The smallest living cells/ organisms :

Options

A. have chlorophyll-a
B. cause only animal diseases
C. do not have cell wall
D. have only one type of nucleic acid

Answer

**Step-by-Step Solution:**

1. **Identify the Question**: The question asks for the smallest living cells or organisms.

2. **Consider the Options**: The options provided in the transcript include characteristics of different organisms. It is important to focus on the specific features that relate to size and cellular structure.

3. **Research the Characteristics**: The transcript mentions Mycoplasma as the smallest living cells. Mycoplasma are unique because they lack a cell wall, which is a defining characteristic that differentiates them from other bacteria.

4. **Understand the Classification**: Mycoplasma belong to the class Mollicutes. They are also referred to as PPLO (Pleuro Pneumonia-Like Organisms) because they were first isolated from cattle suffering from pleuropneumonia.

5. **Summarize Key Features**: Mycoplasma are heterotrophic organisms, meaning they obtain their nutrients from other living organisms. They can be saprophytic (feeding on decaying organic matter) or parasitic (feeding on a host).

6. **Conclude the Answer**: Based on the information gathered, the smallest living cells/organisms are Mycoplasma, which are characterized by their lack of a cell wall.

**Final Answer**: The smallest living cells/organisms are Mycoplasma.

---