CBSE Class 8 Science – Cell: Reproduction in Animals – CBSE NCERT Study Resources
All Question Types with Solutions – CBSE Exam Pattern
Explore a complete set of CBSE-style questions with detailed solutions, categorized by marks and question types. Ideal for exam preparation, revision and practice.
Very Short Answer (1 Mark) – with Solutions (CBSE Pattern)
These are 1-mark questions requiring direct, concise answers. Ideal for quick recall and concept clarity.
Fertilization is the process where the male gamete (sperm) fuses with the female gamete (egg) to form a zygote. This is the first step in the development of a new organism.
The two types of reproduction in animals are:
1. Asexual reproduction (e.g., budding in Hydra)
2. Sexual reproduction (e.g., humans, birds)
The testes produce sperm (male gametes) and secrete the hormone testosterone, which regulates male reproductive functions.
Binary fission involves splitting of a parent organism into two identical daughter cells (e.g., Amoeba).
Budding involves a small outgrowth (bud) developing into a new organism, which may detach (e.g., Hydra).
Reproduction ensures the continuation of species by producing offspring. It maintains genetic diversity and helps in evolution.
The ovary produces eggs (ova) and secretes hormones like estrogen and progesterone, which regulate the menstrual cycle and pregnancy.
Frogs exhibit external fertilization, where eggs and sperm fuse outside the female's body, usually in water.
A zygote is the single-celled structure formed after the fusion of sperm and egg during fertilization. It develops into an embryo.
Internal fertilization protects gametes from environmental hazards (e.g., dehydration) and increases the chances of successful reproduction in land animals.
Metamorphosis is the process of transformation from larva to adult (e.g., tadpole to frog). It involves distinct stages like egg, larva, pupa, and adult.
Hydra reproduces by budding, where a small outgrowth develops into a new organism and detaches from the parent.
Birds lay eggs with hard shells to protect the developing embryo from physical damage and dehydration in terrestrial environments.
Very Short Answer (2 Marks) – with Solutions (CBSE Pattern)
These 2-mark questions test key concepts in a brief format. Answers are expected to be accurate and slightly descriptive.
The testes produce sperm and the hormone testosterone, which regulates male reproductive functions and secondary sexual characteristics.
- Oviparous animals lay eggs (e.g., birds, reptiles).
- Viviparous animals give birth to live young (e.g., humans, cows).
Metamorphosis is the transformation of a larva into an adult through distinct stages (e.g., tadpole to frog).
Example: Butterfly life cycle (egg → larva → pupa → adult).
The uterus is where the embryo implants and develops into a foetus. It provides nourishment and protection during pregnancy.
In binary fission, the amoeba's nucleus divides first.
Then, the cytoplasm splits, forming two identical daughter cells.
Male gamete: Sperm
Female gamete: Ovum (egg)
Budding is asexual reproduction where a new organism grows as an outgrowth of the parent.
Example: Hydra or yeast.
In external fertilization, sperm and egg unite outside the body, usually in water.
Example: Fish and frogs release gametes into water for fertilization.
Short Answer (3 Marks) – with Solutions (CBSE Pattern)
These 3-mark questions require brief explanations and help assess understanding and application of concepts.
Fertilization is the fusion of a male sperm and a female ovum to form a zygote.
1. The sperm enters the female reproductive tract and swims towards the ovum in the fallopian tube.
2. The sperm penetrates the outer layer of the ovum using enzymes.
3. The nuclei of the sperm and ovum fuse, forming a zygote.
Diagram: A labeled sketch showing sperm meeting the ovum in the fallopian tube, with arrows indicating fusion.
Internal fertilization occurs inside the female body (e.g., humans, cows).
External fertilization occurs outside the body, usually in water (e.g., frogs, fish).
- Internal: Higher chance of survival, fewer offspring.
- External: Requires water, many offspring produced.
