Photosynthetic sulphur bacteria differ from higher plants in that they do not have the pigment ............... and they do not use ............... as electron donor in photosynthesis.

Explanation

To answer the question regarding the differences between photosynthetic sulfur bacteria and higher plants, we can break it down into two parts based on the information provided.

### Step-by-Step Solution:

1. **Identify the pigment that photosynthetic sulfur bacteria lack:**
- Photosynthetic sulfur bacteria, also known as purple bacteria, do not possess the green pigments known as chlorophyll a and chlorophyll b, which are present in higher plants. Instead, they have different pigments that allow them to perform photosynthesis.

**Answer for this part:** They do not have the pigment **chlorophyll**.
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