Download Checking Concepts 1. The nucleus is like a black box because there

CHAPTER REVIEW ANSWERS
Checking Concepts
1. The nucleus is like a black box because there are still unknown processes occurring and we are not able to see all
the activity that is happening inside the nucleus.
2. DNA is required in every cell because DNA contains the genes that code for the proteins the cell requires to perform
its functions.
3. The DNA molecule is like a ladder with the sides of the ladder made of sugar and phosphates and the steps of the
ladder made up of bases. The bases pair up, with G combining with C, and A combining with T.
4. The four bases in DNA are A (adenine), G (guanine), T (thymine), and C (cytosine).
5. The diagram should indicate the sugars and phosphates on the sides of the ladder and the
bases correctly paired as the steps of the ladder.
6. Some functions of proteins in cells include enzymes speeding up chemical reactions and hormones acting as
chemical messengers. In addition, there are structural proteins, such as the proteins in muscle, and signalling proteins,
such as antibodies.
7. (a) The parts of the cell that are involved in making a protein for transport out of the cell include the nucleus, the
chromosomes, the ribosome, vesicle, the endoplasmic reticulum, the Golgi body, the nuclear pore, RNA, and the
plasma membrane.
(b) The nucleus receives a chemical signal to make a specific protein. The nucleus contains
the chromosomes, which contain the DNA. On the DNA are genes that carry the message to make a particular protein.
The gene message is copied into RNA, which leaves the nucleus through the nuclear pores to the ribosomes. The
proteins are made on the ribosomes. If the ribosomes are attached to the endoplasmic reticulum, the proteins that are
made travel through the channels in the endoplasmic reticulum and leave the endoplasmic reticulum in vesicles. The
vesicles carry the protein to the Golgi body where it is repackaged. Vesicles leave the Golgi body and carry the proteins
to the cell membrane for export out of the cell.
8. The correct sequence of DNA bases is important because, if the base sequence is incorrect, then the correct protein
will not be made or the protein that is made will not work correctly. The cell will be unable to do its job well if the
proteins are not working correctly.
9. The three types of gene mutation are: (a) substitution, where one base is put in instead of another; (b) deletion, in
which a base is removed from the sequence; and (c) insertion, where an additional base is put into the sequence.
Substitution is the least harmful as the same protein may be made. In deletion and addition, a nonsense message is
created and the correct protein will not be made.
10. Gene mutations are caused by errors in the DNA. They can be caused by mutagens, such as viruses, cigarette
smoke, radiation from X rays and ultraviolet light, and various kinds of chemicals in the environment. (In the next
chapter, students will learn that mutations can also occur during mitosis and meiosis when the DNA is getting copied.)
11. The sequence would be TGACAACA.
12. The sequence is e, a, i, c, f, h, b, d, g.
Understanding Key Ideas
13. To ensure the Spirit Bear does not become extinct, the provincial government has limited logging in the Great Bear
Rainforest so that the bear’s habitat is not destroyed.
14. Although there are only four bases, there are many possible combinations of the sequences of A, G, C, and T
bases, so there are thousands of possible messages to code for different proteins.
15. The amount of DNA in a skin cell and the amount of DNA is a muscle cell would be the same because the DNA
within each body cell is identical.
16. DNA directs a cell to have a particular function when messages are sent to the nucleus of a cell to read certain
genes and make specific proteins. The proteins that are made and function in that cell will determine if the cell is a
muscle cell or a stomach cell.
17. The number of chromosomes in an animal cell or plant cell does not reflect how advanced the organism is. Many
plants have very large numbers of chromosomes. Some amoeba have 40 or more chromosomes. A butterfly has 80
chromosomes, while humans have 46. Chickens have 78 chromosomes. Scientists have found that some DNA is very
repetitive in organisms.
18. If the nucleolus of a cell did not perform its function, then ribosomes would not be made. If ribosomes could not be
made, then proteins could not be made. The cell would not be able to function and would die.
19. Gene therapy is still experimental, and there are obstacles that must be overcome for gene therapy to be
successful. First, the healthy genes must be able to enter the target cells. Then, the healthy genes must be able to be
turned on to make the healthy proteins and turned off when sufficient amounts of the protein are made. During gene
therapy, other non-targeted cells may be affected, which may cause complications.
20. Occupations that could pose greater risks of mutations include: (a) pilots because they are exposed to a lot of
cosmic radiation; (b) construction workers, because they are exposed to a lot of dust and chemicals and sunlight; (c)
firefighters because they are exposed to many toxic substances; (d) dry cleaners because they are exposed to
chemicals used to clean garments; (e) bartenders because they are exposed to smoke in bars; (f) farmers, because of
their exposure to pesticides and fertilizers and ultraviolet light. Accept other possible answers, and
discuss the importance of following proper safety precautions when working in the public or using chemicals at home.
21. (a) The amounts of A and T are the same for each type of cell since A pairs with T, so, if there are 180 000 adenine
bases in a piece of DNA, the DNA should contain 180 000 thymine bases.
(b) The amount of bases is different because these are different organisms. However, the percentage of A=T and G=C
should be the same.
(c) The human liver and human heart sample have the same number of chromosomes because they were taken from
the same person and every cell in the body would have identical DNA.
22. If a cell is producing a lot of proteins to be used inside the cell, it would have less endoplasmic reticulum since the
proteins would be made on ribosomes within the cytoplasm, not attached to endoplasmic reticulum. If a cell is
producing proteins for transport, there will be lots of endoplasmic reticulum with ribosomes attached, lots of vesicles,
and many Golgi bodies.