Download Key Concept Review 1.2

Key Concept Review
1. Cell cycle events: Interphase (growing, making, repairing):
• first growth phase (G 1 ): cell produces new proteins and
organelles
• synthesis phase (S): cell makes an entire copy of DNA and
produces key proteins associated with chromosomes
• second growth phase (G 2 ): cell produces organelles and
structures needed for division
Mitosis (cell division):
• prophase: chromatin condenses and forms chromosomes;
centrioles move toward poles and spindle fibres form
• metaphase: chromosomes line up at centre of cell
• anaphase: sister chromatids separate and move to opposite poles
• telophase: cell splits into two (cytokinesis)
2. Mitosis in plant cells involves a cell plate forming to separate the
cytoplasm during cytokinesis. In animal cells, the centrioles move
to the poles during prophase. Mitotic spindles attach to
centromeres and centrioles. During telophase, the cell membrane
pinches inward to make two cells.
3. Apoptosis is the normal death of a cell that is no longer useful or is
not functioning normally. Death of cells allows space for new,
healthy cells to grow.
4. Students’ answers will vary. The similarities between mitosis in
plant and animal cells include the condensing of the chromosomes
during prophase, the lining up of chromosomes in the centre of the
cell during metaphase, the formation of the mitotic spindle, and the
separation of the chromatids during anaphase. The differences
between mitosis in plant and animal cells include the formation of
a cell plate during cytokinesis in plant cells, the pinching inward of
the cell membrane during telophase in animal cells, and the
centrioles that attach to mitotic spindles and move to opposite
poles in the animal cell during prophase.
5. A cancer cell is a cell that divides uncontrollably.
6. Mitosis ensures genetic continuity because cell division produces
two daughter cells that each contains the same number of
chromosomes and the same genetic information as the parent cell.
7. Mitosis makes growth and repair of cells possible because during
cell division, two daughter cells are formed. These new cells
replace cells that are damaged or that are no longer functioning
effectively. Because there are limits to how large a cell can grow,
an organism grows by forming new cells.
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1.2
48 Unit A: Tissues, Organs, and Systems of Living Things
8. Cells spend most of their cycle in interphase because it is during
that stage that cells grow, duplicate DNA, and prepare for cell
division.
9. As a cell prepares to divide, the chromosomes are duplicated.
10. A cancer cell continuously divides. Cancer cells do not undergo
apoptosis, do not stick to other cells and do not stop reproducing.
Cancer cells behave independently and may move to other
locations in the body.
Connect Your Understanding
11. Differences between mitosis in plant and animal cells include the
formation of a cell plate during cytokinesis in plant cells, the
pinching inward of the cell membrane during telophase in animal
cells, and the centrioles that attach to mitotic spindles and move to
opposite poles in the animal cell during prophase.
12. Cell division must be controlled for cells to be healthy because the
uncontrolled production of cells can lead to tumours and excessive
numbers of cells. Cells need to reproduce to replace injured cells or
cells that have died. Some cells are produced for specific purposes,
such as fighting disease, and need to be removed once the job is
complete so that energy and resources in the organism are used
efficiently.
13. If spindle fibres do not form, the sister chromatids cannot be pulled
apart and cell division cannot be completed successfully. This
would mean that cells would not divide and growth would not
occur.
14. When a daughter cell is formed that does not contain the correct
amount of chromosomes, the cell is missing some of its genetic
information. This cell would not be able to survive.
15. The photo shows anaphase. At this stage, the sister chromatids are
separating into individual chromosomes, which are moving to the
opposite ends (poles) of the cell.
16. Since nerve cells rarely undergo mitosis, nerve cells that are
damaged may not be replaced. If a specific region containing nerve
cells was damaged, there may not be a nerve cell to undergo
mitosis, which results in loss of that nerve centre.
17. Ultraviolet light can cause cells to mutate, which can potentially
cause cancer cells to develop. Sunscreen reduces the amount of
ultraviolet light that reaches the skin cells and reduces the chances
of cellular mutation.
18. Cancer researchers can use their knowledge about mitosis to
decrease a cancer cell’s rate of mitosis without affecting normal
cells. They can also look at stage-specific treatments to stop cancer
cells from reproducing.