Cell Division and Differentiation – Grade Ten
Ohio Standards
Connection:
Life Sciences
Benchmark B
Explain the characteristics
of life as indicated by
cellular processes and
describe the process of cell
division and development.
Indicator 4
Summarize the general
processes of cell division
and differentiation, and
explain why specialized
cells are useful to
organisms and explain that
complex multicellular
organisms are formed as
highly organized
arrangements of
differentiated cells.
Lesson Summary:
The purpose of this lesson is to teach students about mitosis,
meiosis and cell differentiation and their purposes and
implications in the development and functioning of
multicellular organisms. Students will use individual
journaling and a variety of hands-on activities summarized
by group discussions. Understanding of the concepts will be
demonstrated through construction of models of mitosis and
meiosis and individual journal summaries.
Estimated Duration: Five hours
Commentary:
Journaling allows students to reflect and make connections
between physical models and the process of cell division
and development. Constructing physical models and selfreflection may increase the learning and retention of the
material. The use of portfolios or journal post-assessments
provide an alternate means of assessment to meet the needs
of a variety of learners.
Pre-Assessment:
 Journaling: Have each student start a journal section for
this lesson. Emphasize that this will not count as a grade
at this point but will be used to assess the extent of their
previous knowledge. Ask them to record answers to the
following questions in their journal:
1. In your journal, draw a chromosome and indicate the
location of a gene on the chromosome.
2. Skin cells are constantly being shed. How does your
body replace these lost cells?
3. How are genes passed on from the cell of a father to
his son?
4. How are many specialized cells in the human body
generated from one fertilized egg?
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Cell Division and Differentiation – Grade Ten
Scoring Guidelines:
Collect journals. Make positive comments on those who have correct answers, but do not
assign a grade for this portion. Read and return journals before beginning instructional
procedures below. Sample responses can be found in Attachment A, Student Journal
Requirements.
Post-Assessment:
Throughout the pre-assessment and instructional procedures, students have been making
observations and entries in their journals. Encourage students to include diagrams, flow
charts, tables or other representations for clarity. A list of expected journal entries is located
in Attachment A, Student Journal Requirements.
Scoring Guidelines:
Collect and assess individual student journals according to the guidelines in Attachment A,
Student Journal Requirements. Pay special attention to summary sections of discussion
questions. Example student responses are included with the attached grading rubric.
Instructional Procedures:
Part One: Cell Division
1. Ask for a volunteer to share his/her drawing of a chromosome by copying it on the
board. Most students will depict a chromosome as a simple X, or maybe as a squiggly
line. Use student ideas and input to correct any misconceptions and be sure students
understand that the X shape is actually two chromatids (two copies of a chromosome),
and that chromosomes only appear this way when undergoing cell division.
2. Allow a second volunteer to depict how a gene would appear on this chromosome.
Explain that many individual genes are found on each chromosome and each gene carries
information that may be expressed by coding for a protein. The remaining questions in
the pre-assessment journaling exercise will be answered throughout the rest of the lesson.
Instructional Tip:
Do steps three through nine of the instructional procedures first with mitosis only, then repeat
with meiosis only to minimize confusion.
Concept Maps
3. Prepare sets of cards for students to use in this section. Draw or locate a simple
diagram of each of the events of mitosis and meiosis. Put each diagram on a separate
index card along with a brief description of the event. Label the back of each card with
“Mt” (mitosis) or “Me” (meiosis), or use different colored cards for mitosis and meiosis.
4. Have students work independently, in pairs, or in mixed ability groups and give them the
index cards describing the steps of mitosis/meiosis in separately labeled envelopes.
Instruct students to first arrange mitosis cards in order. Allow about 10 minutes for
students to put the events into a logical order based on what they already know about
cells and cell division. Emphasize that this is not a graded activity, but to try their best
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Cell Division and Differentiation – Grade Ten
even if they do not know the answer; they may be surprised at how logical the steps will
be.
5. Combine two groups (four students) to compare results. Instruct the group to tape its
index cards on a poster board in the proper order. Display the posters on the chalkboard.
Instructional Tip:
The process of cell division is the main emphasis for the activity, and replaces rote
memorization of the names of the phases. The terms prophase, metaphase, etc. should be
used during instruction but not made into a memorization exercise. Some students may
require one-to-one instructional support to understand these processes.
Interactive Lecture
6. Go over the concept maps and put the steps of mitosis or meiosis in the correct order,
talking through each step. Use one of the concept map posters as a model. If there are
differences among the groups’ posters allow students to “vote” for first step, second step,
etc. Arrange events in the correct order.
