Short Answer 
Unicellular and multicellular organisms both utilize mitosis for asexual reproduction and engage in meiosis for gamete production, involving similar cell cycle phases like growth and DNA replication. However, unicellular organisms reproduce within a single cell cycle and are typically haploid, whereas multicellular organisms have a more complex cell cycle with multiple divisions and are generally diploid, allowing for specialized development.
Step 1: Understand the Similarities
Both unicellular and multicellular organisms share certain processes in their cell cycles. They primarily utilize mitosis for asexual reproduction, allowing them to generate genetically identical daughter cells. Additionally, meiosis is involved in specific life stages in both types, leading to the production of gametes, essential for sexual reproduction. Both cycles also involve phases for growth and DNA replication prior to cell division, including G1, S, and G2 phases.
Step 2: Recognize the Differences
While they share some processes, unicellular and multicellular organisms differ in significant ways. Unicellular organisms can reproduce entirely within a single cell cycle, while multicellular organisms require multiple divisions in a more intricate process to develop a new organism. Moreover, cells in unicellular organisms are typically haploid, whereas those in multicellular organisms are generally diploid.
Step 3: Explore the Complexity of Multicellular Cycles
The cell cycle in multicellular organisms is notably more complex, incorporating sophisticated developmental phases that vary between different tissues and organs. This complexity ensures that multicellular organisms can effectively grow and develop various specialized structures. In contrast, the cell cycle of unicellular organisms is more straightforward, allowing for rapid and efficient reproduction.