Tropic Movements in Plants MCQs Quiz | Class 10
This quiz covers Class X Science (Code 086), Unit II: World of Living, focusing on Tropic Movements in Plants. Test your knowledge on Phototropism, Geotropism, and Hydrotropism. Submit your answers to view results and download a detailed PDF of your performance.
Understanding Tropic Movements in Plants
Tropic movements are directional growth movements of plants in response to external stimuli. These movements are crucial for plant survival, enabling them to optimize their position for light, water, and nutrients, and to avoid harmful conditions. Unlike nastic movements, which are non-directional, tropisms involve growth towards or away from a stimulus.
Phototropism: Responding to Light
Phototropism is the growth of a plant in response to a light stimulus. This is primarily mediated by the plant hormone auxin. When light falls on a plant stem from one side, auxin migrates to the shaded side, causing cells on that side to elongate more rapidly. This differential growth bends the stem towards the light source.
- Positive Phototropism: Stems and leaves typically grow towards light, maximizing photosynthesis.
- Negative Phototropism: Roots often grow away from light.
Geotropism (Gravitropism): Responding to Gravity
Geotropism, also known as gravitropism, is the growth of a plant in response to gravity. This ensures that roots grow downwards into the soil for anchorage and water absorption, and shoots grow upwards towards light.
- Positive Geotropism: Roots grow downwards, in the direction of gravity. Specialized cells in the root cap contain amyloplasts (starch-filled plastids) that act as statoliths, settling at the bottom of the cells and signaling the direction of gravity.
- Negative Geotropism: Shoots and stems grow upwards, against the direction of gravity.
Hydrotropism: Responding to Water
Hydrotropism is the growth of plant roots towards a water source. This is a vital adaptation for plants, especially in arid environments, as it helps them locate and absorb water essential for survival and growth. The root cap also plays a role in sensing water gradients.
- Positive Hydrotropism: Roots grow towards higher concentrations of water. This response is often stronger than geotropism, meaning roots might grow horizontally or even slightly upwards if a water source is present in that direction.
Other Important Tropisms
While phototropism, geotropism, and hydrotropism are key, plants exhibit other tropic movements:
| Tropism | Stimulus | Example |
|---|---|---|
| Thigmotropism | Touch or contact | Tendrils coiling around a support |
| Chemotropism | Chemicals | Pollen tube growing towards ovule |
| Thermotropism | Temperature | Roots growing towards optimal temperature |
Understanding these tropic movements provides insight into the sophisticated ways plants adapt and survive in diverse environments by constantly adjusting their growth directions in response to various cues.
Quick Revision Points
- Tropism: Directional growth movement in response to a stimulus.
- Phototropism: Response to light (stems positive, roots negative).
- Geotropism: Response to gravity (roots positive, stems negative).
- Hydrotropism: Response to water (roots positive).
- Auxin: Key hormone involved in phototropism and geotropism.
- Statoliths: Gravity-sensing cells in root caps.
Extra Practice Questions
- Which plant hormone is primarily responsible for phototropic movements?
- If a plant is placed horizontally, which way will its roots grow due to geotropism?
- What is the main difference between tropic and nastic movements?
- Name two types of stimuli that can cause tropic movements in plants.
- Why is hydrotropism considered more critical for root growth than geotropism in dry conditions?
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