(a)(i) Define tropic and nastic movements.
(ii) List four differences between tropic and nastic movements.
(b) Describe an experiment to show that auxins are produced in the apical cells of a shoot.
(c)(i) Name two plant hormones, other than auxins.
(ii) Give two examples of tropism.
Explanation
(a) Definition of tropic and nastic movements:
(i) Tropic movement is growth movement of plant organs in response to external unilateral or directional stimulus. Nastic movement is the movement of certain parts of plants in response to diffuse or non-directional stimulus.
(ii)
| Tropic movement | Nastic movement |
|
Movement is not easily reversible. |
Movement is reversible. |
Experiment to show that auxins are produced in the apical cells of a shoot:
Aim: To show that auxins are produced in the apical cells of a shoot.
Material: 3 potted seedlings of maize labelled A, B and C; agar block, sharp knife/cutting instruments, mica sheet / aluminium foil/cover slip.
Methods:
(i) Cut tip of coleoptile/shoot in Ato serve as control
(ii) Leave decapitated shoot for about 48 hours
(iii) Select another potted seedling, B,.and cut off tip of coleoptile/shoot
(iv) Place the cut tip on an agar block for about 2 — 6 hours
(v) Place agar block on stump of the decapitated shoot and leave for about 48 hours
(vi) Select a third seedling, C, and cut off tip of the coleoptile
(vii) Place tip of the cut coleoptile on mica sheet for 2 — 6 hours
(viii)Place mica sheet on cut surface of decapitated shoot and leave for about 48 hours.
Observation: Growth ceased in decapitated shoot A, but when agar block was placed on stump of shoot B in which growth had stopped, growth resumed. When mica sheet was placed on stump of shoot C in which growth had stopped, growth did not take place (resume).
Conclusion: This shows that a chemical substance (auxin) produced at the tip, i.e., apical cell of the shoot is responsible for the growth of the shoot.
(c)(i) Names of plant hormones other than auxins are
- Gibberellic acid / Gibberellin
- 2, 4 - D 2, 4 - Dichlorophenozy acid
- cytokinis/kinins/kinetin
- abscisic acid/abscisin
- ethylene/ethene
- traumatin
- florigen
- dormin
- formin, etc.
(ii) Examples of tropisms are:
- geotropism
- hydrotropism
- thigmotropism/Haptrodropism
- photoropism
- stereotropism
- chemotropism
- thermotropism.