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1. Cell division is necessary in unicellular organisms so that these
organisms can reproduce themselves in great numbers.
2. Cell division is necessary in multicellular organisms for growth and to
replace worn-out cells.
3. The three stages of the cell cycle are interphase, mitosis, and
cytokinesis.
4. Cells are performing the life functions of a cell during interphase.
Digestive system cells will be making enzymes, retina cells will be
performing chemical reactions so that you are able to see. In addition,
the cell is preparing for cell division by duplicating organelles.
5. The checkpoint proteins check for the following:
(a) Are there enough nutrients in the cell to support growth?
(b) Is the DNA damaged?
(c) Has the DNA replicated?
(d) Have the chromosomes become attached to the spindle fibres?
(e) Have the chromosomes moved to the poles in anaphase?
6. If the cell as unable to make the proteins to form spindle fibres,
mitosis could not occur successfully since the chromosomes would not
be able to attach. The result would be that the chromosomes would not
be equally distributed between cells.
7. If there is a mutation in a checkpoint protein, the cell may continue
to proceed through the cell cycle and the result is that the cell may die
or have a mutation.
8. Bacteria grow at an exponential rate through binary fission and
mutations do occur. If a mutation occurs that allows the bacteria to
become resistant to antibiotics, these bacteria will survive and multiply.
9. The chart should include the following:
Interphase: Cell carries out the functions necessary for survival, and if
the cell is going to divide it will prepare for cell division by copying the
DNA and duplicating organelles.
Mitosis: The duplicated chromosomes are divided into two equal parts.
Cytokinesis: The two nuclei and the contents of the cell separate into
two daughter cells.
10. The chart should include the following:
Prophase: The chromosomes become visible, and the spindle fibres
appear and chromosomes attach.
Metaphase: The spindle fibres pull the Xshaped chromosomes into a
single line at the equator.
Anaphase: The spindle fibres contract and shorten, and the chromatids
are pulled to opposite poles of the cell.
Telophase: The spindle fibres disappear, and the nuclear membrane
forms around each set of chromosomes.
11. The daughter plant cells will remain together with a cell plate
between them, which will form the cell membrane and cell wall. The
animal cells will pinch completely apart.
12. The major disadvantage of asexual reproduction is that there is very
little variation so all the offspring are identical. If conditions change, all
of the individuals could die.
13. Three reasons for human-assisted cloning are to save an
endangered species, to mass produce an organism with a desired trait,
or to correct health problems.
14. Reproductive cloning is also known as adult DNA cloning, and it is
used to duplicate an entire individual that has a desired trait.
15. Stem cells are cells that are not yet differentiated to become a
specific kind of cell. They have the potential to become many different
types of cells.
16. Two characteristics of asexual reproduction are that only one
parent is required and all of the offspring are genetic clones of the
parent.
17. The nuclear membrane must disintegrate during prophase so that
the chromosomes are free to attach to the spindle fibres.
18. (a) These cells are plant cells
(b) You know that they are plant cells because there appears to be a
cell wall, there is no centromere for the spindle fibres to attach to, and
the cells remain side by side after cell division.
(c) The correct sequence is C, A, D, B.
(d) Diagram C shows prophase where the chromosomes become
visible. Diagram A show metaphase where the chromosomes are lined
up in single file at the equator. Diagram D shows anaphase where the
chromatids move to opposite poles. Diagram B shows telophase where
the nuclear membrane forms around the sets of chromosomes.
19. If the chromosomes do not separate out correctly during anaphase,
the cell will probably not pass the checkpoints to go through the rest of
the cell cycle. The cell will die, or it may go unchecked so that one
daughter cell will end up with more chromosomes than the other
daughter cell.
20. Cancer cells spread to a new location when they break away and
move into the bloodstream, where they may begin to divide and form a
new tumour.
21. The blood vessels branch into the tumour and deliver nutrients to it,
which allows it to grow even more rapidly.
22. A laboratory technician can identify cancer cells because these cells
have a large abnormal nucleus since there are extra chromosomes
inside.
23. Only less complex forms of life can reproduce asexually because
lower forms have only a few types of cells. Higher forms have many
types of specialized cells to form complex tissues.
24. There are concerns about stem cell research because some people
feel it is wrong to destroy cells that are able to develop into an
individual.
25. To determine the best conditions for reproduction of an amoeba,
the scientist might put the amoeba in different environments such as
more light, less light, warmer temperatures, colder temperatures, more
acidic, or less acidic. The conditions that produced the fastest rate of
growth without any mutations would be the ideal conditions.