Solution:

Importance of Reproduction in Organisms

Reproduction is the biological process by which new individual organisms are produced from their parents. It plays a crucial role in the continuity of species. The importance of reproduction in organisms includes:

• Species Continuity: Reproduction ensures the survival of a species over generations. Without reproduction, species would face extinction.
• Genetic Diversity: Reproduction, especially sexual reproduction, allows for the mixing of genetic material. This creates genetic diversity, which is essential for the adaptation and survival of organisms in changing environments.
• Population Growth: Reproduction helps in increasing the population of a species, which is necessary for maintaining ecological balance.
• Evolution: Through reproduction, beneficial traits can be passed on to the next generation. Over time, this leads to evolution, helping organisms adapt to their environment.

Thus, reproduction is vital for the survival, growth, and development of species, contributing to the overall health and stability of ecosystems.

Solution:

Process of Fertilisation in Human Beings

Fertilisation in human beings is the process in which a male sperm and a female ovum (egg) combine to form a zygote. This process occurs in the fallopian tube.

1. Ovulation: The process begins when the female's ovary releases a mature ovum into the fallopian tube. This typically happens around the 14th day of the menstrual cycle.

2. Entry of Sperm: During sexual intercourse, millions of sperm are ejaculated into the female's reproductive tract. Only a few sperm reach the fallopian tube where fertilisation occurs.

3. Fertilisation: If one of the sperm meets the ovum in the fallopian tube, the sperm penetrates the egg's outer layer. The sperm's nucleus then fuses with the egg's nucleus, forming a zygote. This is called fertilisation.

4. Formation of Zygote: The fertilised egg (zygote) now contains a full set of chromosomes – half from the mother (egg) and half from the father (sperm). The zygote begins to divide and develop into an embryo.

5. Implantation: After several divisions, the embryo travels down the fallopian tube and enters the uterus, where it implants itself in the thickened uterine wall. This is the start of pregnancy.

Solution:

(a) Internal fertilisation occurs

(i) in female body. Correct

(ii) outside female body.

(iii) in male body.

(iv) outside male body.

(b) A tadpole develops into an adult frog by the process of

(i) fertilisation

(ii) metamorphosis Correct

(iii) embedding

(iv) budding

(c) The number of nuclei present in a zygote is

(i) none

(ii) one

(iii) two Correct

(iv) four

Solution:

(a) Oviparous animals give birth to young ones.

False (F)

(b) Each sperm is a single cell.

True (T)

(c) External fertilisation takes place in frog.

True (T)

(d) A new human individual develops from a cell called gamete.

False (F)

(e) Egg laid after fertilisation is made up of a single cell.

True (T)

(f) Amoeba reproduces by budding.

False (F)

(g) Fertilisation is necessary even in asexual reproduction.

False (F)

(h) Binary fission is a method of asexual reproduction.

True (T)

(i) A zygote is formed as a result of fertilisation.

True (T)

(j) An embryo is made up of a single cell.

False (F)

Solution:

Differences Between a Zygote and a Foetus

1. Definition: A zygote is the single cell formed by the fusion of a sperm and an egg during fertilization. A foetus is the developing organism after the embryonic stage, typically from the 9th week of pregnancy until birth.

2. Developmental Stage: A zygote undergoes rapid cell division and development into an embryo. A foetus has developed major organs and structures and is in the later stages of growth before birth.

Solution:

Asexual Reproduction

Asexual reproduction is a mode of reproduction in which only one parent is involved. The offspring produced are genetically identical to the parent, as there is no fusion of gametes.

Methods of Asexual Reproduction in Animals

1. Binary Fission: Binary fission is a method of asexual reproduction in unicellular organisms like amoeba and bacteria. In this process, the organism divides into two equal parts, each becoming a new individual. The parent cell divides its genetic material equally between the two new cells. It is commonly seen in protozoa and bacteria.

2. Budding: Budding is a type of asexual reproduction in which a new organism develops as a small outgrowth or bud from the parent organism. This bud gradually grows, detaches, and becomes an independent individual. Budding is seen in organisms like hydra and yeast.

Solution:

In which female reproductive organ does the embryo get embedded?

The embryo gets embedded in the $uterus$ of the female reproductive system.

Solution:

What is Metamorphosis? Give Examples

Metamorphosis is the process by which an organism undergoes a significant change in its form and structure during its life cycle. This transformation usually involves a series of stages, including a larval or immature stage, a pupal or resting stage, and the final adult stage.

There are two main types of metamorphosis:

• Complete Metamorphosis: In this type, the organism goes through four stages: egg, larva, pupa, and adult. Examples include the butterfly, moth, and frog.
• Incomplete Metamorphosis: In this type, the organism goes through three stages: egg, nymph, and adult. Examples include the grasshopper, cockroach, and dragonfly.

Solution:

Difference between Internal Fertilisation and External Fertilisation

Internal Fertilisation:

• Fertilisation occurs inside the female's body.
• Involves the fusion of male and female gametes within the reproductive tract of the female.
• Occurs in many animals like mammals, birds, and reptiles.
• Generally results in fewer offspring, but the chances of survival are higher.
• Protection of the fertilised egg is provided inside the mother's body.

External Fertilisation:

• Fertilisation occurs outside the female's body, usually in water.
• Male and female gametes are released into the surrounding environment, where fertilisation takes place.
• Occurs in many aquatic animals like fish and amphibians.
• Results in a large number of offspring, but the chances of survival are lower due to environmental factors.
• The fertilised egg is exposed to the external environment and is often vulnerable to predation.

Solution:

Across

Down