1. The cell cycle

2. General information
Multicellular organisms such as humans contain trillions of cells.
Living organisms are always making new cells.

3. General information
New cells are made when an organism grows in size or repairs old or damaged tissues.
Most living cells are between 2 and 200 m in diameter.

4. The cell cycle
The cell cycle is the regular pattern growth and division a cell goes through.
There are 4 main parts: gap 1, synthesis, gap 2 and mitosis.

5. Rate of division
Prokaryotic cells usually divide much faster than eukaryotic cells.
Human cells usually take about 12 hours to divide.

6. Size limitations (diffusion)
Diffusion limits cell size
Materials that a cell needs must pass through the cell membrane by diffusion.
Diffusion is slow and inefficient over long distances.
Cells that are larger would not receive supplies of oxygen and other important molecules in time.

7. Size limitations (DNA)
Most cells contain only one nucleus.
Cells need DNA and RNA (in nucleus) to program its metabolism and make proteins.
Large cells would need a large supply of enzymes, and one nucleus would not supply enough DNA.

8. Size limitations (area to volume ratio)
Volume increases much faster than surface area.
If cell size were doubled, the cell would require 8 times more nutrients and would have 8 times more waste to excrete.
Look at the board for an example