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Plant behaviour

Plant behaviour. Plant BEHAVIOUR?!. Plants are also influenced by external factors/stimuli. Behaviour = reaction to stimulus. Tropisms. The growth of a plant in response to a stimulus Light Water Gravity Touch. Light tropism. Also called PHOTOTROPISM

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Plant behaviour

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  1. Plant behaviour

  2. Plant BEHAVIOUR?! • Plants are also influenced by external factors/stimuli. • Behaviour = reaction to stimulus

  3. Tropisms • The growth of a plant in response to a stimulus • Light • Water • Gravity • Touch

  4. Light tropism • Also called PHOTOTROPISM • Plants will face the light, usually sunlight • If plant FACES light, it is a POSITIVE phototropism. If it turns away from the light, it is a NEGATIVE phototropism

  5. Phototropism experiments • Tips of growing grass were covered • Tips no longer bent toward light • Therefore, region of receiving light messages must be in the tip • We now know that AUXIN, a plant hormone, is produced in the plant tip, and creates new cells for growth of the tip

  6. Auxin moves away from light • If the plant is bathed in even light, there is an even amount of auxin throughout the entire tip. • If the light is concentrated on one side, the auxin moves to the “dark side”, and produces greater growth on that side, elongating one side of the tip, creating a bend.

  7. The action of auxin

  8. Gravity tropism • Geotropism • Roots head down into the ground, while the tip of the plant grows upwards • Again – auxin is the culprit!

  9. Why have a geotropism? • Gain sunlight through green parts • Gain water through root system from ground water

  10. Climbing plants • Thigmotropism – change in growth in response to contact with another object • Twisting comes from elongation of cells that are not touching the object • Where do you think auxin is concentrated?

  11. Rhythmic behaviours in plants • Rhythmic behaviours: behaviours that happen daily, seasonally, yearly • Time stimulus • Solar tracking

  12. Time as stimulus for rhythmic behaviour • Plants have a biological clock • Leaves horizontal in day, “sleep” at night (why?) • 24 hour cycle – circadian rhythm • Opening and closing of flowers is also circadian

  13. Solar tracking • Heliotropism • Leaves and flowers move throughout the day so they are facing sun • Eg. Sunflowers (Helianthus annuus) have the ability to face the sun all day. What is the benefit of this?

  14. Timing of flowering • Photoperiodism – response of plants to different periods of light (relative length of day and night) • Some plants (eg. Chrysanthemum) only flower when day is shorter than night – short-day plants. • Some (eg. Carnations) only flower when day is longer than night – long-day plants • If they flower regardless of day/night length (eg. Dandelions), they are day-neutral plants

  15. Short and long day plants • If the “dark” period is interrupted: • Short-day: no flowering • Long-day: will flower

  16. Short and long day plants • During light hours, hormones are produced • These influence flower growth • The right amount of hormone must be produced for the specific plant

  17. Activities Glossary: tropism, phototropism, auxin, geotropism, thigmotropism, biological clock, circadian rhythm, heliotropism, photoperiodism, short-day plant, long-day plant, day-neutral plant Quick Check Questions: pg 367 Biochallenge pg 368, Chapter Review Q 2, 3, 4, 5, 6, 7, 8, 9, 10.

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