Online Self Test
Learn & Practice Quizzes & Challenges Competitive Exams
 

Reproduction in Organisms – CBSE NCERT Study Resources

Next Chapter
Previous Chapter Next Chapter

Study Materials

12th

12th - Biology

Reproduction in Organisms

Jump to Question Sets

Overview of the Chapter

This chapter explores the fundamental concepts of reproduction in organisms, covering both asexual and sexual modes of reproduction. It explains how reproduction ensures the continuity of species and discusses various reproductive strategies adopted by different organisms.

Types of Reproduction

Asexual Reproduction: A mode of reproduction where offspring arise from a single parent, inheriting identical genetic material. Common methods include binary fission, budding, and vegetative propagation.

Sexual Reproduction: Involves the fusion of male and female gametes, leading to genetic variation in offspring. It includes processes like fertilization and meiosis.

Asexual Reproduction Methods

  • Binary Fission: Seen in unicellular organisms like Amoeba, where the parent cell divides into two identical daughter cells.
  • Budding: Observed in yeast and Hydra, where a new organism develops as an outgrowth from the parent.
  • Vegetative Propagation: Occurs in plants through structures like runners, tubers, and bulbs (e.g., potato, ginger).

Sexual Reproduction in Plants

Flowering plants reproduce sexually through flowers, which contain male (stamen) and female (pistil) reproductive structures. Pollination leads to fertilization, forming seeds and fruits.

Sexual Reproduction in Animals

Animals exhibit various reproductive strategies, including external fertilization (e.g., fish, amphibians) and internal fertilization (e.g., reptiles, birds, mammals).

Significance of Reproduction

  • Ensures species survival.
  • Introduces genetic diversity through sexual reproduction.
  • Helps in adaptation and evolution.

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.

Question 1:
Define binary fission in organisms.
Answer:
Definition: Asexual reproduction where parent divides into two equal daughter cells.
Question 2:
Name the process of gamete formation in animals.
Answer:
Definition: Gametogenesis (spermatogenesis/oogenesis).
Question 3:
What is parthenogenesis? Give one example.
Answer:

Asexual reproduction from unfertilized eggs. Example: Honeybee drones.

Question 4:
Identify the vegetative propagule in potato.
Answer:

Eyes (buds) on tuber.

Question 5:
State the significance of juvenile phase in life cycle.
Answer:

Pre-reproductive growth phase for maturity.

Question 6:
Differentiate zoospores and conidia.
Answer:
  • Zoospores: Motile
  • Conidia: Non-motile
Question 7:
Why is fertilization absent in apomixis?
Answer:

Embryo forms without gamete fusion.

Question 8:
List two external fertilization examples.
Answer:
  • Frog
  • Fish
Question 9:
What triggers menstrual cycle in primates?
Answer:

Hormonal (FSH/LH) fluctuations.

Question 10:
Explain embryogenesis in plants.
Answer:

Zygote develops into embryo within seed.

Question 11:
Name the pollinating agent in maize.
Answer:

Wind (anemophily).

Question 12:
Define clone in reproduction context.
Answer:
Definition: Genetically identical offspring from single parent.
Question 13:
Identify the reproductive mode in yeast.
Answer:

Budding (asexual).

Question 14:
Why is seed dispersal crucial?
Answer:

Reduces competition and colonizes new areas.

Question 15:
Define vegetative propagation.
Answer:

Vegetative propagation is a type of asexual reproduction in plants where new individuals develop from vegetative parts like roots, stems, or leaves. It does not involve seeds or spores.

Question 16:
What is the significance of binary fission in Amoeba?
Answer:

Binary fission in Amoeba ensures rapid multiplication under favorable conditions. It is a simple and efficient method of asexual reproduction, producing genetically identical offspring.

Question 17:
Name the male and female reproductive structures in a flower.
Answer:

The male reproductive structure is the stamen (consisting of anther and filament), and the female reproductive structure is the pistil (consisting of stigma, style, and ovary).

Question 18:
Differentiate between zoospores and conidia.
Answer:
  • Zoospores are motile, flagellated spores formed in algae and fungi.
  • Conidia are non-motile spores produced exogenously on conidiophores in fungi like Penicillium.
Question 19:
Why is fertilization termed as 'syngamy'?
Answer:

Fertilization is called syngamy because it involves the fusion of two gametes (sperm and egg) to form a diploid zygote, restoring the chromosome number.

