Which of the following is an example of circadian rhythm

Options

A. migration in birds
B. flowering in summer
C. hibernation
D. sleep-wake cycle

Answer

To determine which of the following options is an example of a circadian rhythm, let's analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding Circadian Rhythm**:
- Circadian rhythms are natural processes that follow a roughly 24-hour cycle. They are primarily driven by the circadian clock and regulate various physical, mental, and behavioral changes in organisms.

2. **Analyzing the Options**:
- **Option A: Migration in Birds**:
- Migration is a cyclic behavior, but it does not occur on a 24-hour cycle. Birds typically migrate seasonally, which can happen once or twice a year depending on environmental conditions. Therefore, this is not an example of a circadian rhythm.

- **Option B: Flowering in Summer**:
- Flowering in summer is also a cyclic behavior, but it is not tied to a 24-hour cycle. Plants may flower based on seasonal changes rather than daily cycles. Thus, this option is incorrect as well.

- **Option C: Hibernation**:
- Hibernation is a behavioral adaptation that occurs over longer periods, typically during winter months. It is a response to environmental conditions and does not follow a 24-hour cycle, making this option incorrect.

- **Option D: Sleep-Wake Cycle**:
- The sleep-wake cycle is a classic example of a circadian rhythm. It follows a 24-hour cycle, where individuals experience periods of sleep and wakefulness. This is regulated by the circadian clock, making this option the correct answer.

3. **Conclusion**:
- After analyzing all the options, the correct answer is **Option D: Sleep-Wake Cycle**, as it is the only example that fits the definition of a circadian rhythm.

### Final Answer:
**The correct answer is: Sleep-Wake Cycle (Option D)**.