The placenta is a temporary organ that:
1. Supplies oxygen and nutrients from the mother to the embryo.
2. Removes waste like carbon dioxide from the embryo.
3. Acts as a barrier to prevent harmful substances, though some may pass through.
Metamorphosis is the transformation of a larva into an adult through distinct stages.
Example: Frogs (tadpole → adult frog).
- Egg → Tadpole (aquatic, gills)
- Tadpole → Froglet (develops legs)
- Froglet → Adult (lungs, terrestrial)
Binary fission: Parent cell divides into two identical daughter cells (e.g., Amoeba).
Budding: A small outgrowth forms on the parent and detaches (e.g., Hydra).
- Binary fission: Equal division.
- Budding: Unequal division.
Reproduction ensures:
1. Continuity of species by producing new individuals.
2. Genetic variation (in sexual reproduction) for adaptation and evolution.
Without reproduction, species would become extinct.
Fertilization is the fusion of male (sperm) and female (ovum) gametes to form a zygote.
During sexual intercourse, sperm is deposited in the female reproductive tract.
The sperm swims towards the ovum in the fallopian tube.
Only one sperm penetrates the ovum's outer layer, leading to fusion of their nuclei.
This forms a diploid zygote, which later develops into an embryo.
Metamorphosis is the transformation from larva (tadpole) to adult frog.
Stages: Egg → Tadpole → Adult.
Tadpoles live in water, breathe through gills, and feed on algae.
During metamorphosis, they develop lungs, limbs, and lose their tails.
This adaptation allows frogs to live both in water and on land.
- Binary fission: Parent cell divides into two identical daughter cells (e.g., Amoeba).
- Budding: A small outgrowth forms on the parent and detaches (e.g., Hydra).
Binary fission is symmetric, while budding is asymmetric.
The testes produce sperm, which require a temperature 2-3°C lower than body temperature.
Being outside the abdomen in the scrotum helps regulate this temperature.
Higher temperatures inside the body would damage sperm production.
Viviparous animals give birth to live young (e.g., humans, dogs).
Oviparous animals lay eggs (e.g., birds, reptiles).
- Viviparous: Embryo develops inside the mother, receiving nutrients directly.
- Oviparous: Embryo develops outside, relying on yolk for nourishment.
Long Answer (5 Marks) – with Solutions (CBSE Pattern)
These 5-mark questions are descriptive and require detailed, structured answers with proper explanation and examples.
Fertilization is the fusion of male and female gametes to form a zygote. In humans, it occurs internally.
Process Explanation- Sperm enters the female reproductive tract during mating.
- It travels to the fallopian tube, where it meets the egg.
- The nuclei fuse, forming a zygote.
Unlike humans, frogs exhibit external fertilization where eggs and sperm unite outside the body, as shown in our NCERT textbook.
Diagram[Diagram: Human fertilization process in the fallopian tube]
Metamorphosis is the transformation of a larva into an adult through distinct stages.
Process Explanation- Frog eggs hatch into tadpoles with gills.
- Tadpoles develop legs and lungs.
- They become adult frogs, losing their tails.
This adaptation helps frogs survive in both water (as tadpoles) and land (as adults), as explained in our NCERT chapter.
Diagram[Diagram: Lifecycle of a frog showing egg, tadpole, and adult stages]
Asexual reproduction involves one parent, while sexual requires two.
Process Explanation- Asexual: Hydra reproduces by budding, creating clones.
- Sexual: Humans produce offspring through gamete fusion.
Asexual reproduction is faster but lacks genetic diversity, whereas sexual reproduction ensures variation, as seen in NCERT examples.
Diagram[Diagram: Budding in Hydra vs. human reproductive system]
Viviparous animals give birth to live young, while oviparous lay eggs.
Process Explanation- Viviparous: Humans and cows nurture embryos internally.
- Oviparous: Birds and frogs lay eggs externally.
Viviparous offspring have higher survival rates, as seen in NCERT’s comparison of mammals and reptiles.
Diagram[Diagram: Human uterus vs. bird egg structure]
Testes produce sperm, and ovaries produce eggs, both essential for reproduction.
