Life Processes in Plants

1. Life Processes in Plants Plant responses to the Environment J Gerber and J Goliath

2. Plant hormones ◊ General functions of the following plant hormones: • Auxins • Gibberellins • Abscisic acid • Investigate geotropism and phototropism by controlling variables ◊ Role of auxins in geotropism through the regulation of differential growth ◊ Role of auxins in phototropism through the regulation of differential growth ◊ Uses of plant hormones in agriculture: • Auxins as herbicides • Auxins to control apical dominance • Auxins and gibberellins to increase/stimulate fruit development J Gerber and J Goliath

3. Plant defense mechanisms ◊ The role of the following as plant defense mechanisms: • Chemicals (protection) against infection from pathogenic micro-organisms and from being eaten by herbivores) • Thorns (protection from being eaten by animals/to reduce water loss J Gerber and J Goliath

4. Activity 1- Tropism Instructions • Explanation of activity on phototropism and geotropism. • In pairs/groups discuss the information and answer the questions that follow. • After 15 minutes each pair/group give feedback. J Gerber and J Goliath

5. Plant hormones • Performs a specific function, which controls further growth and development of the plant. • Stimulation – a process is turned on or activated. • Inhibition – a process is turned off or stopped. J Gerber and J Goliath

6. Auxins • Group of plant hormones that are mainly produced in the apical meristem of the stems and roots. • Indole acetic acid is the most common natural auxin. • Auxins move down in the phloem to cells lower down in the plant. • Small amounts of auxins are produced in the growing points of roots. J Gerber and J Goliath

7. Functions of auxins • Stimulate cell division. • Stimulate cell elongation. • Promotes apical dominance (agriculture). • Develops adventitious roots. • Cause tropic movement in stems and roots. • Stimulates the development of fruit. J Gerber and J Goliath

8. Functions of gibberellins • Stimulate stem elongation. • Stimulate root growth. • Promote flowering. • Promote the growth of lateral buds. • Stimulate the germination of seeds. J Gerber and J Goliath

9. Functions of abscisic acid • Inhibits cell division and growth in stems and roots. • Prevents bud and seed growth in winter. • Promotes the abscission of leaves and frui.t • Controls the stomata opening and closing. • Speeds up fruit ripening. J Gerber and J Goliath

10. Role of auxins in phototropism • Phototropism is the growth movement of a plant or part of a plant in response to unilateral light stimulus. • A high auxin concentration builds up on the side of the stem furthest of the light source. • Cell division and elongation are stimulated and grow faster. • The stem curves in the direction of the light and positively phototropic. • Negative phototropism occurs in roots – grow away from a light source. J Gerber and J Goliath

11. Role of auxins in geotropism • Young seedling is placed horizontally – roots grow downwards and stem upwards. • Auxins accumulate on the lower side of the root. • Higher auxin concentration on the lower side of the root inhibits cell division and elongation. • Cells on the upper side of the root grow faster – lower auxin concentration. • Root curves downwards – positively geotropism. • Stem curves upwards – negatively geotropism. J Gerber and J Goliath

12. Uses of plant hormones in agriculture • Root formation in cuttings. • Production of seedless fruit. • Ripening of fruit. • Increase in fruit size. • Stimulation of germination of seeds. • Weed control. • Apical dominance. J Gerber and J Goliath

13. Auxins as herbicides • Synthetic herbicides (weed killers) contain high concentrations of auxins. • Accelerate the metabolism of broad-leaved dicotyledonous weeds and stimulate growth. • Weeds grow so fast that water absorption is insufficient. • Plants weaken and die. J Gerber and J Goliath

14. Apical dominance • Apical dominance occurs when the apical bud of the main shoot grows more strongly than lateral bud below. • Removing the apical bud from the top of the plant, auxin is also removed. • More lateral grow below the apical bud. • Pruning promotes the grow of lateral branches. • The value of pruning – plant grows bushier and fruit formation can be controlled. J Gerber and J Goliath

15. Plant defense mechanisms- thorns • Sharp thorns protect the plants against herbivores. • Less damage to plants by herbivores and plants continue to grow. • Reduce water loss. J Gerber and J Goliath

16. Plant defense mechanisms- chemicals • Many plants produce chemicals and play a role in the defence against herbivores and pathogenic-organisms. • Chemicals are poisonous or influence the digestibility of plant material. J Gerber and J Goliath