9.1 KEY CONCEPT Cells come from other cells Roles of cell reproduction Replacement or repair of lost or damaged cells Growth of an organisms Produce offspring. Many organisms reproduce by cell division.

Asexual reproduction is the creation of offspring from a single parent 1. Binary fission is similar in function to mitosis. Binary fission produces two daughter cells genetically identical to the parent cell. Binary fission occurs in single celled organisms- examples prokaryotes-bacteria. parent cell DNA duplicates cell begins to divide daughter cells

Environment determines what form of reproduction is most advantageous. Asexual reproduction is an advantage in consistently favorable conditions. Sexual reproduction is an advantage in changing conditions.

2. Budding Some eukaryotes reproduce through mitosis. Mitosis is asexual reproduction Budding forms a new organism from a small projection growing on the surface of the parent. bud Hydra Yeast

More Examples of Asexual Reproduction 3. Regeneration: Fragmentation is the splitting of the parent into pieces that each grow into a new organism. examples 4. Vegetative propagation Forms a new plant from the modification of a stem or underground structure on the parent plant. examples

Sexual Reproduction Need two parents: Union of gametes- sex cells- egg and sperm. Results in genetically different offspring. Increases diversity in a species. Important in species survival. Occurs in most multicellular organisms And some single celled organisms.

9.2 Cell Cycle KEY CONCEPT Cells have distinct phases of growth, reproduction, and normal functions.

The cell cycle is from the “birth” of a new cell until it completes cell division producing daughter cells. The cell cycle is a regular pattern of growth, DNA replication, and cell division.

2 main stages of the cell cycle Interphase 2. Mitosis Interphase: 90% of time 3 stages Gap 1 (G1): cell grows, replicates organelles,normal functions DNA synthesis (S): DNA replicates. Gap 2 (G2): additional growth Mitosis: 10% time division of the cell nucleus (mitosis) division of the cell cytoplasm (cytokinesis) Mitosis occurs only if the cell is large enough and the DNA undamaged.

Cells divide at different rates. The rate of cell division varies with the need for those types of cells. Some cells are unlikely to divide (G0).

Cell division keeps cells a constant size: Cell size is limited. Volume increases faster than surface area. Which cell is more efficient? Why is cell division important?

Why do different cells have different shapes? Surface area must allow for adequate exchange of materials. Cell growth is coordinated with division. Cells that must be large have unique shapes. Why?

9.3 Cell Division KEY CONCEPT Cells divide during mitosis and cytokinesis.

Chromosomes condense at the start of mitosis. DNA wraps around proteins (histones) that condense it. DNA double helix DNA and histones Chromatin Supercoiled DNA

Chromatids: One half of a duplicated chromosome is a chromatid. Sister chromatids are identical copies. Held together at the centromere. Telomeres –end of the chromsome protect DNA and do not include genes. After 40-60 divisions they are too short and the cell stops dividing. chromatid telomere centromere Condensed, duplicated chromosome

Interphase is not part of Mitosis. Interphase occurs before Mitosis. Mitosis and cytokinesis produce two genetically identical daughter cells. Occurs in body cells ( not egg or sperm cells) Asexual reproduction Parent cell centrioles spindle fibers centrosome nucleus with DNA Remember : Interphase is not part of Mitosis. Interphase occurs before Mitosis. Interphase prepares the cell to divide. During interphase, the DNA is duplicated.

Mitosis has 4 distinct phases: PMAT- acronym for the 4 phases: Prophase, Metaphase, Anaphase and Telophase. I. Prophase: chromosomes condense (become visible) spindle fibers form. nucleolus disappears. nuclear membrane disintegrates.

2. Metaphase: During metaphase, chromosomes line up in the middle of the cell.

3. Anaphase During anaphase sister chromatids separate to opposite sides of the cell.

4. Telophase During telophase, two new (identical) nuclei form. Reverse of Prophase: Nuclear membrane reforms Nuceolus becomes visible. Chromosomes uncoil

Cytokinesis: Division of cytoplasm Cytokinesis differs in animal and plant cells. In animal cells, the membrane pinches closed. In plant cells, a cell plate forms. Occurs almost simultaneously with telophase.