Question 20:
Give an example of a plant that reproduces through rhizomes.
Answer:

Ginger (Zingiber officinale) reproduces vegetatively through underground stems called rhizomes, which store food and give rise to new plants.

Question 21:
What is parthenogenesis? Provide an example.
Answer:

Parthenogenesis is a form of asexual reproduction where an unfertilized egg develops into a new individual. Example: Honeybees (drones develop from unfertilized eggs).

Question 22:
Explain the term embryogenesis.
Answer:

Embryogenesis is the process of development of an embryo from the zygote through cell division and differentiation, leading to the formation of a multicellular organism.

Question 23:
How does budding occur in Hydra?
Answer:

In Hydra, budding involves the formation of a small outgrowth (bud) on the parent body. The bud grows, develops tentacles, and detaches to become a new individual.

Question 24:
What is the role of pollination in sexual reproduction?
Answer:

Pollination transfers pollen grains from the anther to the stigma, enabling fertilization and seed formation, ensuring genetic diversity in plants.

Question 25:
Name the organism that exhibits multiple fission.
Answer:

Plasmodium, the malarial parasite, exhibits multiple fission, producing many daughter cells simultaneously inside the host.

Question 26:
Why is meiosis essential in sexually reproducing organisms?
Answer:

Meiosis reduces the chromosome number by half, producing haploid gametes. It ensures genetic variation through crossing over and maintains chromosome stability across generations.

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.

Question 1:
Define vegetative propagation with an example.
Answer:

Vegetative propagation is a type of asexual reproduction in plants where new individuals arise from vegetative parts like roots, stems, or leaves.
Example: Bryophyllum reproduces through leaf margins where adventitious buds develop into new plants.

Question 2:
Name the event where a diploid cell becomes haploid in sexual reproduction.
Answer:

The event is meiosis, where a diploid cell undergoes two divisions to produce four haploid gametes.

Question 3:
How does budding in Hydra differ from fragmentation?
Answer:
  • Budding: A new organism grows as an outgrowth from the parent (e.g., Hydra).
  • Fragmentation: Parent breaks into pieces, each growing into a new individual (e.g., Spirogyra).
Question 4:
What is the role of pollination in flowering plants?
Answer:

Pollination transfers pollen grains from the anther to the stigma, enabling fertilization and seed formation, ensuring genetic diversity.

Question 5:
Why are offspring of asexual reproduction genetically identical?
Answer:

Offspring are genetically identical because they are produced from a single parent without gamete fusion, retaining the parent's genetic makeup.

Question 6:
Give two advantages of sexual reproduction over asexual reproduction.
Answer:
  • Introduces genetic variation, aiding evolution.
  • Enhances adaptability to environmental changes.
Question 7:
Define vegetative propagation and give one example.
Answer:

Vegetative propagation is a type of asexual reproduction in plants where new individuals arise from vegetative parts like roots, stems, or leaves.
Example: Bryophyllum reproduces through leaf margins.

Question 8:
Why is fertilization called a 'double event' in flowering plants?
Answer:

Fertilization involves two fusions:
1. Syngamy: Fusion of male gamete with egg to form zygote.
2. Triple fusion: Fusion of second male gamete with polar nuclei to form endosperm.

Question 9:
Name the organism that exhibits multiple fission and describe the process.
Answer:

Plasmodium (malaria parasite) exhibits multiple fission.
Under unfavorable conditions, the nucleus divides repeatedly, forming many daughter cells inside a cyst, which are released when conditions improve.

Question 10:
What is parthenogenesis? Give an example.
Answer:

Parthenogenesis is a form of asexual reproduction where an unfertilized egg develops into a new individual.
Example: Honeybees (drones develop from unfertilized eggs).

Question 11:
Explain the term embryogenesis in plants.
Answer:

Embryogenesis is the process of zygote development into an embryo through cell division and differentiation.
In plants, it involves stages like globular, heart-shaped, and mature embryo formation.

