Download Unit4Notes

Name
Unit
4
Cell Division
WHAT I KNOW
WHAT I LEARNED
How do cells grow?
Why don’t cells get
very big?
What is a mutation?
What is cancer?
1
Unit 4 Content Expectations (aka Standards)
 B2.1C Explain cell division, growth, and development as a consequence of an increase in
cell number, cell size, and/or cell products.
 B2.1d Describe how, through cell division, cells can become specialized for specific function.
 B3.5d Describe different reproductive strategies employed by various organisms and explain
their advantages and disadvantages.
 B4.2A Show that when mutation occur in sex cells, they can be passed on to offspring (inherited
mutations), but if they occur in other cells, they can be passed on to descendant cell only (noninherited mutations).
 B4.3A Compare and contrast the processes of cell division (mitosis and meiosis),
particularly as those processes relate to production of new cells and to passing on genetic
information between generations.
 B4.3B Explain why only mutations occurring in gametes (sex cells) can be passed on to
offspring.
 B4.3f Predict how mutations may be transferred to progeny.
 B4.3g Explain that cellular differentiation results from gene expression and/or environmental
influence (e.g., metamorphosis, nutrition).
 B4.4b Explain that gene mutation in a cell can result in uncontrolled cell division called cancer.
Also know that exposure of cells to certain chemicals and radiation increases mutations and thus
increases the chance of cancer.
Unit 4 Big Idea
Through cell division, mitosis explains
while
meiosis explains
.
Unit 4 Core Concepts

The process of mitosis produces
and these cells
.

Meiosis ensures genetic continuity, by producing
, which passes on genes
.
Limits to cell size pg 241
B2.1C Explain cell division, growth, and development as a consequence of an increase in cell number, cell size,
and/or cell products.
The larger a cell becomes, the more
. In
addition, a larger cell is less efficient in
.
2
In other words, it is beneficial for a cell
.
Food, oxygen, and water enter a cell through the
. Waste products
leave in the same way. The rate at which this exchange takes place depends on the
of a cell. The rate at which food and oxygen are used up and waste products
are produced depends on the cell’s
.
As the length of the sides of a cube increases, its volume increases
than its
surface area, decreasing the ratio of surface area to volume.
After watching the video about cell size, answer the following questions. What happened as the cells
grew larger? What was the difference between the large and the small cells? Is this really a problem?
Before a cell grows too large, it
in
a process called
.
Before cell division,
.
It then divides into two “daughter” cells. Each daughter cell
.
Cell division
cell volume. It also results in an I
, for each daughter cell.
3
Cell Division and Reproduction pg 244
B3.5d Describe different reproductive strategies employed by various organisms and explain their advantages
and disadvantages.
Asexual reproduction is reproduction
. The offspring produced are, in
most cases,
.
Asexual reproduction is a
.
Both prokaryotic and eukaryotic single-celled organisms and many multicellular organisms can
reproduce asexually.
In sexual reproduction, offspring are produced by the
. These fuse into a single cell
before the offspring can grow.
The offspring produced
.
Most animals and plants, and many single-celled organisms, reproduce sexually.
Comparing Sexual and Asexual Reproduction. Fill in the table below.
Chromosomes pg 244
The genetic information that is passed on from one
generation of cells to the next is carried by
Every cell must copy its
.
before cell division begins.
Each daughter cell gets
Cells of every organism have a specific number of
.
.
4
The Cell Cycle pg 245
B4.3A Compare and contrast the processes of cell division (mitosis and meiosis), particularly as those processes
relate to production of new cells and to passing on genetic information between generations.
The Prokaryotic Cell Cycle
The prokaryotic
is a regular pattern of growth, DNA replication,
and cell division. Most prokaryotic cells begin to replicate,
once they have grown to a certain size.
When DNA replication is complete, the cells
process known as
through a
.
Binary fission is a form of
.
For example, bacteria reproduce by binary fission.
The Eukaryotic Cell Cycle
The eukaryotic cell cycle consists of four phases: G1, S, G2,
and M.
INTERPHASE is the
. It is a period of growth that consists of the G1,
S, and G2 phases. The M phase is the period of cell division.
Think Intermission when you think of
. If cell division is the show to watch, this is the time
between each division.
G1 PHASE: CELL GROWTH
In the G1 phase, cells
.
S PHASE: DNA REPLICATION
In the S (or synthesis) phase,
.
G2 PHASE: PREPARING FOR CELL DIVISION
In the G2 phase, many of the
.
5
M PHASE: CELL DIVISION
In eukaryotes, cell division occurs in two stages: mitosis and cytokinesis.
Mitosis is the
.
Cytokinesis is the
.
Mitosis
Chromatid –
Centromere –
Centrioles –
Spindle –
PROPHASE (THINK PROLOGUE OF A STORY)
During prophase, the first phase of mitosis,
.
