science F3 1.3

• Plant Stimulus and Response

  Definition

  Plants respond to touch, water, light, and gravity which are divided into two, namely the tropism response and the nastic response.
• Phototropism

  Growth of plant parts towards the light

  The growth of sunflower shoots in the direction of sunlight
• Geotropism

  Growth of plant parts towards gravity

  Root growth of red chili tree according to the direction of gravity
• Hydrotropism

  Growth of plant parts towards the water

  Growth of pandan tree roots in the direction of water
• Tigmotropism

  The movement of plant growth against touch or when in contact with an object

  Cucumbers have suckers that twist an object that touches them
• Nastic response:

  • Plants respond to touch, light, and heat
  • The direction of the response does not depend on the direction of the stimulus
  • For example, the leaves of a semalu tree (Mimosa pudica) are covered when touched
•  importance of each response:

  Phototropism

  Helps shoots get sunlight for photosynthesis

  Geotropism

  Helps the roots penetrate the soil to obtain water and the roots can grip the soil firmly

  Hydrotropism

  Helps plant roots absorb water and mineral salts from the soil

  Thigmotropism

  Helps plants reach the highest position to get sunlight and maintain an upright position

  Nastic movement

  Protects leaves from injury