Download Biology Chapter 8 Review

Ali Loudiyi
Science Chapter 8 Review
1) Chromosomes are rod-shaped structures made of DNA and proteins. There are two types of
chromosomes; sex chromosomes and autosomes. Of the human’s 46 chromosomes, 2 are sex
chromosomes, while the other 44 are autosomes. Every organism born of sexual reproduction
gets one copy of each autosome from both parents. The two copies of each autosome are
called homologous chromosomes, or homologues.
2) Mitosis is the process of cellular division in somatic cells. Meiosis is the process of cellular
division in germ cells. Cytokinesis is the splitting up of the cytoplasm in cells just before they
divide and it occurs in both mitosis and meiosis.
3) An sex chromosome is a unique chromosome that determines the sex of the organism that it is
found in, and is found in much less abundance than autosomes. Autosomes are all other
chromosomes that are not sex chromosomes, and are abundant in organisms. They determine
how the body functions and many other jobs.
4) Kinetochore fibers are the thin fibers that attach to the centromeres in chromosomes during the
early anaphase. Polar fibers, instead, stretch from opposite poles of the cell during cellular
division and connect to the centromere region of chromosomes via the kinetochore fibers in
order separate the sister chromatids and pull them towards opposite poles during the late
anaphase.
5) Diploid refers to cells that have two sets of chromosomes. Diploid cells divide by the process of
mitosis. Haploid refers to cells that have one set of chromosomes, and divide by the process of
meiosis.
6) (d)
7) (c)
8) (b)
9) (d)
10) (a)
11) (d)
12) (a)
13) (a)
14) (b)
15) (d)
16) Binary fission refers to prokaryotic cell division; it occurs in prokaryotes, like bacteria.
17) Cells that exit the cell cycle enter the G0 phase, where they do not recopy DNA or prepare for
cellular division. G1 phase is the first stage of interphase in which offspring cells grow to mature
size. G2 phase is the last phase of interphase in which cells prepare for cellular division.
18) Haploid cells, also known as gametes, are sperm and ova. These haploids then combine in a
process known as fertilization, through which a zygote is formed. The process of fertilization
occurs only through sexual reproduction. When combined, the two haploids make a diploid cell.
19) Mitotic anaphase has double the amount of chromosomes than meiotic anaphase 2.
20) No, they do not. This is because homologues are a result of sexual reproduction, since the
offspring inherits one copy of each autosome from each parent. Since the asexual organism
doesn’t have two parents to get two copies of the same autosome from, homologues can’t
form.
21) Yes. Meiosis II contains the same basic processes as does mitosis. The only real difference is the
end result in that meiosis II produces 4 cells with half the normal number of
chromosomes(haploids) and mitosis only 2 cells with the normal number of chromosomes
(diploids).
22) Sexual reproduction involves two parents, male and female. The offspring is identical to none of
the two. It is characterized by two processes; meiosis and fertilization. Meiosis involves the
creation of the gametes, and fertilization involves the combination of the gametes to form a
zygote. Asexual reproduction, on the other hand, involves one parent. The two offspring are
identical to the parent. It does not involve either meiosis or fertilization, but rather processes
like binary fission, for prokaryotes.
23) The picture shows meiosis. This is because meiosis takes place in germ cells to form gametes,
like the sperm cells seen in the photograph.
Critical Thinking:
1) Yes. Mitosis is nuclear division whereas cytokinesis is cell division. The result would be one cell
with 2 nuclei.
2) The DNA mass of a haploid cell in the G2 phase would be 2, since the DNA was copied in the S
phase for meiosis.
3) No. The cell in metaphase II will have already divided once, which means it will lack the mass of
two chromosomes in comparison to the diploid cell in the G1 phase, which still has not divided
or duplicated its DNA.
4) No. A human haploid cell must have one copy of each chromosome; 22 autosomes, and 1 sex
chromosome. A human cell with 23 randomly selected chromosomes would no longer be a
human cell.
5) Before cells divide, they grow to an optimal size where the surface area is relatively bigger than
the volume. Thus, the cells can divide comfortably and not interfere with homeostasis.
6) Centrioles are useful, but not extremely essential in cell division, unlike spindle fibers. It is the
spindle fibers that pull the sister chromatids apart during prophase in mitosis, not the centrioles.
The centrioles, however, help in the orientation and organization of the spindle fibers. This
means that the centrioles determine where exactly in the cell the spindle fibers develop. Also,
cytokinesis of plant cells occurs by cell plate formation, whereas in an animal cell, cytokinesis
occurs by means of furrows or cleavages. Because of the unchanging shapes of most plant cells,
due to their cell walls, the cell plate will always be formed in the same position regardless of its
orientation. However, in an animal cell, the spindle fibers may develop across any part of the
cell, thus cleavages may form at any part of the cell. Hence, to ensure that the cleavages
develop exactly at the equator of the cell, the centrioles are important.
7) In the late anaphase/early telophase, the chromatids are considered chromosomes. This is
because in the late anaphase, the separated chromatids are pulled towards the opposite poles. In
the early telophase, the chromosomes begin to uncoil, and since the sister chromatids are the
same copies of an autosome, the cell that is beginning to form will get all the genetic information
from just one chromatid; thus, it is considered a chromosome.
8) Meiosis:
MEIOSIS I
4.5
4
3.5
3
2.5
DNA Mass
2
Chromosome Number
1.5
1
0.5
0
Prophase
Metaphase
Anaphase
Telophase
MEIOSIS II
2.5
2
1.5
DNA mass
Chromosome Number
1
0.5
0
Prophase
Metaphase
Anaphase
Telophase