9 C
ellular Reproduction and Sexual
Reproduction
ENCOUNTER THE PHENOMENON
Write the Encounter the Phenomenon question for this module.
Why do some of these cells look so different from each other?
Use the “What I Know” column to list the things you know about the Encounter the Phenomenon
question. Then list the questions you have about the Encounter the Phenomenon question in the
“What I Want to Find Out” column. As you read the module, fill in the “What I Learned” column.
W
What I Want to Find Out
L
What I Learned
Copyright © McGraw-Hill Education
K
What I Know
Science Notebook • Cellular Reproduction and Sexual Reproduction
111
Cellular Reproduction and Sexual Reproduction
1 Cellular Reproduction
NEW VOCABULARY
anaphase
Use the terms in the left column to complete the paragraph below.
Chromatin
is the relaxed form of DNA.
Chromosomes
are
apoptosis
condensed structures that contain the DNA that are visible during
cancer
mitosis. A
carcinogen
consisting of DNA coiled around histones. Cells reproduce by a cycle
cell cycle
of growing and dividing called the
centromere
a cell grows, matures, and replicates its DNA. Mitosis
chromatin
of the cell cycle where the cell’s nucleus and nuclear material
chromosome
divide. In
cyclin
chromosomes.
cyclin-dependent kinase
identical copies of DNA. The structure at the center of the chromosome
cytokinesis
where the sister chromatids are attached is called the
interphase
Prophase continues, and the nucleolus starts to disappear. The
metaphase
nucleosome
is a repeating unit of chromatin fibers,
cell cycle . During interphase
is the stage
prophase , the cell’s chromatin condenses to form
Sister chromatids
spindle apparatus
are structures that contain
centromere
is the structure made of spindle fibers, centrioles,
mitosis
and aster fibers that is involved in moving and organizing chromosomes
nucleosome
before the cell divides. The second stage of mitosis in which
prophase
chromosomes attach to the spindle apparatus and align along the cell’s
sister chromatid
equator is called metaphase . During anaphase , microtubules
spindle apparatus
shorten, moving the chromosomes to opposite poles of the cell.
Telophase is the last stage of mitosis where the nucleoli reappear.
Two new nuclear membranes begin to form, but the cell is not
completely divided. The cell begins cytokinesis , in which the cell’s
cytoplasm divides. This results in two cells with identical nuclei.
Cells have instructions to carry out the cell cycle. Proteins called
cyclins
bind to enzymes called cyclin-dependent kinases in the
stages of interphase and mitosis to initiate various activities at different
stages in the cell cycle. Not all cells survive. Some go through a process
called apoptosis , or programmed cell death. Cancer is the uncontrolled
growth and division of cells, which is a failure in the regulation of the
cell cycle. A carcinogen is a substance that is known to cause cancer.
Science Notebook • Cellular Reproduction and Sexual Reproduction
112
Copyright © McGraw-Hill Education
telophase
.
1 Cellular Reproduction (continued)
Analyze movement of nutrients and wastes as cell size increases.
Accept all reasonable responses.
If a cell
transport of
gets too
and wastes by
large ,
Get It?
a cell.
nutrients
diffusion
Therefore, cells divide
before they become too
slows down .
large .
Explain why a high ratio of surface area to volume benefits
It makes transporting nutrients throughout the cell and removing waste
products easier and more efficient.
Organize information about chromosomes in the concept web.
Accept all reasonable responses.
are the carriers of the
genetic material that is
copied and passed from
generation to generation
contain DNA
For most of the
Copyright © McGraw-Hill Education
cell’s lifetime,
they exist as
chromatin.
Chromosomes
Just before cells divide,
they appear as several
short, stringy structures
in the nucleus.
Without the proper amount of DNA
the cell cannot survive. Therefore,
chromosomes must be accurately
passed on to new cells.
Science Notebook • Cellular Reproduction and Sexual Reproduction
113
1 Cellular Reproduction (continued)
Get It?
repair.
Explain the role of mitosis in the processes of growth and
Mitosis is the process by which new cells needed for growth and repair
are formed.
Complete the diagram of the cell cycle. Describe the main events in
each stage.
Chromosomes to
opposite poles
of the cell.
Nucleus divides.
Cell makes
Cytoplasm
mitosis
microtubules in
divides. Two
preparation for
daughter cells
cell division.
are formed.
