A. All multicellular organisms depend on cell division for growth. B. Repair 1. In order to sustain life, the organism must replace dead or damaged cells

C. Reproduction 1. Allows new organisms to be produced for the continuation of the species 2. Organisms can reproduce in 2 ways: asexual and sexual reproduction

a. Asexual reproduction ▪ simple cell division ▪ a single cell or organism duplicates its genetic material and then splits into two new genetically identical cells ▪ only requires 1 parent ▪ most unicellular organisms, very few multicellular organisms

b. Sexual reproduction: ▪ Genetic material from 2 parents combine to form an offspring ▪ Involves the combination of 2 sex cells, sperm and an egg ▪ Gives genetic variation to the offspring ▪ most multicellular organisms, very few unicellular organisms

A. Chromosomes 1. genes of a eukaryotic cell are located in the cell nucleus 2. Most of the time, DNA appears as chromatin 3. As a cell prepares to divide, its chromatin coils up tightly and become chromosomes.

4. The # of chromosomes in a eukaryotic cell depends on the species. a. Humans - body cells = 46 chromosomes - sex cells = 23 chromosomes Diploid number = 2n = 46 (full set) Haploid number = n = 23 (half set) 5. Each chromosome may contain many hundreds of genes.

Organism Chromosome Number (2n) Human46 Fruit fly8 Lettuce14 Goldfish94 Human Male Karyotype

B. The Cell Cycle 1. Sequence of events that allows for normal division of cell 2. 4 main stages: G1  S phase  G2  Mitosis (followed by cytokinesis) a. G1: the cell grows b. S phase (for DNA synthesis): DNA is duplicated in the nucleus c. G2: the cell prepares to divide Interphase

d. Mitosis: cell division, 4 steps, PMAT ▪ 1 st - prophase ▪ 2 nd - metaphase ▪ 3 rd – anaphase ▪ 4 th - telophase e. Cytokinesis happens after telophase to completely divide the cytoplasm

A. Prophase 1. In the nucleus, the chromatin condenses a. each chromosome can be seen b. pair of sister chromatids joined at the centromere 2. nucleolus disappears 3. the cell stops making ribosomes 4. nuclear envelope breaks down 5. spindle fibers form (made of microtubules) 6. The chromatids now attach to the microtubules - The spindle fibers start tugging the chromosomes toward the center of the cell

B. Metaphase 1. The chromosomes all gather across the middle of the cell. C. Anaphase 1. The sister chromatids separate from their partners. 2. Each chromatid is now considered a daughter chromosome. 3. Proteins at the centromeres help move the daughter chromosomes along the spindle microtubules toward the opposite side of the cell

D. Telophase and Cytokinesis 1. During this stage, the processes that occurred in prophase are reversed. 2. Spindle fibers disappears 3. two nuclear envelopes reform 4. chromosomes uncoil 5. nucleoli reappear. 6. Mitosis is now finished. 7. Cytokinesis completes the cell division

E. Cytokinesis in Animals and Plants 1. Cytokinesis in a plant cell occurs differently due to the cell wall. a. A cell plate forms and divides the cell in two. 2. In animals a cleavage furrow forms to separate the cytoplasm.