7. Discuss the life cycle of reproduction and development using humans as an example.
 A multicellular organism that is diploid (2n) develops gametes (egg or sperm cells)
that are haploid (n).
 Fertilization occurs when an egg and a sperm cell (n + n) join to produce a zygote
(2n).
 The cells of the zygote divide through the process of mitosis and they differentiate to
form various parts of the body. Mitosis continues to promote growth and
development.
 A multicellular organism is produced that is diploid (2n).
Instructional Tip:
There are many excellent online and conventional videos available that depict the processes
of mitosis and meiosis. Using one would help students to understand the continuous flow of
the processes from one step to the next. Show a clip of the type of cell division students have
just finished mapping.
Journal Entry
8. Have students take journal notes that emphasize the sequential logic inherent in the
events of cell division. For example, the nuclear membrane must dissolve before the
chromosomes can attach to spindles and line up. Later on, the nuclear membrane reforms after chromosomes have migrated to their new cells. The steps of mitosis are
simpler and easier to guess than those of meiosis. Tell students that there will be more
practice on these concepts, so they should not worry about memorizing specific details at
this time.
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Cell Division and Differentiation – Grade Ten
Group time: Model Building
9. Have students retrieve their cell division posters and return to their groups. Ask them to
quickly reorganize the concept maps of mitosis and meiosis based on the interactive
lecture.
10. Use the corrected concept maps as a template, have each pair of students construct a
model of mitosis and one of meiosis in an organism with a diploid number (2n) of four
chromosomes. Provide model-building materials.
Instructional Tip:
Materials could include: pipe cleaners with a sticker for centromere, modeling clay of
different colors, paper cutouts with a brad for a centromere, coins for centrioles, tissue paper
for nuclear membrane, wax-coated string.
11. Instruct students to choose roles of reader or artist. They can alternate roles, if they
desire. The reader will read the description and the notes on the first step depicted on the
concept map as the artist creates it, then on to the next step, etc. Have each pair of
students go through all the steps of mitosis and meiosis. Circulate around the room to
keep student groups on track and provide direction.
Instructional Tip:
Encourage students to try to depict steps as accurately as possible and to make cell parts
“move” as they go from one step to the next. Students should realize that in reality there is a
continuous flow through the steps rather than a series of snapshots that suddenly change from
one step to the next. Ask them to “re-enact” the video clip.
12. Assign each pair of students a separate step in mitosis or meiosis to depict for a
classroom summary model. After the students have completed their models, attach them
to one poster board, putting the model next to the index card describing each step.
Display the poster with the models in the room.
Direct Observation
13. Set up microscope stations with slides of various stages of mitosis and meiosis. Slides of
white fish blastulae, ascarid eggs or allium root tips provide good examples. Arrange
microscopes in order of events.
14. Direct students to look for various phases of cell division and draw what they see in their
journals. Allow enough time for an observation and a quick sketch at each station. If
microscopes and/or time are not available, use photographs of different stages of mitosis
and meiosis set out at stations for students to view and sketch. Many Web sites are
available with photo micrographs of cells undergoing mitosis and meiosis.
15. Set out samples or pictures of actual human karyotypes for students to observe.
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Cell Division and Differentiation – Grade Ten
Mitosis and Meiosis Wrap-up
16. Answer the following questions in journals:
a. Note similarities and differences in the processes of mitosis and meiosis.
b. Note similarities and differences in the results of mitosis and meiosis.
c. Note locations and uses for each type of cell division in the body.
After students have had some time to write independently, have them pair up and share
ideas with their partners. They should add new answers or ideas in the journals. Sample
responses can be found in Attachment A, Student Journal Requirements.
Part One Closure Discussion
17. Conduct a class discussion of wrap-up questions (Step 14). Students should contribute to
the discussion and should revise journals with added information as needed.
Part Two: Cell Differentiation
Cell-type Brainstorming
18. Have each group of four students make a list of types of cells in the body and what
organelles or features might be especially important for each type (e.g., muscle cells have
a higher number of mitochondria for energy than other cells and white blood cells have
more lysosomes). Encourage students to think about the main function of the cell and
what structures are needed to perform that function on a cellular level. After some time,
ask for volunteers to share answers. List answers on flip chart or blackboard.
