain lots of chlorophyll. main photosynthetic tissue where photosynthesis occurs, near top leaf for maximum light absorption
spongy mesophyll
cells that provide a mean for gas exchange, have fewer chloroplasts then the palisade layer
xylem
vascular tissue that transport water replacing water lost during transpiration
phloem
vascular tissue transporting photosynthetic products out of leaf
stomata
pores that allow for CO2 to diffuse in and O2 to diffuse out and water loss
guard cells
these form the stomata which allow for the diffusion of gases in and out of the plant, open and close the stomata
transpiration - water movement
- water enters hypertonic root hairs
- water then moves from cell to cell through the root cortex along a concentration gradient
- water enters the xylem and moves up the xylem tubes
- water enters the leaf cells moving through the spongy mesophyll
- water evaporates into spaces behind the stomata and diffuses into the air
adhesion
water rises in the narrow vessels partly because water molecules are attracted to the walls of the vessels
cohesion
water molecules are attracted to each other and as water evaporates from the leaves columns of water are drawn up through the xylem
xerophytes
plants with adaptations to conserve water allowing them to survive in dry arid conditions
- the main problem is the water loss from the leaves due to transpiration
eg cactus
halophytes
plants adapted to living in a salty habitat
xerophyte adaptations
- sunken stomata with hairs, reduces air flow increasing the humidity reducing water loss
- leaf hairs: trap a layer moist air to stop wind removing moisture
- leaves reduced to spines to reduce SA
- waxy epidermis: reduces evaporation
- wide spreading shallow roots: absorbs a lot of water fast
- stomata on underside of leaf
- reduced number of stomata
- rolled leaves
- reduced leaves
- ability to store water in roots stem and leaves
- closure of stomata during the hottest part of the day
xerophyte stomata role
cool night : stomata open absorb CO2 when low H2O loss
hot day: stomata closed, fix CO2 in photosynthesis using light
halophytes problems
- salt concentration in the soil exceeds that in the roots therefore water moves from the roots into the soil by osmosis to equal the concentration of salt inside and outside of the root. therefore the plant loses water, plants need to reverse this process to obtain water
halophyte adaptations
- store salt in vacuoles in root cells so salt concentration in cell exceeds that in the soil making it hypertonic so water moves into the root
- accumulate salt in leaves, discard the leaves reducing the amount of salt in the plant
- prevent salt entering, filtration mechanism at roots, avoids having to deal with excess salt
