Chapter 16 (Plant Responses) Flashcards
How are gibberellins involved in seed germination?
The seed embryo is activated by water, producing gibberellins. These hormones stimulate the production of enzymes (such as amylases and proteases) which break down the food stores found in the seed.
How do auxins affect the growth of the apical shoot?
1) Auxins synthesised in meristem cells at the top of the apical shoot
2) Auxins diffuse away from the tip, binding to receptors on lower cells
3) This causes pH to fall and vacuoles develop (Low pH = flexible cell walls allow expansion of cells)
4) Auxins are destroyed by enzymes and cells can’t grow any more
This is the mechanism that causes apical shoots to grow.
How do auxins affect the growth of lateral shoots?
High concentrations of auxins suppress the growth of lateral shoots. The further down stem, the longer the lateral shoots can grow, because there is a lower concentration of auxin.
How do auxins affect root growth?
Small concentrations of auxins promote root growth. Auxins are produced by root tips and reaches the roots via the stem. If the stem is cut off, then auxin concentration in the roots decreases and their growth slows and stops.
What are the 5 main chemical defences which plants use against herbivory?
1) Tannins- bitter taste and toxic to insects
2) Alkaloids- very bitter, acts as drugs affecting metabolism, sometimes poisonous
3) Terpenoids- Toxic to insects and fungi
4) Pheromones- Communicate with members of the same species
5) Volatile organic compounds (VOCs)- Communicate with other species, such as parisitic wasps
What are the 4 main plant hormones?
Auxins
Gibberellins
Ethene
ABA (Abscisic acid)
What hormone is responsible in producing seedless fruit?
Auxins
Which hormone is responsible for stomatal closure?
Abscisic acid
What is the primary hormone responsible for abscission?
Ethene
