Microgamete and Macrogamete
- A sperm is also known as a
microgamete as it is smaller in size.
- On the other hand, ovum is
known as a macrogamete since it is larger in size.
- A sperm has a flagellum and
is, therefore, motile.
- An egg is non-motile.
Isogamy and Anisogamy
- Isogamy is the fusion of two
similar or identical gametes.
- It occurs in unicellular
organisms like Monocystis.
- Anisogamy is the fusion of two
- It occurs in all higher
organisms, including man.
- Parthenogenesis is a special
type of sexual reproduction in which an ovum develops into a new
organism without fertilisation by the sperm.
- For example, drones in a
colony of honeybees develop parthenogenetically
from unfertilised ova.
- Drones are, thus, haploid
Spermatogenesis and Oogenesis
- Spermatogenesis is the
process of formation of male gametes, i.e. sperms.
- It begins at puberty and
occurs in the seminiferous tubules in the
testes of males.
- It is a continuous process.
- Oogenesis is the process of formation
of ova or eggs.
- It begins even before the
girl child is born. In fact, a baby girl is born with a number of
primary oocytes in prophase I stage.
- After puberty, when the girl
starts menstruating, only one egg matures in about 28-30 days.
Primary and Secondary Sex Organs
- The primary sex organs are
testes in males and ovaries in females.
- These organs produce
gametes, i.e. sperms in males and ova in females.
- They also secrete sex
hormones, i.e. testosterone in males and estrogen and progesterone in
- Their development is under
the control of FSH and LH.
- The examples of secondary
sex organs are prostate and seminal vesicles in males and uterus and
vagina in females.
- They neither secrete sex
hormones nor produce gametes but play an important role in the
functioning of the reproductive system of males and females.
Morula and Blastula
- Morula is a spherical, solid ball
of cells without a cavity.
- It is formed as a result of
first few cleavages.
- Here, the mass of cells are
- Blastula is a hollow,
of cells begin at the blastula stage.
Structures Formed from the Three Germ Layers
- The three germ layers formed
during gastrulation form specific organs. Some
of them are given below:
Ectoderm gives rise to brain, spinal cord and nerves.
Mesoderm gives rise to heart, kidneys and gonads.
Endoderm gives rise to liver, pancreas and urinary bladder.
- The cell groups of these
germ layers move in a perfect order with accuracy to form specific