What is absent in mammalian erythrocytes?

Options

A. Aerobic respiration
B. Nucleus
C. DNA
D. All of these

Answer

**Step-by-Step Solution:**

1. **Understanding Erythrocytes**: Erythrocytes refer to red blood cells (RBCs) in mammals. These cells are primarily responsible for the transport of oxygen throughout the body.

2. **Identifying Organelles**: In mammals, erythrocytes are unique because they lack certain organelles that are typically found in other cells. The key organelles to consider are the nucleus and mitochondria.

3. **Absence of Nucleus**: Mammalian erythrocytes do not have a nucleus. This absence allows more space for hemoglobin, the protein responsible for oxygen transport. The lack of a nucleus also means that these cells cannot divide or synthesize proteins.

4. **Absence of Mitochondria**: Mammalian erythrocytes also lack mitochondria. Mitochondria are the organelles responsible for aerobic respiration, which is the process of producing energy in the presence of oxygen. Without mitochondria, erythrocytes do not perform aerobic respiration.

5. **Absence of DNA**: Since the nucleus is absent in mammalian erythrocytes, there is also no DNA present. DNA is typically housed within the nucleus, and its absence further confirms the lack of a nucleus.

6. **Conclusion**: Given the absence of the nucleus, mitochondria, and consequently DNA, the correct answer to the question "What is absent in mammalian erythrocytes?" is "all of these."

**Final Answer**: All of these (aerobic respiration, nucleus, DNA).

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