Process Explanation- Testes: Located in males, they secrete testosterone.
- Ovaries: In females, they release eggs monthly.
Our NCERT textbook shows how these organs ensure genetic continuity in species like humans and dogs.
Diagram[Diagram: Labeled male (testes) and female (ovaries) reproductive organs]
Binary fission is asexual reproduction where a parent cell divides into two identical daughter cells.
Process Explanation
- The nucleus splits first, followed by cytoplasm.
- It occurs in organisms like Amoeba, as shown in our textbook.
Real-world Application
This method allows rapid population growth, useful for bacteria in decomposing waste, similar to the NCERT example of yeast.
Diagram
[Diagram: Binary fission in Amoeba]
Viviparous animals give birth to live young, while oviparous lay eggs.
Process Explanation
- Humans (viviparous) nourish embryos internally.
- Birds (oviparous) lay hard-shelled eggs, as per NCERT.
Real-world Application
Viviparity in mammals ensures better protection and nutrition, like in cows, compared to external egg development in lizards.
Diagram
[Diagram: Comparison of viviparous and oviparous development]
Budding is asexual reproduction where a new organism grows from the parent's body.
Process Explanation
- A small outgrowth forms on Hydra’s body.
- It detaches to become independent, as shown in NCERT.
Real-world Application
This method allows quick reproduction without mates, similar to yeast used in baking.
Diagram
[Diagram: Budding process in Hydra]
Binary fission is an asexual reproduction method where a parent cell divides into two identical daughter cells.
Process Explanation- Amoeba’s nucleus divides first.
- Cytoplasm splits, forming two new cells.
This process allows rapid multiplication, as seen in NCERT’s example of Amoeba in pond water. It ensures survival in favorable conditions.
Diagram[Diagram: Amoeba undergoing binary fission with labeled nucleus and cytoplasm division]
Viviparous animals give birth to live young, while oviparous animals lay eggs.
Process Explanation- Humans (viviparous) nurture embryos internally.
- Birds (oviparous) lay eggs with hard shells.
Our textbook shows hens as oviparous, while dogs are viviparous. Viviparous animals provide better protection to offspring.
Metamorphosis is the transformation of a larva into an adult through distinct stages.
Process Explanation- Egg → Tadpole → Froglet → Adult frog.
- Tadpoles have gills; adults develop lungs.
NCERT’s frog example shows how tadpoles adapt to water, while adults live on land. This ensures species survival in different habitats.
Budding is asexual reproduction where a new organism grows from an outgrowth of the parent.
Process Explanation- A small bud forms on Hydra’s body.
- It detaches and grows into a new Hydra.
Our textbook shows Hydra budding in freshwater. It allows quick reproduction without a mate.
Diagram[Diagram: Hydra with a bud forming and detaching]
Fertilization is the process where the male sperm fuses with the female ovum to form a zygote. Here's how it happens:
1. During sexual intercourse, sperm are released into the female reproductive tract.
2. The sperm swim through the cervix and uterus to reach the fallopian tube.
3. If an ovum is present in the fallopian tube, one sperm penetrates its outer layer.
4. The nuclei of the sperm and ovum fuse, combining their genetic material.
This fusion forms the zygote, which is the first cell of a new organism. The zygote then undergoes repeated divisions to form an embryo.
Diagram: (Draw a labeled diagram showing sperm entering the ovum in the fallopian tube, with labels for sperm, ovum, nucleus, and zygote formation.)
Additional Information: Fertilization ensures genetic variation as the zygote inherits traits from both parents. It usually occurs in the ampulla of the fallopian tube.
Asexual Reproduction:
1. Involves only one parent.
2. No fusion of gametes occurs.
3. Offspring are genetically identical (clones) to the parent.
4. Examples: Budding in Hydra, Binary fission in Amoeba.
Sexual Reproduction:
1. Involves two parents (male and female).
2. Fusion of male and female gametes (fertilization) occurs.
3. Offspring have genetic variation.
4. Examples: Humans, dogs, birds.
Comparison:
- Asexual is faster but lacks diversity; sexual is slower but promotes adaptation.
