1. Why Do Cells Divide?

2. Cell Size Limitations Getting things into cell at an efficient rate
Nutrients
Water
Oxygen
Removing things from the cell quickly
wastes
DNA limits cell size
If cell is too big then DNA cannot make enough proteins to support the cell

3. What limits the size of cells?
Surface Area to Volume Ratio - How much space is on the outside (cell membrane) compared to the space on the inside of the cell.
As the surface area of something increases, it’s volume increases faster
The larger a cell becomes, the less efficient it is
Cells that grow too large no longer have enough surface area to take in nutrients and remove waste

4. Ratio of Surface Area to Volume in Cells
Cell Size
Surface Area
(length x width x 6)
1 cm x 1 cm x 6
= 6 cm2
2 cm x 2 cm x 6
= 24 cm2
3 cm x 3 cm x 6 = 54 cm2
Volume
(length x width x height)
1 cm x 1 cm x 1 cm
= 1 cm3
2 cm x 2 cm x 2 cm
= 8 cm3
3 cm x 3 cm x 3 cm = 27 cm3
Ratio of Surface Area
to Volume
6 / 1 = 6 : 1
24 / 8 = 3 : 1
54 / 27 = 2 : 1
The volume of the cell increases faster than its surface area
How does a cell most efficiently move material without getting too big?? It divides!!

5. Cells get old and worn out
Another reason to divide – replace old parts
Just like anything else, cells get worn out. They need repair, and, just like an old car, eventually need replacement.
The best way to fix what ails a cell is to replace that cell all together.

6. What does a cell need to do first?
In order to reproduce, a cell must make copies of its DNA and organelles.
The new cell needs all the stuff the old cell has.

7. DNA DNA must be copied in a process called DNA replication.
After replication, the DNA is all stringy and tangled (called chromatin), but must be separated into a new cell. Before this can happen, the DNA must coil up into chromosomes.

8. Chromosomes
Threadlike structures made up of DNA that coil around proteins called histones. Contains genetic information that is passed form parents to offspring.
chromosomes
Genes
(DNA)

9. Chromatids One of two identical parts of a duplicated chromosome
The two identical chromatids are known as sister chromatids and are held together at a central point called the centromere
Centromere
Sister
chromatids

10. Number of Chromosomes Fruit Flies: 8 Carrots: 20 Turkey: 82
White Ash: 138
Fern: 480
Humans: 46

11. Soma – what? The 46 human chromosomes are found in most human cells
These cells are called somatic cells
AKA body cells
Some cells in the body only have 23 chromosomes
These are called gametes
2 types: eggs and sperm

12. Karyotype Visual representation of the chromosomes in a cell
HUMAN CHROMOSOMES

13. Genetic Abnormalities

14. The Cell Cycle
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