Plant hormones Flashcards
What is it called when a plant has directional growth?
tropisms
What does abscisic acid do?
maintains dormancy, stimulates cold protective responses
What does ethene do?
causes fruit ripening, promotes abscission in deciduous trees
What do gibberellins do?
cause stem elongation, trigger the mobilisation of food stores in a seed, stimulate pollen tube growth in fertilisation
What happens at seed germination?
When the seed absorbs water, the embryo is activated and begins producing gibberellins. These stimulate the production of enzymes which break down food stores. These are used to produce ATP so the plant can grow and break out of the seed coat. Evidence suggests gibberellins switch on genes which codes for amylases and proteases.
What is the evidence that suggests gibberellins role in seed germination?
-mutant varieties of seeds have been bred without the gene that enables production of gibberellins, they didn’t germinate
Where is IAA produced?
shoot and root tips and meristems
What is apical dominance?
auxins stimulate growth of the apical shoot and inhibits the growth of the lateral shoots
Why do the lateral shoots at the bottom of the plant grow better than further up?
lower conc of auxin especially as the plant grows taller
What is evidence of apical dominance?
if apical shoot removed then lateral shoots grow faster
or if auxin is applied artificially to the apical shoot apical dominance is reasserted
How are gibberellins involved in stem elongation?
They affect the distance between internodes- the regions on the stem between leaves
Why would farmers want plants with short stems?
reduces waste, makes them less vulnerable to weather and harvesting
What does synergistic mean?
work together
What doe antagonistic mean?
oppose each other
What is called when plants are sensitive to a lack of light in their environment?
photoperiodism
What pigment does sensitivity to day length arise from?
phytochrome
How does abcission occur?
decreasing in day light hours causes auxin levels to drop, the leaves respond to this by producing ethene. At the base of the leaf there is a zone called the abcission zone, made up of two ethene sensitive layers. Ethene initiates gene switching which results in production of new enzymes. These enzymes digest and weaken the outer layer- separation layer. Vascular bundles are sealed off and fatty material is deposited in the cells to prevent entry of pathogens. More strain is put of the cells in separation zone until they fall off.
How do plants prevent freezing?
The cytoplasm and vacuole contains solutes which lowers the freezing point. Anti-freeze
What hormone controls the opening and closing of stomata due to abiotic stress?
ABA is released to cause stomatal closure
What are plants physical defences to herbivory?
thorns, spikes, fibrous tissue, hairy leaves, curled leaves
What are plants chemical defences to herbivory?
Tannins- bitter and toxic,
Alkaloids- bitter,
Terpenoids - toxic
Pheromones
What is a pheromone?
a chemical made by an organism which affects the social behaviour of other members of the same species
What are shoots in terms of tropisms?
positively phototropic
negatively geotropic
What are roots in terms of tropisms?
negatively phototropic
positively geotropic
Do plants grow quicker or slower in the dark?
quicker due to wanting reach light first
What does ethene do to stimulate ripening?
causes enzymes to breakdown cell walls and chlorophyll and convert it into glucose
What hormone is used as a rooting powder and in micropropagation?
ethene
What hormone is used as a weed killer?
auxin because they make weeds grow too fast so they die
What can cytokinins be used to do?
prevent ageing of ripened fruit
What are the commercial uses of plants hormones?
control ripening, rooting powder, weed killer
What are the commercial uses of plants hormones?
control ripening, rooting powder, weed killer