Question 12:
How does budding differ in Hydra and yeast?
Answer:
  • Hydra: Bud grows as an outgrowth, detaches to form a new individual.
  • Yeast: Bud remains attached, forms a chain of cells.
Question 13:
List two advantages of sexual reproduction over asexual reproduction.
Answer:
  • Genetic diversity due to recombination and variation.
  • Better adaptability to environmental changes.
Question 14:
What is the role of pollination in sexual reproduction of plants?
Answer:

Pollination transfers pollen grains from anther to stigma, enabling fertilization.
It ensures genetic diversity and is facilitated by agents like wind, water, or animals.

Question 15:
Why are rhizomes and tubers called underground stems?
Answer:

They store food and bear nodes, internodes, and buds (e.g., ginger is a rhizome, potato is a tuber). Unlike roots, they lack root caps and root hairs.

Short Answer (3 Marks) – with Solutions (CBSE Pattern)

These 3-mark questions require brief explanations and help assess understanding and application of concepts.

Question 1:
Differentiate between asexual and sexual reproduction with two key points.
Answer:

Asexual reproduction involves a single parent and produces genetically identical offspring, while sexual reproduction involves two parents and results in genetically diverse offspring.

Key differences:

  • Asexual reproduction does not involve gamete formation, whereas sexual reproduction requires fusion of male and female gametes.
  • Asexual reproduction is faster and energy-efficient, while sexual reproduction is slower but promotes genetic variation.

Question 2:
Explain the significance of vegetative propagation in plants with an example.
Answer:

Vegetative propagation is a type of asexual reproduction where new plants grow from vegetative parts like roots, stems, or leaves.

Significance:

  • Preserves desirable traits (e.g., disease resistance) as offspring are genetically identical.
  • Faster than seed-based reproduction (e.g., potato tubers sprouting new plants).
Example: Bryophyllum reproduces through leaf margins where plantlets develop and detach.

Question 3:
Describe the process of binary fission in Amoeba with a labeled diagram.
Answer:

Binary fission is an asexual process where a parent cell divides into two identical daughter cells.

Steps in Amoeba:
1. The nucleus divides by mitosis.
2. Cytoplasm constricts inward.
3. Two genetically identical Amoeba are formed.

Diagram: (Draw Amoeba with labeled nucleus, cleavage furrow, and daughter cells.)

Question 4:
Why is external fertilization less common in terrestrial organisms? Give two reasons.
Answer:

External fertilization occurs outside the body, typically in aquatic environments.

Reasons for rarity in terrestrial organisms:

  • Gametes desiccate (dry out) due to lack of water, reducing survival chances.
  • Higher risk of predation or environmental hazards (e.g., temperature fluctuations) compared to protected internal fertilization.

Question 5:
How does parthenogenesis differ from fertilization? Provide an example.
Answer:

Parthenogenesis is asexual reproduction where an unfertilized egg develops into an offspring, while fertilization involves fusion of gametes.

Differences:

  • Parthenogenesis produces haploid offspring (e.g., drones in honeybees).
  • Fertilization ensures diploid offspring with genetic variation (e.g., humans).
Example: Rotifers reproduce via parthenogenesis under favorable conditions.

Question 6:
State two advantages of sexual reproduction over asexual reproduction.
Answer:

Sexual reproduction offers:

  • Genetic diversity: Crossing over and random fusion of gametes enhance adaptability.
  • Evolutionary advantage: Variability helps populations survive environmental changes (e.g., disease resistance).
In contrast, asexual reproduction lacks such benefits due to identical offspring.

Question 7:
Differentiate between asexual and sexual reproduction with two points each.
Answer:

Asexual reproduction involves a single parent and produces genetically identical offspring.
Sexual reproduction involves two parents and produces genetically diverse offspring.

  • Asexual reproduction: No gamete formation, faster process (e.g., binary fission in Amoeba).
  • Sexual reproduction: Involves gamete fusion, slower but promotes genetic variation (e.g., humans).
Question 8:
Describe the process of binary fission in Paramecium.
Answer:

Binary fission is an asexual reproduction method where a single cell divides into two identical daughter cells.
Steps in Paramecium:
1. The nucleus divides by mitosis.
2. Cytoplasm splits longitudinally.
3. Two genetically identical offspring are formed.

Question 9:
Why is external fertilization common in aquatic organisms? Give an example.
Answer:

External fertilization occurs outside the body, typically in water.
Reasons:

  • Water protects gametes from drying.
  • Facilitates gamete dispersal (e.g., fish release eggs/sperm in water).
Example: Frogs release eggs and sperm into ponds for fertilization.