G2
cytokinesis
The Cell Cycle
S
G1
Cell is growing and
its DNA.
performing normal
functions.
Identify four events that occur in a cell during interphase.
1. cell grows
3. cell duplicates chromosomes
chromosomes
prepares for
division
2. cell carries on metabolism 4. cell duplicates
Identify two functions of mitosis in animals.
wound repair
Function of
mitosis in
animals
growth of organism to adult size
Science Notebook • Cellular Reproduction and Sexual Reproduction
114
Copyright © McGraw-Hill Education
Cell replicates
1 Cellular Reproduction (continued)
Model the stages of mitosis and the process of cytokinesis. Draw and
label a cell in each stage, name each stage, and describe what
is happening. Accept all reasonable responses.
Name of Phase
Sketch of Cell
prophase
Description
chromatin coils to form
chromosomes
metaphase
chromosomes move to
the center of the cell
anaphase
centromeres split and
sister chromatids are
pulled to the opposite
sides of the cell
telophase
two new nuclei are
formed and a double
membrane begins to
form between them
cytokinesis
cell’s cytoplasm divides
and separates into two
Copyright © McGraw-Hill Education
new identical cells
Get It?
division.
Summarize the role of the spindle apparatus during cell
The spindle apparatus is important in moving and organizing the
chromosomes before cell division.
Summarize the function of each structure in mitosis.
centromeres: part of chromosome to which spindle apparatus attaches
microtubules: tube-like structures that shorten and pull the chromosomes
to opposite poles of the cell
motor proteins: help microtubules pull chromosomes to poles of the cell
Science Notebook • Cellular Reproduction and Sexual Reproduction
115
1 Cellular Reproduction (continued)
Compare and contrast cytokinesis in plant and animal cells.
Cytokinesis in
Plant Cells
cell plate and new
cell walls form
between the
daughter cells
Both
results in
genetically
identical
daughter cells
Cytokinesis in
Animal Cells
occurs by
microfilaments
constricting the
dividing cell and
pinching it into two
daughter cells
Summarize how cells regulate the cell cycle. Choose from the list of
words to complete the paragraph.
• checkpoints
• cyclin-dependent kinases
• G2 stage
• cyclin/CDK
• cytokinesis
• mitosis
• cyclins
• G1 stage
• S stage
and cyclin-dependent kinases to control
the cell cycle. Different combinations of cyclin/CDK start the cell
Cells use
cyclins
inventory to ensure it is ready to proceed to
mitosis . If the spindle
apparatus malfunctions, the cycle won’t proceed to
cytokinesis .
Summarize information about apoptosis.
Apoptosis is
a process of
programmed cell
death.
Organisms use
apoptosis to
destroy cells that
are no longer
needed.
Two processes that
use apoptosis:
1. trees losing their
leaves in autumn
2. development of
fingers and toes
Science Notebook • Cellular Reproduction and Sexual Reproduction
116
Copyright © McGraw-Hill Education
cycle at different checkpoints and monitor the cycle for quality control.
In the G1 stage , the cell is growing and preparing to replicate DNA.
DNA replication occurs in the S stage . In the G2 stage , the cell takes
1 Cellular Reproduction (continued)
Get It?
Summarize the role of cyclins.
Cyclins help regulate the cell cycle.
Sequence the causes and effects of cancer by completing the flow
chart below.
Cancer is the uncontrolled growth and
division of cells.
Cancer is the result of a failure in regulation of
the cell cycle.
Cells lose control when genes that regulate
the cell cycle are damaged.
Copyright © McGraw-Hill Education
Cancer cells cause damage by crowding out
normal cells, leading to organ failure.
CONNECT
A classmate thinks that cancer and apoptosis are both harmful to organisms. Do you agree or
disagree? Explain your reasoning.
Accept all reasonable responses. Only cancer is harmful to an organism. Apoptosis is a normal process
in which cells that are not needed by an organism die in a controlled way.
Science Notebook • Cellular Reproduction and Sexual Reproduction
117
1 Cellular Reproduction (continued)
CHECK YOUR PROGRESS
1. Relate cell size to cell functions, and explain why cell size is limited.
Transportation of nutrients and wastes across the plasma membrane and control of cell contents by
the nucleus become difficult when the cell increases in size.
2. Summarize the primary stages of the cell cycle.
interphase, mitosis, and cytokinesis
3. Explain why mitosis alone does not produce daughter cells.
Mitosis is the process by which nuclear material is duplicated. A cell must undergo cytokinesis in
order for cell division to be complete.
