Sc 9: Biology
CH 5/6 Review:
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Mitosis+Sex. Repro Review: Answers
1. What are the two main stages in the cell’s cycle?
The 2 main stages of the cell cycle are interphase (for growth, repair and DNA
replication) and mitosis (for cell division).
2. List the 4 stages of mitosis and briefly describe what happens during each of these
stages. Do a sketch to illustrate your answer.
Prophase: Nucleus Disappears
Chromatids duplicate and form distinct chromosomes
Centrioles migrate to opposite poles of the cell
Spindle fibres begin to form
Metaphase: Chromosomes line up at the equator of the cell
Spindle fibres attach to the centromeres of each chromosome
Anaphase: Chromatids are separated and pulled to opposite poles of cell by spindle
fibres.
Telophase: Cell elongates and pinches in at the middle
Cytokinesis occurs to divide the rest of the organelles
(cell divides into two)
3. What is the difference between chromatin, chromosomes, and chromatids?
Chromatin is the indistinguishable mass of DNA molecules that exist in the
nucleus during the normal lifetime of the cell. At the time of cell division, the
chromatin duplicates and organizes into chromosomes. Chromosomes consist of
two chromatids attached together with a centromere. Because of this structure, the
chromosomes resemble the letter X when you see them under a microscope. The
chromatids are separated during anaphase – one copy going north and the other
copy moving south.
4. What is cytokinesis? Cytokinesis is the division of the organelles and other
substances in the cytoplasm. Approximately half of the organelles go to each of
the new daughter cells, making them practically identical when they separate.
5. What is cancer? What causes cancer? Cancer is uncontrolled cell division.
Normally, cells divide in a very coordinated and organized manner. Cancer
cells have lost all of this control, and therefore will often cause a lump or mass
wherever it occurs. Cancer is caused by MANY things, but all cancers are the
result of genetic mutations – the rearrangement of the genetic code inside the
nucleus. The mutations usually occur in the genes that code for enzymes that
are responsible for cell division control. This code can be altered by radiation,
chemicals or just a mistake when the cell is reproducing.
6. Define asexual reproduction. Asexual reproduction produces clones of the
original parent; only one parent is involved.
7. List the 5 different types of asexual reproduction mentioned in the text and briefly
describe each of the processes.
Binary fission: literally dividing the cell into two equal new cells.
Budding: a new organism,( identical genetically)grows on the side of the parent
until it is large enough to break off and live on its own.
Spore formation: A specialized cell containing a complete set of the organism’s
genes is formed with a protective coating. The spore may travel far away from the
parent before settling and beginning to grow an entire new organism.
CH 5/6 Review:
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Mitosis+Sex. Repro Review: Answers
Fragmentation: part of the parent breaks off and regenerates the rest of the body,
while the parent regenerates the part of its body that fell off.
Vegetative reproduction: Special stems or roots are grown that begin the growth of
a new “section” of the parent plant. The new section will either remain attached to
the parent, or become dislodged from it’s connection and continue on it’s own.
8. What are homologous chromosomes?
You have 2 complete sets of chromosomes – one set came from Mom and the other
set (which is homologous) comes from your Dad. Homologous chromosomes
contain the same genes, but they are different versions (Mom’s and Dad’s) of the
same gene. For example, chromosomes #5 might both carry the gene for eye
colour, but the one from your Mom is a blue eye gene, and the one from your Dad
is a brown eye gene.
9. Compare the outcomes of meiosis and mitosis. Mitosis creates 2 genetically
identical, diploid cells. Meiosis creates 4 genetically unique, haploid gametes.
Mitosis is a form of asexual reproduction, while meiosis produces gametes for
the purpose of sexual reproduction.
10. Why do you need the process of meiosis? Why can’t all cells just use mitosis?
Meiosis creates haploid cells – human cells are diploid. If we started using
mitosis all the time, everytime we reproduced sexually, our chromosome
number would double. That would become VERY complicated for the cell.
