Chapter 3: Cell Division
3.1 Cell division occurs in all organisms
3.2 Cell division is part of the cell cycle
3.3 Both sexual and asexual reproduction involve
cell division
3.3 Both sexual and asexual reproduction
involve cell division
 Multicellular organisms: cell
division functions in growth,
repair and development
 Unicellular organisms: each cell is
itself and organism
 Cell division is to reproduce:
asexual reproduction
 One organisms produces one or
more new organisms that are
identical to itself
Paramecium
(binary fission)
Asexual reproduction involved
one parent
 Cells divide to produce two daughter cells
 When the cell is a whole organism, cell division =
reproduction
 An offspring is produced – can live independently
 Identical to parent: parent’s genes = offspring’s genes
 “asexual reproduction”
Cell Division in
Unicellular
Organisms
 Cell division = one form of asexual reproduction
 Occurs in two ways, depending on nucleus or not
 Prokaryotes (no nucleus):
 Binary fission (asexual reproduction)
 parent organisms replicates its DNA then splits in two  two
daughter cells offspring
 Ex: bacteria and archaea
 Eukaryotes
 Unicellular: reproduction by mitosis and cytokinesis
 Ex: algae , some yeasts, and protozoans such as
paramecia
Budding
 Both unicellular and multicellualr
organisms can reproduce using this
method
 The organism develops tiny buds on its
body – same genetic material as parent
 Most often, reaches a certain size and
breaks away (can sometimes remain
attached to parent)
 Some unicellular and some multicellular
organisms reproduce by budding:
 In some multicellular: buds form from any cell of
the body
 In other multicellular organisms, on specialized
cells may bud
 How different in unicellular and
multicellular organisms?
 In unicellular organisms, the bud is a single
cell. In multicellular organisms, the bud
grows by cell division, becoming
multicellular
Regeneration
 The process in which missing body
parts are replaced by the growth of
new tissue
 Specialized cells at the site of a
wound or lost limb are able to
become different types of tissues
 Typically for regrowth of damaged or
missing body parts
 Sometimes for asexual reproduction
 New organism is genetically identical
to the original organism
Asexual Reproduction and Health
 How can you get so sick so fast?
 Bacteria are unicellular prokaryotes, reproduce by
binary fission (can occur very fast!)
 Bacterial reproduce asexually through binary fission: 2
become 4 become 8…
 Generation time of bacteria is often very short: <30
minutes!
 After 24 generations…millions of bacteria!
 Some bacteria are good for your health
Sexual reproduction involves two
parent organisms
 Cell division produces cells identical to the parent cell
 One organism can produce offspring through asexual reproduction
 Parent genetically identical to offspring
 Many multicelluar organisms reproduce by sexual reproduction
 Genes of two parents are combined to produce offspring
 Offspring are not exactly the same as either parent
 Diversity of life possible because of the combining of genetic materials
from two parents in sexual reproduction
Genes from the
parents have to be
combined in a way
that gives the
offspring the right
number and types of
genes to become the
same type of organism
1. Cancer is a disease characterized by rapid,
uncontrolled cell division. Explain why you think
colchicine is sometimes used in cancer chemotherapy.
2. How would a colchicine-treated cell differ from a
nontreated cell?
1.Colchicine can stop cancer cells from dividing.
2.The colchicine-treated cell would have twice as many
chromosomes as a nontreated cell.
 1. Suggest a reason why bacteria do not undergo
mitosis.
 2. Why are employees in the food service industry
required to wash their hands frequently?
 3. Why do you think it is important to defrost foods in
the refrigerator instead of at room temperature?
Answers
 1. Suggest a reason why bacteria do not undergo mitosis.
 2. Why are employees in the food service industry required to
wash their hands frequently?
 3. Why do you think it is important to defrost foods in the
refrigerator instead of at room temperature?
 1. Bacteria have no nuclei or chromosomes, so they do not
undergo mitosis when they divide.
 2. To prevent the spread of bacteria
 3. Refrigeration greatly slows the growth of bacteria.