External respiration is

Options

A. Respiration in skin cells
B. Gaseous exchange between organism and external environment
C. Gaseous exchange between cells and tissue fluid
D. Both B and C

Answer

**Step-by-Step Solution:**

1. **Understanding External Respiration**:
- External respiration refers to the process of gas exchange that occurs between the external environment and the cells of the body. This is a vital function that allows organisms to obtain oxygen and expel carbon dioxide.

2. **Defining the Process**:
- External respiration can be defined as the respiration that occurs between the external environment and the cells of the body.

3. **Stages of External Respiration**:
- External respiration consists of two main stages:
- **Breathing**: This involves the intake of oxygen from the environment and the removal of carbon dioxide from the body.
- **Gas Exchange**: This occurs between the alveoli (air sacs in the lungs) and the blood capillaries. Here, oxygen moves from the alveoli into the blood, and carbon dioxide moves from the blood into the alveoli to be exhaled.

4. **Identifying the Correct Option**:
- Based on the definition and stages of external respiration, we can conclude that it involves gaseous exchange between the organism and the external environment. Therefore, the correct answer is the option that states this relationship.

5. **Final Answer**:
- The correct answer to the question "External respiration is" is the option that describes it as "gaseous exchange between the organism and the external environment."

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