Chapter 8 Cell Division

Chapter 8 Cell Division I. Purpose A. A cell must divide or stop growing to maintain a workable ratio of volume to surface. B. For Multicellular organisms to grow. C. To replace worn out-damaged cells. II.Types of Reproduction A. Asexual: only one parent is involved. Example:Binary

fission: one cell divided into two.

Example:Fragmenting:

a piece breaks off and grows.

B. Sexual: joining of two sex cells called gamete. 1. Fertilization: union of egg and sperm and form one cell. 2. Zygote: name for the cell formed when sperm and egg join. →Fertilized egg. a. Male gamete: sperm b. Female gamete: egg or ovum III.Lifespan A. DNA determines how long an organism will live. Example:In

adult animals, cells live 8 hours to 100 days; shortest lifespan – skin, white blood cells longest - nerve cells.

B. Lifespan depends on: kinds of organism, age, and type of cell. IV.Chromosome structure A. When NOT replicating B. Parts of a chromosome

1. Centromere: point where each pair of chromatids are attached. 2. Chromatids: two identical parts that make up a chromosome – called sister chromatids. V. Formation of body cells (SOMATIC) Mitosis A. Definition: cell division in which each daughter cell receives the same number of chromosomes as the parent. B. Chromosomes occur in like pairs called homologous chromosomes. C. Total number of chromosome is called diploid number. (2n) D. When the cell has only one chromosome of each homologous pair is called haploid number. (n) VI.Mitosis: stages of cell division (CELL CYCLE) A. Interphase: where cell spends most of its time! 1. Replication of DNA B. Four phases of Mitosis 1. Prophase a. The copied DNA coils into chromosomes. b. Characterized by the condensation of the chromosomes and the dissolution of the nuclear envelope. 2. Metaphase a. The chromosomes line up along the midline of the dividing cell. b. Once in the center of the cell, each chromosome is held in place by the kinetochore fibers. 3. Anaphase a. The chromatids of each chromosome separate at the centromere and slowly move, centromere first, toward opposite poles of the dividing cell.

b. After they separate, they are considered to be individual chromosomes. 4. Telophase a. Final stage b. The chromosomes reach opposite poles of the cell, and a cleavage furrow is formed. c. A nuclear membrane forms around each set of new chromosomes. d. Cytokinesis follows. C. Cytokinesis: division of cytoplasm 1. Animal cells: furrow or pinching in at the equator. 2. Plant cells: a cell plate forms at the equator.