Cells divide at different rates. 5.1 Cell Cycle Cells divide at different rates.

5.3 Regulation of the Cell Cycle KEY CONCEPT Cell cycle regulation is necessary for healthy growth.

5.3 Regulation of the Cell Cycle External factors include physical and chemical signals. Growth factors are proteins that stimulate cell division.

5.1 Cell Cycle Cell size is limited. If volume increases faster than surface area then cell divides Surface area to Volume Ratio

5.3 Regulation of the Cell Cycle Apoptosis is programmed cell death. a normal feature of healthy organisms occurs in development of infants webbed fingers

KEY CONCEPT Many organisms reproduce by cell division.

Asexual reproduction is the creation of offspring from a single parent. Binary fission produces two daughter cells genetically identical to the parent cell. occurs in prokaryotes No nucleus Ex: bacteria parent cell DNA duplicates cell begins to divide daughter cells

Budding forms a new organism from a small projection growing on the surface of the parent. Hydra Yeast

Vegetative Reproduction forms a new plant from the modification of a stem or underground structure on the parent plant.

The Cell Cycle has Three main stages.

5.1 Cell Cycle Interphase Gap 1 (G1) – cell growth and normal functions Synthesis (S): copies DNA Gap 2 (G2): additional growth Mitosis (M) Division of the cell nucleus Cytokinesis Division of the cell cytoplasm Some cells (G0) – exit the cell cycle fully developed cells in the CNS

5.2 Mitosis and Cytokinesis Mitosis divides the cell’s nucleus in four phases. Prophase chromosomes condense and spindle fibers form Nucleolus and the nuclear membrane break down & disappear Centrioles (centrosomes) appear

5.2 Mitosis and Cytokinesis Metaphase Chromosomes line up in the middle of the cell. Chromosomes are easier to identify Photomicrograph for Karyotype

5.2 Mitosis and Cytokinesis Anaphase sister chromatids separate to opposite sides of the cell.

5.2 Mitosis and Cytokinesis Telophase New nucleus and nucleolus form Chromosomes begin to uncoil Spindle fibers and centrioles disappear

5.2 Mitosis and Cytokinesis Cytokinesis differs in animal and plant cells. Cleavage furrow - (animal cells) the cell membrane pinches in Cell plate - (plant cells) a cell wall forms between the two cells

5.2 Mitosis and Cytokinesis Results of Mitosis 2 new cells genetically identical to the parent cell 2 identical diploid cells. Single celled eukaryote – asexual reproduction Multi-celled eukaryote – growth

6.2 Process of Meiosis KEY CONCEPT During Meiosis, diploid cells undergo two cell divisions that result in 4 different haploid cells.

6.1 Chromosomes and Meiosis Occurs in sex organs (ovaries & testes) Produces genetically different sex cells - gametes.

6.2 Process of Meiosis DNA coils tightly into chromosomes Stages of Meiosis Interphase – G1, S, G2 Meiosis I Prophase I DNA coils tightly into chromosomes Spindle fibers & centrioles appear Nucleus & nucleolus disappear Synapsis - Every chromosome lines up next to its homologue each pair is called a tetrad – 4 chromatids XX during synapsis the chromatids may twist around each other which may result in… crossing over - portions of chromatids break off & attach to the other chromatids * genetic recombination - the exchange of genetic material between maternal & paternal chromosomes (homologous pair)

6.6 Meiosis and Genetic Variation

6.6 Meiosis and Genetic Variation Metaphase I Tetrads line up randomly along the middle of the cell

6.6 Meiosis and Genetic Variation Anaphase I Tetrads separate Each homologous chromosome moves to an opposite pole Independent Assortment – random separation of the homologous = genetic recombination

6.6 Meiosis and Genetic Variation Telophase I Chromosome reach the opposite pole Cytokinesis begins Each new cells now contains a haploid # of chromosomes (half the original #)

6.2 Process of Meiosis DNA is not replicated between meiosis I and meiosis II (No Interphase)

6.2 Process of Meiosis Meiosis II Prophase II Spindle fibers and centrioles form Metaphase II Chromosomes move to the middle of the cells Anaphase II Chromatids separate & move toward opposite poles Telophase II Nuclear membrane forms around the chromosomes Cytokinesis II – results in 4 new cells each with half the # of chromosomes each genetically different

6.2 Process of Meiosis Meiosis has two cell divisions - mitosis has one Meiosis results in 4 different haploid cells - mitosis results in 2 identical diploid cells

After Meiosis Haploid cells develop into mature gametes. 6.2 Process of Meiosis After Meiosis Haploid cells develop into mature gametes. Gametogenesis - the production of gametes. differs between females and males.

Spermatogenesis – production of sperm cells 6.2 Process of Meiosis Spermatogenesis – production of sperm cells Meiosis = 4 haploid cells – spermatids Each spermatid then develops into a mature sperm cell Sperm cells (plural) – spermatozoa

Oogenesis – production of mature egg cells – ova (plural) 6.2 Process of Meiosis Oogenesis – production of mature egg cells – ova (plural) Meiosis = 1 mature egg cell (ovum) During cytokinesis the cytoplasm is divided unequally One cell receives most of the cytoplasm  develops into ovum Other 3 cells = polar bodies = degenerate (break down)