Plant hormones Flashcards
Tropism:
a directional growth response, dependant on the direction of a stimulus
positive tropism is where something grows towards the stimulus
negative tropism is where something grows away from the stimulus
Describe and explain why shoots and roots grow in different ways due to gravity:
- due to gravity, auxins build up at the bottom side of shoots, this causes cells walls to elongate at the bottom as their walls get elastic and absorb more water so they stretch. this uneven distribution of the concentration of auxins causes the shoots to do negative geotropism.
- due to gravity, auxins also build up at the bottom side of roots, however this inhibits cell elongation, so the areas with the least auxins will elongate, causing the root to do positive geotropism.
Describe and explain why shoots grow in a certain way due to light:
- when exposed to light, a shoot may face the source.
- this causes auxins at the tip of the shoot to travel at the unlit side of the shoot, causing a greater concentration in the shaded area, creating an uneven distribution.
- the cells on the shaded side will react with the auxin and their walls will elasticise and elongate
- this causes the shoot to grow bending towards the light
- this is positive phototropism.
State the 3 different plant hormones humans use:
- gibberellins
- auxins
- ethene
Whats the purpose of gibberellins:
To end seed dormancy (speed up germination for brewery)
To increase the fruit of a plant (seedless grapes have little fruit as seeds produce gibberellins, so by supplying gibberellins to them they increase their fruit size)
To promote flowering all year round.
What’s the purpose of auxins:
To help horticulturists and agricultures in tissue cuttings, by taking a cutting and exposing it to rooting powders we can encourage the growth of roots to make identical clones from one plant.
As weed killers, weeds have a larger surface area than desired crops (wheat) so when they are sprayed with auxins, the weeds absorb more. the overconsumption of auxins cause the weed’s cells to elongate uncontrollably causing mutations and their death, leading the crops alone.
What’s the use of ethene
To encourage fruit (bananas) to ripen to be perfectly ripened by the time they arrive at markets.
Bananas are harvested and transported unripened and chilled as they don’t get as damaged. nearer to the time they arrive to market they are warmed with ethene gas which ripens them.
