Biology Chapter 7 - Central Lyon CSD

Cellular Reproduction
 Describe
the debate surrounding spontaneous
generation and how Redi’s and Pasteur’s
experiments ended that debate.
 Sequence the events of the cell cycle in
which new body cells are produced.
 Analyze the ways in which events of the cell
cycle are controlled.
 Debating
spontaneous generation.
 Some believed nonliving things could give
rise to living things.
 Francesco Redi performed an experiment in
1668 to test this belief.
Maggots were thought to be spontaneously
generated from decaying meat.
Redi observed maggots turned into flies.
He suspected they came from flies themselves.
 In
1675, microorganisms were discovered.
 This reopened the debate on spontaneous
 In 1864, Louis Pasteur finally developed an
experiment to end the debate.
 At this time, air was considered to be an
essential ingredient necessary for
spontaneous generation.
 He conducted experiment in which air was
allowed to enter a flask of nutrient broth.
 Was
the precursor for today’s pasteurization
 His experiment led to a major biological
theory: Theory of Biogenesis
At the present time and under present conditions
on Earth, all organisms are produced from other
Fits in well with the cell theory discussed earlier.
 Cell
reproduction occurs when parent cells
 Two daughter cells are the result.
 Contributes to overall growth of an organism.
 Also helps repair damaged tissue, replace
cells that are lost from outer surfaces (skin),
and helps us to resist disease.
 Smaller is better: SA to volume ratio we
studied in lab.
 Most
cells are in a non-reproducing phase
called interphase.
 Cell spends most of its life in this stage.
 Stage length varies with type of cell.
 Interphase begins when cell reproduction is
 Cell carries out normal cell activities during
this phase.
 Interphase
G1 – cell growth
S – DNA replicated
G2 – preparation for cell division
 Mitosis
 Chromatin
begins to coil up into structures
known as chromatids. Two identical
chromatids are attached at the center in a
location called the centromere.
 A chromosome is this double stranded
structure attached at the centromere.
 Spindle also forms during prophase. It is a
football-shaped band of fibers that originate
from two centrioles.
 Centrioles have migrated to opposite ends of
the cell.
 Nuclear
membrane disintegrates as well:
 Chromosomes
attach to the spindle fibers.
 They then meet in the middle of the cell.
 The
chromosomes separate into sister
chromatids again by being pulled apart at
the centromere by the spindles.
 Chromatids move away from the middle.
 Plasma
membranes in animal cells begin to
pinch together.
 Basically propase in reverse: nuclear
membrane reforms, chromatids relax back
into chromatin form, two sets of identical
chromatin now located at each end of the
 Result of Mitosis: One 2n cell becomes two
2n daughter cells.
 Cell
 Cells
grow at different rates depending on
Red blood cells and skin cells multiply rapidly.
Some muscle and nerve cells remain in
interphase their whole lives.
Liver cells only divide when repairs need to be
 If
cells begin to grow rapidly and growth is
not stopped, cancerous areas can occur.
 Cancer is an example of uncontrollable cell
 Over time, this growth can outcompete vital
cells and tissues for nutrients and space.
 One
way cells regulate growth is by coming
into contact with other cells.
 When this occurs, cells stop reproducing.
 Controlled by proteins in the cell.
 As scientists figure out what triggers cell
growth, information could be used to cure
cancers, replace damaged tissues, etc.
 Have
single chromosome (circular).
 Don’t really have a cell cycle.
 Reproduce by binary fission.
Chromosome attaches to cell membrane
Cell elongates.
Chromosome is replicated.
Cell divides into 2 with 1 chromosome in each.
 Objectives:
Sequence the series of events by which
reproductive cells are produced in complex
plants and animals.
Analyze the significance of meiosis with respect
to adaptation and evolution.
 Number
of chromosomes varies from species
to species.
Fruit flies
King Crab
 How
many chromosomes do your parents
have in their cells? Grandparents?
 How does this number remain the same from
one generation to the next?
 The answer lies in the process of meiosis.
 In
the cells of animals, chromosomes usually
come in pairs.
 Humans
 Cells
with 46 chromosomes have 23 pairs.
with 2 of each chromosome are said to
be diploid (2n) n=number of different pairs.
 The
two members of each pair are referred
to as homologous chromosomes, or
 The DNA for each homologue carries the
information for the same traits, although the
exact information may differ.
 Example: Eye color: One may carry info for
brown eyes and one may carry info for blue
 When
two parent organisms mate to produce
single cell, the single fertilized egg is called
a zygote.
 A zygote results from the union of two
different kinds of gametes, which are the sex
cells (eggs and sperm).
 The fusion of the egg and sperm is called
 Eggs and sperm are haploid (n) cells. They
have one set of the chromosome pairs, so
they have 23 chromosomes in humans.
 Fusion
of sex cells is sexual reproduction.
 Haploid
 Meiosis
cells cannot be produced by mitosis.
– the process by which haploid cells
are formed from diploid cells.
 Not limited to animal cells. Happens in plant
cells also. Haploid cells are called spores
instead of gametes.
 Prophase
 Metaphase I
 Anaphase I
 Telophase I
 Prophase II
 Metaphase II
 Anaphase II
 Telophase II
 Interesting
Meiosis I begins before birth, then process stops.
At sexual maturity, several cells continue on with
the process.
Usually result is only one egg instead of 4.
Why is this an advantage?
 Crossing
over provides for genetic variation.
 Provides for a better chance at survival for
the species as a whole.
 The reshuffling of chromosomes and the
genetic information they carry is one of the
mechanisms for what is called genetic
 This allows for inheritable variation.