WARM UP:

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

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

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.

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.

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

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

Asexual Reproduction vs. Sexual Reproduction

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

Asexual Reproduction: Also occurs in multicellular organisms Ex: hydra

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

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