Question 10:
What is parthenogenesis? Provide one example.
Answer:

Parthenogenesis is a form of asexual reproduction where an unfertilized egg develops into a new individual.
Example: Honeybees—drones (males) develop from unfertilized eggs via parthenogenesis, while workers/queens come from fertilized eggs.

Long Answer (5 Marks) – with Solutions (CBSE Pattern)

These 5-mark questions are descriptive and require detailed, structured answers with proper explanation and examples.

Question 1:
Compare asexual and sexual reproduction in organisms, highlighting their evolutionary significance.
Answer:
Theoretical Framework

Asexual reproduction involves a single parent producing genetically identical offspring, while sexual reproduction involves two parents contributing genetic variation. Our textbook shows asexual methods like binary fission in Amoeba and budding in Hydra.

Evidence Analysis
  • Asexual reproduction is faster but lacks genetic diversity.
  • Sexual reproduction, seen in humans, introduces recombination and mutations.
Critical Evaluation

While asexual reproduction ensures rapid colonization, sexual reproduction enhances adaptability, as seen in antibiotic-resistant bacteria.

Future Implications

Understanding these modes helps in conservation, like cloning endangered species or breeding disease-resistant crops.

Question 2:
Explain the process of oogenesis in human females with a focus on hormonal regulation.
Answer:
Theoretical Framework

Oogenesis is the formation of mature ova from oogonia, occurring in ovarian follicles. Our textbook highlights stages: mitosis, meiosis I, and meiosis II.

Evidence Analysis
  • FSH stimulates follicle growth, while LH triggers ovulation.
  • Progesterone from the corpus luteum prepares the uterus.
Critical Evaluation

Hormonal imbalances, like PCOS, disrupt oogenesis, leading to infertility. IVF treatments mimic these hormones.

Future Implications

Research on hormonal therapies can address rising infertility rates globally.

Question 3:
Analyze the role of pollination and double fertilization in angiosperms, citing two examples.
Answer:
Theoretical Framework

Pollination transfers pollen to the stigma, while double fertilization involves one sperm fusing with the egg and another with polar nuclei. Our textbook describes this in Hibiscus and Wheat.

Evidence Analysis
  • Bees pollinate Hibiscus, ensuring cross-fertilization.
  • In Wheat, wind pollination dominates, followed by endosperm formation.
Critical Evaluation

Pollinator decline threatens crops, but GM crops can reduce dependency.

Future Implications

Sustainable farming must protect pollinators to ensure food security.

Question 4:
Discuss the advantages of vegetative propagation in agriculture, with reference to tissue culture.
Answer:
Theoretical Framework

Vegetative propagation produces clones of plants using stems, roots, or leaves. Tissue culture, a lab method, grows plants from explants.

Evidence Analysis
  • Banana cultivation uses suckers for disease-free yield.
  • Tissue culture in Orchids ensures mass production of hybrids.
Critical Evaluation

While costlier, tissue culture eliminates viruses, unlike traditional methods.

Future Implications

Adopting these techniques can combat food scarcity in arid regions.

Question 5:
Compare sexual and asexual reproduction in organisms, highlighting their evolutionary significance.
Answer:
Theoretical Framework

We studied that asexual reproduction involves a single parent, producing genetically identical offspring, while sexual reproduction involves two parents, introducing genetic variation.

Evidence Analysis
  • Asexual methods like binary fission in Amoeba ensure rapid population growth.
  • Sexual reproduction in humans involves meiosis, creating gametes with recombinant DNA.
Critical Evaluation

Genetic diversity from sexual reproduction enhances adaptability, as seen in antibiotic resistance in bacteria. Asexual reproduction lacks this advantage.

Future Implications

Understanding these mechanisms aids in conservation, such as cloning endangered species asexually or breeding genetically diverse populations.

Question 6:
Explain the process of parthenogenesis with two examples. Discuss its ecological relevance.
Answer:
Theoretical Framework

Parthenogenesis is a form of asexual reproduction where an unfertilized egg develops into a new individual, common in some invertebrates and plants.

Evidence Analysis
  • In honeybees, drones are produced via parthenogenesis from haploid eggs.
  • Whiptail lizards (Aspidoscelis) reproduce exclusively this way, forming all-female populations.
Critical Evaluation

This process ensures reproduction in isolated environments but reduces genetic diversity, making species vulnerable to diseases.

