Transcript 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
generation.
 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
process.
 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
organisms.

Fits in well with the cell theory discussed earlier.
 Cell
reproduction occurs when parent cells
divide.
 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
completed.
 Cell carries out normal cell activities during
this phase.
 Interphase



G1 – cell growth
S – DNA replicated
G2 – preparation for cell division
 Mitosis




Prophase
Metaphase
Anaphase
Telophase
 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
cell.
 Result of Mitosis: One 2n cell becomes two
2n daughter cells.
 Cell
plate
 Cells
grow at different rates depending on
needs.



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
made.
 If
cells begin to grow rapidly and growth is
not stopped, cancerous areas can occur.
 Cancer is an example of uncontrollable cell
growth.
 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.








Humans
Fruit flies
Camel
Porpoise
Bat
King Crab
Soybean
Pea
46
8
70
44
44
208
40
14
 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
homologues.
 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
eyes.
 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
fertilization.
 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
I
 Metaphase I
 Anaphase I
 Telophase I
 Prophase II
 Metaphase II
 Anaphase II
 Telophase II
 Interesting




differences:
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
recombination.
 This allows for inheritable variation.