[Biology Class Notes] on Reproduction in Animals Pdf for Exam

Reproduction in Animals Introduction

Reproduction is the biological process of producing the same kind of individuals. Most organisms reproduce by mating that increases the organism’s genetic variability. The females and males have separate reproductive organs called gonads. These gonads forms gametes that fuse together to produce a single cell called a zygote.

Few animals such as snails, earthworms, slugs, and more are hermaphrodites and possess male and female reproductive organs in the same organism. Most of the animals are diploid organisms, which means their haploid reproductive (gamete) cells and body (somatic) cells are diploid are produced via meiosis. Also, in some cases, reproduction in animals and humans occurs similarly to each other.

Types of Animal Reproduction

Based on the number of parents involved, different modes of reproduction occurs. The two types of animal reproduction include,

• Sexual Reproduction

• Asexual Reproduction

Sexual Reproduction

Male and females have different reproductive organs in animals. The animal’s reproductive parts produce gametes that fuse and form a zygote. The zygote then develops into a new similar species. The reproduction type through the fusion of male and female gametes is called sexual reproduction. Male gametes, produced by testes, are called sperms. Whereas, the female gametes, produced by the ovary, are called ova (or eggs). In the reproduction process, the first step is the fusion of a sperm and an egg (ovum).

The fusion of the sperm and egg is known as fertilization (as shown in the above figure).

During fertilization, the sperm’s nuclei and the egg fuse together and form a single nucleus that results in the formation of a fertilized egg, which is also called a zygote (shown in the figure given below).

Further, the zygote repeatedly divides to give rise to a ball of cells that begin to form groups. The groups develop into various tissues and organs constituting a full body. In this process, the developing structure is called an embryo (represented as in the below image).

The embryo continues its development in the uterus and develops body parts like head, eyes, face, ear, nose, hands, legs, toes, and so on. The embryo stage in which various body parts develop and can be identified is called foetus (shown in the image given below).

In a defined time period, when the foetus development is complete, the mother gives birth to the baby. An animal that gives birth to young ones is the viviparous animal. For example, humans, cows, dogs, and more. The organism that lays eggs is called an oviparous animal – for example, all birds except bats, lizards, and so on.

Asexual Reproduction

This is the other type of animal reproduction in which only a single parent, gets divided into two new offspring. For example, Amoeba and Hydra. In hydra, the individuals develop from the buds, and therefore, this type of asexual reproduction is called budding (as shown in the below image).

The nucleus gets divided into two nuclei in amoeba. Therefore, such kind of asexual reproduction is called binary fission.

Cloning

Cloning is the modern technique of science to produce an exact copy of a cell, any other living part, or a complete organism. Cloning of an animal was successfully performed by Ian Wilmut and his colleagues for the first time at the Roslin Institute in Edinburgh, Scotland.

They cloned a sheep successfully and named Dolly in 1996.

Reproduction in Human Beings

Reproduction in human beings happens by sexual reproduction, where both the male and female gametes fertilize to give rise to an embryo resultantly. The fertilization of the human embryo befalls inside the female body. Therefore, it is called Internal Fertilization. Human Beings are viviparous organisms who give direct rise to Embryos rather than laying eggs.

Male Reproductive System

• Testes – Males have two testes, situated in a bag of skin called the scrotum. Scrotum exists outside the pelvic cavity.

• Sperm Duct – These are the thin ducts that arise from the testes.

• Prostate Gland – This is an accessory gland in males that pours its secretions into the sperm duct onward with the seminal fluid from the testes and into the penis.

• Urethra – It functions similarly to a common pathway for the seminal fluid and urine in males. It is shorter in females and longer in males.

• Penis – This is an organ that lies outside the body and functions to eliminate both semen and urine.

As the male reproductive organ in humans, the primary organs of male reproduction are testes. These are responsible for producing the male gamete called sperm by a process known as spermatogenesis. This happens in the testes seminiferous tubules. Also, the testes are responsible for secreting testosterone, the male reproductive hormone, and it is one of the reproductive organs in humans.

Leydig Cells of the testes integrates testosterone. Not only the hormone testosterone helps in the formation of the sperm but also in the secondary sexual character development in males like facial and pubic hair during puberty, deepening of the voice.