Test: Animal Reproduction - 1 - UPSC

Binary fission is a type of asexual reproduction in which the fully grown parent  cell splits into two halves, producing two new daughter cells. It is common among organisms such as Amoeba, Paramecium.

Spores is a reproductive cell capable of developing into a new individual without fusion with another reproductive cell in a favorable condition. As there is no involvement of fusion of gamete or reproductive cell for the formation new individual is called as asexual reproduction.

A hermaphrodite is an organism that has complete or partial reproductive organs and produces gametes normally associated with both male and female sexes. Many taxonomic groups of animals do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which either partner can act as the "female" or "male." For example, the great majority of tunicates, pulmonate snails, opisthobranch snails, earthworms and slugs are hermaphrodites. Hermaphroditism is also found in some fish species and to a lesser degree in other vertebrates. Most plants are also hermaphrodites.

These are the viviparous mammals. Other animals that hold their eggs internally then give birth to live young are the ovoviviparous animals. They include some snake and lizards , some insects, some sharks and rays.All the rest are egg layers or oviparous like birds and most snakes, lizards and insects .

Testis, plural testes, also called testicle, in animals, the organ that produces sperm, the male reproductive cell, and androgens, the male hormones. In humans the testes occur as a pair of oval-shaped organs. They are contained within the scrotal sac, which is located directly behind the penis and in front of the anus.

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.

Oogenesis is the process of the formation of a mature ovum from the oogonia in females. It takes place in the ovaries. During oogenesis, a diploid oogonium or egg mother cell increases in size and gets transformed into a diploid primary oocyte. This diploid primary oocyte undergoes first meiotic division i.e., meiosis I or reductional division to form two unequal haploid cells. The smaller cell is known as the first polar body, while the larger cell is known as the secondary oocyte. This secondary oocyte undergoes second meiotic division i.e., meiosis II or equational division and gives rise to a second polar body and an ovum. Hence, in the process of oogenesis, a diploid oogonium produces a single haploid ovum while two or three polar bodies are produced.

The middle piece of human sperm contains mitochondria which are coiled around an axial filament called mitochondrial spiral. These provide energy for the movement of sperm.

Testosterone is the main sex hormone found in men. It controls male physical features. The testes (testicles) make testosterone. Women have testosterone too but in much smaller amounts than in men.

The male reproductive system creates sperm that is manufactured in the seminiferous tubules within each testicle. The head of the sperm contains the DNA, which when combined with the egg's DNA, will create a new individual. The tip of the sperm head is the portion called the acrosome, which enables the sperm to penetrate the egg. The midpiece contains the mitochondria which supplies the energy the tail needs to move. The tail moves with whip-like movements back and forth to propel the sperm towards the egg. The sperm have to reach the uterus and the fallopian tube in order to fertilize a woman's egg.

Binary fission is a kind of asexual reproduction. It is the most common form of reproduction in prokaryotes such as bacteria. It occurs in some single-celled Eukaryotes like the Amoeba and the Paramoecium.

Fertilization in frogs takes place outside the female body called external fertilisation. Females lay eggs inside the water. These eggs are surrounded by a jelly like layer for protection. At the same time male frog releases sperms in water. These sperms travel to the eggs and fertilized them.

In asexual reproduction, the planarian detaches its tail end and each half regrows the lost parts by regeneration, allowing neoblasts (adult stem cells) to divide and differentiate, thus resulting in two worms. and hydra is reproduce by budding.

Parthenogenesis is a type of asexual reproduction in which the offspring develops from unfertilized eggs. It is particularly common amongst arthropods and rotifers, can also be found in some species of fish, amphibians, birds, and reptiles, but not in mammals. Parthenogenetic development also occurs in some plants species, such as roses and orange trees.

Animals that lay eggs, with little or no other embryonic development within the mother are called oviparous. This is the reproductive method of most fish, amphibians, reptiles, all birds, and the monotremes.

Gonads are where male and female gametes are produced. The production of sperm cells is known as spermatogenesis. This process occurs continuously and takes place within the male testes. The male germ cell or spermatocyte undergoes a two-part cell division process called meiosis. Meiosis produces sex cells with one half the number of chromosomes as the parent cell. Haploid male and female sex cells unite during fertilization to become one diploid cell called a zygote. Hundreds of millions of sperm must be released in order for fertilization to take place.

The accessory glands of the male reproductive system are the seminal vesicles, prostate gland, and the bulbourethral glands. These glands secrete fluids that enter the urethra.

The menstrual cycle, which is counted from the first day of one period to the first day of the next, isn't the same for every woman. Menstrual flow might occur every 21 to 35 days and last two to seven days. For the first few years after menstruation begins, long cycles are common. However, menstrual cycles tend to shorten and become more regular as you age.

• Estrogen: A female sex hormone produced by the ovaries, the adrenal gland, and (in small quantities) by body fat. Estrogen helps to retain calcium in bones, regulates the balance of high density lipoprotein (HDL) and low density lipoprotein (LDL) cholesterol in the bloodstream, and aids the maintenance of blood-sugar levels, memory functions, and emotional balance, just to mention a few.
• Progesterone: A female sex hormone produced in largest amounts during and after ovulation that prepares the uterus for the implantation of a fertilized egg. It also helps reduce body fat, aids in relaxation and reduction of anxiety, and promotes hair growth.

Implantation is a process in which a developing embryo, moving as a blastocyst through a uterus, makes contact with the uterine wall and remains attached to it until birth. The lining of the uterus (endometrium) prepares for the developing blastocyst to attach to it via many internal changes.

IUD stands for Intrauterine Device — a birth control method that sits inside your uterus. A non-hormonal IUD is a small piece of flexible plastic shaped like a T that has copper wrapped around it. That’s why it’s also called the copper IUD.

The two reasons for the rapid increase in population in recent times are :
(i) The death rate in India has fallen down due to increased scientific and medical knowledge.
(ii) Improved standard of living due to increased food production and industrial development and education has brought about an increase in population.