Future Implications

Studying parthenogenesis helps in pest control and understanding evolutionary trade-offs in asexual lineages.

Question 7:
Describe the haplo-diplontic life cycle in plants, using mosses and ferns as examples.
Answer:
Theoretical Framework

The haplo-diplontic cycle alternates between haploid (gametophyte) and diploid (sporophyte) phases, seen in bryophytes and pteridophytes.

Evidence Analysis
  • In mosses, the dominant gametophyte produces sporophytes dependent on it.
  • Ferns exhibit a free-living sporophyte, while the gametophyte (prothallus) is short-lived.
Critical Evaluation

This cycle balances genetic recombination (via meiosis) and dispersal efficiency (via spores).

Future Implications

Understanding these cycles aids in crop breeding and studying plant adaptation to terrestrial habitats.

Question 8:
Analyze the role of pollination syndromes in ensuring reproductive success in flowering plants.
Answer:
Theoretical Framework

Pollination syndromes are suites of flower traits (color, scent) adapted to specific pollinators, enhancing cross-pollination efficiency.

Evidence Analysis
  • Bird-pollinated flowers (e.g., Hibiscus) are red and lack scent.
  • Moth-pollinated flowers (e.g., Jasmine) are white and night-blooming.
Critical Evaluation

These adaptations reduce interspecies competition but are vulnerable to pollinator decline due to habitat loss.

Future Implications

Conserving pollinator-specific plants is crucial for maintaining biodiversity and agricultural productivity.

Question 9:
Explain the process of binary fission in Paramecium with a labeled diagram. How does it differ from multiple fission?
Answer:
Theoretical Framework

Binary fission in Paramecium is a transverse division yielding two identical daughter cells, while multiple fission produces many offspring simultaneously.

Evidence Analysis
  • Binary fission involves mitosis, cytoplasmic division, and organelle replication.
  • Multiple fission, seen in Plasmodium, forms schizonts releasing merozoites.
[Diagram: Paramecium dividing into two with labeled nucleus, oral groove, and contractile vacuole]Critical Evaluation

Our textbook shows binary fission ensures uniformity, whereas multiple fission aids survival in hostile conditions.

Future Implications

Studying these helps combat pathogens like Plasmodium by targeting their reproductive stages.

Question 10:
Analyze the role of pollination and fertilization in flowering plants. How do they ensure genetic diversity?
Answer:
Theoretical Framework

Pollination transfers pollen to the stigma, while fertilization involves zygote formation after gamete fusion.

Evidence Analysis
  • Cross-pollination in Hibiscus introduces variability via agents like bees.
  • Double fertilization in angiosperms produces diploid zygote and triploid endosperm.
Critical Evaluation

Our textbook shows cross-pollination reduces inbreeding depression, unlike self-pollination in Wheat.

Future Implications

Understanding these processes aids hybrid crop development, enhancing yield and resilience.

Question 11:
Discuss the advantages of vegetative propagation in agriculture. Provide two examples with their economic importance.
Answer:
Theoretical Framework

Vegetative propagation produces clones from plant parts, preserving desirable traits.

Evidence Analysis
  • Sugarcane (Saccharum) propagated via stem cuttings ensures high sugar yield.
  • Banana (Musa) grown from suckers maintains seedless fruit quality.
Critical Evaluation

Our textbook shows this method is cost-effective but risks monoculture susceptibility to diseases.

Future Implications

It supports food security, e.g., rapid potato (Solanum) tuber production for global consumption.

Question 12:
Explain the process of binary fission in Amoeba with a labeled diagram. Discuss how this mode of reproduction is advantageous for the organism.
Answer:

Binary fission is a type of asexual reproduction where a single parent cell divides into two identical daughter cells. In Amoeba, the process occurs as follows:


Steps:
1. Replication of DNA: The genetic material duplicates to ensure each daughter cell receives an identical copy.
2. Elongation of cell: The cell elongates, and the nucleus divides into two.
3. Constriction formation: A constriction appears in the middle of the cell, dividing the cytoplasm.
4. Separation: The constriction deepens, splitting the parent cell into two genetically identical daughter cells.

Advantages:

  • Rapid multiplication: Allows quick population growth in favorable conditions.
  • Energy efficiency: No need for gamete formation or mating.
  • Genetic uniformity: Offspring are clones, maintaining successful traits.

