The Cell Cycle, Mitosis, Cell Growth and Cell Specialization
Textbook Reference: Page 26 – 41
Complete and answer the following in your notes:
The Cell Cycle:
1. Read pages 26 – 27
a. How many skin cells do we lose every minute? What would be the
approximate weight of this in a year? We lose about 30000 to
40000 skin cells every minute. This translates into about 3kg of skin
cells in a year.
b. How do skin cells change to become ‘skin’? Skin cells on the
surface are old and dead and have become tough and flattened.
The change in structure allows them to form a protective layer for
your body.
c. Why do younger people have ‘fresher’ looking skin? In younger
people, skin cells mature in about 4 weeks, whereas older people’s
cells may stay in the skin for up to 75 days.
2. Read pages 28 – 32
a. What is the difference between interphase and mitosis? Make sure
to explain the G1, S and G2 phases of interphase. Interphase is
when a cell is preparing for cell division. The actual process of the
nucleus dividing into two equal portions is called mitosis. Interphase
is broken up into three phases: G1 is the growth phase of a cell,
when it creates new proteins and organelles. S is when the cell
makes a copy of the DNA. G2 is when the cell creates organelles
and structures needed for cell division.
b. Describe each phase of mitosis. With each description, draw a
diagram of what a cell looks like during each phase of mitosis.
i. Prophase – the chromatin condenses, the chromosome is
two identical copies called sister chromatids attached at the
center with a centromere
ii. Metaphase – the chromosomes move toward the center of
the cell and line up at the middle of the cell
iii. Anaphase – the sister chromatids separate at the
centromere and the chromatids are now separate, they start
to move to the opposite ends of the cell
iv. Telophase – the cell divides the cytoplasm into two portions
Interphase
1.
2.
3.
4.
5.
Prophase
Metaphase
Anaphase
Telophase
c. Compare the amounts of time that a cell spends in interphase and
mitosis. Further break this down to compare how much time a cell
spends in each stage of mitosis. Use figure 1.28 to assist you with
this. For comparison, consider one complete cycle to be
approximately 24 hours. Less than ¼ of the time (approximately 4
hours) is spent in mitosis. Further, the cell spends (almost) equal
amounts of time in each phase of mitosis ~ <1 hour per stage.
d. Page 32 # 1 – 5
The main goal of the cell cycle is cell division. Cell division allows for the
process of growth and repair.
Interphase is the stage in which the cell spends most of its time. During
interphase, the cell grows and prepares for cell division.
Mitosis is the process of cell division. Genetic information in the nucleus is
packaged into two equal portions. Mitosis is important for growth and
repair.
Chromosomes: a long piece of coiled DNA and proteins; Centromere:
place at which the two sister chromatids are joined together; Sister
chromatids; the identical copies of a chromosome that are attached
together.
Cytokinesis is the process by which the cytoplasm splits into two portions.
This produces two new cells that enter interphase.
Purpose of Mitosis and Cell Growth
3. Read pages 32 – 33, then answer the following questions.
a. What does cell division provide? (pg 32) Cell division provides new
cells to replaces cells that wear out or break down.
b. Where does rapid rates of mitosis occur? Give an example. (pg 33)
Rapid rates of mitosis occurs in areas of growth. Cells that have
been damaged or injured also have high rates of mitosis. Examples
– intestinal cells, root tip of a plant.
c. What factors affect mitosis? (pg 33) Environment (change in
altitude would affect rates of mitosis in your blood, plants bend
toward light because of changes in the rates of mitosis in the stem),
antibiotics (some stop bacteria from growing by interfering with
mitosis or inhibit the replication of DNA)
d. What is apoptosis? Why is it necessary? (pg 33) Apoptosis is
regulated or controlled cell death of cells that are no longer useful.
It is necessary because it removes cells that are not necessary or
that have lost their ability to perform efficiently. Without apoptosis
we would not be able to maintain a size.
Regeneration and Cell Specialization
4. Read pages 38 – 41, then answer the following questions.
a. Define regeneration and give an example of an organism that has the
ability to regenerate body parts. Regeneration is the process whereby
a body part is replaced or regrown. An example of this would be a
salamander.
b. Do humans have the ability to regenerate…explain. (pg 38 – 39) It is
generally thought that regeneration does not occur in humans,
however, the human liver is the only human organ that has the ability
to naturally regenerate. Human fingertips have a limited ability to
regenerate in young children. Scientists have has some success in the
laboratory regenerating parts of the human body on a scaffold and
extracellular matrix.
c. Page 41 # 1 – 5
1)
A stem cell is an unspecialized cell. There are two types of stem
cells: embryonic and adult stem cells.
2)
A stem cell becomes specialized when it is exposed to the proper
environmental conditions. Embryonic stems cells undergo
differentiation into cells that look different and perform different
functions.
3)
Embryonic stems cells are able to differentiate into other cell types.
Adult stem cells have a limited ability to create a variety of cell
types and are involved in the replacement of damaged tissue.
4)
For example…replacement of damages tissues and organs or,
treatment of various diseases including cancer and heart disease.
5)
Meristematic cells are stem cells in plants. They are found where
growth takes place: root tips, stems, and the cambium.
d. Define differentiation. Differentiation means that the cells look different
from one another and perform different functions.