Plant Control Mechanisms and tropisms

Control Mechanisms and Responses to Stimuli

Plant Behavior

• Plants respond to their environments in various ways.
• Example: A plant bending towards sunlight is a beneficial behavior.

Plant Responses

• Plants lack brains or a nervous system but still respond to their environments.
• The sensitive plant folds its leaves when touched to protect itself from herbivores.

Nastic Movement

• Nastic Movement: The movement of a plant part in response to a stimulus.
• Types of nastic movement:
  • Phototropism
  • Gravitropism
  • Thigmotropism
  • Hydrotropism

Phototropism

• Plants use chemicals to move or change shape without brains or nervous systems.
• Tropism: When plants move in response to a stimulus.
• Phototropism: Plants moving towards sunlight to make food.
• "photo" = light

Tropism and Seed Growth

• Seeds buried in the dark know which direction to grow when stems and roots emerge.
• Roots typically grow downwards, not upwards.
• Plants respond to gravity to determine growth direction.

Gravitropism

• Gravitropism: Plants responding to gravity.
• Stems grow away from gravity.
• Roots grow towards gravity.

Thigmotropism

• Thigmotropism: A response to touch.
• The sensitive plant folding leaves when touched is an example of thigmotropism.
• Vines rely on touch to grow around objects.
• "thigmo" = touch

Hydrotropism

• Hydrotropism: Directional growth in response to water concentration.
• Root cells sense moisture gradients and grow towards or away from moisture.
• "hydro" = water
• Example: Mangrove roots growing towards water.

Plant Hormones

• Plants produce hormones like animals.
• Hormones:
  • Signal molecules produced in response to a stimulus.
  • Transported to other parts of the organism.
  • Bind to a receptor.
  • Have an effect (a response).

Plant Hormones - Auxin

• Auxin is a plant hormone involved in phototropism.
• Auxin concentrates on the side of the plant away from the sun to control phototropism.