Module 5: Plant hormones and growth in plants Flashcards
What are the 4 main plant hormones
auxins
gibberellin
ethene
ABA
Plant hormones and seed germination:
When a seed absorbs water , the embryo is activated and begins to produce which hormone?
What is the role of this hormone in seed germination?
gibberellins - these stimulate the production of enzymes that break down food stores within the seed
Plant hormones and seed germination:
What are the food stores within the embryo of seeds used for?
the production of ATP which is then used for building materials so that the embryo can grow and break out through the seed coat
Make 1 point about what evidence suggests about the role of gibberellins in seed germination
What is the role of ABA in seed germination?
make 1 more point about the effect of these 2 hormones combined
-gibberellins switches on genes which code for amylases and proteases which are the digestive enzymes required for germination
ABA-acts as an antagonist to gibberellins
(the relative levels of both hormones determine when a seed will germinate)
Give 2 pieces of experimental evidence that support the role of gibberellins in seed germination
1)varieties of seeds have been bred that lack the gene enabling them to make gibberellins , these seeds don’t germinate but if gibberellins is then applied they do germinate
2)if gibberellin biosynthesis inhibitors are applied to seeds they do not germinate , if the inhibitors are removed they do germinate
Make 1 point about the role of gibberellins in stem growth
it causes elongation of stems during growth by increasing the length of internodes
What are the internodes of a plant stem?
the regions between the leaves on a stem
In terms of seed germination , what is meant by the term dormancy?
a period of inactivity that allows the seed to withstand adverse environmental conditions
Where in the plant are auxins synthesised?
Name 3 aspects of plant growth that auxins regulate
in the growing tips of shoots and roots (meristems)
1)cell expansion and differentiation
2)suppression of lateral bud growth (apical dominance)
3)directional growth responses (tropisms)
High auxin concentrations inhibit … and promote …
Low auxin concentrations inhibit … and promote …
inhibit-root growth
promote-shoot growth
inhibit-shoot growth
promote-root growth
Make 6 points about the role of auxins in stem elongation
(start with where auxins are synthesised)
1)auxins synthesised by meristem cells in shoot tips
2)auxins diffuse down the shoot away from the tip
3)auxins bind to receptor sites on the cell surface membranes
4)a low pH develops in cell walls
5)cells absorb water by osmosis forming vacuoles and increasing internal pressure which causes cell walls to expand
6)cells elongate and the plant grows
Make 1 point about the role of auxins in apical dominance
Describe what would happen if the apical bud of a plant was removed (make 3 small points)
auxins are synthesised in the shoot tips so stimulate growth of the main apical shoot and suppress growth of lateral shoots
the source of auxin would be removed , releasing the inhibition of lateral bud growth , this would allow for a bushier plant to develop
