5.5 PLANT RESPONSE Flashcards
Describe the two types of response to external stimuli in plants
1) Tropism = a directional growth towards an external stimulus
2) Nastic response = a nondirectional response to external stimuli (usually chemical release)
Describe the five physical defences of plants
1) Cellulose cell wall - physical barrier
2) Ligin thickening of cell walls - waterproof and indigestible
3) Waxy cuticle - prevents water from collecting on surface so pathogens are not attracted
4) Callose - deposited in sieve tubes to block flow of pathogens
State the three chemicals released to prevent plants being eaten
1) Tannins
2) Alkaloids
3) Phermones
Describe the action of tannins
- Toxic to microorganisms and larger herbivores
- Taste bad
Describe the action of alkaloids
- Taste bitter
- Found in growing tips and flowers
Describe the action of pheromones
- When released affect the behaviour of others
State the four types of tropism
1) Phototropism
2) Geotropism
3) Chemotropism
4) Thigmotropism
Define phototropism
- Where shoots grow towards light (positive phototropism)
Define geotropism
- Where roots grow towards gravity (positive geotropism)
Define chemotropism
- On a flower, pollen tubes grow down the style (attracted by chemicals) towards the ovary where fertilization can take place
Define thigmotropism
- Shoots of climbing plants wind around other plants or solid structures to gain support
Define photoperiod
- The period of time in a day that an organism is exposed to light
State the five plant hormones
1) Auxins
2) Cytokinins
3) Gibberellins
4) Ethylene
5) Abscisic acid
Describe the location and four effects of cytokinin hormone
(ROOTS but transported from there)
1) Promote cell division
2) Delay leaf senescence (delays aging)
3) Promote cell expansion
4) Overcome apical dominance
Describe the location and two effects of abscisic acid hormone
(MATURE LEAVES/ROOTS)
1) Inhibits seed germination and growth
2) Causes stomatal closure when the plant is stressed by lower water availibility
Describe the location and three effects of auxin (IAA) hormone
(APICAL SHOOT TIP BUDS)
1) Promotes cell elongation
2) Inhibits growth of side shoots (from lateral buds)
3) Inhibits leaf fall
Describe the location and two effects of gibberellin hormone
(APICAL BUDS OF ROOTS AND SHOOTS)
1) Promotes seed germination
2) Promotes stem growth (via cell elongation by loosening cell walls) and (via cell division by stimulating the production of a protein that controls the cell cycle)