The centrioles move to opposite sides of nucleus and
.
The spindle forms and DNA strands attach at a point called their
.
The
and nuclear envelope
breaks down.
Spindle fibers –
METAPHASE (MIDDLE)
During metaphase, the second phase of mitosis, the
.
6
The spindle fibers
.
ANAPHASE (APART)
During anaphase, the third phase of mitosis, the
.
The chromosomes
.
TELOPHASE (TWO NUCLEI)
During telophase, the fourth and final phase of mitosis, the chromosomes
.
A
around each cluster of chromosomes.
The spindle breaks apart, and
.
CYTOKINESIS (CELL SPLITTING)
Cytokinesis is the
.
Cytokinesis in Animal Cells
The cell membrane is drawn in until
.
Each part contains its own nucleus and organelles.
Cytokinesis in Plant Cells
In plants, the cell membrane is not flexible enough
to draw inward because of the rigid cell wall.
Instead, a cell plate forms between the divided
nuclei that develops into cell membranes.
A
in between the two new
membranes.
7
Cell Cycle Review
What are chromosomes?
A body cell
, as shown in the figure. Four
.
These two sets of chromosomes are homologous, meaning that each of the four chromosomes from
the male parent has a corresponding chromosome from the female parent.
Chromosomes—
.
The genes are located in specific positions on chromosomes.
Also, humans have 23 pairs of chromosomes while this organism has only 4 pairs. One of our 23
pairs are either XX (female) or XY (male) which defines our gender.
This is a picture of the
. You can clearly see the 23rd pair (XY) which indicate
this human is genetically a male.
Diploid Cells have
of chromosomes.
Haploid Cells have
as many chromosomes.
Meiosis is a process in
through the separation of homologous chromosomes in a diploid cell.
Meiosis usually involves two distinct divisions, called meiosis I and meiosis II.
By the end of meiosis II, the diploid cell becomes four haploid cells.
8
Meiosis I
Just prior to meiosis I, the cell undergoes a round of
.
Each replicated chromosome consists of two identical chromatids joined at the center.
Prophase I
The cells begin to divide, and the
, which contains four chromatids.
As homologous chromosomes pair up and form tetrads, they undergo a process called crossingover.
First, the chromatids of the homologous
.
Then, the crossed sections of the
.
Crossing-over is important because it
in the cell.
Metaphase I
As prophase I ends, a spindle forms and attaches to each tetrad.
During metaphase I of meiosis,
.
Anaphase I
During anaphase I, spindle fibers pull each homologous chromosome pair
.
When anaphase I is complete, the separated chromosomes cluster at opposite ends of the cell.
Telophase I
During telophase I,
around each cluster of
chromosomes.
Cytokinesis
Cytokinesis follows telophase I, forming
.
Meiosis I
Meiosis I results in
.
9
Because each pair of homologous chromosomes was separated, neither daughter cell has
the two complete sets of chromosomes that it would have in a diploid cell.
The two cells produced by meiosis I
.
Meiosis II
The two cells produced by meiosis I now enter a second meiotic division.
Unlike the first division,
.
Prophase II
As the cells enter prophase II, their
—each consisting of two
chromatids—
.
The chromosomes do not pair to form tetrads, because the homologous pairs were
already separated during meiosis I.
Metaphase II
During metaphase of meiosis II,
.
Anaphase II
As the cell enters anaphase, the paired chromatids
.
Telophase II and Cytokinesis
In the example shown here,
produced in
meiosis II
These four daughter cells now contain the
(N)—half the chromosomes each.
Gametes to Zygotes
The haploid cells produced by meiosis II are
.
In male animals, these gametes are called sperm. In some plants, pollen grains contain haploid sperm
cells. In female animals, generally only one of the cells produced by meiosis is involved in
reproduction. The female gamete is called an egg in animals and an egg cell in some plants.
10
Comparing Meiosis and Mitosis
In mitosis, when the two sets of genetic material separate, each daughter cell receives one complete
set of chromosomes. In meiosis, homologous chromosomes line up and then move to separate
daughter cells.
Mitosis does not normally change
. This is not the case for meiosis, which
.
Mitosis results in the production of
,
whereas meiosis produces
.
Mitosis is a form of
, whereas meiosis is an
.
In mitosis, when the two sets of genetic material separate,
.
In meiosis, homologous chromosomes line up and then move to separate daughter cells.
As a result,
.
The
in meiosis result
in a
than could result from mitosis.
Mitosis
of the original cell.
Meiosis
.
11
Changes in Chromosome Number
A diploid cell that enters mitosis with
will
divide to produce
, each of
which also has
.
is a single cell division, resulting in the production of
.
requires
, and, in
most organisms, produces a total of
.
Chromosomal Disorders
What happens if there are errors during meiosis?
