Biology 12
Reproduction and the Reproductive Systems
Learning Outcomes: see LO’s P
Reference: Chapters 5, 21 & 22 Mader 11th edition
1. Significance of the process of meiosis. Pages 88-93.
a. Define meiosis. A type of cell division where the chromosome compliment is reduced by onehalf. Where does it occur in the body? It occurs in the testis or ovraries. Why is this form of
cell division necessary? It keeps the chromosome number constant from generation to
generation.
b. Meiosis is a special form of cell division. Describe the cell(s) produced by meiosis in terms of the
chromosomes they contain. Up to four cells can be produced from one. Each cell will have ½ the
chromosome number as the parent cell and the chromosomes may contain different alleles of
genes than the original chromosome due to crossing over during meiosis.
c. Define homologous chromosomes. They are a pair of chromosomes that contain the genes for
the same traits, one comes from each parent. Why is it necessary to have homologous
chromosomes for meiosis to occur? If the new cells formed from meiosis are to have genes for
each trait, then each cell will need one of those homologous chromosomes and in so doing
ensure that the next generation will have the correct (diploid) number of chromosomes when
they fuse.
d. What is meant by the term synapsis? The coming together of homologous chromosomes at the
cell equator during meiosis I. It is the independent assortment of homologous chromosomes.
When does it occur? Metaphase I (meiosis I). Why do you think it happens? It ensures the
chromosomes can be divided up evenly and accurately (haploid number), and brings about a
huge variation between the chromosomes of haploid cells.
e. What does crossing-over accomplish? It adds additional variation to the gametes since pieces of
homologous chromosomes are broken and reattached to its homologue. Sister chromosomes
are no longer identical. When does it occur? Metaphase I.
f. At the end of the1st division of meiosis, each daughter cell contains the haploid number of
chromosomes, one of each type of homologous pairs of chromosomes. These chromosomes each
consist of 2 sister chromatids joined at the centromere. Describe the process that reduces the diploid
number of chromosomes to the haploid number (steps in meiosis I). The homologous
chromosomes first duplicate themselves (chromatids attached at the centromere). These
tetrads then migrate to the equator so that they are aligned with the homologous
chromosomes on either side of the equator. As a result when they attach to the spindle fibers
they will be pulled and separated from each other. Each cell will end up with one of each kind
of chromosome (haploid number).
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g. At the end of the 2nd division of meiosis, each daughter cell will have the haploid number of
chromosomes but the sister chromotids will have been separated resulting in 4 daughter cells. How
many chromosomes would be present in a human cell at this time? 23 different chromosomes.
h. Spermatogenesis is the production of sperm in males and oogenesis is the production of eggs in
females. Both involve meiosis. Where do each occur (oogenesis is completed in two places)?
Sperm and egg are very different. List the differences and explain the need for the structural
differences between these cells. In spermatogenesis there are 4 very small flagellated cells
called sperm; in oogenesis there is only one very large cell (the egg) which contains two polar
bodies if the egg has been fertilized or one polar body if fertilization has not occurred.
Spermatogenisis occurs wholely in the testis while only meiosis I occurs in the ovary (meiosis
II occurs in the fallopian tube if the egg is fertilized). The egg must be large in order to
nurish the embryo during its journey to the uterus. The polar bodies donate their cytoplasm
to increase the size of the egg and they also act to “take away” extra chromosomes. Also there
must be many more sperm cells produced to ensure fertilization and they must be able to
swim to make their way to the egg.
2. Male reproductive system
a. Draw and label accurately a mature sperm cell. Provide the structure & function of each part: tail,
mid piece, head, acrosome. Tail is the structure that propels the sperm up the female
reproductive tract. Midpiece contain many mitochondria and so are the ATP producers for
the swimming activity of the sperm. Head of the sperm contains the nucleus and so the
chromosomes (N) to form the zygote. Acrosome contains the enzymes that will digest the
follicular cells and egg membrane in order for the sperm to reach the egg nucleus.
b. Identify each of the following structures on a diagram and provide a function for each.
i testes: (seminiferous tubules & interstitial cells are internal can’t be labeled, but give their
function anyway.) testes contain the seminiferous tubules which produce and temporarily
store the sperm plus they make inhibin a hormone that is a neg. feedback substance on the
hypothalamus and anterior pituitary to inhibit their stimulation of the production of
testosterone; and the interstitial cells which produce testosterone the male sex hormone.
ii epididymis: the tightly coiled tube that lies just outside the testes that hold and allow for
the maturation of the sperm, i.e. acquire the ability to swim.
iii vas deferens: the tube that leads from the testes that stores sperm until ejaculation and
then conducts them to the urethra when ejaculation is nearing.
iv seminal vesicles: The seminal vessicle releases the nutrients (fructose) for the sperm.
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v prostate gland: produces the alkaline substances to adjust pH which makes the sperm more
active.
vi bulbourethral gland: also called Cowper’s gland produces the lubricating fluid and the
prostaglandins.
vii penis: the structure which houses the urethra and is made of specilized erectile tissue and
blood sinuses to allow for erection and copulation.
viii urethra: the tube which allows for the elimination of urine and seminal fluid from the penis.
