Problem 9 - 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 Growth response to touch

Step-by-Step Solution

Answer

thigmotropism

Step 1 - Identify Definition

The definition provided is 'Growth response to touch'.

Step 2 - Analyze Terms

Analyze the list of terms to find the one that matches 'Growth response to touch'.

Step 3 - Match Term

The term that matches 'Growth response to touch' is 'thigmotropism'.

Key Concepts

Thigmotropism

Thigmotropism is the growth response of a plant to physical touch or contact with a solid object. When a plant encounters a physical object, such as a trellis or neighboring plant, it may start to grow in a particular way, curling or coiling around the object. This response allows climbing plants like vines to navigate their environment and gain structural support.

Examples include:

• The way a tendril curls around a support.
• Roots changing direction upon encountering a rock.

Thigmotropism helps plants grow in environments where they need to compete for light and space.

Phototropism

Phototropism is the growth response of a plant to light. Plants generally grow towards the light to maximize their ability to perform photosynthesis, which is crucial for their energy production.

Some key points about phototropism:

• Stems exhibit positive phototropism, meaning they grow towards light sources.
• Roots may show negative phototropism, growing away from light and deeper into the soil.
• Auxins, a class of plant hormones, play a significant role by accumulating on the side of the stem that is away from the light, causing it to grow faster and bend towards the light.

Phototropism is vital for plants as it ensures they receive the optimum amount of sunlight.

Gravitropism

Gravitropism is the growth response of a plant to the pull of gravity. It is also known as geotropism. This response allows plants to grow in the correct orientation regardless of how their seeds are planted.

Key features of gravitropism:

• Roots demonstrate positive gravitropism, growing downwards, following the direction of gravity.
• Stems exhibit negative gravitropism, growing upwards, against the force of gravity.
• Statoliths, which are dense starch granules, settle at the bottom of plant cells and trigger the growth hormones that guide the direction of root and stem growth.

Gravitropism ensures that roots anchor the plant properly and that shoots reach towards light efficiently.

Circadian Rhythm

Circadian rhythm refers to the internal biological clock that controls the daily cycles of an organism. Plants, just like animals, have circadian rhythms that regulate various physiological processes.

Important points about circadian rhythms in plants:

• They influence processes such as the opening and closing of stomata, leaf movements, and flower opening.
• The rhythm is typically set to a 24-hour cycle, but it can be adjusted by changes in light and temperature.
• This internal clock helps plants anticipate daily changes in the environment, optimizing their growth and energy use.

Understanding circadian rhythms in plants can improve agricultural practices by aligning watering, fertilizing, and light exposure to the plants' natural cycles.