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Chapter 3: Cell Division
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.