Therefore, for SEX, we need to divide the # of chromosomes in half =
MEIOSIS.
11. How is it that you are a mixture of your mother, father and all four of your
grandparents? When your parent’s cells begin the process of meiosis(before you
were even a fertilized egg), THEIR parent’s homologous chromosomes found
each other an mixed up (CROSS-OVERS!). Then meiosis occurred and one of
the products was the sperm and the egg that eventually became YOU. THEN the
sperm and the egg got together, and the two sets of genes were expressed
depending on their dominance relationship with each other. Sometimes your
mom’s genes were expressed (which were a mixture of the genes from you
maternal grandparents) and sometimes your Dad’s genes were expressed (they
were a mixture of your paternal grandparents).
12. What types of cells perform meiosis? In humans, where are these cells?
Reproductive cells perform meiosis to produce gametes. In humans, the
reproductive cells are found in the ovaries or testes.
13. What is the advantage of sexual reproduction?
Sexual reproduction mixes up the genes of a species, which provides them with
more natural variation in the species. Natural variation allows the species to adapt
or evolve to changes in the environment. If we were all exactly the same, a single
pathogen might be able to wipe us all out completely. However, natural variation
helps ensure that at least SOMEONE will have the natural ability to resist the
disease, so the species will survive.
14. What are the advantages of asexual reproduction?
Asexual reproduction does not require as much energy as internal fertilization
sexual reproduction. You don’t require a mate (which is sometimes hard to
find). You can produce large numbers of offspring easily.
CH 5/6 Review:
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Mitosis+Sex. Repro Review: Answers
(DISADVANTAGE: your offspring are all clones)
15. What is a mutation? A change in the sequence or structure of the DNA
molecule. It can be negligible, advantageous or deleterious. It usually causes a
change in the protein that was being coded for at that location of the change in
the DNA.
16. What is therapeutic cloning? What kinds of cells are used in therapeutic cloning?
How are these types of cells different that other body cells?
Therapeutic cloning uses stem cells to correct health problems. Embryonic
Stem cells are undifferentiated cells that retain the ability to develop into ANY
type of cell. Most of our normal body cells have lost this ability because their
“parent” cells have already differentiated into specialized cell types. These cells
can be implanted into tissues that are defective and potentially grow into new,
heathly normal cells of the original tissue type. Adult stem cells are found in
our bone marrow. They have the ability to develop into any type of blood cell
(but ONLY blood cells). They are not as diverse as the embryonic ones.
17. At what stage of development are embryonic stem cells harvested?
Embryonic stem cells are formed in the blastula.
18. Describe the difference between external and internal fertilization. The difference
is just as the titles imply – internal fertilization (what humans do!) involves the
sperm fertilizing the egg INSIDE the females’ body. External fertilization (fish
do this) involves both parents releasing their gametes outside of their body
where they will be mixed for fertilization. This type of fertilization takes less
energy to find an appropriate mate, and decreases some of the risks associated
with INTERNAL fertilization.
19. Describe the difference between Artificial insemination, In vitro fertilization,
gamete intrafallopian transfer and Intracytoplasmic sperm injection.
Artificial Insemination: sperm is collected from the male and then inserted into
the vagina of the female using a specialized instrument.
In Vitro Fertilization: Sperm and eggs are removed from the male and female
and mixed in a Petri dish. After the fertilized eggs begin to divide, the embryos
are introduced into the uterus of a female in hopes that the embryo will embed
in the lining and begin to develop.
Gamete intrafallopian transfer – sperm and eggs are mixed in a Petri dish and
immediately implanted into the fallopian tube of a female. Ideally, the
fertilization event will not actually happen until they are in the fallopian tubes.
Intracytoplasmic sperm injection – one sperm is injected into an egg in a Petri
dish. Then the zygote (fertilized egg) is inserted into the uterus of a female.