Question

Phototropism is the a. production of flowers in response to a particular day length. b. production of flowers in response to a particular night length. c. growth response of a plant, organ system, or organ to directional light. d. growth response of a plant, organ system, or organ to gravity. e. growth response of a plant, organ system, or organ to touch.

Short answer

The correct answer is c. Phototropism describes the growth response of a plant, organ system, or organ to directional light.

Step-by-step solution

Understanding the Term

Phototropism is a biological phenomenon that involves responding to light. In the case of plants, it's their growth response toward or away from a light source.

Evaluating the Options

Each given option a, b, d, e corresponds to a different kind of plant growth response: a and b are related to photoperiodism (response to day or night length), d is about gravitropism (response to gravity), and e is about thigmotropism (response to touch). Hence, these options are incorrect as they do not describe phototropism.

Selecting the Correct Option

Option c indicates a growth response of a plant to directional light, which describes the phenomenon of phototropism. Therefore, option c is the correct answer.

Key concepts

Plant Growth Response

Plants have fascinating ways of adapting and growing in response to their environment. This process is known as a plant growth response. These responses are specific reactions to external stimuli, allowing plants to survive and thrive in various conditions. As plants cannot move from place to place, they have evolved the ability to change their growth patterns.

• Phototropism is their response to light.
• Gravitropism is how they orient themselves with gravity.
• Thigmotropism is their reaction to physical touch or contact.

All these adaptations help plants maximize their chances of survival. It is a way of dynamically interacting with the environment. This is especially important since plants are rooted in one spot. Understanding these responses highlights the resilience and adaptability of plant life.

Directional Light

Plants use directional light to determine where to grow. This is known as phototropism. You might see a plant bending towards a window, seeking the sunlight. This movement is not by accident but a strategic growth response.

Phototropism allows plants to maximize their exposure to light. This is crucial for photosynthesis, the process that lets plants convert light into energy. In this way, phototropism can be thought of as the plant's way of "reaching out" to gather the necessary light for energy production.

• Growth towards light is known as positive phototropism.
• Growth away from light is negative phototropism.

Through this simple mechanism, plants optimize their ability to harness energy from the sun.

Photoperiodism

Photoperiodism is how plants respond to the length of day and night. This response regulates seasonal activities such as flowering and dormancy. This is a crucial adaptation in environments where seasons are distinct.

A plant's ability to time its growth to the seasons is vital. This helps ensure that flowering occurs when conditions are optimal for reproduction. Plants can measure the duration of light they receive through special cells that detect light.

• Short-day plants flower when nights are longer.
• Long-day plants flower as nights get shorter.

By using photoperiodism, plants master the art of timing, which is essential for survival in changing seasons.

Gravitropism

Gravitropism is the plants' growth response to gravity. It allows plants to orient themselves correctly in their environment. This is key for roots to grow downwards into the soil and for shoots to rise towards the light.

This response ensures that the plant can take in nutrients and water from the soil while reaching up to capture light. The roots exhibit positive gravitropism as they grow towards gravity. The shoots or stems, however, demonstrate negative gravitropism as they grow upward, away from gravity. This coordinated growth supports the plant's overall structure and function.

• Positive gravitropism is growth towards gravity.
• Negative gravitropism is growth against gravity.

This mechanism ensures plants grow in correct orientation and obtain resources necessary for survival.

Thigmotropism

Thigmotropism occurs when plants respond to physical contact or touch. This is often observed in climbing plants and vines, like peas or ivy, which use thigmotropism to coil around supports.

The growth response is triggered by touch, allowing the plant to gain structural support and access sunlight by growing upwards. When a plant senses touch on one side, growth hormones cause it to bend around or cling to the object it touches.

• Helps climbing plants access sunlight by using nearby objects for support.
• Supports structural stability in a plant.

Thigmotropism is an ingenious way that plants use the environment to support themselves and optimize their growth conditions.