cells reproduce… organisms reproduce… why do cells need to ... · organisms to grow, replace...

-This week we are talking about how cells reproduce… Next week we will talk about how organisms reproduce…

Why Do Cells Need to Reproduce? -Growth, Repair, Replacement Cells divide whenever a tissue / organ / organism is growing or needs repair. -What is the result of cell reproduction?

A cell divides into two cells by making a copy of itself. The result is two genetically identical cells.

-Cell Division = Cell Reproduction (this can be confusing!)

Mitosis �

Mitosis is part of a cell’s life cycle. �Cell division occurs during the stage of

Mitosis. ��

During this stage, new cells with identical genetic information are

formed. �The genetic material and cytoplasm are

equally divided between two cells. � �

What is the genetic material? à �

Chromosomes are structures located in the

nucleus of the cell.

Chromosomes are made of DNA and protein.

Chromosomes contain genes.

Genes control the

physical characteristics of a

species. All the genes of an organism make up

the organism’s genome.

All organisms of

the same species

contain the same number of

chromosomes in their nuclei.

The Cell Cycle All cells develop from existing cells. This enables multicellular organisms to grow, replace dead cells, and reproduce. A cell’s life can be described with the cell cycle. There are three stages of the cell cycle:

–  Interphase –  Cell Division (mitosis

or meiosis) –  Cytokinesis

Interphase (occurs before mitosis begins) Three Parts of Interphase: G1 phase: The cell is growing and performing its day to day functions. S phase: The cell replicates its DNA. G2 phase: The cell is preparing for cell division.

Main Point of Interphase: DNA (chromosomes) are copied (# doubles)

BEFORE Interphase AFTER Interphase

What Interphase looks like under the microscope: Distinct nucleus. You should be able to easily distinguish the nucleus from the cytoplasm. Chromatin DNA. Chromosomes are yet fully condensed, this is called chromatin. Because chromatin is very thin, you can not see individual DNA strands. There are indistinct swirls of chromatin dispersed throughout the nucleus.

Cell Cycle Poster 1.  Count the number

of cells in each phase and write this on your poster.

Interphase = Prophase = Metaphase = Anaphase = Total = 73

2. Calculate the percentage of time the cells are in each phase. Create a pie chart representing your data and answer the analysis questions.

Interphase Notes

THE CELL CYCLE

-During Interphase the DNA replicates. -This organism’s body cell has 4 chromosomes at the beginning of Interphase. -Before prophase, there will be 8 chromosomes.

What Interphase looks like under the microscope: Distinct nucleus. You should be able to easily distinguish the nucleus from the cytoplasm. Chromatin DNA. Chromosomes are yet fully condensed, this is called chromatin. Because chromatin is very thin, you can not see individual DNA strands. There are indistinct swirls of chromatin dispersed throughout the nucleus.

Prophase Notes

THE CELL CYCLE

-The chromosomes form pairs during prophase. -The nuclear membrane begins to break down.

This organism’s body cell had 4 chromosomes at the beginning of Interphase.

After DNA replication, the cell has 8 chromosomes (as shown above) and the cell

enters prophase.

Prophase

Metaphase Notes -The nuclear membrane has completely disappeared.

-The paired chromosomes line up in the middle.

-Centrioles release spindle fibers.

THE CELL CYCLE

Metaphase

Anaphase Notes

The centrioles pull the spindle

fibers back, which result in

the chromosomes being pulled

apart to opposite sides.

THE CELL CYCLE

Anaphase

Telophase Notes

A nuclear membrane forms around each set of the separated chromosomes (chromatin).

THE CELL CYCLE

Telophase

Cytokinesis (the stage after mitosis) Notes

-The cell membrane forms around each of the two cells. -The resulting cells are identical to the original parent cell.

After mitosis, there are 2 cells with 4 chromosomes (chromatin) in each cell.

Cytokinesis

Cell Cycle Interphase

Prophase

Metaphase

Anaphase

Telophase

Cytokinesis

Cell Cycle Interphase

Prophase

Metaphase

Anaphase

Telophase

Cytokinesis

What is the result of Mitosis?

two identical cells each with the same number of chromosomes

Videos: Mitosis Cell Reproduction