Problem 8 - Campbell Biology Concepts & Connections

Question

Match each definition with the correct term. a. phytochrome b. photoperiod c. sleep movement d. circadian rhythm e. thigmotropism f. phototropism g. gravitropism Bending of a shoot toward light

Step-by-Step Solution

Answer

phototropism

Step 1: Understand the Definition

The definition given is 'Bending of a shoot toward light'. Identify the key terms in the definition. The key term here is 'light'.

Step 2: Analyze the Terms

Look at each term provided:- phytochrome: a pigment involved in light detection- photoperiod: the length of day and night- sleep movement: movement in plants that occurs in response to light and dark cycles- circadian rhythm: a natural, internal process that regulates the sleep-wake cycle and repeats roughly every 24 hours- thigmotropism: a directional growth response of a plant to touch- phototropism: growth of an organism in response to light- gravitropism: a turning or growth movement by a plant in response to gravity

Step 3: Match the Definition

The term 'phototropism' refers to the growth of an organism in response to light. Since the given definition involves bending toward light, it matches with phototropism.

Key Concepts

Phototropism

Phototropism is a plant's growth response to light. When a plant detects light from a particular direction, it grows towards it. This allows the plant to maximize its exposure to light, which is essential for photosynthesis.

Phototropism mainly involves the plant hormone auxin. Auxin accumulates on the side of the plant that is away from the light. This causes the cells on the shaded side to elongate more than those on the lighted side, making the plant bend towards the light.

Let's break it down further:

• Plant detects light using photoreceptors.
• Auxin hormone is redistributed to the shaded part.
• Cells on the shaded side grow longer.
• Plant bends towards the light.

This mechanism helps plants survive by optimizing their ability to harness sunlight for energy.

Circadian Rhythm

Circadian rhythms are natural processes in plants that follow a roughly 24-hour cycle. These rhythms are influenced by external cues like light and temperature but are controlled internally.

Circadian rhythms ensure that various physiological processes in plants happen at the most appropriate times. For example, they regulate when a plant opens and closes its stomata (tiny openings on leaves) for gas exchange.

Key points about circadian rhythms:

• They are endogenous, meaning they are generated within the plant.
• They help optimize the plant's daily cycles of growth and activity.
• Circadian rhythms can adapt to changes in environmental conditions.

These rhythms are essential for plant health and efficiency in energy use.

Gravitropism

Gravitropism refers to a plant's growth response to gravity. This ensures that roots grow downward into the soil and shoots grow upward towards the light.

In roots, the growth towards gravity is called positive gravitropism. In shoots, the growth away from gravity is called negative gravitropism.

Here's how it works:

• Gravity is detected by specialized cells called statocytes.
• These cells contain statoliths, which are dense particles that settle under gravity's influence.
• Applying gravitational force causes redistribution of auxin.
• In shoots, auxin accumulates on the lower side, causing cells to elongate and the shoot to bend upwards.
• In roots, auxin inhibits cell elongation, causing the root to bend downwards.

This mechanism ensures that plants grow correctly and can access resources like water and sunlight effectively.