Cell Size Limitations and Cell Division

Cells are the main structural and functional unit of an organism.
Cells are small because of the need for fast, easy food.
The larger a cell gets, the more difficult it is for nutrients and gases to move in and out.
As a cell grows, its volume increases more quickly than its surface area.
If a cell were to get very large, the small surface area would not allow enough nutrients to enter the cell quickly enough for the cell's needs.

As the cell grows, its volume increases much more rapidly than the surface area.
The cell might have difficulty supplying nutrients and expelling enough waste products.
Substances move by diffusion or by motor proteins.
Diffusion over large distances is slow and inefficient.
Small cells maintain more efficient transport systems.

The need for signaling proteins to move throughout the cell also limits cell size.
Cell size affects the ability of the cell to communicate instructions for cellular functions.

The ability of organisms to reproduce best distinguishes living things from nonliving matter.
The continuity of life is based on the reproduction of cells, or cell division.
In unicellular organisms, division of one cell reproduces the entire organism.
Multicellular organisms depend on cell division for:
- Development from a fertilized cell
- Growth
- Repair
Cell division is an integral part of the cell cycle, the life of a cell from formation to its own division.
Cell division results in genetically identical daughter cells
Most cell division results in daughter cells with identical genetic information, DNA.
A special type of division produces nonidentical daughter cells (gametes, or sperm and egg cells).

All the DNA in a cell constitutes the cell's genome.
A genome can consist of a single DNA molecule (common in prokaryotic cells) or a number of DNA molecules (common in eukaryotic cells).
DNA molecules in a cell are packaged into chromosomes.

Cell division prevents the cell from becoming too large.
It also is the way the cell reproduces so that you grow and heal certain injuries.
Cells reproduce by a cycle of growing and dividing called the cell cycle.
Interphase is the stage during which the cell grows, carries out cellular functions, and replicates.
Mitosis is the stage of the cell cycle during which the cell's nucleus and nuclear material divide.
Cytokinesis is the method by which a cell's cytoplasm divides, creating a new cell.

First stage of interphase, G₁
- The cell is growing, carrying out normal cell functions, and preparing to replicate DNA.
The Second Stage of Interphase, S
- The cell copies its DNA in preparation for cell division.
The Third Stage of Interphase, G₂
- The cell prepares for the division of its nucleus.