Diagram: (Draw a labeled diagram showing the stages of binary fission in Amoeba.)

Question 13:
Compare and contrast sexual and asexual reproduction in organisms. Provide examples and discuss their significance in biodiversity.
Answer:

Sexual reproduction involves the fusion of male and female gametes, while asexual reproduction does not require gametes and produces genetically identical offspring. Below is a comparison:


  • Genetic Variation: Sexual reproduction introduces genetic diversity due to meiosis and fertilization, whereas asexual reproduction produces clones.
  • Examples: Sexual reproduction is seen in humans, flowering plants, etc., while asexual reproduction occurs in Hydra (budding), Planaria (regeneration), etc.
  • Energy Requirement: Sexual reproduction is energy-intensive due to mating and gamete formation, while asexual reproduction is quicker and requires less energy.

Significance in Biodiversity:

  • Sexual reproduction promotes adaptability and evolution, enhancing species survival in changing environments.
  • Asexual reproduction ensures rapid colonization in stable environments but limits genetic diversity.
Question 14:
Explain the process of binary fission in Amoeba with a labeled diagram. Discuss how it differs from multiple fission.
Answer:

Binary fission is a type of asexual reproduction observed in unicellular organisms like Amoeba. Here’s a step-by-step explanation of the process:


1. Growth Phase: The Amoeba grows in size and replicates its genetic material (DNA).


2. Nuclear Division: The nucleus divides into two identical nuclei through mitosis.


3. Cytoplasmic Division: The cytoplasm divides, leading to the formation of two daughter cells.


4. Separation: The cell membrane pinches inward, resulting in two genetically identical daughter Amoebae.


Diagram: (Draw a labeled diagram showing the stages of binary fission in Amoeba.)


Difference from Multiple Fission:

  • In binary fission, one parent cell divides into two daughter cells, whereas in multiple fission, one parent cell divides into many daughter cells.
  • Binary fission occurs under favorable conditions, while multiple fission occurs during unfavorable conditions (e.g., formation of spores).
  • Examples: Binary fission—Amoeba, Paramecium; Multiple fission—Plasmodium.

Value-added point: Binary fission ensures rapid multiplication, while multiple fission helps organisms survive harsh conditions by producing resistant spores.

Question 15:
Explain the process of binary fission in Amoeba with the help of a labeled diagram. Discuss how this mode of reproduction is advantageous for the organism.
Answer:

Binary fission is a type of asexual reproduction observed in unicellular organisms like Amoeba. The process involves the following steps:


  1. Karyokinesis: The nucleus of the Amoeba divides into two daughter nuclei through mitosis.
  2. Cytokinesis: The cytoplasm divides, leading to the formation of two daughter cells.
  3. Separation: The two daughter cells separate and grow into independent organisms.

Advantages of binary fission:

  • Rapid reproduction: Allows quick population growth under favorable conditions.
  • Energy efficiency: No need for gamete formation or mating, saving energy.
  • Genetic uniformity: Offspring are genetically identical to the parent, maintaining successful traits.

Diagram: (Draw a labeled diagram showing the stages of binary fission in Amoeba, including the parent cell, nuclear division, cytoplasmic division, and two daughter cells.)

Question 16:
Explain the process of binary fission in Amoeba with a labeled diagram. Discuss how it differs from multiple fission in terms of advantages and disadvantages.
Answer:

Binary fission is a type of asexual reproduction observed in unicellular organisms like Amoeba. Here’s a step-by-step explanation:


1. Karyokinesis: The nucleus of the Amoeba divides first through mitosis, ensuring genetic material is equally distributed.
2. Cytokinesis: The cytoplasm divides, leading to the formation of two nearly identical daughter cells.
3. Completion: The parent cell splits into two independent daughter cells, each a clone of the parent.


Labeled Diagram: (Draw a simple sketch showing Amoeba before division, during nuclear division, and after splitting into two daughter cells. Label the nucleus, cytoplasm, and cell membrane.)


Comparison with Multiple Fission:

  • Binary Fission: Produces only two offspring, ensuring faster energy utilization and higher survival rates under stable conditions.
  • Multiple Fission: Produces many offspring simultaneously (e.g., in Plasmodium), which is advantageous in harsh environments but risks resource depletion.

