1. What is fertilisation? What is a zygote?
- Fertilisation is the process where the male gamete (sperm) and the female gamete (egg) fuse together.
- The single cell formed immediately after fertilisation is called a zygote. This is the very first stage of a new individual.
2. What is metamorphosis? In which organisms does it take place?
- Metamorphosis is the process where a young animal undergoes a dramatic and distinct change in its body structure and form to become an adult.
- It takes place in organisms like frogs (tadpole to frog) and butterflies (caterpillar to butterfly).
3. Name the male and female gamete in human body. Where in the body they are produced?
- Male Gamete: Sperm
- Produced in: Testes (male reproductive glands)
- Female Gamete: Ovum (Egg)
- Produced in: Ovaries (female reproductive glands)
4. What are viviparous and oviparous animals?
- Viviparous Animals: Animals that give birth to live young ones. The development of the embryo happens inside the mother’s body. Example: Humans, dogs, cows.
- Oviparous Animals: Animals that lay eggs. The development of the embryo happens inside the egg outside the mother’s body. Example: Birds, frogs, lizards.
5. What is gestation period? What is the duration of gestation in humans?
- Gestation period is the time between the fertilisation of the egg and the birth of the baby. It is the duration of pregnancy.
- In humans, the gestation period is approximately nine months (about 280 days).
6. Give reason for the following:
- (a) Some characters in you are similar to those of your father or mother.
- Reason: We inherit genetic information in the form of DNA from our parents through their sperm and egg cells. These genes carry instructions for various traits, which is why we share similarities with our parents.
- (b) The male egg cell has a long tail.
- Reason: The sperm cell (male gamete) has a long tail called a flagellum. This tail helps it to swim actively through the female reproductive tract to reach and fertilise the egg.
LONG ANSWER TYPE QUESTIONS
1. What is internal fertilisation? Explain with example.
- Internal fertilisation is the process where the fusion of the sperm and egg occurs inside the body of the female parent.
- In this method, the male deposits sperm inside the female’s body, where they travel to meet the egg. This method requires less number of gametes to be produced and offers better protection to the developing embryo.
- Examples: This occurs in humans, cows, dogs, birds, and reptiles.
2. How are chicks born?
Chicks are born from eggs laid by the hen. Here is the process:
Fertilisation: Internal fertilisation occurs inside the hen.
Egg Formation: The fertilised egg (zygote) is enclosed in a protective shell along with nutrients (yolk and albumen) and laid by the hen.
Incubation: The hen sits on the eggs to keep them warm (brooding). The warmth is essential for the development of the embryo inside.
Development: The embryo develops inside the egg using the stored food.
Hatching: After about 21 days, the fully developed chick breaks open the eggshell (a process called pipping) and comes out.
3. Describe the development of embryo.
- After fertilisation, the zygote begins to divide repeatedly to form a ball of cells called an embryo.
- The embryo gets embedded in the thick, nourishing lining of the uterus (implantation).
- A special tissue called the placenta develops, which connects the embryo to the mother. The placenta supplies oxygen and nutrients from the mother’s blood to the embryo and removes waste products from the embryo’s blood.
- The embryo is protected in a fluid-filled sac called the amniotic sac.
- Over the gestation period, the embryo grows and develops various body parts and organs to become a foetus, and finally a fully developed baby ready for birth.
4. What is budding? Name an organism that reproduces by budding.
- Budding is a type of asexual reproduction where a new organism develops as a small outgrowth or bud on the body of the parent organism.
- The bud grows, and once it is fully developed and mature, it detaches from the parent to become a new, independent individual.
- Example: Hydra is an organism that reproduces by budding.
5. In the given figure, name the parts X, Y and Z. Also mention their functions.
If X is the Ovary:
- Function: Produces female gametes (eggs) and the hormones oestrogen and progesterone.
- If Y is the Fallopian Tube (Oviduct):
- Function: The site where fertilisation occurs. It carries the egg from the ovary to the uterus.
- If Z is the Uterus (Womb):
- Function: It is the site where the embryo implants and develops into a baby during pregnancy.
HIGHER ORDER THINKING SKILLS
1. What purpose does the tail in a sperm serve?
- The tail of a sperm, called a flagellum, acts like a propeller. It moves in a whip-like motion, providing motility (ability to move). This movement is crucial for the sperm to swim through the fluids of the female reproductive system, travel a long distance, and reach the egg for fertilisation.
2. Why do fish and frog lay eggs in hundreds, whereas a hen lays only one egg at a time?
- Fish and frogs practice external fertilisation (eggs are fertilised outside the body in water). Their eggs and young ones are exposed to many dangers like predators, water currents, and environmental changes. Producing hundreds of eggs increases the chance that at least a few will survive to adulthood.
- A hen practices internal fertilisation and lays protected eggs with hard shells. The parents also often provide care (like brooding). Since the chances of survival for each individual egg are much higher due to this protection and care, hens do not need to produce as many eggs. They lay one (or a few) well-protected egg(s) at a time.