Tropism (Types, positive & negative) | Control & Coordination | Biology | Khan Academy

Summary

This video explains the concept of tropism, a directional plant movement in response to environmental stimuli such as light, gravity, touch, water, and chemicals. Tropic movements, like phototropism and gravitropism, involve growth and bending toward or away from stimuli. The video also distinguishes tropism from nastic movements, which are non-directional. Key tropisms such as phototropism, gravitropism, thigmotropism, hydrotropism, and chemotropism are discussed with clear examples, showing how plants adapt and grow in response to their environment. The video emphasizes the importance of understanding these movements in plant biology.

Takeaways

• 😀 Tropism is a plant's directional movement in response to an external stimulus, such as light, gravity, or touch.
• 😀 Tropisms involve growth or turning movements towards or away from a stimulus, unlike nastic movements which are non-directional.
• 😀 Phototropism is a type of tropism where plants grow towards light. Shoots exhibit positive phototropism (towards light), while roots show negative phototropism (away from light).
• 😀 Gravitropism (also known as geotropism) is the growth of plants in response to gravity. Roots grow towards gravity (positive gravitropism), while shoots grow away from gravity (negative gravitropism).
• 😀 Thigmotropism is the growth response to touch. Creeper plants coil around stems when they come into contact with them.
• 😀 Hydrotropism is the growth of plant roots towards or away from water, depending on the stimulus.
• 😀 Chemotropism is the growth response to chemicals, where plants grow towards or away from chemical stimuli.
• 😀 Tropism is typically growth-related, involving directional movement, while nastic movements do not depend on direction and are not growth-related.
• 😀 Positive tropism occurs when a plant grows towards a stimulus (e.g., shoots towards light), while negative tropism occurs when a plant grows away from a stimulus (e.g., roots away from light).
• 😀 Nastic movements are plant responses to stimuli like touch or temperature, but these movements are non-directional, such as the closing of mimosa leaves or the Venus flytrap.
• 😀 Plants can exhibit complex movement responses to environmental stimuli, with tropism being a key mechanism for survival and adaptation in various conditions.

Q & A

What is tropism in plants?

Tropism is a type of plant movement where the plant turns or grows towards or away from a stimulus, such as light, gravity, or touch.

How does a plant respond to sunlight?

When a plant is exposed to sunlight, its shoot will bend towards the light, a phenomenon known as phototropism.

What is the difference between phototropism and gravitropism?

Phototropism is the growth of a plant towards light, while gravitropism (or geotropism) is the growth of a plant's roots towards gravity and the shoot away from it.

Why do plant roots move away from sunlight?

Roots move away from sunlight as part of gravitropism, where they grow towards the force of gravity to anchor the plant in the soil.

What is an example of a plant movement that is not a tropism?

An example of non-tropic movement is seen in the 'touch-me-not' Mimosa plant, whose leaves close in response to touch, but without any directional movement towards or away from the stimulus.

What are nastic movements in plants?

Nastic movements are plant responses to stimuli that do not depend on the direction of the stimulus. Unlike tropic movements, nastic movements do not involve turning towards or away from the stimulus.

What is the term for plant movement in response to touch?

The movement in response to touch is called phygmotropism, where plants bend or grow around objects they come in contact with.

How does hydrotropism work in plants?

Hydrotropism is the movement of plant roots towards or away from water. Roots grow towards areas with higher moisture content.

What is chemotropism in plants?

Chemotropism is the movement of plants in response to chemicals. For example, a pollen tube growing towards the ovary follows chemical signals.

What is the difference between positive and negative tropism?

Positive tropism occurs when the plant moves towards the stimulus, while negative tropism happens when the plant moves away from the stimulus. For example, positive phototropism involves the shoot growing towards light, while negative phototropism involves roots growing away from light.