Members of Chondrichthyes have to swim continuously , because they

Options

A. live in sea water
B. lack operculum
C. lack air bladder
D. have venous heart

Answer

**Step-by-Step Solution:**

1. **Understanding Chondrichthyes**: Chondrichthyes is a class of animals that includes sharks, rays, and skates. They are characterized by having a skeleton made of cartilage rather than bone.

2. **Identifying Key Features**: One of the significant features of Chondrichthyes is that they lack an air bladder (also known as a swim bladder), which is a gas-filled organ that helps many fish maintain buoyancy in the water.

3. **Function of the Air Bladder**: The air bladder allows fish to control their buoyancy and maintain their position in the water column without expending much energy. It helps them to stay at a certain depth without sinking or floating.

4. **Consequences of Lacking an Air Bladder**: Since members of Chondrichthyes do not have an air bladder, they cannot regulate their buoyancy. This means they would naturally sink if they stop swimming.

5. **Need for Continuous Swimming**: To avoid sinking, Chondrichthyes must swim continuously. This constant movement helps them to stay afloat and maintain their position in the water.

6. **Choosing the Correct Option**: Given the options:
- A) Live in seawater
- B) Lack operculum
- C) Lack air bladder
- D) Have venous art

The correct answer is **C) Lack air bladder**, as this is the reason they must swim continuously to avoid sinking.

**Final Answer**: Members of Chondrichthyes have to swim continuously because they **lack air bladder**.

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