The Cell Cycle

Chapter 10, Section 2

Why do cells divide?

For growth, repair, and reproduction

When do cells divide?

Most limiting factor in size is the size of the cell membrane.

A cell has to stay small so that all the things that need to go in and out don’t have too far to travel. The surface area to volume ratio must be small so cells stay tiny and divide instead of growing too big.

How Do Cells Divide?Cell cycle - sequence of phases

in the life cycle of the cell

Interphase3 parts: G1, S and G2

G1 - cell growth; make new organellesS – DNA replicationG2 – short; organelles for cell

division are produced

What is Mitosis?The process whereby body

cells(somatic) are made by cell division

How does it work?

4 Stages

1st - Prophase

Chromosomes become visibleCentrioles go to opposite sidesSpindle fibers formNuclear membrane breaks down

-2- Metaphase- Chromosomes line up along the equator in pairs-3- Anaphase- Chromosomes

move to opposite ends of the cell-4- Telophase- a cleavage

furrow forms and…each cell now has exactly the

same number of chromosomes!

Cytokinesis

Cytoplasm pinches in half

Mitosis

Results in an exact duplicate of the same cell. There is no change.

Interphase

Prophase

Metaphase

Anaphase

Telophase

MEIOSISChapter 11

So, What is Meiosis?

The process whereby gametes or, sex cells are made by cell divisionExamples are sperm & eggs

only!

How does it work? 8 Stages Prophase I

(includes chromosomes crossing over and exchange)

Metaphase IAnaphase ITelophase I

Prophase IIMetaphase IIAnaphase IITelophase II

The same things occur with chromosomes except the number of chromosomes is halved

Meiosis results in cells that have only 23 chromosomes in humansMen make 4 sperm cellsWomen make 1 egg and 3

polar bodies (which are excreted as waste products

Why is meiosis so important?

It provides for genetic variation crossing over occurs in

prophase I and IIshuffling of chromosomes

(or genetic information)

Mitosis MeiosisBody cells/

somatic cells4 Stages 1 divisionResults in 2

daughter cellsAsexual Growth2n - diploid

Sex cells / gametes8 stages 2 divisionsResults in 4 sperm or 1

egg & 3 polar bodiesSexual reproductionCrossing over – prophase I

1n - haploid