PLANT RESPONSES

Syllabus links 3.5.2 Responses in the Flowering Plant Growth regulation.

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

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

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

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.

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

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.

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

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

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

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

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

Effects of auxins Tropisms Apical dominance Fruit formation Root growth

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

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

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

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

The mechanism of a plant response to light (phototropism)

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

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

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

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

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

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

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