Problem 11 - 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 Pigment that helps control flowering

Step-by-Step Solution

Answer

phytochrome

Step 1: Identify the term

Read through each option to identify which term best matches the definition: 'Pigment that helps control flowering'.

Step 2: Understand the definition

The definition 'Pigment that helps control flowering' suggests a substance involved in the regulation of flowering in plants.

Step 3: Match with correct term

Among the given options, 'phytochrome' is known as a pigment that helps control flowering and other photomorphogenic responses in plants.

Key Concepts

phytochrome

Phytochrome is a light-sensitive pigment found in plants. It plays a crucial role in how plants sense and respond to light conditions. This pigment exists in two forms, Pr and Pfr. These forms interchange based on the light conditions. Pr absorbs red light, while Pfr absorbs far-red light.

• In daylight: Pr converts to Pfr.
• In darkness: Pfr converts back to Pr.

Phytochrome regulates many plant processes, including seed germination, stem elongation, and most importantly, flowering. This pigment ensures that plants flower at the right time of year by measuring the length of day and night. This functionality connects phytochrome to other critical plant processes, like photomorphogenic responses.

flowering regulation

Flowering in plants is tightly regulated by several factors, with light being a primary one. Phytochrome is pivotal in this regulation due to its ability to measure light duration. Plants use this photoperiod to determine when to flower.

• Short-day plants flower when nights are long.
• Long-day plants flower when nights are short.

This decision-making process ensures plants flower at the most favorable time for survival and reproduction.
Besides phytochrome, other hormones and environmental cues also play roles. Gibberellins, for instance, promote flowering in some plants. Environmental signals like temperature and water availability can also influence flowering, showing how plants integrate multiple signals for a coordinated response.

photomorphogenic responses

Photomorphogenic responses are growth and developmental changes in plants triggered by light. Phytochrome is again central here, as it detects light signals and initiates these changes. Photomorphogenesis includes a wide range of processes.

• Seedling emergence: Plants grow towards light to optimize photosynthesis.
• Leaf expansion and stem growth: This is an adaptive response to light quality and quantity.
• Shade avoidance: Plants in shaded conditions grow taller to reach light.

These responses ensure that plants make the best use of light for their growth and survival.
Each of these processes highlights the importance of light as a signal and phytochrome’s role in interpreting and responding to that signal. Understanding these responses provides insight into plant biology and their adaptation strategies.