Interactive Lecture
19. Relate the concept that specific genes are “turned on” or activated in different types of
cells to enable that particular cell to be differentiated for a specific function. All cell types
carry the full complement of genetic material (DNA), but only a select amount of genetic
material will be expressed in a given cell. The genes that are translated into proteins will
determine structures present in a particular cell and, therefore, the functions of that cell.
Emphasize that structure relates to function in the cell.
Exploring Embryogenesis
20. Divide students into four groups and have each student fill out a nametag with one of the
following: endoderm (three to four students), ectoderm (three to four students) mesoderm
(three to four students) and trophoblast (remaining students).
21. Explain that they are a zygote that has just undergone a series of mitotic divisions without
gaining new cytoplasm. This “late cleavage” stage with its ball of small cells (stem cells)
is now about to form an early embryo.
22. Ask students to review the number of chromosomes in each stage: gamete, zygote and
now cells of the blastocyst. (Answers: n, 2n, 2n)
23. Direct the students as they represent the different types of cells present in the early
embryo. Have “Trophoblast” students form a circle around the other three groups. Next
have “Ectoderms” stand in a row, “Mesoderms” form a second row and “Endoderms”
form a third row.
24. Ask a student from each group to recall word roots: ecto-, meso-, endo- and troph5
Cell Division and Differentiation – Grade Ten
25. Give clues as needed.
(Answers: outside, middle, inner, nourish.)
26. Tell students what each will be able to become:
 Ectoderm—epithelium and nervous system;
 Mesoderm—connective tissue, muscles, bones, most organs;
 Endoderm—mucous membrane linings of digestive and respiratory tracts;
 Trophoblasts—part of the placenta (nourishment).
26. Compare these groups of cells (students) to actors at a casting call prepared to take on
different roles, then trained specifically for their parts. Direct students in each group to
choose a cell type to portray as you go through these lists.
Instructional Tip:
A person in the ectoderm group might become a brain cell, a skin cell, the lens of the eye, or
a hair. Mesoderm can become a bone, blood, a vocal cord, a bicep muscle, a kidney or an
appendix. Endoderm can line your nose, stomach or lung bronchioles. Trophoblasts will stay
in their circle and lend support and nourishment to the developing embryo.
Direct Observation
27. Set up stations around the room for the following three activities:
 Set up microscope stations with starfish development composite slides. Observe and
sketch. Record observations and sketches in journal;
 Give students an unlabeled handout picturing the fertilized ovum, early and late
cleavage, blastocyst with inner cell mass and trophoblast, implantation and early
embryo showing three germ layers (ectoderm, mesoderm and endoderm). Ask
students to label the diagram with help from textbook or other visual aids set out at
stations. In the embryo picture, students should circle the layers they represented in
the embryogenesis exploration and give examples of what type of cells they could
become. Add this handout to journal.
 A third station has pictures or Websites featuring embryos of different species.
Students sketch at least three different embryos in their journal.
 All students should rotate through all three stations.
Have students record answers to the following questions in their journal:
1. What were some similarities and differences you saw between the embryos of the
various species?
2. Which part of the embryo did you portray in the skit? What possible cell types could
you have become?
3. Comparing the cells of the late cleavage stage with an ectoderm cell, which one do
you think has a greater capacity for differentiation? Explain your answer.
Sample responses can be found in Attachment A, Student Journal Requirements.
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Cell Division and Differentiation – Grade Ten
Conclusion Discussion
28. Lead a discussion to review the concepts of specialized cells differentiated for specific
functions, arising from three embryonic germ layers and allowing for complex
multicellular life. Connections should be made back to chromosomes, genes, and
specific genetic expression in specific cells.
 What are embryonic stem cells in light of what we have just learned?
 “Pluripotent cell” is the current way of referring to the cells of the embryonic
ectoderm, endoderm and mesoderm that have a potential to become many different
types of cells.
 “Totipotential cells” are early developmental cells that can be duplicated and have
the potential to become any type of cell.
Student Journaling
29. Give students time to summarize cell differentiation in terms of how and when it occurs
and why it is necessary in multicellular organisms.
30. Have the students address the following critical thinking questions to conclude the lesson:
a. Why are the offspring produced by sexual reproduction both similar to and different
from the parents?
b. How do the processes of cell division and cell differentiation illustrate the
interdependence of structure and function?
Sample responses can be found in Attachment A, Student Journal Requirements.
Differentiated Instructional Support:
Instruction is differentiated according to learner needs, to help all learners either meet the
intent of the specified indicator(s) or, if the indicator is already met, to advance beyond the
specified indicator(s).
