Chapter 4: Reproduction and Growth
4.1 Gamete Formation
1. Why need to reproduce?
 to replace those that die
 continuation of species
2. Types of reproduction
 Asexual reproduction
 microorganisms dividing into two
 invertebrates binary fission, budding, fragmentation
 Sexual reproduction
 various inherited traits
 better survival chances
Fusion of
two
gametes
Zygote
Embryo
offspring
identical
to
parents
Foetus
3. Necessity for the formation of gametes- to preserve number of chromosomes in
offspring
Gamete Formation
Male
Gonads
Testes
Femal
e
Ovaries
Sperm
(23 chromosomes)
Ovum
(23 chromosomes)
Zygote
(46 chromosomes)
4. Formation of sperm (Spermatogenesis)
 takes place in testis (made up of many small seminiferous tubules)
 from puberty onwards, mature diploid cells at the outer layer of the seminiferous
tubules divide by meiosis
Stages of sperm formation
Sertoli cell
helps to
nurture
sperm cell
Section through part of
a seminiferous
tubule
The structure of a human sperm
5. Formation of ovum (Oogenesis)
 occurs in ovary
 from foetus to before puberty
-Primordial germ cell divides mitoticallyto form oogonium. It then grows into
primary oocytes. Each primary oocyte is surrounded by follicle cell. This
structure forms primary follicle.
 After puberty
- A few primary follicles develop but only one completes its development, while
others degenerate. Primary oocyte undergoes first meiotic division to form
secondary oocyte and polar body. Secondary oocyte surrounded by follicle cell is
known as secondary follicle. Secondary follicle matures and forms Graafian
follicle, while polar body degenerate.
 Ovulation
- Graafian follicle which contains secondary oocyte bursts and releases
secondary oocyte
 After ovulation
-Follicle cells left form corpus luteum
-Secondary oocyte enters Fallopian tube where it may be fertilised by a sperm
-If egg is not fertilised, corpus luteum degenerates
 Fertilisation
-secondary oocyte completes second mitotic division to form another polar body
and ovum
6. Cycle of formation of Graafian follicle, ovulation and corpus luteum is called ovarian
cycle
Stages of ovum formation
Stages of the
ovarian
cycle in ovary
7. Comparison between sperm and ovum formation
 Similarities
 occur in reproductive organs
 involve meiosis
 produce haploid gametes
 Differences
Spermatogenesis
Oogenesis
Produces sperm
Produces ovum
diploid cell divide equally
cytoplasm does not divide equally in
meiosis
Takes place continuously from puberty
Begins in the ovary of a foetus
onwards
Forms 4 haploid cell (sperm)
Forms one large ovum and 3 polar
bodies
Produces two spermatocytes of same
Produces the secondary oocyte that is
size in meiosis I
big and polar body that is small in
meiosis I
Meiosis II occurs continuously
Meiosis II occurs only if the secondary
oocyte is penetrated by the sperm cell
4.2 Role of Hormones in the Menstrual Cycle
1. What is menstruation?
 Process of excess blood and tissue of the endometrium leave the uterus through
the vagina
2. What is menstrual cycle?
 Monthly cycle of ovulation and menstruation in the human female (mostly 28
days)
3. What are the events of menstrual cycle?
Time (days)
In the ovary
1-5
Primary follicle develops
6-13
Graafian follicle matures
14
15-24
25-28
Ovulation occurs
(secondary oocyte is
released)
Corpus luteum develops
Corpus luteum
degenerates if
In the uterus
Menstruation occurs
Endometrium is repaired
and thickens to prepare
for the implantation of a
zygote
Endometrium continues
to thicken
Endometrium becomes
thicker. Many blood
vessels develop in it.
Endometrium that is fully
thickened begins to break
down
fertilisation does not
occur
4. What are the hormones involved in the menstrual cycle?
 Follicle stimulating hormone (FSH)
 causes a Graafian follicle to develop in the ovary
 stimulates follicle cells and the tissues of the ovary to secrete oestrogen
 Luteinising hormone (LH)
