CHAPTER- 6 REPRODUCTION IN ANIMALS
NOTES
1. Methods of reproduction in animals- 1. Sexual reproduction, 2. Asexual reproduction.
1. Sexual Reproduction- In this method, the fusion of male and female gametes occurs. This is called sexual reproduction.
A. Male Reproductive Organs- The male reproductive organs include a pair of testes, two sperm ducts, and a penis. The testes produce male gametes, which are called sperm.
- Every sperm contains the basic components of a cell.
- Sperm are single cells consisting of a head, a middle part, and a tail. The tail helps in movement.
B. Female Reproductive Organs- The female reproductive organs include a pair of ovaries, oviducts (fallopian tubes), and a uterus. The ovaries produce female gametes, which are called ova (eggs). The uterus is the part where the development of the baby takes place. Like sperm, the ovum is also a single cell.
C. Fertilization- The first step in the process of reproduction is the fusion of sperm and ovum. This fusion is called fertilization.
- During fertilization, the sperm and ovum fuse to form a single entity. As a result of fertilization, a zygote is formed.
- Fertilization that occurs inside the female's body is called internal fertilization. Examples-humans, cows, dogs, and chickens.
- Fertilization in which the fusion of male and female gametes occurs outside the female's body is called external fertilization. Examples-aquatic animals like fish and starfish.
D. Test-tube Baby- In some women, the fallopian tubes are blocked, preventing the sperm from reaching the ovum. In such cases, doctors collect fresh eggs and sperm and keep them together in a suitable medium for a few hours, allowing IVF (in vitro fertilization) or artificial fertilization outside the body to occur.
- If fertilization occurs, the zygote is developed for about a week, after which it is implanted into the mother's uterus. The baby continues to develop in the uterus, and the birth happens just like a normal childbirth. A baby born through this technique is called a test-tube baby.
E. Embryonic Development- As a result of fertilization, a zygote is formed, which develops into an embryo. The zygote continuously divides and forms a ball of cells. Later, the cells begin to group together and differentiate into various tissues and organs. This developing structure is called an embryo.
- The embryo continuously develops in the uterus. Gradually, various body parts such as hands, legs, head, eyes, ears, etc., begin to form.
- The stage of the embryo in which all the body parts can be identified is called the fetus. When the development of the fetus is complete, the mother gives birth to the newborn baby.
- In animals with external fertilization, the development of the embryo occurs outside the female's body. The embryo continues to develop inside an egg membrane. Once the development of the embryo is complete, egg hatching occurs.
F. Viviparous and Oviparous Animals-
1. Viviparous- Animals that give birth to live offspring are called viviparous animals.
2. Oviparous- Animals that lay eggs are called oviparous animals.
From Infant to Adult- A newborn organism or an organism that emerges from an egg continues to grow until it becomes an adult.
- Life cycle of a frog - Egg -> Tadpole (Larva) -> Adult
- The transformation of a tadpole into an adult, with some specific changes, is called metamorphosis.
2. Asexual Reproduction- Reproduction in which only one parent gives birth to a new organism is called asexual reproduction.
- In Hydra, a new organism develops from a bud, so this type of reproduction is called budding.
Binary Fission- In this type of asexual reproduction, the parent organism divides to produce two offspring, and this process is called binary fission.
Cloning- The process of artificially producing an identical cell, part of an organism, or a whole organism is called cloning.
