Question

Match the response with its main trigger. $$ \text {phototropism } \quad \quad \text {a. contact with an object} $$ $$ \text {gravitropism } \quad \quad \text {b. blue light} $$ $$ \text {thigmotropism } \quad \quad \text {c. night length} $$ $$ \text {photoperiodism } \quad \quad \text {d. gravity} $$

Short answer

Phototropism - b; Gravitropism - d; Thigmotropism - a; Photoperiodism - c.

Step-by-step solution

Understanding Phototropism

Phototropism is the growth of an organism, usually a plant, in response to light. The main trigger for this response is blue light, which plants detect and grow toward. Thus, the main trigger for phototropism is blue light (b).

Examining Gravitropism

Gravitropism is a directional growth movement that occurs in response to gravity. It is essential for roots to grow downward and for shoots to grow upward. Therefore, the main trigger for gravitropism is gravity (d).

Defining Thigmotropism

Thigmotropism is the growth movement in response to touch or physical contact with an object. This response is seen in climbing plants and vines that wrap around structures for support. The trigger for thigmotropism is contact with an object (a).

Explaining Photoperiodism

Photoperiodism is the physiological reaction of organisms to the length of day or night. Plants use this process to time seasonal activities, such as flowering. Night length is crucial for photoperiodism, particularly in determining flowering time. So, the main trigger for photoperiodism is night length (c).

Key concepts

Phototropism

Phototropism is a fascinating concept in the world of plant biology. It refers to the way plants grow in response to light, specifically blue light. This type of growth allows plants to maximize their exposure to sunlight, which is crucial for photosynthesis.
Plants have specialized cells that detect light. When these cells sense blue light from a particular direction, they trigger a series of changes within the plant. Auxins, which are plant growth hormones, gather on the side of the plant that is away from the light. This results in faster growth on the shaded side, causing the plant to bend towards the light source.
Key points to remember about phototropism are:

• It primarily involves the plant hormone auxin.
• It ensures that leaves are positioned optimally to capture sunlight.
• Varies between different plant species and environmental conditions.

Gravitropism

Gravitropism, also known as geotropism, is the way plants orient their growth in response to gravity. This mechanism ensures that roots grow downward into the soil while shoots grow upward toward the sky.
The gravitational pull influences the distribution of auxins in the plant. In roots, an accumulation of auxin on the lower side inhibits growth, causing the root to grow downward. In shoots, auxin promotes growth on the lower side, making the plant grow upward.
Important aspects of gravitropism include:

• It functions differently in roots and shoots.
• Helps anchor the plant and ensures nutrient uptake is effective.
• Critical for plant stability and orientation.

Thigmotropism

Thigmotropism is the growth movement of a plant in response to touch, often seen in climbing plants and vines. When these plants come into contact with structures, they respond by growing around them for support.
This response is facilitated by a combination of physical touch and chemical signaling within the plant. As vines or tendrils touch an object, they experience differential growth rates on opposite sides, causing the plant to coil around the item.
Some features of thigmotropism to note are:

• Common in plants with tendrils, like peas and cucumbers.
• Helps support weaker stem structures.
• Key for plants growing in competitive environments.

Photoperiodism

Photoperiodism is the response of plants to the relative lengths of day and night. It is crucial for the timing of several vital plant processes, particularly flowering.
Plants have photoreceptors that detect changes in light duration. These receptors influence the plant's internal biological clock, dictating when to flower, set seed, or go dormant. Night length is particularly important for this mechanism, as certain plants require a specific amount of uninterrupted darkness to trigger flowering.
Considerations about photoperiodism include:

• Influences seasonal behaviors in plants, like flowering and germination.
• Critical for agricultural planning and crop yields.
• Varies significantly across plant species in different climates.