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
3 examples of physical defenses in plants
Thorns
Inedible tissue
Spiny leaves
Give 3 plant chemical defenses
Tannins
Alkaloids
Terpenoids
What do tannins do?
They give plants a very bitter taste, which puts animals off eating them, and are toxic to insects
What do alkaloids do?
A large group of compounds, that often act as drugs, affecting the metabolism of animals that take them in, sometimes poisoning them
What do terpenoids do?
They often act as toxins to insects and fungi that might attack the plant
What are pheromones?
Chemicals made by an organism which affects the social behaviour of members of the same species
Do plants rely a lot on pheromones and why?
No they do not, as they do not behave socially
Give an example of where plants could be regarded as using pheromones
If a maple tree is attackes by insects, it releases a pheromone that is absorbed by leaves on other branches, causing them to prepare to protect themselves against the insect
What do plants use more often than pheromones?
VOCs
What are VOCs?
Volatile organic compounds.
They act similarly to pheromones, but between themselves and other species
Why do plants initially grow more rapidly in the dark?
Because the biological imperative is to grow upwards rapidly to reach the light
How do shoots respond to geotropism?
Shoots are negatively geotropic (meaning they grow away from the gravitational pull)
How do roots respond to geotropism?
They are positively geotropic (meaning they grow towards the gravitational pull)
