Biology Unit 4 Exam Study Guide
Cell Cycle, Viruses, and Specialized Cells
1. Describe what occurs in each stage of the cell cycle:
Interphase G1: Cell growth is an important part of the cell cycle immediately following cytokinesis. The cell
develops the necessary cytoplasm and other organelles necessary for cellular operation.
Interphase S: During the synthesis phase, the DNA in the cell is copied producing an extra set for the new cell.
Interphase G2: During G2, the cell continues to grow and develop in preparation for mitosis.
Mitosis: The cell goes through prophase, metaphase, anaphase, and telephase which produces a new nucleus
containing all of the genetic material for the new cell.
Cytokinesis: The cell’s cytoplasm is divided equally among the two new cells as the cell pinches in half at the
cleavage furrow. In a plant cell, a cell wall is built between the two new nuclei.
2. Describe the results of the cell cycle compared to the results of mitosis. During the cell cycle, one cell is copied
producing two identical cells. The cell cycle includes Interphase, Prophase, Metaphase, Anaphase, Telephase, and
Cytokinesis.
Mitosis produces two identical nuclei in the same cell. As mitosis ends, the cleavage furrow is forming signaling
the beginning of cytokinesis
3. Human mitotic cell division begins with __1___ # of cells with ___46___ # of chromosomes.
Human mitotic cell division ends with __2__ # of cells with ___46___ # of chromosomes.
4. Below, list the four phases of mitosis in order, draw a representation of each, and give a short explanation of
what is occurring.
1. Prophase – the cell’s
centrioles or
centrosomes appear
and begin moving to
opposite ends of the
cell. The cell’s
chromatin coils into
chromosomes.
2. Metaphase – The
cell’s DNA aligns along
the midline as
centrioles begin
extending their
microtubules.
3. Anaphase – The
chromosomes are
pulled to opposite ends
of the cell by the
spindles or
microtubules and the
cell elongates.
4. Telophase – the cell’s
nuclear envelope
reforms around the two
new sets of DNA and
cytokinesis begins.
5. Explain why DNA and cell organelles are duplicated before the cell completely divides.
The cell must duplicate all its material before it divides because the new and existing cell must have all the
necessary equipment it needs to survive before it divides.
6. Describe how animal cell division differs from plant cell division.
Animal cells undergo cytokinesis where the cell pinches in half at the cleavage furrow. Because plants’ cell walls
are rigid, they are unable to undergo cytokinesis so instead, they build an additional cell wall in between the two
nuclei.
7. Explain why complex multi-cellular organisms need specialized cells (different types of cells with
specific jobs)? Complex organisms must have specialized cells because not all cells come in contact with the
external environment. Unicellular organisms can retrieve all the nutrients they need from the environment while
multicellular organisms must depend on other tissues and systems to provide them with the raw materials they
need to function.
8. Why do the various types of cells in your body come in different shapes and sizes?
Cells come in different shapes and sizes because they each have specific jobs they must complete. Without
specialized structures, they would not be able to complete their jobs.
9. If all of your body cells contain identical DNA, explain how they can perform different functions from
each other. Body cells all contain the same DNA but they are different structurally and functionally because
there are different genes that expressed.
10. Explain how the genes in a cell’s genome are expressed
A cell’s genes are expressed when the cell begins producing different types of proteins. DNA codes for different
proteins which is what determines how an organism looks and functions.
11. Can environmental factors have an effect on your gene expressions? Defend your answer.
Certain environmental conditions can change the way an organism looks. Temperature, diet, water quality among
other things can all determine how genes are expressed. An organism may develop different features based on
the environment.
12. Explain why there would be more mitochondria found in a sperm cell than in a skin cell? What other types of
cells in the human body would contain a larger amount of mitochondria?
Mitochondria produce energy for the cell and a sperm cell must be able to move to function. Movement requires
a great deal of energy which is why a sperm cell contains a larger number of mitochondria. Heart cells, muscle
cells, and nervous tissue all have high numbers of mitochondria because they all use great amounts of energy.
13. How are cancer cells different from “normal” cells?
Cancer cells are unable to control how often they divide. Certain tumor suppressor genes have been inactivated
which causes cancer cells to divide uncontrollably. Also, the presence of an oncogene can cause uncontrolled cell
division.
14. Describe three ways viruses are different from and three ways viruses are similar to living cells.
Viruses do not use energy, they do not grow or develop, and they do not reproduce on their own. Viruses are
unique in that they have features of living and nonliving organisms but most scientists consider them nonliving.
15. Can a specific virus (such as HIV) attach and replicate in any type of cell? Explain your answer.
One specific virus cannot attack any type of cell it wants. It must be able to identify the surface receptors of the
cell it attacks in order to infect it. Viruses are like a lock and key in that they can only attack the cells that they fit
into.
16. For each virus below, give the body system it affects.
-Influenza: respiratory and immune
-Tuberculosis: respiratory
-Chicken Pox: integumentary system (skin or exterior body tissues)
-AIDS: immune system
-Polio: nervous and muscular systems
17. Why is this statement correct?: ‘No one dies from HIV/AIDS.’
No one dies from HIV or AIDS because those conditions attack the immune system. When they immune system
has been incapacitated, the simplest of infections or diseases ravage the body without protection.
18. Explain what is happening in each stage of the Lytic Cycle.
A. The virus identifies the cell’s surface receptors and attaches to the outside of the cell.
B. The virus injects its DNA into the cell
C. The cell is producing virus pieces or proteins after it has
incorporated the virus’s DNA.
D. The cell assembles the virus pieces into full viruses
E. The cell lyses releasing viruses into the immediate
environment. Those viruses invade nearby cells.
19. Explain how the Lysogenic Cycle is different from the Lytic Cycle. The lytic cycle causes the death of the cell as
the cell lyses and the lysogenic cycle allows the cell to propagate until the cells begin to make virus pieces.