4. Describe the events of each stage of mitosis.
Prophase: nuclear membranes disintegrate and chromosomes condense; metaphase: chromosomes
attach to spindle and line up along the equator; anaphase: chromosomes move to the opposite poles;
telophase: nuclear envelope reforms and chromosomes decondense
5. Describe how cyclins control the cell cycle.
Certain cyclin proteins regulate mitosis and the cell cycle by allowing or stopping cell cycle
6. Explain how the cancer cell cycle is different from a normal cell cycle.
It is shorter; cancer cells divide in an unrestrained way.
7. Hypothesize what might happen if a drug that stopped microtubule movement but
did not affect cytokinesis was applied to a cell.
Answers will vary. Accept all logical hypotheses, such as, if the movement of microtubules was
stopped chromosomes would not be separated properly into the two daughter cells.
8. If a plant cell completes the cell cycle in 24 hours, how many cells will be produced
in a week?
128 cells
Science Notebook • Cellular Reproduction and Sexual Reproduction
118
Copyright © McGraw-Hill Education
processes.
Cellular Reproduction and Sexual Reproduction
2 Meiosis and Sexual Reproduction
NEW VOCABULARY
Use the terms in the left column to complete the paragraph below.
autosome
A segment of DNA on a chromosome that controls the production of
cell differentiation
a protein is called a
crossing over
diploid
copies of each chromosome. A sex cell, or
haploid , meaning it contains one copy of each chromosome.
fertilization
Gametes form during
gene
homologous chromosome
nondisjunction
sex chromosome
stem cell
telomere
diploid
cell contains two
gamete , is
meiosis
Homologous chromosomes
haploid
meiosis
.A
, the process by which one haploid
gamete combines with another is called fertilization .
gamete
karyotype
gene
are pairs of chromosomes, one from
sex chromosomes
each parent. One of these pairs include the
that determines the individual’s sex. Segments of homologous
chromosomes exchange during Prophase I in a process known as
crossing over
. Homologous chromosomes consist of sister
chromatids, which sometimes fail to separate properly; this is known
nondisjunction . The other 22 pairs of chromosomes
as
are called
autosomes
. Chromosomes have protective caps
telomeres
called
. Homologous chromosomes can be
karyotype
arranged in a micrograph called a
, according
to size.
Copyright © McGraw-Hill Education
The process by which an unspecialized cell develops into a
specialized cell with a defined structure and function is called
cellular differentiation , which produces and maintains a complex
organism.
Stem cells
are a type of cell that can be directed to
become a specialized cell.
Get It?
Compare and contrast sexual and asexual reproduction.
The chromosome number is maintained by mitosis during asexual
reproduction. The organism inherits all its chromosomes from one
parent. In sexual reproduction, the organism inherits chromosomes from
two parents. Meiosis maintains the chromosome number.
Science Notebook • Cellular Reproduction and Sexual Reproduction
119
2 Meiosis and Sexual Reproduction (continued)
Identify three characteristics that are the same in each member of a
pair of homologous chromosomes. Name one thing that is different.
Same
Different
1. exact version of each gene
1. length
2. centromere position
3. position of genes
Compare and contrast the phases of Meiosis I and Meiosis II. Sketch
each phase. Accept all reasonable responses. Sketches should be
similar to those in the text.
Meiosis I
Prophase I
Description chromosomes
condense
and pair up,
spindle
forms
Metaphase I
spindle fiber
attaches to
centromere,
pulls
Anaphase I Telophase I
chromosomes each pole
contains
move apart
from each
other toward
one member of a pair
chromosomes poles of cell
to center of
of homolo-
cell
mosomes,
gous chrocell divides
Sketch
Meiosis II
Prophase II Metaphase II
Telophase
II
haploid
sister
nuclear
number of
chromatids
membrane
chromo-
are pulled
and nucleus
somes line
apart
reforms, cell
up at center
divides into 4
of cell
haploid cells
Sketch
Analyze the chart above to determine the phase of meiosis when
crossing over can occur. Mark a star on the correct phase. Students
should place a star by Prophase I.
Science Notebook • Cellular Reproduction and Sexual Reproduction
120
Copyright © McGraw-Hill Education
Description chromosomes
condense
and spindle
apparatus
forms
Anaphase
II
2 Meiosis and Sexual Reproduction (continued)
Get It? Distinguish between homologous chromosomes and sister
chromatids.
