1. INTERACTION FUNCTION IN PLANTS
UNIT 3
The interaction function
Natural Science 2. Secondary Education
INTERACTION FUNCTION IN PLANTS

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UNIT 3
This is how plants react
PLANT REACTIONS
There are 3 types:
TROPISMS
NASTIC MOVEMENTS
CHANGES IN THE PLANT’S VITAL PROCESSES
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Natural Science 2. Secondary Education

3. This is how plants react
UNIT 3
This is how plants react
Tropisms
These responses consist of a plant directing its growth towards (or away from) a stimulus. There are various types:
Phototropism. A response to light. The shoots of a plant grow towards the light; the roots, towards the dark.
Geotropism. A response to gravity. Roots grow towards the direction of gravitational pull.
Hydrotropism. A response to the presence of water. Roots grow towards water.
Thigmotropism. A response to contact: the shoots of creepers, for example, grow around the objects they touch.
Natural Science 2. Secondary Education

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UNIT 3
This is how plants react
An example of geotropism:
1. The stem grows away from the gravitational pull, and the roots grow towards it.
2. If we turn the plant on its side…
3. …it will begin to grow in a different direction, continuing to develop according to the gravitational pull.
Natural Science 2. Secondary Education
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5. This is how plants react
UNIT 3
This is how plants react
Nastic movements
These are plant responses which consist of rapid movements of some parts. They are usually reversible. For example:
Photonasty. A response to light. Some leaves or flowers turn towards sunlight, and there are some flowers that open or close depending on whether it is day or night.
Thigmonasty. A response to contact. Some plants fold their leaves when touched, and carnivorous plants trap their prey by snapping their leaves shut when an insect brushes against them.
Natural Science 2. Secondary Education

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This is how plants react
Photonasty
3: The leaves follow the direction of the sunlight, absorbing as much light as possible for photosynthesis.
1: The leaves are positioned to capture maximum sunlight.
2: As time goes by the Sun moves.
Natural Science 2. Secondary Education
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7. This is how plants react
UNIT 3
This is how plants react
Changes in the plant’s vital processes
Some plants react to stimuli by modifying some of their vital processes.
The most characteristic reactions of this type are the seasonal changes in plants, like flowering in spring, fruit maturing in the summer and leaves falling in autumn. These changes all depend on factors like temperature, light, the length of the day and night, etc.
Natural Science 2. Secondary Education

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This is how plants react
Seasonal changes in plants
1: Flowering
2: Fruit maturing
3: Leaves falling
Temperature oC
Temperature
Daylight hours
Daylight hours J
Months of the year
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