Sexual Reproduction in Animals

Sexual Reproduction

• Definition: The process by which living things produce offspring of their own kind.
• Importance: Ensures the continuation of species.
• Types:
  • Asexual Reproduction: Involves a single parent. Examples include budding (offspring grows from the parent's body, e.g., Hydra) and binary fission (the parent splits into two, e.g., Amoeba).
  • Sexual Reproduction: Involves the fusion of the male and female gametes. Examples include internal fertilization (occurs inside the female's body) and external fertilization (occurs outside the female's body). Specific examples include humans (internal), fish and amphibians (external).

Additional Points

• Metamorphosis: The process of transformation from an immature form to an adult form. (e.g., insects, amphibians)
• Reproductive Systems: Crucial for species continuation, though not immediately essential for individual survival.

Reproduction in Animals

• Types of Reproduction:
  • Asexual Reproduction: Involves a single parent. Examples include budding (offspring grows from the parent's body, e.g., Hydra) and binary fission (the parent splits into two, e.g., Amoeba).
  • Sexual Reproduction: Involves the fusion of male and female gametes. Examples include internal and external fertilization.

Gametes

• Male: Sperm cells
• Female: Egg cells (ova)
• Hermaphrodites: Organisms that possess both male and female reproductive organs (e.g., earthworms, leeches).
• Fertilization: The fusion of sperm and egg forming a zygote.
  • External Fertilization: Occurs outside the female's body (e.g., fish, amphibians)
  • Internal Fertilization: Occurs inside the female's body (e.g., birds, reptiles, mammals)

Reproduction in Humans

• Involves two sexes (male and female).
• Internal fertilization.
• Development of the zygote into a fully formed individual occurs inside the female body.

Human Reproductive System (Male)

• Organs:
  • Testes: Located in the scrotum, produce sperm and testosterone.
  • Scrotum: Sac that holds testes outside the body to maintain cooler temperature for sperm production.
  • Epididymis: Coiled tubes attached to the testes where sperm mature and are stored.
  • Vas Deferens: Tubes that carry sperm from the epididymis to the ejaculatory ducts.

Human Reproductive System (Female)

• Organs:
  • Ovaries: Produce eggs (ova) and hormones (estrogen and progesterone).
  • Oviducts (Fallopian Tubes): Carry eggs from the ovaries to the uterus. Typically fertilization occurs here.
  • Uterus: Muscular organ where a fertilized egg implants and develops into a fetus.
  • Vagina: Muscular canal that receives sperm during intercourse and serves as the birth canal.
  • Cervix: The opening of the uterus.

Puberty

• Onset of sexual maturity.
  • In males: Voice deepening, increased facial hair, muscle development and sperm production.
  • In females: Breast development, hip widening, and menstruation.

Fertilization

• Fusion of a sperm and an egg.
• Occurs in the oviduct.
• The fertilized egg (zygote) travels to the uterus and implants in the uterine wall.

Key Hormones

• Male: Testosterone
• Female: Estrogen and Progesterone

Sperm

• Produced in millions.
• Each sperm has a head, middle piece, and tail.

Ovulation

• Release of an egg from the ovary.

Semen

• Mixture of sperm and fluids.

Development of the Embryo

• Cell division after fertilization.

• Differentiation of cells (muscle, nerve, and blood cells).

• Embryo: Developing structure during early stages (up to 8 weeks).

• Fetus: Structure from the 9th week of pregnancy or later.

Impantation

• Embryo implants itself in the uterine lining (endometrium).
• Rich blood vessels in the uterine lining provide nourishment.

Development of the Fetus

• Fetus continues growth and development.
• Different organs and systems develop during this stage.
• Fetus receives nourishment and oxygen through the placenta.

Test Tube Baby (IVF)

• Technique used for couples unable to conceive naturally.
• Eggs and sperm collected, combined in a lab dish to allow fertilization.
• Fertilized eggs (embryos) implanted in the woman's uterus.

Viviparous vs. Oviparous Animals

• Viviparous: Give birth to fully developed young ones (e.g., humans, cows, dogs)
• Oviparous: Lay eggs that contain developing embryos (e.g., birds, reptiles, fish, amphibians)

Key Points (Viviparous)

• Fertilization happens internally.
• Zygote develops inside the mother's body.
• Mother provides nourishment and protection to the developing embryo.
• Fully developed young are born.

Key Points (Oviparous)

• Zygote undergoes development in an egg.
• Egg provides protection and nourishment to the embryo.
• Embryo hatches from the egg.

Metamorphosis

• Complete change in an animal's form as it develops from a young one to an adult.

Cloning

• Dolly the Sheep: A landmark scientific achievement of cloning in 1997.
• Processes: Collected cells (mammary gland), removed nucleus, extracted nucleus from an unfertilized egg, inserted nucleus, fertilized egg grows.
• Significance: First mammal cloned from an adult somatic cell (body cell).

Asexual Reproduction (Examples)

• Frog: Egg → Tadpole (larva) → Frog (adult)
• Mosquito: Egg → Larva → Pupa → Adult
• Butterfly/Moth: Egg → Larva (caterpillar) → Pupa (chrysalis) → Adult

Asexual Reproduction (Types)

• Binary Fission: Single-celled organism divides into two identical daughter cells (e.g., Amoeba).
• Budding: A small outgrowth (bud) forms on the parent organism, grows, and eventually separates to become a new individual (e.g., Hydra).