If
occurs during meiosis, gametes with an
may result, leading to a disorder of chromosome numbers.
The parent cell has 8 chromosomes (paired in 4 sets). If nondisjunction hadn't occurred, the
two daughter cells formed after Meiosis I would each have 4 chromosomes (2 pairs). There
would be two red and two yellow.
But, because nondisjunction occurred during Meiosis I, the daughter cells
have an abnormal number of chromosomes. Therefore, as they split again
in Meiosis II, the sex
cells that will be used during sexual reproduction have an
.
If two copies of an autosomal (paired) chromosome fail to separate during
meiosis, an individual may be born with
, meaning “three
. This condition is known as a
bodies.” The most common form of trisomy, involving three copies of chromosome 21, is
, which is often characterized by mild
to severe mental retardation and a high frequency of certain birth defects.
Nondisjunction of the
can lead to a disorder known
as
.
A female with Turner’s syndrome usually inherits only
.
Women with Turner’s syndrome are sterile, which means that they are unable to reproduce.
Their sex organs do not develop properly at puberty.
12
Genetically, females lack a Y chromosome while males are characterized by the presence
of a Y chromosome.
In males, nondisjunction may cause
,
resulting from the inheritance of an
,
which interferes with meiosis and usually prevents these individuals from reproducing.
There have been no reported instances of babies being born without an X chromosome,
indicating that this chromosome contains genes that are vital for the survival and
development of the embryo.
B4.3B Explain why only mutations occurring in gametes (sex cells) can be passed on to offspring.
B4.3f Predict how mutations may be transferred to progeny.
Genetic disorders result from
.
The offspring's cells replicate the abnormal DNA during Mitosis and therefore the problem
is replicated in all the cells of the offspring.
Genetic disorders could also result from mutations that happen to an offspring's DNA
(chromosomes) during the early stages of development. Those mutations/changes in DNA
are also replicated in all the cells of the offspring.
Genetic Disorders Sickle-shaped cells are more rigid than normal red blood cells, and they tend to
get stuck in the capillaries.
B4.4b Explain that gene mutation in a cell can result in uncontrolled cell division called
cancer. Also know that exposure of cells to certain chemicals and radiation increases
mutations and thus increases the chance of cancer.
The
can
be turned on and off.
For example, when an injury such as a broken bone occurs, cells are
stimulated to divide rapidly and start the healing process. The rate of cell
division slows when the healing process nears completion.
are a family of proteins that regulate the timing of the
cell cycle in eukaryotic cells.
This graph shows how cyclin levels change throughout the cell cycle in
fertilized clam eggs.
Internal regulators are proteins that respond to events inside a cell. They allow the cell
cycle to proceed only once certain processes have happened inside the cell.
External regulators are proteins that respond to events outside the cell. They direct cells
to speed up or slow down the cell cycle.
13
Growth factors are external regulators that stimulate the growth and division of cells. They
are important during embryonic development and wound healing.
is a process of programmed cell death. Apoptosis plays a role
in development by shaping the structure of tissues and organs in plants and animals.
How do cancer cells differ from other cells?
Cancer cells do not respond to the signals that regulate the growth of most cells. As a
result, the cells
is a disorder in which body cells lose the ability to control cell growth.
Cancer cells divide uncontrollably to form a mass of cells called a
.
A
is noncancerous. It does not spread to
surrounding healthy tissue.
A
is cancerous. It invades and
destroys surrounding healthy tissue and can spread to other parts of the body.
The spread of cancer cells is called metastasis. Cancer cells absorb nutrients
needed by other cells, block nerve connections, and prevent organs from functioning.
Cancers are caused by
and division.
Some sources of gene defects are
in genes that regulate cell growth
.
A damaged or defective p53 gene is common in cancer cells. It causes cells to lose the
information needed to respond to
.
B2.1d Describe how, through cell division, cells can become specialized for specific function.
B4.3g Explain that cellular differentiation results from gene expression and/or environmental
influence (e.g., metamorphosis, nutrition).
All organisms start life as just one cell.
Most multicellular organisms pass through an early stage of development called an
embryo, which gradually develops into an adult organism.
During development, an organism’s cells become more
for particular functions.
The process by which cells become specialized is known as
.
During
, cells differentiate into many different types
and become specialized to perform certain tasks.
Differentiated cells carry out the jobs that multicellular organisms need to stay alive.
Cell differentiation in mammals is controlled by a number of interacting factors in the
embryo.
14
generally reach a point at which their differentiation is
complete and they can no longer become other types of cells.
Regulating
is especially important in shaping
the way a multicellular organism develops.
Each of the specialized cell types found in the adult originates from the same fertilized egg
cell.
As an embryo develops, different sets of genes are regulated by transcription factors and
repressors.
helps cells undergo differentiation, becoming
specialized in structure and function.
15