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Chapter 24

Chapter 24 . Plant Response to Stimuli. 3.5.2 Responses in the Flowering Plant . Objectives – What you will need to know from this section. Describe the organs used by plants to respond to stimuli Explain the term: growth regulation.

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Chapter 24

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  1. Chapter 24 Plant Response to Stimuli

  2. 3.5.2 Responses in the Flowering Plant Objectives – What you will need to know from this section Describe the organs used by plants to respond to stimuli 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.

  3. 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

  4. 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].

  5. 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 • and others.

  6. Plant growth regulators [hormones] 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 cell division called meristems— the tips of shoots, roots and sidebuds.

  7. Plant Growth Regulators • Chemicals that control the growth of plants • They are produced in the meristems • They are transported in the xylem and phloem • Even a small amount of growth regulator can have great effect on growth

  8. LEARNING CHECK • The ability to detect change and to respond is called? • Plants adapt to new situations by? • What is a growth regulator? • List the properties of plant growth regulators. • What is a meristem?

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

  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.

  11. Thigmotropism is the growth of a plant in response to contact,e.g. ivy wraps around objects which help support it.

  12. Hydrotropism is the response of roots to water – they willgrow towards it.

  13. Chemotropism is the response tochemicals, e.g. pollen tubesgrowing down the carpel in response to chemicals releasedby the ovule.

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

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

  16. Auxins • Growth promoters i.e. promote cell enlargement and growth, • are involvedin phototropism and apical dominance APICAL DOMINANCE PHOTOTROPISM

  17. Apical dominance • Auxins are responsible for apical dominance, where the main bud inhibits the growth of buds lower down stem. • This photograph shows side buds sprouting when the main stem is cut off [pruned].

  18. Quicker growth here due to more hormones Phototropism When light shines on plants it causes auxin to move down the shaded part of the stem, causing the shoot to bend and grow towards the sunlight - phototropism

  19. Gibberellins cause stem lengthening, mobilise the stored foodin germinating seeds, breakdormancy in buds and seeds in Spring.

  20. Cytokinins Cytokinins stimulate cell division (mitosis) and trigger leafgrowth in spring.

  21. Abscisic Acid Abscisic acid triggers bud and seed dormancy in autumn andinhibits cell growth.

  22. Ethene promotes ripening of fruit and the fall of leaves, flowersand fruits. Ethene

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

  24. 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]

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

  26. Plant Defences • Some adaptations that plants use to protect themselves include: • 1. Anatomical: • Spines, thorns or stinging hairs to deter animals from eating them, e.g. cacti, nettles.

  27. 2. Chemical: • Toxins that cause illness or death, e.g. Oak produces tannins in their leaves to protect them against caterpillars. The leaves and acorns of the oak tree are poisonous to cattle, horses, sheep, and goats in large amounts due to the toxin tannic acid, and cause kidney damage and gastroenteritis.

  28. 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]?

  29. AUXINS -- HIGHER LEVEL Auxins affect virtually every aspect of plant development, and how they respond to environmental stimuli. Auxins influence includes phototropism, geotropism, cell enlargement and growth, apical dominance, root growth, fruit development, vascular development, and senescence [aging].

  30. AUXINS Growth – the zone of elongation grows, extending the shoot & root. Apical dominance – auxin produced in the shoot tip inhibits the growth of buds lower down stem. Tropisms - involved in phototropism —stem bends towards lightdue to cell enlargement

  31. IAA (Indoleacetic acid) is an auxin that is made in the meristems of shoots, buds and roots, and in the tips of coleoptiles [of grasses].

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

  33. Auxin Animations of auxin

  34. LEARNING CHECK • What is an auxin? • List 4 effects of auxins in a plant. • List the properties of auxins. • What does elongation mean? • What is IAA? • What is a meristem? • What is a coleoptile?

  35. Quicker growth here due to more auxin Phototropism & Auxins • If a plant receives light from one side only: • the light causes auxin to travel down by active transport in the phloem tissue • from the stem / meristem • down the ‘dark’ side of the stem (orcoleoptile).

  36. Phototropism & Auxins • The extra auxin loosens the cellulose fibres in plant cell walls & • this allows the cells to elongate (get longer) faster than cells onthe ‘bright’ side. • causing the stem to bend towards the light

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