Integrated Guidance Programme of General Studies for IAS
(Pre) - 2013
Subject - General Science
Chapter : The Reproductive System
Asexual reproduction allows an organism to rapidly
produce many offspring without the time and resources committed to
courtship, finding a mate, and mating.
Fission, budding, fragmentation, and the formation of
rhizomes and stolons are some of the mechanisms that allow organisms to
The hydra produces buds;
starfish can regenerate an entire body from a fragment of
the original body.
The lack of genetic variability in asexually reproducing
populations can be detrimental when environmental conditions change quickly.
In sexual reproduction new individuals are produced by
the fusion of haploid gametes to form a diploid zygote.
Sperm are male gametes, ova (ovum singular) are female
Meiosis produces cells that are genetically distinct from
fertilization is the fusion of two such distinctive
Human Reproduction and Development
Human reproduction employs internal fertilization, and
depends on the integrated action of hormones, the nervous system, and the
Gonads are sex organs that produce gametes. Male gonads
are the testes, which produce sperm and male sex hormones. Female gonads are
the ovaries, which produce eggs (ova) and female sex hormones.
The Male Reproductive System
Testes are suspended outside the abdominal cavity by the
scrotum, a pouch of skin that keeps the testes close or far from the body at
an optimal temperature for sperm development.
Seminiferous tubules are inside each testis, and are
where sperm are produced by meiosis. About 250 meters (850 feet) of tubules
are packed into each testis.
Spermatocytes inside the tubules divide by meiosis to
produce spermatids that in turn develop into mature sperm.
Sperm production begins at puberty and continues
throughout life, with several hundred million sperm being produced each day.
Once sperm form they move into the epididymis, where they mature and are
Male Sex Hormones
The anterior pituitary produces follicle-stimulating
hormone (FSH) and luteinizing hormone (LH).
Action of LH is controlled by the gonadotropin-releasing
LH stimulates cells in the seminiferous tubules to
secrete testosterone, which has a role in sperm production and developing
male secondary sex characteristics
FSH acts on cells to help in sperm maturation. Negative
feedback by testosterone controls the actions of GNRH.
Sperm pass through the vas deferens and connect to a
short ejaculatory duct that connects to the urethra.
The urethra passes through the penis and opens to the
Secretions from the seminal vesicles add fructose and
prostaglandins to sperm as they pass. The prostate gland secretes a milky
The bulbourethral gland secretes a mucus-like fluid that
provides lubrication for intercourse
Sperm and secretions make up semen.
Detail Description, Analysis and More MCQs of the Chapter Buy this Study
The Female Reproductive System
The female gonads, are ovaries, which are located within
the lower abdominal cavity
The ovary contains many follicles composed of a
developing egg surrounded by an outer layer of follicle cells.
At birth each female carries a lifetime supply of
developing oocytes, each of which is in ProphaseI.
A developing egg (secondary oocyte) is released each
month from puberty until menopause, a total of 400-500 eggs.
Hormones and Female Cycles
- The ovarian cycle is hormonally regulated in two phases. The follicle
secretes estrogen before ovulation; the corpus luteum secretes both estrogen
and progesterone after ovulation.
- Hormones from the hypothalamus and anterior pituitary control the
ovarian cycle. The ovarian cycle covers events in the ovary; the menstrual
cycle occurs in the uterus.
- Menstrual cycles vary from between 15 and 31 days. The first day of the
cycle is the first day of blood flow (day 0) known as menstruation.
- During menstruation the uterine lining is broken down and shed as
- FSH and LH are secreted on day 0, beginning both the menstrual cycle and
the ovarian cycle.
Sexually Transmitted Diseases
- STDs can affect the sex partners, fetus, and newborn infants. STDs are
grouped into three categories.
- Category One : STDs that produce inflammation of the urethra,
epididymis, cervix, or oviducts. Gonorrhea and chlamydia are the most common
STDs in this category. Both diseases can be treated and cured with
antibiotics, once diagnosed.
- Category Two : STDs that produce sores on the external genitals.
Genital herpes is the most common disease in this class. Symptoms of herpes
can be treated by antiviral drugs, but the infection cannot be cured.
Syphilis is a bacterially caused infection, and can, if left untreated,
cause serious symptoms and death. However, the disease is curable with
- Category Three : This class of STDs includes viral diseases that
affect organ systems other than those of the reproductive system. AIDS and
hepatitis B are in this category. Both can be spread by sexual contact or
blood. Infectious individuals may appear symptom-free for years after
Fertilization And Cleavage
Fertilization has Three Functions
1. transmission of genes from both parents to offspring
2. restoration of the diploid number of chromosomes reduced during meiosis
3. initiation of development in offspring
Steps in Fertilization
- Contact between sperm and egg
- Entry of sperm into the egg
- Fusion of egg and sperm nuclei
- Activation of development
Cleavage is the first step in development of all multicelled organisms.
Cleavage converts a single-celled zygote into a multicelled embryo by mitosis.
Usually, the zygotic cytoplasm is divided among the newly formed cells.
Various Stages of Fertilization
- Fertilization, the fusion of the sperm and egg, usually occurs in the
upper third of the oviduct. Thirty minutes after ejaculation, sperm are
present in the oviduct, having traveled from the vagina through the uterus
and into the oviduct. Sperm traverse this distance by the beating of their
flagellum. Of the several hundred million sperm released in the ejaculation,
only a few thousand reach the egg.
- Only one sperm will fertilize the egg. One sperm fuses with receptors on
the surface of the secondary oocyte, triggering a series of chemical changes
in the outer oocyte membrane that prevent any other sperm from entering the
oocyte. The entry of the sperm initiates Meiosis II in the oocyte. Fusion of
the egg and sperm nuclei forms the diploid zygote.
Facts from NCERT
- Fertilization which takes place inside the female body is called
internal fertilization e.g. - humans, cow’s, dogs etc.
- Fertilization in which the fusion of a male and female gamete takes
place outside the body of the female is called external fertilization e.g.:-
it is common in aquatic animals such as fish, starfish, frogs etc.
- The animals which give birth to young ones are called vivi parous
- Those animals which lay eggs are called oviparous animals.
- Life cycle of the silk worm: - egg-larva or caterpillar–pupa-adult.
- Life cycle of a frog—egg—tadpole (9larva)—adult.
- The transformation of the larva into an adult through drastic changes is
- Cloning of an animal was successfully performed for the first time by
Ian wilmat and his team in Scotland. They cloned a sheep named dolly in
Detail Description, Analysis and More MCQs of the Chapter Buy this Study
<< Go Back to IGP