plant structures and their functions Flashcards
why do plants photosynthesise
they use energy from the Sun to make glucose which allows the plant to make more complex molecules needed for it to grow so is responsible for its increase in biomass
where does photosynthesis occur
the chloroplasts
word reaction photosynthesis
carbon dioxide + water -> glucose + oxygen
symbol reaction photosynthesis
6CO2 + 6H2O -> C6H12O6 + 6O2
what kind of reaction is photosynthesis
endothermic reaction (takes in energy)
what are the three 3 limiting factors of PHOTOSYNTHESIS
temperature
light intensity
carbon dioxide concentration
how does temperature affect photosynthesis
if a plant gets too hot, the enzymes needed for photosynthesis will be denatured
this occurs at about 45°C
how does light intensity affect photosynthesis
at first as light level is raised, the rate of photosynthesis increases up to a point (directly proportional)
what is the inverse square law
light intensity ∝ 1/ distance ^2
light intensity and distance from light source are inversely proportional
how does CO2 concentration affect photosynthesis
increasing CO2 concentration increases rate of photosynthesis up to a point
after which light intensity or temperature need to be increased
describe the pondweed experiment to measure the rate of photosynthesis
1) set up an LED lamp at different distances from the plant in a beaker of water with SODIUM HYDROGEN CARBONATE added to it (to provide the CO2 reactant)
2) pondweed is left to photosynthesise for set period of time
3) oxygen released is collected in the gas syringe so volume can be accurately measured OR oxygen bubbles could be counted but its less accurate
4) repeat experiment at different distances
rate of oxygen production formula
rate of oxygen production = volume produced/time taken
adaptations of root hair cells
hairs stick out into the soil
they have a large surface are which increases absorption of water via osmosis and mineral ions via active transport
role of phloem cells
where translocation occurs
transports food substances, mainly sucrose, made in the leaves to immediate use or storage
translocation
the movement of sucrose and other substances
structure of phloem cells
LIVING cells (elongated) with small pores in the end walls which allow substances to flow through
role of xylem cells
part of the transpiration stream
take water up from the roots , transporting water and minerals (dissolved in it)
structure of xylem cells
dead cells joined end to end with no end walls and a hole down the middle
strengthened with lignin
transpiration
the loss of water from a plant
descirbe the transpiration stream
water evaporates at the leaves leaving a slight shortage of water in the leaf
more water is therefore drawn up from the xylem to replace it
in turn, more water is drawn up from the roots so there is a constant transpiration stream
the transpiration stream carries water and the mineral ions dissolved in it
stomata
tiny pored on the underside of a leaf that allow gas exchange and water vapour to escape
how does water vapour escape through the stomata
water escapes via diffusion because there is more inside the plant than outside
if the guard cells are flaccid/turgid, what state are the stomata in
flaccid - stomata close
turgid - stomata open
what 3 environmental factors affect transpiration rate
light intensity
temperature
air flow
how does light intensity affect transpiration rate
the brighter the light, the greater the transpiration rate
- stomata start to close as it gets darker as photosynthesis can’t happen so CO2 doesn’t need to be released and very little water can therefore escape
how does temperature affect transpiration rate
the warmer it is, the greater the transpiration rate
when its warm , water particles have more energy to evaporate and diffuse out of the stomata
how does air flow affect transpiration rate
the better the air flow, the greater the transpiration rate
with poor air flow, the water vapour doesn’t move away from the leaf
- there is a high concentration of water outside so diffusion is slower
potometer
measures water uptake by a plant which is assumed to be directly related to the water being lost by transpiration
how to set up a potometer to measure transpiration wate
beak of water connected to a capillary tube with a scale which flows into a tube containing a plant
record the bubble in the capillary tube’s starting position
start a stopwatch and record the distance moved per unit of time by the bubble
what are the 5 layers of the leaf (from top to bottom)
waxy cuticle upper epidermis palisade mesophyll tissue spongy mesophyll tissue lower epidermis
give 6 adaptations of the leaf
broad leaves - large surface area for absorbing light for photosynthesis
palisade layer - lots of chloroplasts near the top of the leaf to absorb lots of light
transparent upper epidermis - lets light pass through to the palisade layer
xylem and phloem form supportive structure to provide water and remove glucose
waxy cuticle reduces loss of water by evaporation
lower epidermis has lots of stomata and spongy mesophyll has lots of air space which makes gas exchange more efficiently
adaptations
features that help an organism to survive in its environment
give 3 adaptations that help to reduce water loss by evaporation
small leaves or spines ( reduces surface area for water loss and spines deter animals from eating it and consuming water)
thick, waxy cuticle
fewer stomata/stomata only open at night
give two adaptations that help to reduce air flow near the leaf
stomata sunken in pits
curled leaves or leaves with hairs on the surface
- both of these adaptations trap water vapour and reduce diffusion from leaf to air
give an adaptation of plants to store water
having a thick, fleshy stem
auxins
plant hormones controlling growth of roots and shoots ; move through solution
what do auxins in the roots do
inhibit growth
what do auxins in the shoots do
promote growth
where are auxins produced
in the tips and they diffuse backwards to stimulate cell elongation
phototropism
growth responses of plants to light
gravitropism
growth responses of plants to gravity
describe the tropisms of shoots
positively phototropic
- accumulates auxins on the SHADED side so cells elongate on the shaded size, forcing it to bend towards the light
negative gravitropic
- when a shoot is growing sideways, the auxin is unevenly distributed along the lower side so the lower side grows faster, forcing the shoot to bend up
describe the tropisms of roots
negatively phototropic
- auxins accumulate on the shaded side where they inhibit cell elongation so the root bends away from the light
positively gravitropic
- when growing sideways, they gather on the lower side, inhibiting growth so cells on the top elongate faster causing the root to grow downwards
to investigate tropisms
1) place cress seeds in a petri dish with moist filter paper
2) surround with black card
3) cut a hole in one side of the card and shine a light through it
4) leave the cress for a week and observe the plant’s response
what are two commercial uses of auxins
selective weedkillers
rooting powder
selective weedkillers
commercial use of auxins
only affect broad leaved plants , often weeds
they disrupt regular growing patterns, soon killing them but leaving everything else untouched
rooting powder
commercial use of auxins
allows a cutting to rapidly produce roots and start growing as a new plant
growers can produce lots of clones quickly
what are three commercial uses of gibberellins
germination (at unusual times of year)
seedless fruit
fruit and flower formation
gibberellins
plant hormones that stimulate seed germination, stem growth and flowing
germination ( at unusual time of year )
commercial use of gibberellins
many seeds won’t germinate if they have endured a period of cold and dark
using gibberellins can cause them to germinate at unusual times of year, enabling crop production year round
seedless fruit
commercial use of gibberellins
if a flower isn’t pollinated, the fruit and seeds won’t grow
using gibberellins, the fruit is produced without the seeds
fruit and flower formation
commercial use of gibberellins
gibberellins can be used to stimulate germination in a plant flower when it wouldn’t normally
they can reduce flower formation by causing few plants to flower so higher quality fruit is produced
one commercial use of ethene
ethene is a ripening hormone
fruits that have been picked whilst unripe can be ripened to perfection as it arrives in the supermarkets
how do stomata open
guard cells take in water via osmosis
they become turgid
stomata open
how do stomata close
guard cells lose water via osmosis
they become flaccid
stomata close
