Pgs 161 and 165

Here are the Answers to Pg 161


p. 161
1. The four phases of mitosis are: prophase,
metaphase, anaphase, and telophase.
2. During prophase, the nucleolus disappears and
the nuclear membrane begins to break down.
The chromosomes become visible and they
attach themselves to spindle fibres at their
centromeres.
3. During cytokinesis in animal cells, the cell
membrane pinches together and the cytoplasm
divides (Figure 5.9). During cytokinesis in
plant cells, a cell plate forms across the middle
and contains material to form a new cell wall
and cell membrane (Figure 5.10).
4. The importance of checkpoints in the cell
cycle is that at these checkpoints the cell can
be stopped from growing or dividing if conditions
are unsuitable. This precise control is
important to the survival of the organism.
5. If a checkpoint protein no longer functions,
which could occur when a mutation occurs in
a gene producing the instructions for a checkpoint
protein, cell cycle control will be lost,
and this could lead to cancer.

PG 165 # 1-6


1. (a) During growth and preparation, the cell
increases in size and makes the proteins
and molecules necessary for it to function.
Some organelles begin to duplicate.
(b) During replication, the DNA copies itself.
(c) In the continued growth and preparation
phase, the cell makes materials such as proteins
and duplicates organelles such as
mitochondria and chloroplasts.
2. The steps in DNA replication are: (a) the
DNA molecule unwinds, (b) the steps of the
DNA ladder break apart to form a template,
(c) the new side forms with A pairing with T
and G pairing with C.
3. The function of mitosis is to divide the contents
of the cell’s nucleus so that each daughter
cell will have the same number and kinds of
chromosomes as the original cell.
4. Mitosis is occurring only in cells that are
preparing to divide. Some cells stay in the
growth and preparation phase for a long
period of time. For example, brain cells get
replaced every 30 to 50 years. Cells that
become worn out easily, such as stomach
lining, intestinal lining, and skin cells, undergo
mitosis more frequently. Figure 5.3 on page
152 gives examples of different cell replacement
times.
5. Spindle fibres function to guide attached chromosomes
to opposite poles of the cell as they
contract and shorten.
6. (a) A; (b) A; (c) D; (d) C, B A, D
(e) You could tell whether a cell is just entering
mitosis by observing if the chromosomes
appear duplicated like an X where
two chromatids are attached at a centromere.
The cell would be just completing
mitosis if the chromatids are single.


1. In binary fission in bacteria, there is no
nucleus. Bacteria have only one chromosome
ring, so there is no mitosis as seen in eukaryotic
cells where the nuclear membrane disappears
and the X-shaped chromosomes move to
the equator and then separate.
2. Binary fission occurs in unicellular organisms,
but budding occurs in multicellular organisms.
In budding, repeated mitosis and cell division
occurs within an area of the individual so that
a multicellular outgrowth or bud is produced.
3. Fragmentation occurs when a piece of a plant
or animal breaks away. A new organism is able
to grow from the multiplication of the cells of
the fragmented piece.
4. In plant grafting, the stem of a desired plant is
attached to another plant that already has
roots.
5. In therapeutic cloning, stem cells can be used
to replace damaged or diseased cells.
(Embryonic stem cells, as well as egg and
sperm cells, have the potential to become any
type of cell. If the nucleus of a skin cell of a
person who has a disease is removed and
inserted into an enucleated stem cell or egg
cell, the nucleus will make proteins unique to
that individual. These new cells can be chemically
induced to become the desired type of
cell, such as kidney cells. When the kidney
cells are put back into the patient, they will
not be rejected because the patient’s body recognizes
these cells as belonging to them since
the cells will be making unique molecules
coded in the DNA of the nucleus.)