Objectives – What you will need to know from this section

1. 3.5.2 Responses in the Flowering Plant Objectives – What you will need to know from this section • Explain the term: growth regulation. • Define the following terms: tropisms, phototropism, geotropism, thigmotropism, hydrotropism, chemotropism. • Name examples of phototropism & geotropism. • Define the term: growth regulator. • Outline the transport of regulators via the vascular system.

2. Explain the term: Combined Effect • Explain the term: Growth Promoter. • Explain the term: Growth Inhibitor • Name 4 methods of anatomical/chemical adaptations that protect plants. • State 2 examples of the use of plant regulators. • Mandatory Activity :Effects of I.A.A. Growth Regulators on Plants

3. 3.5.2 Responses in the Flowering Plant • The ability to detect change and to respond is called sensitivity. Response is a form of defence that allows organisms to survive. • Plant adapt to new situations by modifying their growth, by means of chemicals called growth regulators [hormones]. • Growth is the increase in the number, size and volume of cells.

4. A hormone is a chemical produced in one part of an organism, transported to other tissues where it has its effect. • External factors that regulate the growth of plants are light intensity, day length, gravity, temperature. • Developmentmeans the changes that lead to specialised tissues and organs.

5. Plant growth regulators [hormones] are chemicals that interact with one another to control a particular development or response. • Plants only grow at their tips, in small regions of active celldivision called meristems—the tips of shoots, roots and sidebuds. • Plant growth regulators are produced in the meristems and transported through the vascular system of the plant.

6. Plant 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

7. LEARNING CHECK • What is the difference between growth and development? • What is a growth regulator? • List the properties of plant growth regulators • What is a meristem?

8. A tropism is a plant’s response to a stimulus coming from onedirection, e.g. sunlight, gravity. • Phototropism is a growth response of a stem towards light, sothat it can receive the maximum amount of light forphotosynthesis.

9. The coleoptile is the sheath around the leaves and shoot of grass seedlings, such as corn or oats.

10. Geotropism is the growth of a plant in response to gravity—itallows the root to get the water and nutrients it needs fromthe soil, and raises the leaves up into the light forphotosynthesis. • Thigmotropism is the growth of a plant in response to contact,e.g. vines wrap around objects which help support the plant.

11. Hydrotropism is the response of roots to water – they willgrow towards it. • Chemotropism is the response tochemicals, e.g. pollen tubesgrowing down the carpel in response to chemicals releasedby the ovule.

12. LEARNING CHECK • What is meant by the term “tropism”. • What is a coleoptile? • What is a stimulus. • Name 5 different tropisms and the stimulus involved in each case. • List the advantage to the plant of each tropism.

13. New roots developing Growth shut down for winter Plant growth regulators • Plant growth regulators interactwith one another to control a particular development or response. • Some regulators promote growth e.g. auxins, gibberellins, cytokinins. • Some regulators inhibit growth e.g. abscisic acid and ethene.

14. Auxins • promote cell enlargement and growth, • are involvedin phototropism and apical dominance APICAL DOMINANCE PHOTOTROPISM

15. Quicker growth here due to more hormones In shoots, light causes auxin to move down the shaded part of the stem, causing the shoot to grow towards the sunlight. This is called PHOTOTROPISM. Artificial auxins can also be used to kill weeds, stimulate root formation in cuttings, …

16. Gibberellins • cause stem lengthening, • Mobilise the stored foodin germinating seeds • Breakdormancy in buds and seeds in Spring.

17. Cytokinin • Cytokinins stimulate cell division (mitosis) and trigger leafgrowth in spring. Abscisin • Abscisic acid triggers bud and seed dormancy in autumn andinhibits cell growth. Ethene • Ethene promotes ripening of fruit and the fall of leaves, flowersand fruits.

18. Uses of plant regulators • Artificial auxins are used in rooting powders to stimulate root formation in stem cuttings. • A synthetic auxin [2,4-D] is used as a selective weedkiller, making the plants grow too fast. • Fruit is transported green and unripe, and can then be quickly ripened by spraying it with ethene.

19. LEARNING CHECK • What is a plant growth regulator? • Explain the terms “promote” and “inhibit”. • Name 5 growth regulators and a function of each. • Give 3 examples of how we make use of plants growth regulators [natural or artificial]

20. Plant Defences • The growth and development responses described so far are a form of defence that allows a plant to survive difficult conditions [environmental stress] in its habitat. • Plants can’t move and so need to defend themselves against being eaten or damaged.

21. Some adaptations that plants use to protect themselves include: • Spines, thorns or stinging hairs to deter animals from eating them, e.g. cacti, nettles.

22. Cassava plant • Cassava root tuber • 2. Toxins that cause illness or death, e.g. Cassava is an important food source in tropical countries, but its leaves and roots produce cyanide poison to protect it against insects and other herbivores. The roots must be processed properly if humans are not to be poisoned.

23. 3. In autumn, trees recycle all the nutrients they can out of the leaves for storage in phloem tissue. The red pigments of autumn serve as a kind of botanical sunscreen, a defence mechanism against sun damage that could interfere with the storage process and cause a leaf to drop before the tree was done with it.

24. Heat-shock proteins [stress proteins] are created when cells are exposed to higher temperatures or to other kinds of environmental stress, such as UV light. Their activities are part of a cell's repair system and allow the plant to tolerate extra heat, light, etc. for a limited period, and resume normal cellular activities when the stress ends. • Stress proteins act like chaperons and provide "shelters" in which new protein chains can be "incubated" until they have folded properly

25. Plant protection • Plants need to protect themselves from their environment They protect themselves against: • Loss of water • Overheating • Infection from micro organisms • Being eaten by herbivores

26. Adaptations for Protection in Plants Plants can adapt themselves for protection in two ways: • Structural or anatomical adaptations • Chemical adaptations

27. 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

28. Chemical Adaptations • Production of Tannins to make the plant indigestible • Production of toxicchemicals 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

29. Most important adaptation Plants can grow and regenerate throughout their life. They can produce new roots, stems, leaves.

30. LEARNING CHECK • Why is defence important to plants? • List four methods used by plants to defend themselves. • Explain the term “structural adaptation”. • What is a toxin? • What advantage is it to a plant that it grows throughout its life [from meristems]?