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  1. Ecology theory
    5 Topics
    |
    1 Quiz
  2. Unit 1
    Nutrient recycling
    4 Topics
    |
    1 Quiz
  3. Ecological relationships and population dynamics
    2 Topics
  4. Human impact on the ecosystem
    2 Topics
  5. Study of a grassland ecosystem
    3 Topics
  6. Responses in the Flowering Plant
    4 Topics
    |
    1 Quiz
  7. Unit 3
    Sexual reproduction in the flowering plant
    1 Topic
  8. The human reproductive system
    3 Topics
  9. The menstrual cycle
    2 Topics
  10. Pregnancy
    2 Topics
  11. The circulatory system
    4 Topics
  12. Blood
    5 Topics
  13. The heart
    5 Topics
Lesson 6, Topic 1
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Topic 1: Plant tropisms

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What are plant tropisms ?

  • A tropism is the growth response of a plant to an external stimulus
  • Tropisms help plants to achieve the best growing conditions

Types of tropism

PHOTOTROPISM

The growth response of a plant to light

  • Stems are positively phototropic (i.e. grow towards them light)
  • Roots are negatively phototropic (i.e. grow downwards towards water ), e.g. ivy, where the roots grow away from the light, towards the wall

GEOTROPISM

The growth response of a plant to gravity

  • Roots are positively geototropic (they grow in the direction of gravitational pull, i.e. downwards)
  • Stems are negatively geototropic (they grow in against the direction of the gravitational pull, i.e. upwards )

THIGMOTROPISM

The growth response of a plant to touch

Here are some examples of thigmotropism in plants:

Mimosa pudica or “sensitive” plant responds to touch by completely folding its leaf when touched. Scientists think that this response is to help protect the plant from insects.

An example of this tropism is the curling of a vine tendril around objects that it touches. This helps the plant securely position itself and keep growing, as these types of plants do not usually have a strong stem to keep themselves upright.

The Venus fly trap is another plant that responds to the external touch stimulus. When the hairs on the inside of the leaf are triggered, usually when an insect has landed, the leaf closes shut. Why? Insects provide nutrients to the plant. Over time, the insect is dissolved and the nutrients will be absorbed by the plant.

HYDROTROPISM

The growth response of a plant to water

CHEMOTROPISM

The growth response of a plant to chemicals

Topic quiz