Photoautotrophs lacking chlorophyll a are

Options

A. Cyanobacteria
B. Red algae
C. Brown algae
D. Bacteria.

Answer

To answer the question "Photoautotrophs lacking chlorophyll a are:", we can follow these steps:

### Step 1: Understand the Types of Photoautotrophs
Photoautotrophs are organisms that can produce their own food using light energy, typically through the process of photosynthesis. They usually contain chlorophyll, which is essential for capturing light energy.

### Step 2: Identify the Options
The options provided are:
1. Cyanobacteria
2. Red alga
3. Brown alga
4. Bacteria

### Step 3: Analyze Each Option
- **Cyanobacteria**: Also known as blue-green algae, they contain chlorophyll a, similar to that found in eukaryotic photoautotrophs.

- **Red Alga**: This type of algae contains chlorophyll a and additional pigments, but it does not lack chlorophyll a.

- **Brown Alga**: Like red algae, brown algae also contain chlorophyll a along with other types of chlorophyll (such as chlorophyll c).

- **Bacteria**: Certain photosynthetic bacteria, such as purple bacteria and sulfur bacteria, do not contain chlorophyll a. Instead, they possess bacteriochlorophyll, which is different from chlorophyll a.

### Step 4: Conclusion
Based on the analysis, the only group among the options that lacks chlorophyll a is **Bacteria**. Therefore, the correct answer is bacteria.

### Final Answer
**Bacteria** are the photoautotrophs lacking chlorophyll a.

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