Which pigment absorbs the red and infrared light

Options

A. Cytochrome
B. Phytochrome
C. Carotenoids
D. Chlorophyll

Answer

**Step-by-Step Solution:**

1. **Understanding the Question:**
The question asks which pigment absorbs red and infrared light. We need to identify the pigment that specifically absorbs light in the wavelength range of 700 to 780 nanometers.

2. **Identifying the Wavelengths:**
Red light typically falls within the wavelength range of approximately 620 to 750 nanometers, while infrared light ranges from about 750 to 1000 nanometers. Therefore, we are particularly interested in pigments that absorb light in the 700 to 780 nanometer range.

3. **Reviewing Photosynthetic Pigments:**
The main photosynthetic pigments include:
- **Chlorophyll:** Absorbs light primarily in the blue (400-500 nm) and red (600-700 nm) ranges.
- **Carotenoids:** Absorb light in the blue and green ranges (400-500 nm).
- **Cytochrome:** Absorbs light in the range of 500-600 nm.
- **Phytochrome:** A pigment that is specifically known to absorb red and infrared light.

4. **Determining the Correct Pigment:**
Among the pigments listed, phytochrome is known to absorb light in the 700 to 780 nanometer range. It exists in two forms: Pr (phytochrome red) and Pfr (phytochrome far-red), which interconvert upon absorbing light.

5. **Conclusion:**
Based on the information provided, the pigment that absorbs red and infrared light is **phytochrome**. Therefore, the correct answer is option B.

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