 Journaling may be more directed using written questions and providing a specific format
for student entries.
 Provide a handout with steps of mitosis and meiosis for students to cut out, illustrate and
put in order for instructional support and home practice.
 Have cell cycle tutorials from Internet educational sites.
 Students create a study guide with graphic organizers to reinforce key vocabulary and
processes.
 Challenge students to research and review steps of cell division and come up with their
own file cards with illustrations for concept mapping.
 Have students study and present the differentiation of a hemocytoblast into various blood
cells in a variety of presentation modes including poster, presentation software, etc.
Extensions:
 Research the arguments for and against stem-cell research. Review quotes from
witnesses given to Congress in hearings on stem-cell research legislation. Explore
questions such as: What diseases might be cured using stem-cell technology? What are
some advantages and disadvantages to using adult stem cells vs. embryonic stem cells?
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Cell Division and Differentiation – Grade Ten




Are science and technology ahead of society’s preparation for new ideas? Write an
essay, article or editorial based on your research.
Make a collection of recent major newspaper and magazine articles regarding
embryology and stem-cell research.
Explore the ideas of surface area to volume ratios and cues for mitosis. Calculate cell
surface areas and volumes. Relate these ideas to why cells are microscopic.
Research current articles about cancer that focus on cell signals for mitosis to start or
stop. What is different in cancer cells that causes them to undergo continuous mitosis?
Invite a guest speaker from the American Cancer Society or other medical groups.
Choreograph a mitosis or meiosis dance using classmates as chromatids/chromosomes.
You be the “caller” or choreographer, depending on the style of the dance.
Interdisciplinary Connections:
English Language Arts
 Acquisition of Vocabulary
Benchmark E: Apply knowledge of roots and affixes to determine the meanings of
complex words and subject area vocabulary.
Indicator 5: Use knowledge of Greek, Latin and Anglo-Saxon roots, prefixes and
suffixes to understand complex words and new subject-area vocabulary (e.g., unknown
words in science, mathematics and social studies).
Materials and Resources:
The inclusion of a specific resource in any lesson formulated by the Ohio Department of
Education should not be interpreted as an endorsement of that particular resource, or any of
its contents, by the Ohio Department of Education. The Ohio Department of Education does
not endorse any particular resource. The Web addresses listed are for a given site’s main
page, therefore, it may be necessary to search within that site to find the specific information
required for a given lesson. Please note that information published on the Internet changes
over time, therefore the links provided may no longer contain the specific information related
to a given lesson. Teachers are advised to preview all sites before using them with students.
For the teacher: Pipe cleaners, modeling clay of different colors, paper, coins, tissue paper,
wax-coated string, index cards, slides or photos of mitosis and meiosis in
white fish blastulae, ascarid eggs or allium root tips, photos of embryonic
development.
For the students: Journals, pipe cleaners, modeling clay of different colors, paper, coins,
tissue paper, wax-coated string, index cards, slides or photos of mitosis and
meiosis in white fish blastulae, ascarid eggs or allium root tips, photos of
embryonic development.
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Cell Division and Differentiation – Grade Ten
Vocabulary:
 mitosis
 meiosis
 gonad
 gene
 chromosome
 chromatid
 centromere
 centriole
 nuclear membrane
 cytokinesis
 replication
 stem cell
 pluripotential cells
 totipotential cells
 cell differentiation
 embryo
 cell
 tissue
 diploid
 haploid
 tetrad
 crossing over
 ectoderm
 endoderm
 mesoderm
 trophoblast
 blastocyst
 gamete
 zygote
Technology Connections:
 There are many cell-cycle tutorials available for student use on the Internet.
 Use Web sites for extension exercises.
Research Connections:
Marzano, R., Pickering, D., Pollock, J. Classroom Instruction that Works: Research-based
Strategies for Increasing Student Achievement, Alexandria, Va: Association for Supervision
and Curriculum Development. 2001.
Identifying similarities and differences enhance students’ understanding of and ability to
use knowledge. This process includes comparing, classifying, creating metaphors and
creating analogies and may involve the following:
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Cell Division and Differentiation – Grade Ten
 Presenting students with explicit guidance in identifying similarities and differences;
 Asking students to independently identify similarities and differences;
 Representing similarities and differences in graphic or symbolic form.
Nonlinguistic representations help students think about and recall knowledge. They
include the following:
 Creating graphic representations (organizers);
 Making physical models;
 Generating mental pictures;
 Drawing pictures and pictographs;
 Engaging in kinesthetic activity.