Sphincters prevent urine release during erection.
c.
i. Develop a feedback system that illustrates the roles of GnRH, FSH, LH, testosterone and
inhibin in the male reproductive system. . A negative feedback system controls very tightly the
levels of testosterone in the blood. Secretion of testosterone from the interstitial cells of the
testes is prompted by the release of first GnRH from the hypothalamus which then causes the
release of LH from the anterior pituitary. LH is the stimulus for testosterone production and
release. It is low levels of testosterone in the blood that stimulate the hypothalamus and
pituitary gland and it is high levels of testosterone in the blood that inhibit these structures.
Inhibin, a hormone released by the seminiferous tubules, also inhibits the production of
testosterone by acting on the hypothalamus & anterior pituitary.
ii. What are the functions of testosterone? Testosterone controls the secondary sex characteristics
(beard, auxillary hair, deep voice, large muscles, broad shoulders…), growth of sex organs
and their maintenance, maturation of sperm and development of the sex drive.
3. Female reproductive system
a. Identify each of the following structures on a diagram and provide structure & function for each.
i ovaries (follicles, Grafian follicle and corpus luteum are inside this organ but give their s & f
too) the ovaries are the egg producing bodies (gonads) of the female. The eggs develop from
follicles of which a woman has about 400 000 at birth. One follicle will mature per month
forming a Graffian follicle around it. The mature follicle is made of several layers of cells.
These cells produce estrogen which effects a negative feedback control on FSH as well as
promoting the proliferative phase of the uterine cycle. On ovulation, follicle becomes the
corpus luteum which produces progesterone which effects a negative feedback control on LH
as well as promoting the secretory phase of the uterine cycle.
ii oviducts (AKA fallopian tubes) in close proximity to the ovary is the fallopian tube. The
fringes at its entrance, the fibriae, draw the egg into the tube where it is swept along by cilia to
the uterus. It is in the oviduct that fertilization will occur.
iii uterus (define endometrium and give its role too) a smooth muscle organ the size of a pear.
The site for embryo implantation and growth of the fetus. The endometrium becomes
thickened and secretory to sustain the life of the embryo.
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iv vagina the birth canal. The uterus is emptied thru this passage as well as sperm are
brought to the uterus via the canal.
v cervix the opening at the narrow end of the uterus, it links the uterus to the vagina.
vi clitoris erectile tissue, involved in female orgasm.
b. What are the functions of estrogen? Female sex hormone that produces the secondary female
sex characteristics (wider hips, fat storage, breast development, etc.), causes maturation of the
female sex organs, controls the release of FSH and causes the proliferative phase of the uterine
cycle.
4. Fertilization
a. Describe how the penis is structured to carry out its precise reproductive function. How is the
nervous system involved (be specific as to what parts of the nervous system are involved)?
Through some form of stimulation (touch, sight, thought) the parasympathetic nervous system
causes the dilation of the arteries in the penis. Because of the specialized erectile tissue the
penis becomes erect as the tissue fills with blood. Since the viens are compressed by this
increasing pressure, the blood remains in the tissue and an erection is maintained. The penis
becomes flaccid after orgasm as the stimulation from the brain stops, blood vessels return to
normal and the blood flows back into the viens.
b. Trace the path of a mature sperm from the seminiferous tubules to the urethral exit.
Seminiferous tubules to the epididymis to the vas deferns to the ejaculatory duct to the
urethral exit.
c. Where does fertilization occur? In the fallopian tube. What process is completed with
fertilization? Meiosis II of the egg.
d. What is implantation? Describe hormonal changes that occur with implantation. Implantation is
the act of attaching the embryo to the uterine wall. The progesterone released from the
corpus luteum supports the secretory phase of the endometrium and the embryo continues to
grow. The placenta is forming and releases HCGn, a hormone that stimulates the corpus
luteum and keeps it producing progesterone until the placenta can produce enough of its own
to keep the endometrium healthy. Estrogen will also be produced by the placenta so between
the 2 hormones the hypothalamus and anterior pituitary are inhibited from producing FSH
and LH therefore no new follicles will be matured.
5. Postive Feedback System
a. What is meant by a positive feedback system? A system that responds to high levels of a
hormone by causing an increasing amount of that hormone to be produced rather than
preventing or stopping its production. It intensifies the response and leads to nonhomeostatic
situations.
b. Describe in detail the feedback system involving oxytocin. In the 3rd trimester of pregnancy the
stretched uterus will begin mild contractions. The nervous stimulation from this causes the
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hypothalamus to stimulate the posterior pituitary and oxytocin is released into the blood.
Oxytocin targets the uterine muscle causing it to contract harder. This stimulation causes
further stimulation of the hypothalamus and pituitary resulting in MORE oxytocin to be
released. As levels of oxytocin increase the contractions become longer, harder and more
frequent. The baby is born and nervous stimulation of the hypothalamus diminishes. Now
less oxytocin is released, the after birth is delivered, the uterus begins contracting into its
smaller size. Levels of oxytocin will diminish as the contractions become smaller and then
nonexistent.
Please read the text on the following topics. They are not going to be tested but they provide valuable
information. Evaluate the effectiveness for each control method in #6,and the risk/problems for both # 6 &
7.
6. Control of reproduction: See page 404 Table 21.4 for explanation and effectivness.
a. Vasectomy
b. tubal ligation
c. birth control pill
d. diaphragm
e. condom
f. coitus interruptus
g. spemicidal foams, jellies and creams
7. Sexually transmitted diseases: See section 21.5 for explanation and consequences.
a. AIDS
b. Genital herpes
c. Gonorrhea
d. Chlamydia
e. syphilis
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