- Asexual doesn’t require mates; sexual does.
Additional Information: Some organisms like sponges can reproduce both ways. Sexual reproduction is crucial for evolution as it introduces new gene combinations.
Fertilization in humans is an internal process where the male gamete (sperm) fuses with the female gamete (ovum) inside the female's body. Here's how it occurs:
1. During copulation, sperm is deposited in the female reproductive tract.
2. The sperm swims through the cervix and uterus to reach the fallopian tube.
3. If an ovum is present, one sperm penetrates its outer layer, leading to fusion of nuclei.
4. This forms a zygote, which later develops into an embryo.
Differences from external fertilization (frogs):
- In frogs, fertilization occurs outside the body in water.
- Both male and female release gametes simultaneously, requiring water as a medium.
- No direct physical contact is needed, unlike humans.
(Diagram: A labeled sketch showing sperm entering the ovum in the fallopian tube, with annotations for zygote formation.)
Metamorphosis in frogs is a biological process where they undergo drastic physical changes from the larval stage to adulthood. The stages are:
- Egg: Laid in water, protected by jelly-like substance.
- Tadpole: Hatches from egg, breathes through gills, and has a tail for swimming.
- Froglet: Develops hind legs, then front legs; tail shortens.
- Adult frog: Loses tail, develops lungs for land respiration, and becomes carnivorous.
Importance for survival:
Metamorphosis allows frogs to adapt from aquatic to terrestrial life. Tadpoles feed on algae, while adult frogs control insect populations, maintaining ecological balance.
Comparison with human development:
- Humans do not undergo metamorphosis; development is gradual inside the mother's womb.
- Frog eggs are vulnerable externally, while human embryos are protected internally.
- Human babies resemble adults in body structure, unlike tadpoles which look entirely different from frogs.
Metamorphosis is the transformation of a larva into an adult through distinct stages. In frogs, it occurs as follows:
1. Egg Stage: Fertilized eggs are laid in water as jelly-like masses.
2. Tadpole Stage: Hatched larvae have gills and tails for swimming.
3. Growth Stage: Hind legs develop first, followed by forelegs; gills are replaced by lungs.
4. Adult Stage: Tail is absorbed, and the frog becomes land-adapted.
Importance for survival:
- Prevents competition for resources between young and adults (tadpoles eat algae; adults eat insects).
- Adapts to both aquatic and terrestrial habitats, increasing survival chances.
- Reduces predation risk by occupying different niches at different stages.
Fertilization is the process where the male sperm fuses with the female ovum (egg) to form a zygote, which eventually develops into an embryo. Here’s how it occurs:
1. Sperm Entry: During sexual intercourse, millions of sperm are released into the female reproductive tract. They travel through the vagina, uterus, and reach the fallopian tube where the ovum is present.
2. Fusion of Gametes: Only one sperm successfully penetrates the outer layer of the ovum, leading to the fusion of their nuclei. This forms the zygote, which contains genetic material from both parents.
3. Zygote Formation: The zygote begins dividing through mitosis as it moves toward the uterus for implantation.
Importance: Fertilization ensures genetic diversity by combining traits from both parents. It also marks the beginning of a new life, initiating embryonic development.
Diagram: (Draw a labeled diagram showing sperm entering the ovum in the fallopian tube, with labels for sperm, ovum, zygote, and fallopian tube.)
Asexual Reproduction involves a single parent and produces genetically identical offspring. Examples include budding in hydra and binary fission in amoeba.
Sexual Reproduction involves two parents (male and female) and results in offspring with genetic variation. Examples include humans, dogs, and birds.
Comparison:
- Number of Parents: Asexual – 1; Sexual – 2
- Genetic Variation: Asexual – None; Sexual – High
- Speed: Asexual – Faster; Sexual – Slower
Advantage of Sexual Reproduction: It promotes genetic diversity, which helps species adapt to changing environments and resist diseases. This diversity is crucial for evolution, as it allows natural selection to favor beneficial traits.
