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Natural Science 2. Secondary Education
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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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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.
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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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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.
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Natural Science 2. Secondary Education
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Changes in the plants 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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Seasonal changes in plants
1 Flowering
2 Fruit maturing
3 Leaves falling
Temperature oC
Daylight hours
Temperature
Daylight hours
J
Months of the year
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Natural Science 2. Secondary Education