Reproduction and Cell Reproduction and Cell Division Division

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Reproduction and Cell Division Reproduction and Cell Division (5.8) (5.8)

The Cell Cycle and Mitosis (5.5)The Cell Cycle and Mitosis (5.5)

The Cell CycleThe Cell Cycle

Division Phase:Division Phase: PProphaserophase MMetaphaseetaphase AAnaphasenaphase TTelophaseelophase

InterphaseInterphase

What is and is not Mitosis?What is and is not Mitosis?

Mitosis is nuclear division plus Mitosis is nuclear division plus cytokinesis, and produces two cytokinesis, and produces two identical daughter cells during identical daughter cells during prophase, metaphase, anaphase, prophase, metaphase, anaphase, and telophase.and telophase.

Interphase is often included in Interphase is often included in discussions of mitosis, but interphase discussions of mitosis, but interphase is technically not part of mitosis.is technically not part of mitosis.

InterphaseInterphaseThe cell is engaged in metabolic The cell is engaged in metabolic

activity and performing its prepare activity and performing its prepare for mitosis (the next four phases for mitosis (the next four phases that lead up to and include nuclear that lead up to and include nuclear division). division).

Chromosomes are not clearly Chromosomes are not clearly discerned in the nucleus, although discerned in the nucleus, although a dark spot called the nucleolus a dark spot called the nucleolus may be visible.may be visible.

The cell prepares for cell division by The cell prepares for cell division by duplicating its genetic material.duplicating its genetic material.

ProphaseProphaseChromatin in the nucleus begins Chromatin in the nucleus begins

to condense and becomes to condense and becomes visible in the light microscope as visible in the light microscope as chromosomes. chromosomes.

The nucleolus disappears.The nucleolus disappears.Centrioles begin moving to Centrioles begin moving to

opposite ends of the cell and opposite ends of the cell and fibers extend from the fibers extend from the centromeres. centromeres.

Some fibers cross the cell to form Some fibers cross the cell to form the mitotic spindle.the mitotic spindle.

MetaphaseMetaphaseSpindle fibers align the Spindle fibers align the

chromosomes along the middle chromosomes along the middle of the cell nucleus.of the cell nucleus.

This line is referred to as the This line is referred to as the metaphase plate.metaphase plate.

This organization helps to ensure This organization helps to ensure that in the next phase, when that in the next phase, when the chromosomes are the chromosomes are separated, each new nucleus separated, each new nucleus will receive one copy of each will receive one copy of each chromosome.chromosome.

AnaphaseAnaphaseThe paired chromosomes The paired chromosomes

separate and move to opposite separate and move to opposite sides of the cell.sides of the cell.

The two halves move to opposite The two halves move to opposite poles of the cell.poles of the cell.

If anaphase proceeds correctly, If anaphase proceeds correctly, each of the daughter cells will each of the daughter cells will have a complete set of genetic have a complete set of genetic informationinformation

TelophaseTelophaseChromosomes arrive at opposite Chromosomes arrive at opposite

poles of the cell, and new poles of the cell, and new membranes form around the membranes form around the daughter nuclei.daughter nuclei.

The chromosomes disperse and The chromosomes disperse and are no longer visible under the are no longer visible under the light microscope.light microscope.

The cytoplasm and organelles The cytoplasm and organelles separate into roughly equal separate into roughly equal parts, and the two daughter parts, and the two daughter cells are formed.cells are formed.

CytokinesisCytokinesis

In animal cells, cytokinesis results In animal cells, cytokinesis results when a fiber ring composed of a when a fiber ring composed of a protein called actin around the protein called actin around the center of the cell contracts, pinching center of the cell contracts, pinching the cell membrane in the middle and the cell membrane in the middle and forming two new daughter cells.forming two new daughter cells.

In plant cells, the rigid wall requires In plant cells, the rigid wall requires that a new cell wall forms along the that a new cell wall forms along the middle, creating two new cells.middle, creating two new cells.

Reproduction and Cell Reproduction and Cell DivisionDivision

Reconsider the modern cell theory:Reconsider the modern cell theory: All living things are made up of one or All living things are made up of one or

more cells.more cells. The cell is the functional unit of life.The cell is the functional unit of life. All cells come from pre-existing cells.All cells come from pre-existing cells.Cell division, the process by which cells Cell division, the process by which cells

come from pre-existing cells, is the come from pre-existing cells, is the process that perpetuates life and allows process that perpetuates life and allows species to continue. species to continue.

Just as cells reproduce as part of the cell Just as cells reproduce as part of the cell cycle, living organisms reproduce as part cycle, living organisms reproduce as part of their life cycle. of their life cycle.

Note that some organisms use both Note that some organisms use both methods of reproduction. For methods of reproduction. For example, bacteria reproduce mostly example, bacteria reproduce mostly in an asexual process called binary in an asexual process called binary fission, which is basically cell division fission, which is basically cell division as you have learned it. However, as you have learned it. However, bacteria are also able to exchange bacteria are also able to exchange genetic information in a form of genetic information in a form of sexual reproduction. sexual reproduction.

Similarly, most plants reproduce Similarly, most plants reproduce sexually, in the process that results sexually, in the process that results in seeds, but many also reproduce in seeds, but many also reproduce asexually in various other ways.asexually in various other ways.

Reproduction of CellsReproduction of Cells