Cooperative-learning groups have a powerful effect on student learning. This type of
grouping includes the following elements:
 Positive interdependence;
 Face-to-face promotive interaction;
 Individual and group accountability;
 Interpersonal and small-group skills;
 Group processing.
Setting objectives and providing feedback establish a direction for learning and a way to
monitor progress. This provides focus on learning targets and specific information to
allow the student to make needed adjustments during the learning process, resulting in
increase student learning.
Attachments:
Attachment A, Student Journal Requirements
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Cell Division and Differentiation – Grade Ten
Attachment A
Student Journal Requirements
1.
2.
3.
4.
5.
6.
7.
8.
Pre-assessment questions and revised answers
Sketches of mitosis and meiosis from microscope observation
Human karyotype sketch
Mitosis and meiosis wrap-up questions and revised answers
Cell types and specializations list (at least five)
Embryo sketches and observation questions
Cell differentiation summary
Answers to the following critical thinking questions:
a. Why are the offspring produced by sexual reproduction both similar to and different
from the parents?
b. How do the processes of cell division and cell differentiation illustrate the
interdependence of structure and function?
9. Any extension activities completed
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Cell Division and Differentiation – Grade Ten
Attachment A (continued)
Student Journal Requirements
Scoring Guidelines:
Criteria
Required elements
Understanding:
Accuracy
Processes of mitosis
and meiosis
Level 4
All parts completed,
including an
extension.
Similarities and
differences are
accurate,
thoughtfully
explained.
Communication:Clarity, Information is
Focus, Organization
communicated
clearly and
precisely,
effectively focused
and organized and
also may include
inventive/expressive
dimensions.
Evidence of Inquiry:
Analyses are
Analysis and
accurate.
conclusions
Conclusions are
Embryogenesis
valid, detailed and
observations and
consistent with data.
questions,
Level 3
All parts
completed.
Level 2
Level 1
At least six
Fewer than six
parts completed. parts completed.
Similaritites and
differences are
accurate.
Similarities and
differences have
occasional
inaccuracies or
are simplified.
Information is
communicated
clearly, and is
focused and
organized.
Information has
some clarity,
focus and
organization.
Analyses are
accurate.
Conclusions are
valid and
consistent with
data.
Analyses are
mostly
accurate.
Conclusions are
related to the
data.
Analyses are
unclear or
inaccurate.
Conclusions are
unclear or
unrelated to the
data.
Applications to
personal and
societal issues
are identified.
Applications to
personal and
societal issues
are suggested or
implied.
Applications are
unclear or
absent.
Critical-thinking
questions
Relevance to Society:
Person and society
Cell differentiation
summary,
Critical-thinking
questions
Relevant
applications to
personal and
societal issues are
identified and
insightfully
described.
Similarities and
differences have
major
inaccuracies or
are overly
simplified.
Information is
unclear, lacks
focus and
organization.
Adapted from Council of Chief State School Officers State Collaborative on Assessment and
Student Standards (SCASS) Science Project, April 1997.
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Cell Division and Differentiation – Grade Ten
Attachment A (continued)
Student Journal Requirements
Examples of acceptable student responses:
Pre-assessment Questions:
1. Answers will vary from a simple X or a wavy line to an attempt at a double helix
structure, DNA. Students should circle a small area or areas along the chromosome they
have drawn to indicate the location of a gene.
2. The process of mitosis makes an exact copy of the DNA for each daughter cell. Lost
surface cells are constantly being replaced by new cells being produced my mitosis in a
deeper cell layer.
3. The process of meiosis results in a sperm cell with one copy of each gene from the father
to be included in the fertilized egg.
4. Every cell holds a complete copy of an individual’s DNA. Cell differentiation occurs
throughout embryonic and fetal development as stem cells become various cell types
depending on which portions of their DNA are expressed.
Mitosis and Meiosis Wrap-up Questions:
a. Note similarities and differences in the processes of mitosis and meiosis.
Sample Answer: a. Mitosis involves only one nuclear division, whereas in meiosis the
nucleus undergoes two divisions. In mitosis, chromosomes are copied and distributed
identically to daughter cells, whereas in meiosis, chromosomes undergo crossing over
and redistribution of genes to gametes.
b. Note similarities and differences in the results of mitosis and meiosis.
Sample Answer: Mitosis results in identical daughter cells, two, each containing the
diploid (2n) number of chromosomes. Meiosis results in gametes containing the haploid
(n) number of chromosomes. Each of four resulting gametes will differ from one another
genetically.
c. Note locations and uses for each type of cell division in the body.
