2. WARM UP:

3. When a living thing grows, what happens to its cells?

4. Limits to Cell Size:
Most cells grow by increasing in size, but eventually cells divide after growing.
2 reasons cells divide:
1. the larger a cell becomes, the more demands the cell places on its DNA
2.A larger cell is less efficient in moving nutrients & waste materials across the cell membrane

5. Information Overload:
Cells store critical information in DNA
As a cell grows, that information is used to build the molecules needed for cell growth.
As the cell gets bigger, the DNA does not.
If a cell were to grow too large, an “information crisis” would occur.

6. Exchanging Materials:
Food, water & oxygen enter a cell through its cell membrane.
Waste products leave through the cell membrane, also.
The rate of this exchange (in/out) depends on the surface area of the cell.
The rate at which food and oxygen are used up depends on the volume of the cell.

7. Ratio of Surface Area: Volume
For a growing cell, a decrease in the amount of cell membrane available creates serious problems.

8. Division of the Cell:
Cell division = the process by which a cell divides into two new “daughter” cells
Before cell division, the cell copies its DNA.
Cell division results in an increase in the ratio of surface area: volume for each new daughter cell

9. Asexual Reproduction vs. Sexual Reproduction

10. Asexual Reproduction:
For many single-celled organisms, cell division is the only form of reproduction
Asexual reproduction = the production of genetically identical offspring from a single parent

11. Asexual Reproduction:
Also occurs in multicellular organisms
Ex: hydra

12. Sexual Reproduction:
Involves the fusion of two separate parent cells (special reproductive/sex cells)
Offspring inherit some of their genetic information from each parent

13. Asexual Reproduction:
The faster they reproduce, the better their chance of survival
Offspring that are genetically identical
Lack of genetic diversity can be a disadvantage
Requires more time
Provides genetic diversity