Test: Animal Reproduction - 2 - UPSC MCQ

Reproduction is an important characteristic feature of living organisms. It is an essential life process which not only helps in survival but also helps in continuity of that race and group immortality, as by reproduction. Young ones replace the old and dying ones. These young ones feed, grow and reproduce again.

Importance of Reproduction

• Reproduction maintains a balance between the birth rate and death rate.
• The new individuals replace the old and the dying population.
• It also helps in increasing the number of species in the ecosystem.
• The genes are transmitted from the parents to the offspring.
• This leads to the evolution of species.
• Variations in species and their ability to survive in different environments is the result of reproduction.

Twins absolutely resembling each other in sex and external appearance are referred to as Identical Twins. Identical twins are formed when one egg after being fertilized by one sperm, divides into two halves. The two halves are genetically identical and of the same sex. Because these twins come from one zygote, they are also known as monozygotic.

Because fertilization of egg starts in 11 to 21 th days after that the unfertilized egg will ready to come out due to which copulation results in fertilization between 11 to 21 th days. 

In meiosis, the chromosome number is halved in the daughter cells ie., the diploid mother cell gives rise to four haploid daughter cells. 

Meiosis is a type of cell division that reduces the number of chromosomes in the parent cell by half and produces four gamete cells. This process is required to produce egg and sperm cells for sexual reproduction.

Amniocentesis is a medical procedure used primarily in prenatal diagnosis of chromosomal abnormalities and the fetal infections as well as for sex determination. 

Placenta is the tissue where maternal and foetal blood come in contact, and nutrients and oxygen are transferred from maternal blood to foetal blood while waste products are transferred from foetal to maternal blood.

On the other hand, Umbilical cord is a tube like structure (made up of one vein and two arteries) that act as a connection between foetus and placenta, and transfer the foetal blood to placenta. Placenta is attached to fetus through Umbilical cord, the lifeline between mother and baby.

Budding is an asexual mode of producing new organisms. In this process, a new organism is developed from a small part of the parent’s body. A bud which is formed detaches to develop into a new organism. The newly developed organism remains attached as it grows further. It is separated from the parent organism when it gets matured by leaving scar tissues behind. As this is an asexual reproduction, the newly developed organism is a replica of the parent and is genetically identical.

For reproduction, Hydra uses regenerative cells where a bud expands as an outgrowth because of repeated cell division at one specific location. These buds then developed into new small individuals which when completely matured, detach from the parent body.

For example- Both hydra and yeast reproduce by the process of Budding.

Mitosis is used to produce daughter cells that are genetically identical to the parent cells. The cell copies - or 'replicates' - its chromosomes, and then splits the copied chromosomes equally to make sure that each daughter cell has a full set.

In cells after they attain a certain size, its internal volume enlarges and the cell membrane expands. But the volume increases more rapidly than the surface area, and so the relative amount of surface area available to pass materials to a unit volume of the cell steadily decreases.
Finally, at some point, there is just enough surface available to service all the interior; if it is to survive, the cell must stop growing.
Most importantly, the surface area to the volume ratio gets smaller as the cell gets larger.
If the cell grows beyond a certain limit, not enough material will be able to cross the membrane fast enough to accommodate the increased cellular volume. When this happens, the cell divides into smaller cells with favorable surface area/volume ratios, or ceases to function.

Puberty is the stage of development when a child's body begins to transform into an adult body capable of sexual reproduction. In girls, puberty is characterized by the development of breasts, growth of pubic and underarm hair, and the onset of menstruation.

The age at which puberty begins can vary from person to person, but the average age for girls to start puberty is around 10-16 years of age.

• Genetics: Puberty onset is largely determined by genetics, so if a girl's mother or older sisters started puberty early or late, it is likely that she will follow a similar pattern.


• Body weight: Girls who have a higher body weight or body mass index (BMI) may experience puberty earlier than girls with lower body weight.


• Environmental factors: Certain environmental factors such as exposure to endocrine-disrupting chemicals or stress can influence the timing of puberty.

• Growth spurt: Girls will experience a rapid growth in height.


• Breast development: The breasts will start to develop, and the nipples may become tender.


• Body hair growth: Girls will start to grow pubic hair and underarm hair.


• Menstruation: Menstruation, also known as the first period, usually occurs towards the end of puberty.


• Acne: Many girls may experience an increase in acne or pimples during puberty.

In conclusion, the puberty age in girls is typically between 10-16 years of age. However, it's important to remember that every individual is unique, and the exact timing of puberty can vary. If there are concerns or questions about puberty development, it is recommended to consult a healthcare professional for guidance and support.

Human fertilization is the union of a human egg and sperm, usually occurring in the ampulla of the fallopian tube. The result of this union is the production of a zygote cell, or fertilized egg, initiating prenatal development. Scientists discovered the dynamics of humanfertilization in the nineteenth century.

The cells from each parent that combine to form the zygote are called gametes. In humans, the male gamete is called sperm, and the female gamete is called an egg. When the gametes join they form a cell called a zygote. Human sperm and eggs contain 23 chromosomes. Human zygotes contain 46 chromosomes.

Regeneration means the regrowth of a damaged or missing organ part from the remaining tissue. As adults, humans can regenerate some organs, such as the liver. If part of the liver is lost by disease or injury, the liver grows back to its original size, though not its original shape. And our skin is constantly being renewed and repaired. Unfortunately many other human tissues don’t regenerate, and a goal in regenerative medicine is to find ways to kick-start tissue regeneration in the body, or to engineer replacement tissues.

Sperm cells are the smallest human cells. They are no more than a nucleus with a small amount of cytoplasm, some mitochondria (the energy suppliers of the cell) and a long tail. They have hardly any content and are the straightest cells.