1. PLANT RESPONSES

2. Syllabus links 3.5.2 Responses in the Flowering Plant
Growth regulation.

3. Stimulus and response
A stimulus is anything that causes a reaction in an organism or in any of its parts
A response is the activity of a cell or organism as a result of a stimulus

4. The structures required for response by organisms
Chemical or hormonal (plants and animals)
Nerve and sense organ system (animals)
Growth, muscular and skeletal systems
A defence or immune system
Plants do not possess nervous systems but depend on chemical co – ordination for their responses – much slower!!
Plant responses involve growth and changes in growth

5. Responses in flowering plants
External factors
Light
Day length
Gravity
Temperature
Internal factors
Plants produce a number of chemicals called growth regulators
These are produced are produced in the meristematic regions of the plant – root tip or shoot tip

6. Syllabus links 3.5.2 Responses in the Flowering Plant
Tropisms: definition of the following: "phototropism", "geotropism", "thigmatropism", "hydrotropism", and "chemotropism".
Examples of phototropism and geotropism.

7. Tropisms
“A tropism is a change in the growth of a plant in response to an external stimulus”
Phototropism
Geotropism
Thigmotropism
Chemotropism
Hydrotropism

8. Syllabus links 3.5.2 Responses in the Flowering Plant
Regulatory system: definition of a “growth regulator”, transport through the vascular system, combined effect, growth promoter and growth inhibitor.
CIT: Use of plant regulators: any two examples.
PA: Investigate the effect of I.A.A. growth regulator on plant tissue.

9. Growth Regulators Plant responses are due to growth regulators
A growth regulator is a chemical that controls the growth of a plants
Regulator that promotes growth - Auxin stimulates cell elongation
Regulator that inhibits growth
Ethene inhibits cell elongation

10. Growth Regulators They are active in very small amounts
They are produced in the meristems
They are transported in the xylem and phloem
Their effects are dependent on concentration
A small amount of growth regulator can have great effect on growth

11. Auxins Auxins cause: Stem growth Root growth
Fruit formation ( at certain concentrations)
Example of Auxin = IAA Indoleacetic acid

12. Auxins Production sites • Apical Meristems • Seed Embryos
• Young leaves

13. Functions of Auxins Stem elongation Root growth Cell differentiation
Development of fruit (IAA)
Apical dominance ( inhibit side branches)
Phototropism
Geotropism

14. Effects of auxins Tropisms Apical dominance Fruit formation
Root growth

15. Causes cell elongation and growth or bending
Tropisms
Causes cell elongation and growth or bending

16. Apical dominance
Auxin produced in the apex (tip) will pass down the stem and inhibit lateral buds
This means that the apex will grow at the expense of the lateral buds will grow at the expense of the side branches
Clearly seen in cacti and conifers
If the apex is removed the side branches are allowed to develop
Produces low bushy forms in this case

17. Fruit formation
IAA is made in developing seeds which stimulates food to form in the fruit
If IAA is artificially applied to flowers before pollination and fertilisation occur, the ovary enlarges and forms seedless fruit – parthenocarpic fruit (virgin fruit)
Examples include seedless grapes, oranges and tomatoes

18. Root growth
At low concentrations, IAA causes roots to grow. IAA can be applied artificially to stimulate rooting

19. The mechanism of a plant response to light (phototropism)

20. Growth Inhibitors Ethene is a gas. It is produced in: It causes:
• Stem nodes
• Ripe fruits
• Decaying leaves
It causes:
• Fruits to ripen
• Leaves to fall in autumn
• Plants to age

21. Commercial Growth Regulators
Ripen bananas
Bananas are picked green – ethene is used to stimulate ripening just before distribution
Rooting Powders
Contain synthetic growth regulator NAA. It stimulates rapid root formation on stem cuttings

22. Syllabus links 3.5.2 Responses in the Flowering Plant
Name four methods of anatomical or chemical adaptation that protect plants.

23. Adaptations for Protection in Plants
They protect themselves against:
Loss of water
Overheating
Infection from micro organisms
Being eaten by herbivores

24. Plant protection
Plants can adapt themselves for protection in two ways:
1. Structural or anatomical adaptations
2. Chemical adaptations

25. Structural Adaptations
Bark/epidermis prevents entry of microbes and reduces loss of water
Thick cuticle on stem or leaves in plants that live in dry places
Thorns prevent plants from being eaten by herbivores
Stinging cell in epidermis prevent plants been eaten
Guard cells change shape when they lose water which causes stomata to close and this reduces water loss

26. Chemical Adaptations
Production of Tannins to make the plant indigestible
Production of toxic chemicals to prevent growth of insect larvae
Production of strychnine and nicotine in legumes that damage nerves and muscles
Production of heat shock proteins to protect enzymes when temperatures are high