❯ Rapid Review
You should be familiar with the following terms:
Binary fission:prokaryotic cell division; double the DNA, double the size, then split apart.
Cell cycle:G 1 →S→G 2 →M→growth 1 →synthesis→growth 2 →mitosis→etc.
Interphase:G 1 +S+G 2 =90 percent of the cell cycle.96 ❯ STEP 4. Review the Knowledge You Need to Score High
❯ Answers and Explanations
- B—Bryophytes, or mosses, are the plant type that
has the gametophyte (haploid) as its dominant
generation. The others in this question have the
sporophyte (diploid) as their dominant generation. - C—Crossover occurs in humans only in
prophase I. Prophase I is a major source of vari-
ation in the production of offspring. - C
- A
- E
- B
- C—The life cycle for fungi is different from that
of humans. Fungi exist as haploid organisms,
and the only time they exist in diploid form is as
a zygote. Like humans, the gametes for fungi are
haploid (n) and combine to form a diploid
zygote. Unlike in humans, the fungus zygote
divides by meiosis to form a haploid organism. - B—Human cells start with 46 chromosomes
arranged in 23 pairs of homologous chromo-
somes. At this time they are 2nbecause they have
two copies of each chromosome. After the S phase
of the cell cycle, the DNA has been doubled in
preparation for cell division. The first stage of
meiosis pulls apart the homologous pairs of
chromosomes. This means that after meiosis I,
the cells are n, or haploid—they no longer con-
sist of twofull sets of chromosomes.- A—CDK is present at all times during the cell
cycle. It combines with a protein called cyclin,
which accumulates during interphase of the cell
cycle, to form MPF. When enough MPF is
formed, the cell is pushed to begin mitosis. As
mitosis continues, cyclin is degraded, and when
the concentration of MPF drops below a level
sufficient to maintain mitotic division, mitosis
grinds to a halt until the threshold is reached
again next time around the cycle. - C—Answer choices A, B, D, and E are all cor-
rect. C is incorrect because homologous pairs of
chromosomes pair together only during meiosis.
During mitosis, the sister chromatid pairs align
along the metaphase plate, separate from the
homologous counterpart.
STAGE MITOSIS MEIOSIS
Prophase Nucleus, nucleolus disappear;
mitotic spindle forms —
Metaphase Sister chromatids line up at middle —
Anaphase Sister chromatids are split apart —
Nuclei of new cells reform;
Telophase chromatin uncoils —
Prophase I — Each chromosome pairs with its homolog;
there is crossover