Multicellular brown algae make up this group. The brown algae are composed of either branched filaments (e.g. Ectocarpus) or Leaf like out growth (Laminaria) Giant kelps may reach upto 100m long. These brown algae are placed under class -

Options

A. Rhodophyceae
B. Phaeophyceae
C. Chlorophyceae
D. Chrysophyceae

Answer

To determine the class to which multicellular brown algae belong, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Characteristics of Brown Algae**:
- Brown algae are multicellular organisms.
- They can have branched filaments (like Ectocarpus) or leaf-like outgrowths (like Laminaria).
- They are known for their large size, with some species like giant kelps reaching lengths of up to 100 meters.

2. **Classify Algae**:
- Algae are categorized into different classes based on their characteristics and pigments.
- The main classes of algae include:
- **Rhodophyceae** (Red Algae)
- **Phaeophyceae** (Brown Algae)
- **Chlorophyceae** (Green Algae)
- **Chrysophyceae** (Golden Algae)

3. **Determine the Correct Class for Brown Algae**:
- Since the question specifies that we are discussing brown algae, we need to identify which class they belong to.
- Brown algae are specifically classified under the class **Phaeophyceae**.

4. **Confirm the Characteristics of Phaeophyceae**:
- Members of Phaeophyceae contain chlorophyll pigments A and C.
- They have a characteristic brown color due to the presence of the pigment **fucoxanthin**.
- Their stored food includes mannitol and laminarin, and their cell walls contain cellulose.

5. **Final Answer**:
- Based on the above analysis, the correct class for multicellular brown algae is **Phaeophyceae**.