5.5.1 Plant responses to stimuli

• Phototropism is a growth response to light
• What is geotropism a response to?

  Gravity
• Hydrotropism is the growth response to water, where roots grow towards areas of higher moisture.

  True
• What is thigmotropism a response to?

  Touch/physical contact
• Tropisms allow plants to optimize their growth in response to environmental factors.


  True
• Which plant growth hormone promotes cell elongation in shoots, leading to phototropism and geotropism?

  Auxin
• Abscisic acid (ABA) inhibits growth and promotes stomatal closure in response to drought stress.


  True
• ABA helps plants respond to drought stress, affecting their growth in hydrotropism
• Auxin promotes cell elongation in shoots, leading to phototropism and geotropism
• Match the plant growth hormone with its function in tropisms:

  Auxin ↔️ Promotes cell elongation

  Gibberellins ↔️ Stimulates stem elongation

  Ethylene ↔️ Involved in fruit ripening

  ABA ↔️ Inhibits growth

  Cytokinins ↔️ Promotes cell division
• Abscisic Acid (ABA) inhibits growth and promotes stomatal closure, helping plants respond to drought stress and affecting hydrotropism
• Auxin accumulates on the shaded side of a plant stem in response to light, causing it to bend towards the light source.


  True
• Statoliths are dense, starch-filled organelles that signal the direction of gravity
• Steps of geotropism in roots:

  1️⃣ Statoliths in root cap sense gravity

  2️⃣ Auxin redistributes to lower side

  3️⃣ Differential growth causes bending

  4️⃣ Roots grow downwards
• What is the stimulus for hydrotropism in plants?

  Moisture gradient
• What are tropisms defined as?

  Directional growth responses
• In phototropism, shoots grow towards light while roots grow away from it.


  True
• In geotropism, roots show positive growth, meaning they grow downwards
• Match the tropism with its stimulus:

  Phototropism ↔️ Light

  Geotropism ↔️ Gravity

  Hydrotropism ↔️ Water

  Thigmotropism ↔️ Touch
• In thigmotropism, tendrils and climbing stems wrap around supports
• Steps in phototropism caused by auxin redistribution

  1️⃣ Light source is detected

  2️⃣ Auxin accumulates on the shaded side

  3️⃣ Cells on the shaded side elongate more

  4️⃣ Stem bends towards the light
• Gibberellins stimulate stem elongation and germination
• Which plant growth hormone is involved in fruit ripening, abscission, and thigmotropism?

  Ethylene
• What hormone promotes cell elongation in shoots, leading to phototropism and geotropism?

  Auxin
• Gibberellins stimulate stem elongation and germination, contributing to geotropism.

  True
• What hormone is involved in fruit ripening and abscission, as well as thigmotropism?

  Ethylene
• What environmental stimulus triggers phototropism in plants?

  Light
• What is the primary hormone responsible for regulating phototropism?

  Auxin
• What hormone regulates cell elongation and growth in geotropism?

  Auxin
• Roots exhibit positive geotropism by growing downwards.


  True
• Match the tropism with its stimulus:

  Hydrotropism ↔️ Moisture gradient

  Phototropism ↔️ Light

  Geotropism ↔️ Gravity
• What is the directional growth response of plants to environmental stimuli called?

  Tropisms
• Thigmotropism is growth in response to touch
• In geotropism, which two hormones redistribute to cause differential growth?

  Auxin and Gibberellins
• Gibberellins aid geotropism by stimulating stem elongation and seed germination.

  True
• Statoliths are dense organelles that signal the direction of gravity
• When unidirectional light strikes a plant, the hormone auxin redistributes to the shaded
• Statoliths are dense, starch-filled organelles located in the root cap cells that signal the direction of gravity
• Hydrotropism is the directional growth of plant roots towards a moisture source
• In hydrotropism, roots grow towards moisture to maximize water absorption.


  True