Cell division is needed to…
Grow – most organisms grow by producing more cells
Repair wounds and damaged cells
Develop and change
Why do cells divide? (Aka, why are cells small?)
More cells to grow and not enough DNA (it’s too demanding)
Surface to volume ratio decreases as size increases
Before the cell gets to big it must divide
When do cells divide?
When cells crowd each other
Internal signals tell it
External chemicals, or physical signals
(Cancer is an example of un-controlled cells)
What is the cell cycle?
The series of phases that a cell goes through as it grows and divides
A continuous process of 3 stages:
1. Interphase
2. Mitosis
3. Cytokinesis
Stage 1: Interphase
Cell life between divisions
The longest stage
Nucleus is still present
Phases:
GAP 0, (G0) grows and functions
GAP 1,(G1) Duplicates Organelles and molecules needed for cell division
Synthesis (S) Duplicates DNA (in chromatin form)
GAP 2 (G2) Checks for errors and centrioles are increased

Stage 2: Mitosis
Duplication and division of the cell nucleus
Phases:
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
Stage 3: Cytokinesis
Pinching off the cytoplasm (often grouped as part of mitosis)
(Review….) Interphase:
Nucleus is still intact and the nucleolus is visible
DNA is in chromatin form
Includes G1, S and G2
Mitosis Step 1: Prophase:
Centrioles separate and move to opposite poles, and produce spindle fibers
Chromatin condenses to form chromosomes (becomes