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.