Fertilization is the fusion of a male sperm and a female ovum (egg) to form a zygote. In humans, this process occurs in the fallopian tube of the female reproductive system. Here’s how it happens:
- The sperm enters the female body during mating and travels through the vagina, uterus, and finally reaches the fallopian tube.
- If an ovum is present in the fallopian tube, one sperm penetrates its outer layer, leading to fertilization.
- The nuclei of the sperm and ovum fuse, forming a single-celled zygote.
After fertilization, the zygote undergoes multiple rounds of cell division (mitosis) as it moves toward the uterus. This forms a morula, which further develops into a blastocyst. The blastocyst attaches to the uterine wall (implantation) and differentiates into an embryo.
Development of Zygote to Embryo:
1. The zygote divides repeatedly to form a ball of cells.
2. These cells organize into layers, forming the embryonic disc.
3. The outer layer becomes the placenta, while the inner layers develop into the embryo.
4. By the 8th week, major organs begin forming, marking the transition from embryo to fetus.
(Diagram: A labeled illustration of fertilization in the fallopian tube and zygote development stages.)
Asexual Reproduction:
In asexual reproduction, a single parent produces offspring without the involvement of gametes. Examples include budding in Hydra and binary fission in Amoeba.
Advantages:
1. Faster process, allowing quick population growth.
2. No need for a mate, useful in isolated environments.
3. Offspring are genetically identical (clones), preserving favorable traits.
Sexual Reproduction:
In sexual reproduction, two parents (male and female) contribute gametes to form a zygote. Examples include humans, birds, and most mammals.
Advantages:
1. Genetic variation due to the mixing of traits, increasing adaptability.
2. Better survival chances in changing environments.
3. Elimination of harmful mutations through recombination.
Comparison:
- Number of Parents: Asexual (1), Sexual (2).
- Genetic Variation: Asexual (none), Sexual (high).
- Speed: Asexual (faster), Sexual (slower due to mating and gestation).
Both methods ensure species survival but under different conditions.
Fertilization is the process where the male sperm fuses with the female ovum (egg) to form a zygote. In humans, this occurs in the fallopian tube of the female reproductive system.
Steps of Fertilization:
1. The sperm travels through the vagina, uterus, and reaches the fallopian tube.
2. Only one sperm successfully penetrates the outer layer of the ovum.
3. The nuclei of the sperm and ovum fuse, forming a zygote.
Development of Zygote into Embryo:
1. The zygote undergoes repeated cell divisions (mitosis) to form a blastocyst.
2. The blastocyst implants itself into the uterus lining (endometrium).
3. Over time, specialized cells form the placenta and embryo.
4. The embryo develops organs and grows into a fetus.
Labeled Diagram: (Draw a simple diagram showing sperm entering the ovum in the fallopian tube, zygote formation, and implantation in the uterus.)
Asexual Reproduction:
1. Involves a single parent.
2. Offspring are genetically identical (clones).
3. Examples: Budding in Hydra, Binary fission in Amoeba.
Sexual Reproduction:
1. Involves two parents (male and female).
2. Offspring have genetic variation.
3. Examples: Humans, dogs, birds.
Why Sexual Reproduction Creates Genetic Diversity:
1. During meiosis, gametes (sperm and egg) receive half the genetic material.
2. Fertilization combines genes from both parents, creating unique combinations.
3. Crossing over and random assortment of chromosomes increase variation.
Comparison Table: (Create a table with columns for Asexual and Sexual Reproduction, comparing features like number of parents, genetic variation, and examples.)
Case-based Questions (4 Marks) – with Solutions (CBSE Pattern)
These 4-mark case-based questions assess analytical skills through real-life scenarios. Answers must be based on the case study provided.
Farmers noticed frog eggs in ponds, with only some developing into tadpoles.
