Unicellular cells grow primarily through cell division.
Essentially, a unicellular organism, being a single cell, increases in size to a certain point, then replicates its DNA and cellular components before physically splitting into two identical (or nearly identical) daughter cells. This process, also known as binary fission in many prokaryotes, represents both growth and reproduction for these organisms.
Here's a more detailed breakdown:
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Increasing in Size: Before cell division, the unicellular cell increases its volume by synthesizing new proteins, lipids, and other essential molecules. It takes up nutrients from its environment to build these components.
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DNA Replication: The cell's genetic material (DNA) is duplicated to ensure that each daughter cell receives a complete copy of the genome.
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Cell Division (e.g., Binary Fission):
- In prokaryotes, the cell elongates, and the replicated DNA separates. The cell membrane then invaginates (pinches inward) in the middle of the cell. A new cell wall forms, eventually dividing the original cell into two separate daughter cells.
- Eukaryotic unicellular organisms, like yeast or protists, may use mitosis followed by cytokinesis to divide. Mitosis ensures accurate chromosome segregation, and cytokinesis physically divides the cell.
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Growth as Reproduction: For unicellular organisms, cell division is not only a means of growth for the population but also a form of reproduction, creating new individual organisms.
In summary, unicellular cell growth is tightly linked to cell division, encompassing a period of enlargement followed by DNA replication and cellular separation to produce new, individual cells.
