Name: _______________ Period___
Cell Division Reading Packet
Part 1: All Cells Come From Other Cells
When cells divide, one cell splits into two or more cells. This is called cell division. Cell division has three purposes:
1)Growth. Multicellular organisms grow from a single fertilized cell into a larger, mature organism. Depending on the
organism, the mature form may consist of several thousand cells up to several trillion cells.
2) Repair: Damaged and old cells are replaced with new cells.
3) Reproduction: In some organisms such as Paramecium and yeast, reproduction occurs by cell division. The offspring
is identical to its one parent. Reproduction that occurs by simple cell division is called asexual reproduction. In other
organisms, two parents are needed to produce offspring. Each of the parents produces sex cells during a specialized
form of cell division. Offspring are produced when these sex cells join. This process, called sexual reproduction, results
in offspring that are different from either parent.
1) How does cell division help us grow? Use an example.
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2) Describe the two main methods of reproduction.
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3) Use an example to describe how cell division helps repair injured tissue.
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4) In asexual reproduction, are the offspring identical to the parent, or different? ________________________________
5) In sexual reproduction, are the offspring identical to the parent, or different? _________________________________
Part 2: All Cells Have a Cycle
The cycle of a cell is called the cell cycle. It is divided into a number of stages in which specific activities occur.
The cell cycle is divided into periods of time, during which the cell performs certain functions. Interphase is the time in
which a cell grows and carries out cellular processes in the body. Interphase is divided into three parts: G1, S, and G2
phases.
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1) Name the stages of the cell cycle in order.
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2) What occurs during interphase of the cell cycle?
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3) What occurs during mitosis (M-Phase) of the cell cycle?
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Part3: Cells Undergo Changes Before They Can Divide
The genetic material (DNA!) in the nucleus of cells usually forms into long, thin
fibers called chromatin. As a cell gets ready to divide, the chromatin becomes
shorter and thicker, forming chromosomes. Each species of organism has a
certain number of chromosomes that form in each cell. Human body cells, for
example, have 46 chromosomes.
Every chromosome in a cell is copied before the cell divides. The two
copies of each chromosome are called sister chromatids. They are joined at the
middle point called the centromere. During cell division, the sister chromatids
separate. The two resulting cells each receive one copy of each chromosome.
1.) What is the difference between chromosomes and chromatin?
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2.) In the picture above, labeled which one is the chromosome and which is the chromatin.
3.) When a cell is ready to divide, which form is the DNA in? ________________________________________________
Part 4: Cancer Cells Grow Out of Control
Although cell reproduction usually happens in a controlled way, cells sometimes reproduce at the wrong time or in the
wrong place. Uncontrolled cell reproduction produces a mass of cells called a tumor. A benign tumor contains normal
cells. Other tumors, called malignant tumors, are composed of cancer cells. Cancer is a disease in which the controls on
the cell cycle do not work and cells divide out of control.
Malignant tumors are dangerous because cells from the tumor can spread to other parts of the body. These
cells can form more tumors. The spread of cancer in the body is called metastasis.
There are three main forms of cancer treatment. Surgery is often used to remove malignant tumors from the
body. To treat remaining cancer cells, physicians can use radiation or chemotherapy. Both techniques disrupt cell
division. Since cancer cells divide more frequently than normal cells, they are more likely to be destroyed by radiation
and chemotherapy than normal cells.
1) Compare and contrast benign and malignant tumors.
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2) Describe how radiation and chemotherapy destroys cancer cells.
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3) What causes cancer (at the cellular level, based on this reading)?
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Part 5: Cells Divide During Mitosis Phase
Mitosis is the part of the cell cycle in which the parent cell
divides in two to produce two genetically identical daughter
cells. Mitosis is one of the shortest phases of the cell cycle.
When a cell is not undergoing mitosis, it is not dividing, and it is
said to be in interphase. Interphase accounts for 90% of the cell cycle.
Mitosis is a continuous cycle (it does not pause at different points). However, it is divided into stages for easier
reference and study. In animal cells, centrioles form the spindle, which is a structure that guides chromosomes during
mitosis. The spindle is a framework of microtubules.
The mitotic phase of the cell cycle can be divided into four main stages, Prophase, Metaphase, Anaphase, and
Telophase. (See the picture below for details on each phase.) After mitosis occurs, a separate phase called Cytokinesis
divides the cytoplasm in two. Cytokinesis usually starts happening at the same time as telophase. In animal cells,
cytokinesis occurs when a band of microfilaments in the middle of the cell pinches the cell in two. In plant cells, a
structure called a cell plate forms in the middle of the cell. The cell plate contains the cell wall material. As the cell plate
grows outward, two daughter cells form.
1.) What is the purpose of mitosis? ____________________________________________________________________
2.) What must occur BEFORE mitosis takes place? ________________________________________________________
Part 6: Cells Differentiate into Specialized Cells
Recall that when a cell divides by mitosis, it produces genetically identical cells. However, a multicellular
organism is made up of many different TYPES of cells, each specialized to carry out a particular role. How can it be that
all of an organism’s cells have the same genetic material, but the cells have a wide variety of shapes and functions? The
answer is through cellular differentiation. Although each cell has the same genetic material (genes), different genes are
turned on (activated) or off in different patterns during development in particular types of cells. The differences in gene
activation controls what type of cell forms. Once the development of a cell is determined, it cannot change its path and
change into another cell type.
1.) Name the cell from which all other cells are derived:
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2.) Explain how so many different types of cells can be formed, even though
all cells have the same DNA:
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3.) Why do some types of cells have shorter cell cycles than others?
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