Plant reponses Flashcards
What is a tropism
a plant that shows directional growth in response to environmental cues
Key roles of auxins
- cell elongation
- prevent leaf fall
- fruit ripening
- involved in tropisms
- ethene release
Key roles of gibberelins
- stem elongation
- trigger mobilisation in of food stores in seed germination
- stimulate pollen tube growth in fertilisation
Key roles of ethene
- fruit ripening
- abscission in deciduous trees
Key roles of abscisic acid (ABA)
- stimulate stomatal closing
- stimulate cold protective responses
- maintain seed and bud dormancy
What is a cotyledon
a food store in a dicot seed
How do gibberellins stimulate seed germination
- gibberellins begin to be produced when a seed absorbs water and the embryo is activated
- gibberellins stimulate the production of enzymes that break down food stored
- embryo uses food stores to produce ATP for building materials to break through seed coat
Role of auxins in growth
Apical dominance- growth of the main branch only
How do auxins affect cell wall plasticity
- auxin present means the wall stretches more easily
- auxin molecules bind to receptors in the plant cell membrane, causing the pH to fall to 5
- pH 5 is the optimum for enzymes to keep the walls stretchy
- as the cells mature, auxin is destroyed, causing pH to rise so enzymes maintaining plasticity are inactive
- walls become rigid so cells can no longer grow and expand
What do high concentrations of auxins do
- suppress the growth of lateral shoots (branches)
- results in apical dominance
- shoots lower down aren’t affected so that lower lateral shoots grow better
What is an internode
- regions between leaves on a stem
What is synergism
- different hormones work together, complimenting each other
- give a response greater than they would individually
What is antagonism
- substances have opposite effects, the balance between them determines the plants response
- give an effect smaller than they would individually
Why do plants lose their leaves as a result of abiotic stress
- glucose required for respiration and to maintain leaves > glucose produced by photosynthesis
What is photoperiodism
- the idea that plants are sensitive to lack of light in their environment
What is phytochrome
-a light sensitive pigment, existing in 2 forms, Pr and Pfr
- each of the forms absorbs a different type of light