AP Biology Questions on Plant Tropisms

📚 Quick Study Guide

• 🌱 Tropism Definition: A tropism is a biological phenomenon, indicating growth or turning movement of a biological organism, usually a plant, in response to an environmental stimulus.
• ☀️ Phototropism: Growth response to light. Positive phototropism is growth towards light; negative is growth away.
• 🌿 Gravitropism: Growth response to gravity. Roots show positive gravitropism (grow downward), shoots usually show negative gravitropism (grow upward).
• 💧 Hydrotropism: Growth response to water concentration. Roots grow towards areas with higher water availability.
• 🧭 Thigmotropism: Growth response to touch or physical contact. Common in climbing plants.
• 🧪 Auxin's Role: Auxin, a plant hormone, plays a key role in phototropism and gravitropism. It promotes cell elongation on the shaded side in phototropism and the lower side in gravitropism.
• ⏱️ Receptors and Signal Transduction: Plants use photoreceptors (e.g., phototropins) and complex signaling pathways to detect and respond to stimuli.

🧪 Practice Quiz

1. Which of the following best describes phototropism?
   1. A) A plant's growth response to gravity.
   2. B) A plant's growth response to light.
   3. C) A plant's growth response to touch.
   4. D) A plant's growth response to water.
2. Roots growing downward demonstrate which type of tropism?
   1. A) Negative gravitropism
   2. B) Positive phototropism
   3. C) Positive gravitropism
   4. D) Negative phototropism
3. What hormone is primarily responsible for phototropism and gravitropism?
   1. A) Gibberellin
   2. B) Cytokinin
   3. C) Ethylene
   4. D) Auxin
4. A vine wrapping around a trellis exhibits which type of tropism?
   1. A) Hydrotropism
   2. B) Thigmotropism
   3. C) Phototropism
   4. D) Gravitropism
5. What is the likely response of a plant root encountering a dry patch of soil with a moister area nearby?
   1. A) Grow away from the moister area due to negative hydrotropism.
   2. B) Continue growing straight, unaffected by the moisture gradient.
   3. C) Grow toward the moister area due to positive hydrotropism.
   4. D) Exhibit no growth.
6. Which of the following is NOT an example of a tropism?
   1. A) The closing of a Venus flytrap.
   2. B) A sunflower tracking the sun.
   3. C) Roots growing towards a water source.
   4. D) A stem bending towards a light source.
7. How do plants detect light for phototropism?
   1. A) Through chloroplasts in the leaves.
   2. B) Through photoreceptors like phototropins.
   3. C) Through the roots.
   4. D) Through stomata on the leaf surface.