Cell Division by Mitosis

all living things start life as a single cell Growth results when your body forms new cells. New cells are formed by cell division

There are two types of cell division 1. mitosis (division of body cells) 2. mieosis (division of sex cells)

- two cells are formed from one cell new cells are similar to the cell from which they came the new cells replace old cells root cells, skin cells, muscle cells are just a few examples of cells that divide by mitosis

- for many simple organisms (like bacteria and some algae) mitosis = reproduction

mitosis is not a one step process as a cell divides some of the cell parts change as a cell divides it forms two new cells. The number of cells increases every time cells divide. the number of chromosomes in each cell remains the same

Interphase (resting) “resting” describes cells that have not started to divide occurs between cell divisions longest part of the cell cycle

chromatin is coiled DNA inside the nucleus,later in the cell cycle chromatin condenses to form chromosomes during interphase, the DNA is replicated (copied) and the cell prepares for division

Interphase in an Onion Root Tip

Prophase (mitosis begins) during this phase the chromatin condenses to form chromosomes The original chromosome and the copied chromosome form a pair.

Each member of the pair is called a chromatid (pair of sister chromatids = chromosome) they are joined together at a central point called the centromere the membrane surrounding the nucleus begins to disappear

Prophase in an Onion Root Tip

Metaphase membrane surrounding the nucleus totally disappears sister chromatids line up in the middle of the cell (metaphase plate)

Metaphase in an Onion Root Tip

Anaphase chromatids separate at the centromere and move to opposite ends of the cell once separated, the chromatids are now identical daughter chromosomes

Anaphase in Onion Root Tip

Telophase nucleus forms around both sets of daughter chromosomes cell splits and two new cells are formed (cytokinesis)

Telophase in an Onion Root Tip

a cell that divides too fast can form a tumor cells divide too fast because of mutations (changes) in the cells DNA - mutations can occur because of 1. genetics 2. environmental factors - UV radiation from sun - cigarette smoke

1. In mitosis, how many cells are formed from each dividing cell? 2. What is copied in the nucleus before the cells divide? 3. If a cell has 46 chromosomes and divides by mitosis, how many chromosomes will each new cell have? 4. Identify the phases of cellular division in the diagrams below. ABCD E