_________ are believed to be on the borderline between living and non-living things.

Options

A. Virus
B. Bacteria
C. Fungi
D. Algae

Answer

**Step-by-Step Solution:**

1. **Understanding the Question:**
The question asks for an entity that is considered to be on the borderline between living and non-living things.

2. **Identifying the Options:**
The options provided are:
- A) Virus
- B) Bacteria
- C) Fungi
- D) Algae

3. **Analyzing Each Option:**
- **Bacteria:** These are single-celled organisms that are considered living because they can reproduce and carry out metabolic processes independently.
- **Fungi:** These are also living organisms that can grow, reproduce, and carry out life processes.
- **Algae:** These are photosynthetic organisms that are considered living as they can produce their own food and reproduce.
- **Virus:** Viruses are unique in that they cannot reproduce independently and do not carry out metabolic processes outside a host organism.

4. **Determining the Correct Answer:**
- Viruses exhibit characteristics of both living and non-living things. Outside a host, they behave like non-living entities (they cannot reproduce or carry out metabolic activities). However, once they enter a living host, they can reproduce and exhibit living characteristics by utilizing the host's cellular machinery.

5. **Conclusion:**
Based on the analysis, the correct answer is **A) Virus**. Viruses are indeed believed to be on the borderline between living and non-living things.

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