Homologous chromosomes are pairs of chromosomes, one from each
parent that control genes of the same traits. Sister chromatids are held
together by centromeres; they are formed when the chromosomes
replicate.
Compare meiosis and mitosis by filling in the chart below.
Mitosis
Meiosis
1
1
Number of cell divisions
1
2
Number of daughter cells
2
4
Chromosome number of daughter cells
2n
n
Number of DNA replications
Organize information on how meiosis produces genetic variation.
Meiosis produces
random arrangement of chromosomes at equator
crossing over
Copyright © McGraw-Hill Education
Compare sexual reproduction and asexual reproduction by
completing the paragraph with the terms below.
• sexual reproduction
• protists
• animals
• genes
• asexual reproduction
• mammals
• plants
• genetic diversity
In asexual reproduction an organism inherits its genetic material
genes
from a single parent. The new organism has the same
as its parent. In sexual reproduction , an organism inherits genetic
material from two different parents. Sexual reproduction increases
genetic diversity
, whereas asexual reproduction does not.
Protists
, simple
animals
reproduce sexually or asexually.
plants
, and most
can
Mammals only reproduce
sexually.
Science Notebook • Cellular Reproduction and Sexual Reproduction
121
2 Meiosis and Sexual Reproduction (continued)
Describe telomeres by completing the paragraph.
Accept all reasonable sketches.
protein
DNA
Telomeres are made of
and
the ends of chromosomes
located at
to protect the chromosomes .
. They are
. Their function is
Model a picture showing the ways that nondisjunction during meiosis
can produce a sex cell with an extra copy of a chromosome.
Sketches should be similar to parts of Figure 21 and should show
nondisjunction during meiosis I and meiosis II.
Model a karyotype of a girl with Down syndrome.
chromosomes. There should be 3 copies of chromosome 21.
Science Notebook • Cellular Reproduction and Sexual Reproduction
122
Copyright © McGraw-Hill Education
The karyotype should show 22 pairs of autosomes and XY sex
2 Meiosis and Sexual Reproduction (continued)
Compare and contrast adult and embryonic stem cells by writing
characteristics in the Venn diagram.
Adult
Both
come from
unspecialized
100–150 cells
cells that have
formed after
the potential to
fertilization; will
become
become specialized
specialized
as embryo grows
various tissues in
the body; present
from infancy
through adulthood
Embryonic
Get It?
Describe some ways that adult stem cells can be used to
treat conditions that result from injury or illness.
Sample answer: Stem cells might be used to repair cardiac tissue after a
Copyright © McGraw-Hill Education
heart attack.
SUMMARIZE
Analyze how nondisjunction during meiosis could lead to Klinefelter’s syndrome.
A person with Klinefelter’s syndrome has two X chromosomes and one Y chromosome.
Nondisjunction in meiosis I or meiosis II could produce an egg with two sex chromosomes.
Klinefelter’s syndrome would result when an XX egg is fertilized with a sperm carrying a
Y chromosome.
Science Notebook • Cellular Reproduction and Sexual Reproduction
123
2 Meiosis and Sexual Reproduction (continued)
CHECK YOUR PROGRESS
1. Explain how the structure of DNA determines the structure of proteins which carry
out most of the work of cells.
DNA segments called genes code for the formation of proteins.
2. Assess how meiosis contributes to genetic variation, while mitosis does not.
During meiosis, the independent assortment of the pairs of chromosomes and crossing over provide
a large amount of genetic variation. Mitosis produces identical cells.
3. Illustrate how nondisjunction occurs during meiosis.
Sketches should demonstrate an understanding of nondisjunction.
4. Summarize the role differentiation plays in the production and maintenance of a
complex organism.
Differentiation allows the development of specialized cells that form the tissues and organs in
complex organisms.
5. Describe a possible application for stem cells.
6. Compare and contrast mitosis and meiosis by creating a Venn diagram.
Diagrams should reflect similarities and differences.
7. Conduct research on the consequences of nondisjunction other than trisomy 21.
Write a paragraph about your findings.
Paragraphs should show understanding of nondisjunction. Paragraphs should not describe Down
syndrome.
Science Notebook • Cellular Reproduction and Sexual Reproduction
124
Copyright © McGraw-Hill Education
Answers may include cures for medical conditions and genetic defects.