### Step-by-Step Solution:
1. **Understanding Meiosis**: Meiosis is a type of cell division that reduces the chromosome number by half, resulting in the formation of four haploid cells from one diploid cell. It is essential for sexual reproduction and occurs in organisms that reproduce sexually.
2. **Diploid Organisms**: Meiosis can occur in diploid organisms, which have two sets of chromosomes (2N). This means that for every chromosome, there is a homologous pair.
3. **Formation of Haploid Cells**: During meiosis, the diploid organism undergoes two rounds of division (meiosis I and meiosis II) to produce haploid cells (N). This is crucial for maintaining the chromosome number across generations during sexual reproduction.
4. **Polyploid Organisms**: In organisms that are polyploid (e.g., 4N or 6N), meiosis can still occur, but the end products will vary. For example, a 4N organism can produce 2N gametes, and a 6N organism can produce 3N gametes. However, the fundamental requirement for meiosis is that the organism must start as diploid (2N) or higher.
5. **Unicellular and Multicellular Organisms**: Meiosis is not limited to multicellular organisms. Unicellular organisms, such as certain protists, can also be diploid and undergo meiosis. However, not all unicellular organisms can perform meiosis, particularly those that are haploid.
6. **Exclusion of Bacteria**: Bacteria, which are prokaryotic and typically haploid, do not undergo meiosis. They reproduce asexually through binary fission, which is a different process.
7. **Conclusion**: Therefore, meiosis can occur primarily when an organism is diploid (2N), and it is not restricted to multicellular organisms. The correct answer to the question is that meiosis can occur when an organism is diploid.
### Final Answer:
Meiosis can occur when an organism is diploid (2N).
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