 causes ovulation and formation of corpus luteum from the follicle cell
 Oestrogen
 to heal and repair the uterine wall
 causes the endometrium to thicken in preparation for implantation
 when its level reaches certain point, it stops pituitary gland from producing
FSH and stimulates it to produce LH
 Progesterone
 released by corpus luteum
 stimulates the growth and development of blood vessels in the endometrium
and further thickens the endometrium
Hormone levels and the menstrual cycle
7.Endometrium
breaks down and
discards tissues
1. Pituitary gland
secretes FSH
6.Corpus luteum
disintegratesthus producing
less progesterone
2. Oestrogen is
secreted
5.Secondary
oocyte not
fertilised by
sperm
3.Pituitary gland
is stimulated to
secrete LH
4.Corpus luteum
produces
progesterone
5. Levels of reproductive hormones are controlled by negative feedback mechanism
 FSH stimulates production of oestrogen
 Oestrogen inhibits production of FSH
 Lack of FSH causes level of oestrogen to fall
 Progesteron inhibits production of FSH, thus inhibiting development of another
Graafian follicle
6. What is premenstrual syndrome (PMS)?
 a group of symptoms related to the menstrual cycle
 occurs in the week or two weeks before the menstruation
 usually goes away after menstruation starts
 some women are more sensitive than others towards the changes in hormones
 can affect menstruating women of any age
 Physical symptoms
 headaches, fatigue, feel bloated, breast tenderness, abdominal pain, sleep
disturbances, and appetite changes including food cravings
 Emotional symtoms
 irritability, tension, depression, confusion, anxiety, crying, oversensitivity,
and mood swings with alternating anger and sadness and lack of
concentration
7. What is menopause?
 normal change in a woman’s life when he r menstruation stops
 A woman’s body slowly produces less oestrogen and progesteron
 often happens between the ages of 45 and 55
 a woman has reached menopause when she has not had menstruation for 12
months in a row
 may experience symptoms such as hot flushes, night sweats, sleeping problems,
osteoporosis, mood changes, weight gain and hair loss
4.3 Early Development of a Zygote in Humans
1. What is fertilisation?
 The union of two nuclei producing a zygote
 Occurs inside the Fallopian tubes of a woman
2. Development of zygote
 The zygote travels down the Fallopian tubes and enters the uterus. While in the
Fallopian tubes, the zygote undergoes a series of cell divisions. The single cell
forms two cells, then four cells, and so on to produce a solid ball of cells called
morula. Eventually, the growing mass of hundred of cells forms a hollow ball
called blastocyst. The blastocyst attaches to the endometrium of the uterus. This
process is known as implantation. For the next eight weeks or so, the developing
human is called an embryo. The young embryo is nourished at first by nutrients
absorbed directly from the mother’s endometrium, but as further development
takes place the placenta is formed. From the ninth week of development until
birth, the embryo is called a foetus. After about 9 months of development inside
the uterus, the baby is ready to be born.
3. Formation of twins
Twins
Fraternal
Identical
have identical
inherited
traits and are
of same sex
develop from
single zygote
early in the
development, embryo
splits into two identical
embryo
4. Role of placenta in foetal development
may or may
not be of
same sex
formed when two eggs
are released from
ovary and are fertilised
by two different
sperms
 forms selective barrier between the mother’s blood and the foetal blood
 allows oxygen and nutrients to pass from the mother to the foetus
 allows carbon dioxide and nitrogenous waste materials to pass from the foetus
to the mother
 can give protection to the foetus by passing antibodies which gives temporary
immunity to the foetus
 prevent mixing of the blood of the mother and the foetus
 secretes hormones that are essential in pregnancy
 after third month, it takes over the function of corpus luteum and secretes
progesterone and oestrogen
5. Advantages of having a separate circulatory system from that of the mother
 prevents the exchange of some substances such as blood cells and pathogens
 to prevent the higher blood pressure of the mother’s blood from damaging the
delicate foetal blood vessels
 Prevents agglutination if the foetus is of a different blood group from the mother
4.4 Contributions of Science and Technology to Human Reproduction
1. Infertility- inability to have any children
 happens due to damage in the female Fallopian tubes, uterus or cervix, or due to
low sperm count or impotence in the male
 Technology that is associated with reproduction
 Artificial Insemnation
 In Vitro Fertilisation
 Sperm bank
 Frosen embryos
 Cloning
 Surrogate mother
2. Family planning
 allows spacing and timing of the birth of children
3. Birth control techniques
 Natural methods used
 the calendar technique
 the temperature technique
 the mucous technique
 the withdrawal technique
 Physical barrier methods used
 the condom
 the diaphragm
 the intrauterine device (IUD)
 Chemical preventive methods used
 the contraceptive pills
 spermicides
 Sterilisation methods used
 Tubal ligation (female)
 Vasectomy (male)
 Abortion
4. Sexually transmitted diseases (STD)
 diseases that are spread from one person to anther during sexual contact
 are caused either by bacteria or viruses
 Bacterial STDs
 chlamydia, syphilis, gonorrhea
 can be treated with antibiotics
 Viral STDs
 hepatitis B, genital herpes, genital warts, AIDS
 cannot be treated with antibiotics
 can be avoided by
 avoiding sexual contact before marriage
 both partners in a marriage to remain faithful
Prepared By: William Kuen