Homeostasis - Plant Hormones 146-148 Flashcards
(15 cards)
what is auxin
2 points
1) a plant hormone that controls growth near the tips of shoots and roots
2) controls the growth of a plant in response to light and gravity
what happens when a shoots grows towards light
2 points
1) a shoot is exposed to light, more auxin goes to the side in the shade
2) this makes the cells grow (elongate) faster on the shaded side so the shoot bends towards the light
what happens when shoots grow away from gravity
2 points
1) when a shoot is growing sideways, gravity produces an unequal distribution of auxin in the tip
2) this causes the lower side to grow faster, bending the shoot upwards
what happens when a roots grows towards gravity
2 points
1) a root growing sideways will always have more auxin on its lower side
2) but in a root the extra auxin inhibits growth, this means the cells on top elongate faster and the root bends downwards
what is it called when a plant grows in response to light
phototropism
what is it called when a plant grows in response to gravity
geotropism or gravitropism
how can you investigate the effect of light on the growth of seeds
3 points
1) put 10 cress seeds into 3 different Petri dishes, each lined with moist filter paper
2) shine a light onto one of the dishes from above and two of the dishes from different directions
3) leave the seeds alone for about 1 week, then you can observe the seeds growing towards the light
why do you need to have control variables when investigating how light effects plant growth
you need to know the growth response of the seeds is due to light only
what are some control variables when investigating how light effects plant growth
5 points
1) number of seeds
2) type of seed
3) temperature of surroundings
4) amount of water the seeds get
5) light intensity
what are the uses of auxins
3 points
1) killing weeds - most weeds are broad leaved, weed killers have been developed using auxins that only affect broad leaved plants, they disrupt their normal growth patterns whilst leaving grass and crops
2) growing cuttings - if you add rooting powder to cuttings they will produce roots quickly and start growing as new plants, this lets growers produce lots of clones of a really good plant fast
3) growing cells in tissue culture - this can be used to grow clones of a plant from its cells, auxins are added to it to stimulate the cells to divide to form roots and shoots
what is gibberellin
a plant hormone that stimulates seed germination, stem growth and flowering
what are the uses of gibberellin
3 points
1) controlling dormancy - many seeds won’t germinate until they’ve been through certain conditions, which is called dormancy, gibberellin alters dormancy and make plants germinate at times they wouldn’t normally
2) inducing flowering - plants that need certain conditions to flower can be treated with gibberellin to make them grow, it will also produce bigger flowers
3) growing larger fruit - seedless varieties of fruit (grapes) often don’t grow as big as normal ones, add gibberellin and they will
what is the use of ethene with fruit
stimulates ripening of fruit
how does ethene stimulate fruit ripening
4 points
1) ethene is produced by the aging parts of plants and it influences the growth of the plant by controlling cell division
2) it also stimulates enzymes that cause fruit to ripen
3) it can be used to ripen fruit while they’re still on the fruit or while they’re being transported to shops
4) this means fruits can be picked while still unripe, therefore less easily damaged, and the gas is added while it’s being transported
how can ripening of fruit be delayed
2 points
1) when the fruit is in storage chemicals can be added that block the effects of ethene or reduce the amount of ethene the fruit can produce
2) some chemicals can be added that react with ethene to remove it from the air
