Biology 12 Cell Division Intro. Review: Cell Theory 1. All living things are composed of one or more cells 2. The cell is the smallest entity that retains.

Cell Division

Biology 12Cell Division Intro

Review:Cell TheoryAll living things are composed of one or more cellsThe cell is the smallest entity that retains the properties of lifeNew cells arise from existing cells.

Extensions and Implications:Living things come in a variety of sizes but all cells are roughly the same size, the difference is the number of cells.vs.

Different cells have different life spansHuman skin cells: 20 daysHuman brain cells: 30-50 years

Extensions and Implications cont`d:All organisms must grow and divide as part of their life cycle

There are 25 million cell divisions occurring every second in a human adult!

Think about it!

Review: Two type of cell reproduction:Asexual vs. sexual

Asexual reproduction involves a single cell dividing to make 2 new, identical daughter cellsExamples: Mitosis & binary fission

Sexual reproduction involves two cells (egg & sperm) joining to make a new cell (zygote) that is NOT identical to the original cellsExample: meiosis

Purpose of cell division:

GrowthEarly in the development of an organism, cells are dividing to increase the overall number of cells (i.e. Human fetus)DifferentiationCells divide to produce different types of cellsRepair damaged tissue Replace cells from outer surfaces (i.e. Skin)Immune functions (i.e. Memory T cells)

What cells divide often?What cells rarely/never divide?Skin Stomach liningRed Blood cellsEmbryoPlant rootsHairNailsNervous SystemLiver

Some important vocabulary (C Terms):ChromosomesLong threads of genetic materialFound in nucleus

ChromatidOne side of a duplicated chromosome

CentromereStructures that hold sister chromatids together

NOTE: 2 sister chromatids = 1 duplicated chromosome

ChromatinDNA tangled around a histone (a protein)Condensed chromatin = chromosome

Histone is a protein that helps package the DNA12Once more

B. ChromatinA. DNAhistoneC. Duplicated chromosomeThe Cell Cycle:The cell cycle is the series of events that take place in a cell leading to its division and replication.It consists of 3 major stagesInterphaseMitosisCytokinesis

Note: it is a continuous process!

1. InterphaseIn this phase DNA is copied in preparation for cell divisionThis is a non-reproducing stageA cell spends most of the time in this phase

2. MitosisNuclear divisionTwo identical sets of chromosomes are allocated to the 2 daughter nuclei

3. CytokinesisCytoplasmic divisionThe cytoplasm is equally divided between the two daughter cells

Short clip: cell divisionhttp://www.youtube.com/watch?feature=player_detailpage&v=Q6ucKWIIFmg

To do:Cell Cycle colouring sheet

If time permits: read pg 82-90 and start questions 1-10 on page 90