Cell Division Intro
Biology 12
Review:
Cell Theory
1. All living things are composed of one or more cells
2. The cell is the smallest entity that retains the properties of
life
3. New 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 spans
 Human skin cells: 20 days
 Human 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 cells
 Examples: Mitosis & binary fission
 Sexual reproduction involves two cells (egg & sperm) joining to
make a new cell (zygote) that is NOT identical to the original
cells
 Example: meiosis
Purpose of cell division:
Growth
1.

Early in the development of an organism, cells are dividing to
increase the overall number of cells (i.e. Human fetus)
Differentiation
2.

Cells divide to produce different types of cells
Repair damaged tissue
4. Replace cells from outer surfaces (i.e. Skin)
5. Immune functions (i.e. Memory T cells)
3.
What cells divide often?
 Skin
 Stomach lining
 Red Blood cells
 Embryo
 Plant roots
 Hair
 Nails
What cells rarely/never
divide?
 Nervous System
 Liver
Some important vocabulary (“C” Terms):
1.
Chromosomes
 Long threads of genetic material
 Found in nucleus
2.
Chromatid
 One side of a duplicated chromosome
3.
Centromere
 Structures that hold sister
chromatids together
 NOTE: 2 sister chromatids
= 1 duplicated
chromosome
4.
Chromatin
 DNA tangled around a histone (a protein)
 Condensed chromatin = chromosome
Once more…
C. Duplicated
chromosome
A. DNA
B.
histone
Chromatin
The 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 stages
1.
2.
3.
Interphase
Mitosis
Cytokinesis
 Note: it is a continuous
process!
1. Interphase
 In this phase DNA is copied in preparation for cell division
 This is a non-reproducing stage
 A cell spends most of the time in this phase
2. Mitosis
 Nuclear division
 Two identical sets of chromosomes are allocated to the 2
daughter nuclei
3. Cytokinesis
 Cytoplasmic division
 The cytoplasm is equally divided between the two daughter
cells
Short clip: cell division
 http://www.youtube.com/watch?feature=player_detailpag
e&v=Q6ucKWIIFmg
To do:
 Cell Cycle colouring sheet
 If time permits: read pg 82-90 and start questions 1-10 on
page 90