Bellringer Mon, 11/231. Why do cells need to divide?

List at least 2 reasons.

CELL GROWTH & CELL GROWTH &

REPRODUCTIONREPRODUCTION

Why do cells divide?Why do cells divide?Why can’t we just be one giant cell?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 ratioSurface 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 mm2 Volume = 1 mm3

Surface area = 24 mm2 Volume = 8 mm3

1 mm 1 mm

1 mm

2 mm 2 mm

2 mm

4 mm 4 mm

4 mm

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 ratioSurface area-to-volume ratio

Surface area = 6 mm2 Volume = 1 mm3

Surface area = 24 mm2 Volume = 8 mm3

1 mm 1 mm

1 mm

2 mm 2 mm

2 mm

4 mm 4 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 VocabCell Reproduction Vocab ChromosomesChromosomes = condensed DNA, = condensed DNA,

they form when cell is ready to they form when cell is ready to dividedivide

Made up of 2 halves held together Made up of 2 halves held together in the center by the in the center by the centromerecentromere

Chromatin= Chromatin= a form of a form of chromosomes that look like loose, chromosomes that look like loose, unorganized spaghetti (this is what unorganized spaghetti (this is what we see in Interphase)we see in Interphase)

Sister chromatids- Sister chromatids- exact copies of exact copies of a chromosome held together by a a chromosome held together by a centromere (this is what we see in centromere (this is what we see in the S phase when DNA is copied)the S phase when DNA is copied)

The Life of a CellThe Life of a Cell

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

InterphaseInterphase

The majority of a cell’s life is spent in the growth period known as interphase.

Interphase

interphaseinterphase G1: Cells grow and makes proteins G1: Cells grow and makes proteins (enzymes)(enzymes)S: Chromosomes containing DNA are S: Chromosomes containing DNA are copiedcopiedG2: Cell prepares for divisionG2: Cell prepares for division

2. Mitosis2. Mitosis Mitosis- Mitosis- Division of the cell nucleusDivision of the cell nucleus Divided into 4 phases Divided into 4 phases

ProphaseProphase MethaphaseMethaphase AnaphaseAnaphase TelophaseTelophase

PMATPMAT

Purple Monkeys Attacking TokyoPurple Monkeys Attacking Tokyo

PProphase – rophase – PPlump lump chromosomeschromosomes

Chromatin Chromatin coils coils (condenses) into (condenses) into visible (plump) visible (plump) chromosomes ( 2 sister chromosomes ( 2 sister chromatids)chromatids)

Nuclear Membrane Nuclear Membrane and nucleolusand nucleolus breaks breaks downdown

CentriolesCentrioles start start sending out sending out Spindle Spindle FibersFibers

2. 2. MMetaphaseetaphase – – MMeet in the eet in the MMiddleiddle

ChromosomesChromosomes line line up in the center of up in the center of the cellthe cell

Spindle FibersSpindle Fibers attach attach to the chromatids at to the chromatids at the centromere of the centromere of each chromosome each chromosome and pulls them in the and pulls them in the middlemiddle

3.3. A Anaphase – naphase – AAway way

Spindle fibers Spindle fibers shortenshorten

Sister chromatids are Sister chromatids are pulled away from pulled away from each other to each other to opposite ends of the opposite ends of the cellcell

4. 4. TTelophase – elophase – TTwo nucleiwo nuclei

ChromatidsChromatids are are pulled to opposite pulled to opposite ends of the cell ends of the cell (poles)(poles)

Nuclear membrane Nuclear membrane and nucleolus and nucleolus re-formsre-forms

Cytokinesis

Following mitosis, the cytoplasm divides, separating the two daughter cells.

New daughter cells have identical DNANew daughter cells have identical DNA

CytokinesisCytokinesis Division of the cytoplasmDivision of the cytoplasm

Cleavage (pinch) Cleavage (pinch) in animalsin animals

Cell PlateCell Plate (new wall) in plants (new wall) in plants

IInterphasenterphase

PProphaserophase

MMetaphaseetaphase

AAnaphasenaphase

TTelophaseelophase