Modes of Reproduction
- Reproduction is the ability of living organisms to produce living beings similar to themselves.
- It helps to maintain biodiversity and ensure continuity of life.
Sexual Reproduction in Humans
Male Reproductive System
|Testes (Testicles)||A pair of testes is located below the abdomen in the scrotal sac or scrotum. Testes produce the male gametes or sperms. Sperms can withstand low temperatures. To maintain the temperature at 2-3°C lower than the body temperature, the scrotum is located outside the body cavity.|
|Epididymis||Tubes present in testes join to form the epididymis. The epididymis stores sperms temporarily.|
|Vas deferens (Sperm duct)||Each epididymis continues further as sperm duct or vas deferens. The two sperms ducts from both sides open at the top of the urethra.|
|Seminal vesicles||Seminal vesicles are a pair of glands. A seminal vesicle produces a secretion that is responsible for the transportation of sperms.|
|Penis||The urethra passes through the penis. It carries either urine or semen at a time.|
Structure of Sperm
- A sperm cell is composed of four parts- head, middle piece and tail.
- The head carries genetic information. It contains a sac-like structure called acrosome which helps in fertilisation.
- The middle part carries spirally coiled mitochondria needed for energy production for the movement of sperm.
- The tail is like a flagellum which helps in movement of sperm in the fluid medium towards the egg cell.
Female Reproductive System
|Ovaries||Two ovaries are present in the pelvic cavity, one on each side of the uterus. Ovaries produce ova or female gametes. One ovum is released by one ovary every month.|
|Oviducts (Fallopian tubes)||There are two oviducts or fallopian tubes present in the female body. Each one is situated close to one ovary of its side. When the egg is released by the ovary, it passes down to the uterus through the oviduct.|
|Uterus (Womb)||Hollow pear-shaped, muscular organ. The inner lining of the uterus called the endometrium protects and nourishes the developing embryo.|
|Vagina (Birth Canal)||The uterus opens into the vagina. The vagina is a muscular narrow tube.|
|Vulva|| The vagina and urethra both open into the vulva.|
|Internal Fertilisation||External Fertilisation|
|Takes place inside the female’s body.|
Examples: Dogs, cows, humans
|Fusion of male and female gametes occurs outside the body of the female.|
Examples: Amphibians, echinoderms, fish
Test Tube Baby
- In case a woman is unable to conceive, doctors collect freshly released egg from her and sperms from her male partner and keep the collected gametes together for some hours.
- If feritilisation occurs, the zygote is developed in-vitro or in the laboratory and then placed in the mother’s uterus for further development.
- This process is called in-vitro fertilisation and a baby born through this technique is called test tube baby.
Development of Embryo
- If the ovum is not fertilised, then the lining of the uterus breaks down and disintegrates.
- The ovum, lining of the uterus and some blood is discharged out of the body.
- This is called menstruation.
- The bleeding lasts for four days.
- After menstruation, the ovum is released and the uterus again prepares itself for
Viviparous and Oviparous Animals
- Animals which give birth directly to their young ones are called viviparous animals.
- The zygote grows in the mother’s womb.
- Dogs, cows, humans and other placental mammals are examples of viviparous animals.
- Animals which lay eggs are called oviparous animals.
- The mothers lay eggs outside their bodies. The eggs are laden with yolk.
- The development of embryo takes place outside the mother’s body.
- Frogs, lizards, reptiles, insects such as butterflies and moths, hens, crows and other birds are all oviparous animals.
The morphological, anatomical and physiological changes which occur in a young one when being transformed into an adult is known as metamorphosis.
Metamorphosis in Frog
The lifecycle of a frog has three distinct stages- egg, tadpole or larva, and adult frog.
- A small outgrowth called bud arises on the parent body.
- The bud grows and develops a mouth and a ring of tentacles.
- The bud breaks off from the parent body and develops into a new individual.
- Examples: Hydra, Sponges, Corals
- Most common method in unicellular organisms.
- Binary fission is the division of the parent cell.
- When the organism matures, it grows in size.
- Its nucleus duplicates.
- Cytoplasm divides in the middle.
- A single parent organism gives rise to two identical daughter organisms.
- Examples: Amoeba, Paramoecium
- Cloning is the process in which an exact copy of a cell, any other living part or an entire organism can be produced.
- In animal cloning, an entire organism is produced from a single cell of the body.
Advantages of Cloning
- Enables us to produce exactly identical copies of animals with favourable characteristics.
- Helps in preserving desirable features of the parent animal for future generations.
Disadvantages of Cloning
- Many cloned animals die before birth or die soon after birth.
- Often, cloned animals are born with severe abnormalities.