Scientific Principle
In external fertilization, eggs and sperm meet outside the body (e.g., frogs, fish). Environmental factors like water temperature or predators may prevent development.
Solution Approach
- Unlike internal fertilization (e.g., humans), external fertilization depends on external conditions.
- Our textbook shows that only a few eggs survive to ensure species continuity.
Rahul observed hydra reproducing by budding.
Scientific Principle
In budding, a new organism grows from the parent (e.g., hydra), while binary fission splits the parent into two (e.g., Amoeba).
Solution Approach
- Both are asexual methods, but budding is unequal division.
- Advantage: Faster population growth, as seen in yeast (NCERT example).
Zebra (live birth) and snake (egg-laying) show different reproductive modes.
Scientific Principle
Viviparous (zebra) give birth to young ones, while oviparous (snake) lay eggs.
Solution Approach
- Zebra: Protection inside mother’s body (NCERT example).
- Snake: Eggshell protects embryo, as seen in birds.
Butterflies lay eggs, leading to caterpillars.
Scientific Principle
This is the larval stage of complete metamorphosis (egg → larva → pupa → adult).
Solution Approach
- Frogs undergo incomplete metamorphosis (egg → tadpole → adult).
- Our textbook shows butterflies transform entirely, unlike frogs retaining some features.
Farmers noticed frog eggs in ponds, with varying survival rates due to external fertilization.
Scientific Principle- Frogs release eggs/sperm in water, making fertilization external.
- Eggs may not survive due to predators or environmental factors.
Unlike cows (internal fertilization), frogs lack protection for eggs. Our textbook shows cows nurture embryos internally, ensuring higher survival.
Butterflies lay many eggs, while dogs give birth to fewer offspring.
Scientific Principle- Butterflies use oviparous reproduction (eggs hatch outside).
- Dogs are viviparous, nurturing young internally.
Butterflies need more eggs as external threats (birds, weather) reduce survival. Our textbook shows puppies get parental care, needing fewer births.
Students compared Amoeba (binary fission) and Hydra (budding).
Scientific Principle| Process | Parent Involvement | Offspring Count |
|---|---|---|
| Binary Fission | Parent splits completely | 2 identical cells |
| Budding | Parent remains intact | 1+ buds |
NCERT shows Amoeba divides equally, while Hydra grows buds detached later.
Hen eggs need warmth to develop, unlike mammal embryos.
Scientific Principle- Birds rely on external heat (incubation) for embryo growth.
- Mammals regulate temperature internally.
Our textbook shows hens depend on parents/artificial heat. Mammals like humans maintain body heat, protecting embryos.
Scientific Principle: Different modes of reproduction.
Explain why frogs use external fertilization and cows do not.
Scientific Principle: External fertilization needs water, but internal fertilization protects embryos.
Solution Approach:
- Frogs: Eggs fertilized outside, as water prevents drying (NCERT example).
- Cows: Internal fertilization ensures embryo safety (real-world application).
Our textbook shows water-dependent species use external fertilization for survival.
Scientific Principle: Asexual vs. sexual reproduction.
Compare the two methods using NCERT examples.
Scientific Principle: Budding creates clones; sexual reproduction brings variation.
Solution Approach:
- Yeast: Fast reproduction (NCERT example).
- Dogs: Genetic diversity (real-world application).
We studied that asexual methods lack variation, unlike sexual reproduction.
Scientific Principle: Embryo development differences.
Why do lions need viviparity?
Scientific Principle: Viviparity protects young, while oviparity relies on eggs.
Solution Approach:
- Lions: Internal development ensures safety (NCERT example).
- Snakes: Eggs adapt to environment (real-world application).
Our textbook shows mammals use viviparity for better survival rates.
Scientific Principle: Lifecycle stages.
How does metamorphosis help butterflies?
Scientific Principle: Metamorphosis adapts species to different needs.
Solution Approach:
- Butterflies: Larva eats leaves, adult pollinates (NCERT example).
- Humans: No metamorphosis as needs stay similar (real-world application).
