Cell Division & MitosisSection 4.1 - Cell Reproduction

• Everyday _________________ of skin cells wear out and are replaced.

Why is Cell Division Important?

• Cell division is how single cell organisms reproduce.

• Everyday _________________ of red blood cells wear out and are replaced.

billions

millions

Cell Division

How do little elephants grow up to be BIG elephants?

Why is Cell Division Important?

Cell Division & the Cell Cycle

Mitosis is a cycle that occurs in most of our cells.

Length of a Cycle

• The cell cycle is a series of events that takes place from one cell division to the next.

• The time it takes to complete a cell cycle is not the same in all cells.

Mitosis & Asexual Reproduction• Mitosis is the process in which the nucleus divides

to form two new nuclei.

• Mitosis is a form of asexual reproduction.

• Asexual Reproduction - when a cell doubles its contents and then divides into two identical cells- the production of offspring that are genetically identical

Mitosis & Asexual Reproduction

• The process of asexual reproduction begins after a sperm fertilizes an egg.

Why Asexual Reproduction?

3 reasons why cells reproduce asexually:

• growth

• repair

• replacement

• Interphase

• PROPHASE

• METAPHASE

• ANAPHASE

• TELOPHASE

• Cytokinesis

Steps of Mitosis

• Interphase

• PROPHASE

• METAPHASE

• ANAPHASE

• TELOPHASE

• Cytokinesis

Steps of Cell Cycle

I Pray More At The Church

How can I remember the order?

• Most of the life of any eukaryotic cell is spent in a period of growth and development called interphase.

• Cells in your body that no longer divide, such as nerve and muscle cells, are always in interphase.

• An actively dividing cell, such as a skin cell, copies its hereditary material and prepares for cell division during interphase.

Interphase

• During interphase, each chromosome duplicates.

• When the nucleus is ready to divide, each duplicated chromosome coils tightly into two thickened, identical strands called chromatids.

Interphase

• A chromosome is a structure in the nucleus that contains hereditary material (DNA).

• A chromatid is one-half of a replicated chromosome.

Chromosome

Chromosome

Chromosome

Chromosome

Chromosome

_________________

Chromosome

chromosome

chromatid

animal cell plant cell

Interphase

• The pairs of chromatids are fully visible when viewed under a microscope.

• The nucleolus and the nuclear membrane disintegrate.

Prophase

• Two small structures called centrioles move to opposite ends of the cell.

• Between the centrioles, spindle fibers begin to stretch across the cell.

Prophase

• Plant cells also form spindle fibers during mitosis but do not have centrioles.

Prophase

Prophase

animal cell plant cell

• The pairs of chromatids line up across the center of the cell.

• The centromere of each pair usually becomes attached to two spindle fibers—one from each side of the cell.

Metaphase

Metaphase

animal cell plant cell

• Each centromere divides and the spindle fibers shorten.

Anaphase

• Each pair of chromatids separates, and chromatids begin to move to opposite ends of the cell.

Anaphase

Anaphase

animal cell plant cell

• The spindle fibers start to disappear.

• The chromosomes start to uncoil.

• A new nucleus forms.

Telophase

Telophase

animal cell plant cell

• For most cells, after the nucleus has divided, the cytoplasm separates and two new cells are formed.

Cytokinesis - division of cytoplasm

• In animal cells, the cell membrane pinches in the middle, like a balloon with a string tightened around it, and the cytoplasm divides.

Cytokinesis - division of cytoplasm

• In plant cells, the appearance of a cell plate tells you that the cytoplasm is being divided.

• Why is this step different for plant cells?

Cytokinesis - division of cytoplasm

• New cell walls form along the cell plate, and new cell membranes develop inside the cell walls.

• Now, the period of growth, or interphase, begins again.

Cytokinesis - division of cytoplasm

Cytokinesis - division of cytoplasm

Cytokinesis

animal cell plant cell

Interphase

Prophase

Metaphase

Anaphase

Telophase

Interphase

Animal Mitosis -- Review

Interphase

Prophase

Metaphase

Anaphase

Telophase

Interphase

Plant Mitosis -- Review

4 important things to remember about Mitosis & Cell Division1. Mitosis is the division of a nucleus.2. Mitosis produces 2 new nuclei that are identical to the

original nucleus• Every cell in your body copies the same hereditary information.

• All of your cells use different parts (genes) of the same hereditary material to become different types of cells.

3. The original cell no longer exists.4. Cell division allows growth and replaces worn out or

damaged cells.

Results of Mitosis

• Bacteria cannot reproduce through mitosis because of what mitosis is. Mitosis is the division of a nucleus.

• Bacteria do not have a nucleus, so they cannot undergo mitosis.

• The process they use is called fission.

Other forms of Asexual Reproduction

Fission

• Binary fission is the simplest form of asexual reproduction.

• Bacteria cells split into approximately two equal halves. The process in bacteria is relatively rapid.

Fission

• The two new organisms are identical genetically, except for a random mutation that may occasionally occur.

• Hydra, a freshwater animal, reproduces using budding. The bud is an exact copy of the adult plant.

• Part of the adult buds off, or breaks off, and a new organism grows.

Budding

Regeneration replaces lost body parts. It uses mitosis and cell division.

Regeneration