Question

Plant growth toward a light source (A) Phytochrome (B) Phototropism (C) Photoperiodism (D) Thigmotropism (E) Gravitropism

Short answer

The plant growth towards a light source refers to (B) Phototropism.

Step-by-step solution

Understanding the terms

Phytochrome is a photoreceptive protein in plants that regulate many aspects of growth and development. Phototropism is movement that occurs when a plant responds to light stimulus, growing towards the source of light. Photoperiodism is the physiological response of organisms to the length of day or night. Thigmotropism is a directional growth movement that occurs as a mechanical stimulation or touch. Gravitropism is a turning or growth movement by a plant or fungus in response to gravity.

Matching the phenomenon

We are considering the situation where plant growth is towards a light source. As per the definitions and understanding provided in step 1, the term that matches this phenomenon is Phototropism as it refers to a plant's response towards light and growing in that direction.

Key concepts

Phytochrome

Plants have incredible ways of sensing their environment, and phytochrome is a perfect example. Phytochrome is a type of protein found in plants that acts as a light receptor. This protein plays a significant role in the plant's growth and development.
It absorbs light primarily in the red and far-red wavelengths. This helps the plant to differentiate between light and dark conditions.
A key function of phytochrome is to regulate processes like seed germination and flowering. When a seed detects light through phytochrome, it might trigger the processes needed to start growing.
Phytochrome also helps the plant sense the changing seasons by detecting day length.

• Regulates plant growth and development.
• Absorbs red and far-red light.
• Involved in seed germination and flowering.

Understanding phytochrome is essential because it influences many of the plant's responses to its surroundings.

Photoperiodism

Photoperiodism is all about how plants respond to the length of day and night. This process helps plants determine the best time to flower or germinate. Plants can sense changes in day length using light receptors like phytochrome.
This sensing helps plants decide the right season to bloom or start growing.
Photoperiodism is crucial for plants because it helps them synchronize with their environment.

• Decides the timing for flowering.
• Helps plants adapt to seasonal changes.
• Involves detection of light duration and intensity.

For example, some plants require long nights to flower, known as "short-day" plants, while others flower when nights are short, called "long-day" plants.

Thigmotropism

Thigmotropism describes how plants can respond to touch or a mechanical stimulus. Have you ever seen vines winding around a post? That's thigmotropism at work. This movement allows plants to make the best use of their physical environment for support and growth.
An example of thigmotropism is the tendrils of climbing plants curling around structures.
When a plant's tendril makes contact with an object, signals are triggered for cells on the opposite side to grow, causing the tendril to curl around the object.

• Triggered by physical contact or touch.
• Helps plants use their environment better.
• Common in climbing plants and vines.

This response to touch helps plants find stability and access sunlight, making it vital for their survival.

Gravitropism

Gravitropism is the way plants orient themselves in response to gravity. This ensures that the roots grow down into the soil and the shoots grow upward towards the light. It’s a smart way plants position themselves for optimum resource acquisition.
The growth direction in response to gravity ensures correct positioning for nutrient absorption and photosynthesis.
Roots display positive gravitropism, as they grow downward, while shoots show negative gravitropism by growing upward.

• Determines growth direction based on gravity.
• Roots grow downward (positive gravitropism).
• Shoots grow upward (negative gravitropism).

Gravitropism is crucial for plants to anchor themselves and reach necessary light and nutrients needed for growth.