We studied that metamorphosis maximizes resource use in insects.
(a) Why do frogs lay so many eggs?
(b) What is the term used for the process of fertilization in frogs?
(c) How does the development of a tadpole into an adult frog showcase metamorphosis?
(a) Frogs lay hundreds of eggs because they undergo external fertilization, where eggs and sperm meet outside the body. Many eggs are eaten by predators or get destroyed due to environmental factors, so producing a large number increases the chances of survival for at least a few.
(b) The process of fertilization in frogs is called external fertilization, as it occurs outside the female's body in water.
(c) The development of a tadpole into an adult frog is an example of metamorphosis because the tadpole undergoes drastic changes:
- It starts as an aquatic larva with gills and a tail.
- Over time, it develops lungs for breathing air, limbs for movement on land, and loses its tail.
- This transformation allows the frog to adapt from an aquatic to a terrestrial lifestyle.
(a) Why do some eggs not develop into chicks?
(b) What is the difference between fertilized and unfertilized eggs in hens?
(c) Explain the role of incubation in the hatching process.
(a) Some eggs do not develop into chicks because they are unfertilized, meaning they were not fertilized by a rooster's sperm. Only fertilized eggs can develop into chicks under proper conditions.
(b) The differences are:
- Fertilized eggs contain a developing embryo and can hatch into chicks if incubated.
- Unfertilized eggs do not contain an embryo and will never hatch; these are the eggs commonly used for eating.
(c) Incubation is crucial because:
- It provides the right temperature (around 37.5°C) and humidity for the embryo to grow.
- Turning the eggs regularly ensures even heat distribution and prevents the embryo from sticking to the shell.
- Without proper incubation, even fertilized eggs will not hatch.
(a) Why do frogs lay so many eggs?
(b) What is the term used for the process of transformation from egg to adult frog?
(c) How does this process differ from reproduction in mammals?
(a) Frogs lay hundreds of eggs to increase the chances of survival. Since the eggs are exposed to predators and environmental conditions, many may not survive. Producing a large number ensures that at least some will develop into adults.
(b) The process of transformation from egg to adult frog is called metamorphosis. It involves distinct stages: egg → tadpole (larva) → adult frog.
(c) Unlike frogs, mammals give birth to live young ones (viviparous) and do not undergo metamorphosis. Mammals also provide parental care, increasing the survival rate of their offspring, whereas frogs do not.
(a) A hydra budding to form a new hydra.
(b) A hen laying fertilized eggs that hatch into chicks.
Compare these two modes of reproduction based on:
(i) Type of reproduction
(ii) Genetic similarity between parent and offspring
(iii) Examples of other animals using these methods
(i) Type of reproduction:
Hydra reproduces by asexual reproduction (budding), where a new organism grows out of the parent's body.
Hen reproduces by sexual reproduction, involving fertilization of an egg by sperm.
(ii) Genetic similarity:
In budding, the offspring is genetically identical to the parent (clone).
In sexual reproduction, the offspring has genetic material from both parents, making it unique.
(iii) Examples:
- Asexual reproduction: Yeast, Amoeba
- Sexual reproduction: Humans, Dogs
(a) Why do frogs lay so many eggs?
(b) What is the term used for the process of transformation from egg to adult frog?
(a) Frogs lay hundreds of eggs because external fertilization occurs in water, where many eggs may not get fertilized or may be eaten by predators. Survival rate is low, so producing more eggs ensures at least some offspring survive.
(b) The process of transformation from egg to adult frog is called metamorphosis. It involves distinct stages:
- Egg → Tadpole (larva) → Adult frog.
(a) What is the key difference between the reproduction methods of dogs and hens?
(b) Why do some animals lay eggs while others give birth to young ones?
(a) The key difference is that dogs show viviparous reproduction (giving birth to live young), while hens are oviparous (laying eggs). In viviparous animals, the embryo develops inside the mother's body.
(b) Animals lay eggs or give birth based on their evolutionary adaptations.
