Chapter 16 - Plant Responses Flashcards
Give 4 important plant hormones
Auxins
Gibberellin
Ethene
ABA
Where are auxins made?
At the tips of roots and shoots
How do auxins cause cell elongation?
- Auxins bind to receptor sites on cells
- Causes the pH to fall to 5
- pH 5 is optimal for enzymes that make the cell walls flexible
- This allows the cell to expand as they absorb more water, as the vacuoles get bigger
- Eventually, a large central vacuole is formed
What happens in cells once the cell has matured/finished elongation?
- Auxins destroyed by enzymes
- Cell walls become rigid
- No further cell elongation is possible
What is the effect of high auxin concentrations on the shoots?
High concentrations of auxins suppress the growth of lateral shoots. This causes apical dominance
What is apical dominance?
Where the plants main shoot dominates and inhibits the growth of other shoots
How can we show experimentally that apical dominance occurs due to auxins?
If the apical shoot tip is removed, the auxin-producing cells are removed. As a result, the lateral shoots, freed from the dominance of the apical shoot, grow faster
What is the role of gibberellin in germination?
They stimulate the production of enzymes that break down food stores found in the seed
How do gibberellins impact the elongation of plant stems during growth?
Gibberellins affect the length of internodes on the stem
What are internodes?
The regions of the stem between leaves (nodes)
Why do some scientists breed varieties of plants where the gibberellin synthesis pathway is interrupted?
So less gibberellins are produced, making the plant stems shorter, reducing waste and making the plants less vulnerable to damage
What is synergism in plants?
Where different hormones work together, complimenting each other and giving a greater response than they would on their own
What is antagonism in plants?
Where different hormones have opposite effects (e.g. one promoting and one inhibiting growth).
Give 3 examples of abiotic stresses
Lack of or excess of water
High winds
Hot or cold temperatures
What is phytochrome?
The light sensitive pigment that allows plants to respond to changing day lengths