Sample Answer: Mitosis occurs in all cells of the body with the exception of the gonads.
Meiosis takes place in the ovary and testis and produces the gametes for sexual
reproduction.
Cell types and specializations:
 White blood cells: lysosomes;
 Muscle cells: mitochondria;
 Skin cells: flat sheets, melanin pigment;
 Red blood cells: no nucleus, full of hemoglobin protein;
 Nerve cells: cell extensions (axons), rough endoplasmic reticulum;
 Intestinal lining cells: microvilli for absorption, tight junctions between cells;
 Gland cells: secretory granules, rough endoplasmic reticulum, hormone receptors;
 Sensory receptor cells: stereocilia, chemical receptors.
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Cell Division and Differentiation – Grade Ten
Attachment A (continued)
Student Journal Requirements
Questions about the embryo observations:
1. What were some similarities and differences you saw between the embryos of the various
species?
Sample Answer: There are differences in size, shape, tail length, limb development. The
similarities lie in the shape of the embryos, especially in the early stages.
2. Which part of the embryo did you portray in the skit? What possible cell types could you
have become?
Sample Answer: Ectoderm: brain cell, a skin cell, the lens of the eye, or a hair.
Mesoderm: bone, blood, subcutaneous fat, vocal cord, muscle, heart, kidney or appendix.
Endoderm: inside of mouth and nose, stomach lining or lung air sacs. Trophoblast:
support and nourishment for developing embryo.
3. Comparing the cells of the late-cleavage stage with an ectoderm cell, which one do you
think has a greater capacity for differentiation? Explain your answer.
Sample Answer: Late-cleavage cells have greater capacity for differentiation because
they can become all of the different germ layers and, ultimately, every type of body cell.
Once in the embryo stage, the different germ layer cells can differentiate, but only within
limits.
Cell Differentiation Summary:
Summarize cell differentiation in terms of how and when it occurs and why it is necessary in
multicellular organisms.
Answer should include the following points:
 Specializations are needed for cells to perform specialized functions;
 Specialized cells are needed for division of labor in multicellular organisms;
 Structure of specific cell types reflects their functions;
 Specializations are made possible because all cells contain the full complement of DNA
but not all DNA is expressed in every cell. Certain genes are activated in specific cells;
 Differentiation of the major germ layers occurs as the embryo is formed. As the embryo
develops further these germ layer cells (eg. Ectoderm) further differentiate into specific
cell types found in the fully developed fetus.
Critical Analysis Questions:
a. Why are the offspring produced by sexual reproduction both similar to and different from
the parents?
During the process of meiosis, which results in gametes (egg or sperm cells),
chromosomes from the father or mothers’ parents are randomly arranged and divided so
that alleles (sections of DNA encoding specific proteins) from both the grandfather and
grandmother will be present for various traits in each gamete formed. Most alleles are
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Cell Division and Differentiation – Grade Ten
Attachment A (continued)
Student Journal Requirements
passed on independently from one another (independent assortment), although many
appear to be connected and will be passed on together. The randomness of which alleles
will be received by a given egg or sperm cell is increased due to a process during meiosis
called “crossing over,” where parts of homologous chromosomes from the grandparents
are exchanged before chromosomes divide and move into their respective gametes. Each
gamete (egg or sperm) contains genes from both grandparents with only half the normal
number of chromosomes. When egg and sperm unite, the genetic material unites as well
and a complete set of chromosomes results in the fertilized egg. Both parents contribute
to the DNA of the offspring, and, in turn, the genes of the grandparents also are present.
The assortment of combinations of the traits from previous generations allows for
offspring to be different from either parent, yet similar at the same time.
b. How do the processes of cell division and cell differentiation illustrate the
interdependence of structure and function?
Cell division can occur only because specific structures such as centrioles,
spindle fibers and DNA polymerase are present in the cell. Each of these structures is
specifically designed to carry out its specific function. Without any part of the cell
machinery present, cell division could not occur.
As a result of cell differentiation, one sees the various organelles and structural proteins
in the cell or tissue that determine the function of that cell or tissue. Examples include
mitochondria for making ATP in skeletal muscle, lysosomes in white blood cells that
engage in phagocytosis and collagen fibers produced by connective tissue cells that
impart strength to skin, cartilage and bone. Each cell and tissue type is uniquely fit to
carry out its given functions because of the structures it possesses.
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