- Oviparous animals (like birds) lay eggs to protect the developing embryo in a hard shell.
- Viviparous animals (like mammals) provide better nourishment and safety by retaining the embryo internally.
(a) Why do frogs lay so many eggs?
(b) What is the significance of this reproductive strategy?
(a) Frogs lay hundreds of eggs because they exhibit external fertilization, where eggs are fertilized outside the female's body.
This process is highly unpredictable, and many eggs may not get fertilized or may be eaten by predators.
Additionally, the survival rate of tadpoles is low due to environmental factors like water pollution, lack of food, or predators.
(b) The significance of this reproductive strategy is to ensure the continuation of the species despite high mortality rates.
By producing a large number of eggs, frogs increase the chances that at least a few offspring will survive to adulthood.
This is an example of r-selection, where organisms produce many offspring with minimal parental care to maximize survival in unstable environments.
(a) Name these stages in the correct sequence.
(b) Explain why this type of reproduction is called metamorphosis.
(a) The four stages in the life cycle of a butterfly are:
- Egg
- Larva (caterpillar)
- Pupa (chrysalis)
- Adult butterfly
(b) This process is called metamorphosis because the butterfly undergoes a complete transformation in body structure and function at each stage.
For example, the caterpillar (larva) looks entirely different from the adult butterfly and has different feeding habits.
During the pupa stage, the caterpillar's body breaks down and reorganizes into a completely new form.
This drastic change is why it is termed metamorphosis, derived from Greek words meaning 'change of form.'
(i) Why do frogs lay so many eggs?
(ii) What is the advantage of external fertilization in frogs?
(i) Frogs lay hundreds of eggs because external fertilization (fertilization outside the body) is less efficient, and many eggs may not get fertilized or survive due to environmental factors like predators, water currents, or lack of nutrients. Producing a large number of eggs increases the chances of at least a few developing into adults.
(ii) The advantage of external fertilization in frogs is that it allows a large number of eggs to be fertilized at once, increasing genetic diversity. It also does not require complex reproductive structures, making it energy-efficient for the parents. However, it requires a water medium for sperm to swim and reach the eggs.
(i) How can the farmer distinguish between fertilized and unfertilized eggs?
(ii) What is the role of the yolk in the development of a chick?
(i) The farmer can distinguish between fertilized and unfertilized eggs by candling (holding the egg against a bright light). A fertilized egg will show tiny blood vessels or a dark spot (embryo), while an unfertilized egg appears clear.
(ii) The yolk acts as the primary source of nutrition for the developing chick. It provides proteins, fats, and vitamins required for growth. The yolk is absorbed by the embryo as it develops inside the egg.
(a) Why do frogs lay so many eggs?
(b) What is the term used for the process of fusion of male and female gametes in frogs?
(c) How does this process differ from internal fertilization?
(a) Frogs lay hundreds of eggs because external fertilization occurs in water, where many eggs may not get fertilized or may be eaten by predators. Producing a large number of eggs increases the chances of survival for at least a few offspring.
(b) The fusion of male and female gametes in frogs is called fertilization, specifically external fertilization as it happens outside the body in water.
(c) In external fertilization, the fusion of gametes occurs outside the body (e.g., in water), while in internal fertilization, the fusion happens inside the female's body (e.g., humans, cows). Internal fertilization provides better protection to the developing embryo.
(a) Why do dogs give birth to young ones while parrots lay eggs?
(b) Name the reproductive method in dogs and parrots.
(c) How does the development of the embryo differ in these two animals?
(a) Dogs are mammals and undergo viviparous reproduction, where the embryo develops inside the mother's body, leading to live birth. Parrots are birds and follow oviparous reproduction, where they lay eggs that hatch outside the body.
(b) Dogs reproduce through vivipary, while parrots reproduce through ovipary.
(c) In dogs, the embryo develops inside the mother's uterus, receiving nutrients directly from her. In parrots, the embryo develops inside a hard-shelled egg, relying on the yolk for nourishment until hatching.