Red algae differ from green algae and brown algae in having :

Options

A. no chlorophyll a
B. no differentiated cells
C. haemoglobin within their cells
D. no flagellated stages in their life cycles

Explanation

To solve the question "Red algae differ from green algae and brown algae in having:", we will analyze the characteristics of red algae in comparison to green and brown algae.

### Step-by-Step Solution:

1. **Identify the Types of Algae**:
- Red algae belong to the division Rhodophyta.
- Green algae belong to the division Chlorophyta.
- Brown algae belong to the division Phaeophyta.

2. **Examine the Characteristics of Red Algae**:
- Red algae are primarily marine organisms.
- They contain chlorophyll A and D.
- They have pigments such as phycobilins and may have fucosanthin.
- Their reserve food material is Floridian starch.
- Importantly, red algae do not have motile stages in their life cycle.

3. **Compare with Green and Brown Algae**:
- Green algae contain chlorophyll A and B, while brown algae contain chlorophyll A and C.
- Both green and brown algae have motile stages, which are flagellated.
- Brown algae have fucosanthin as an abundant pigment, while green algae do not have it.

4. **Analyze the Options**:
- **Option A**: No chlorophyll A - Incorrect, as red algae do have chlorophyll A.
- **Option B**: No differentiated cells - Incorrect, as red algae have differentiated cells.
- **Option C**: Hemoglobin within their cells - Incorrect, as none of these algae have hemoglobin.
- **Option D**: No flagellated stages in their life cycles - Correct, as red algae do not have flagellated stages, unlike green and brown algae.

5. **Conclusion**:
- The correct answer is **Option D: no flagellated stages in their life cycles**. This is the key difference between red algae and the other two types of algae.