Reproduction in Animals Class 8 Important Questions with Solutions: Free PDF Download
FAQs on Important Questions for CBSE Class 8 Science Chapter 6 - Reproduction in Animals
1. What are the key differences between sexual and asexual reproduction? Which is considered more advantageous for species survival and why?
For your exams, it's important to differentiate between sexual and asexual reproduction on these key points:
- Parents Involved: Asexual reproduction involves only one parent, while sexual reproduction requires two parents (a male and a female).
- Gamete Fusion: There is no fusion of gametes in asexual reproduction. Sexual reproduction is defined by the fusion of male and female gametes.
- Offspring Genetics: Offspring from asexual reproduction are genetically identical to the parent. In contrast, offspring from sexual reproduction have a mix of genetic material from both parents, leading to variation.
Sexual reproduction is generally considered more advantageous for the long-term survival of a species because the genetic variation it creates allows the species to better adapt to changing environments.
2. Explain the difference between oviparous and viviparous animals, providing two examples for each category.
This is a frequently asked question. The primary difference lies in how the young ones develop:
- Oviparous animals: These are animals that lay eggs. The embryo develops outside the mother’s body, inside the egg, which provides nourishment. After a period of incubation, the young one hatches. Examples: Hen, frog, lizard, and most fish.
- Viviparous animals: These are animals that give birth to live young. The embryo develops inside the mother's body, receiving nourishment directly from her. Examples: Humans, dogs, cats, and cows.
3. A hen lays a hard-shelled egg, but a frog lays a mass of eggs without shells in water. What is the biological reason for this difference?
This is a Higher Order Thinking Skills (HOTS) question. The reason is linked to their mode of fertilisation:
- Hen (Internal Fertilisation): In a hen, the egg is fertilised inside the female's body. The hard shell is then formed around the fertilised egg (zygote) to protect it from predators and prevent it from drying out after it is laid on land.
- Frog (External Fertilisation): In a frog, fertilisation occurs outside the female's body, in water. The female releases her eggs (ova) into the water, and the male releases sperm over them. A hard shell would prevent the sperm from reaching and fertilising the eggs. The jelly-like layer around the frog's eggs holds them together and offers some protection in their aquatic environment.
4. What is metamorphosis? Describe the stages in the life cycle of a frog to illustrate this process.
Metamorphosis is the biological process of transformation from an immature form (larva) to an adult form in two or more distinct stages. It involves drastic changes in the organism's body structure.
The life cycle of a frog is a classic example expected in exams:
- Stage 1: Egg - The female frog lays eggs in water.
- Stage 2: Tadpole (Larva) - The egg hatches into a tadpole. A tadpole lives in water, breathes through gills, and has a tail for swimming, resembling a fish.
- Stage 3: Froglet - The tadpole gradually develops legs, its tail shortens, and lungs begin to form.
- Stage 4: Adult Frog - The tail disappears completely, and the froglet transforms into an adult frog that can live on land and breathe through lungs.
5. Why do male animals produce millions of sperm when only one is required to fertilise an ovum?
This is a conceptual question that tests your understanding of the fertilisation process. Millions of sperm are produced to ensure the success of fertilisation because the journey to the ovum is very challenging. Many sperm are lost or destroyed on the way due to:
- The acidic environment of the female reproductive tract.
- The long distance they must travel to reach the ovum.
- Many failing to find the correct path to the fallopian tube.
Producing a massive number of sperm drastically increases the probability that at least one sperm will successfully survive the journey and fertilise the egg.
6. Describe the process of fertilisation in humans and state where the embryo gets implanted.
Fertilisation in humans is the fusion of the male gamete (sperm) with the female gamete (ovum or egg). Here's the step-by-step process:
- Sperm are deposited into the female reproductive tract.
- They travel towards the fallopian tube (oviduct).
- If an ovum is present in the fallopian tube, one sperm fuses with it.
- This fusion results in the formation of a single cell called the zygote. This marks the moment of fertilisation.
After fertilisation, the zygote begins to divide repeatedly to form a ball of cells, becoming an embryo. The embryo then travels down the fallopian tube and gets implanted in the thick lining of the uterus, where it continues to develop.
7. A baby develops inside its mother's body, yet it inherits characteristics from both parents. How is this possible?
This is possible because the baby develops from a zygote. A zygote is the very first cell of a new individual and it is formed by the process of sexual reproduction. It contains genetic information from both parents:
- The sperm from the father carries his genetic material.
- The ovum (egg) from the mother carries her genetic material.
When the sperm and egg fuse during fertilisation, their genetic information combines. Therefore, the resulting zygote, and the baby that develops from it, has a unique combination of genes from both the father and the mother, leading to the inheritance of traits from both.
8. What is IVF, and in what situations might this medical technique be recommended?
IVF stands for In Vitro Fertilisation. It is a medical procedure where fertilisation occurs outside the body, in a laboratory setting ('in vitro' means 'in glass').
The process involves:
- Collecting freshly released eggs from the female and sperm from the male.
- Keeping them together in a controlled environment for a few hours to allow fertilisation to occur and a zygote to form.
- Once the zygote has developed into an early-stage embryo, it is placed in the mother's uterus for further development.
IVF is often recommended for couples who are unable to have children due to issues like blocked fallopian tubes in the female, which prevent the sperm from reaching the egg naturally.
