Bellringer Mon, 11/23 1.Why do cells need to divide? List at least 2 reasons.

CELL GROWTH & REPRODUCTION

Why do cells divide? Why can’t we just be one giant cell?   Small cells are more efficient   Small cells have a greater Surface Area- to-Volume Ratio   When cells get too big, their surface area is not large enough for oxygen, food, and wastes to diffuse across the cell membrane   The large cell would starve to death or be poisoned from waste

Surface area-to-volume ratio  As a cell’s size increases, its volume increases much faster than its surface area.  If cell size doubled, the cell would require eight times more nutrients and would have eight times more waste to excrete Surface area = 6 mm 2 Volume = 1 mm 3 Surface area = 24 mm 2 Volume = 8 mm 3 1 mm 2 mm 4 mm

Section 8.2 Summary – pages  The surface area, however, would increase by a factor of only four.  The cell would either starve to death or be poisoned from the buildup of waste products Surface area-to-volume ratio Surface area = 6 mm 2 Volume = 1 mm 3 Surface area = 24 mm 2 Volume = 8 mm 3 1 mm 2 mm 4 mm

Diffusion limits cell size   Although diffusion is a fast and efficient process over short distances, it becomes slow and inefficient as the distances become larger.   Because of the slow rate of diffusion, organisms can’t be just one giant-sized cell.

Cell Reproduction Vocab  Chromosomes = condensed DNA, they form when cell is ready to divide  Made up of 2 halves held together in the center by the centromere  Chromatin= a form of chromosomes that look like loose, unorganized spaghetti (this is what we see in Interphase)  Sister chromatids- exact copies of a chromosome held together by a centromere (this is what we see in the S phase when DNA is copied)

The Life of a Cell   Cell Cycle = growth & division of a cell   1. Interphase   2. Mitosis   3. Cytokinesis

Section 8.2 Summary – pages Interphase  The majority of a cell’s life is spent in the growth period known as interphase. Interphase interphase G1: Cells grow and makes proteins (enzymes) S: Chromosomes containing DNA are copied G2: Cell prepares for division

2. Mitosis  Mitosis- Division of the cell nucleus  Divided into 4 phases  Prophase  Methaphase  Anaphase  Telophase

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Prophase – Plump chromosomes  Chromatin coils (condenses) into visible (plump) chromosomes ( 2 sister chromatids)  Nuclear Membrane and nucleolus breaks down  Centrioles start sending out Spindle Fibers

2. Metaphase – Meet in the Middle  Chromosomes line up in the center of the cell  Spindle Fibers attach to the chromatids at the centromere of each chromosome and pulls them in the middle

3. Anaphase – Away  Spindle fibers shorten  Sister chromatids are pulled away from each other to opposite ends of the cell

4. Telophase – Two nuclei  Chromatids are pulled to opposite ends of the cell (poles)  Nuclear membrane and nucleolus re-forms

Cytokinesis   Following mitosis, the cytoplasm divides, separating the two daughter cells.  New daughter cells have identical DNA

Cytokinesis  Division of the cytoplasm Cleavage (pinch) in animals Cleavage (pinch) in animals Cell Plate (new wall) in plants Cell Plate (new wall) in plants

Interphase Prophase Metaphase Anaphase Telophase