Value-Added Insight: Binary fission ensures rapid population growth with minimal energy expenditure, while multiple fission is a survival strategy during unfavorable conditions, though it may reduce individual fitness due to competition among offspring.

Question 17:
Compare and contrast sexual and asexual reproduction in organisms. Provide examples and discuss the significance of each type.
Answer:

Sexual reproduction involves the fusion of male and female gametes, while asexual reproduction does not. Here’s a detailed comparison:


  • Genetic variation: Sexual reproduction introduces diversity due to recombination (e.g., humans). Asexual reproduction produces identical offspring (e.g., Hydra via budding).
  • Energy requirement: Sexual reproduction is energy-intensive (mate finding, gamete production). Asexual reproduction is efficient (e.g., binary fission in Paramecium).
  • Adaptability: Sexual reproduction enhances survival in changing environments. Asexual reproduction is advantageous in stable conditions.

Significance:

  • Sexual reproduction: Promotes evolution and disease resistance.
  • Asexual reproduction: Ensures rapid colonization and resource utilization.

Value-added: Some organisms (e.g., Planaria) exhibit both modes, adapting to environmental demands.

Question 18:
Compare and contrast sexual and asexual reproduction in organisms. Provide examples and discuss their significance in evolution.
Answer:

Sexual reproduction involves the fusion of male and female gametes, while asexual reproduction does not require gametes. Below is a detailed comparison:


  • Genetic variation: Sexual reproduction introduces genetic diversity due to recombination and fertilization (e.g., humans). Asexual reproduction produces genetically identical offspring (e.g., Hydra through budding).
  • Energy requirement: Sexual reproduction is energy-intensive due to gamete formation and mating. Asexual reproduction is energy-efficient.
  • Adaptability: Sexual reproduction enhances adaptability to changing environments, while asexual reproduction is advantageous in stable conditions.

Evolutionary significance:

  • Sexual reproduction drives natural selection by creating genetic diversity.
  • Asexual reproduction ensures rapid colonization but limits evolutionary flexibility.

Both strategies contribute to species survival under different ecological conditions.

Question 19:
Compare and contrast sexual and asexual reproduction in organisms. Provide examples and discuss the significance of each mode in ensuring species survival.
Answer:

Sexual reproduction involves the fusion of male and female gametes, while asexual reproduction does not require gametes and produces genetically identical offspring.


Comparison:
  • Genetic variation: Sexual reproduction introduces genetic diversity due to recombination, while asexual reproduction lacks variation.
  • Number of parents: Sexual requires two parents, whereas asexual involves only one.
  • Speed and energy: Asexual is faster and energy-efficient, while sexual is slower but promotes adaptability.

Examples:
  • Asexual: Binary fission in Amoeba, budding in Hydra.
  • Sexual: Humans, flowering plants.

Significance:
  • Asexual: Ensures rapid colonization in stable environments.
  • Sexual: Enhances survival in changing environments due to genetic diversity.

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.

Question 1:
A farmer observed that some vegetative propagules like potato tubers and ginger rhizomes sprouted even without soil. Explain the biological significance of this phenomenon and its agricultural implications.
Answer:
Case Deconstruction

The sprouting of vegetative propagules without soil demonstrates their dormancy-breaking capability using stored nutrients. Our textbook shows that tubers and rhizomes have meristematic tissues for regeneration.

Theoretical Application
  • Enables clonal propagation for uniform crop yield.
  • Reduces dependency on seeds, aiding in crop resilience.
Critical Evaluation

This trait is evolutionarily advantageous but may limit genetic diversity. Example: Potato famines due to monoculture.

Question 2:
In a lab, binary fission in Amoeba was observed to complete in 30 minutes, while Leishmania took 2 hours. Analyze the factors influencing this difference with two examples.
Answer:
Case Deconstruction

Binary fission duration varies due to cytoplasmic volume and DNA replication speed. Our textbook highlights kinetoplast DNA complexity in Leishmania.

Theoretical Application
  • Amoeba has simpler organelle distribution.
  • Leishmania requires mitochondrial genome replication.
Critical Evaluation

Example: Rapid fission aids Amoeba in nutrient-rich ponds, while Leishmania prioritizes accuracy as a parasite.

Question 3:
A study found parthenogenesis in honeybees produces drones. Evaluate the genetic consequences and ecological role of this asexual reproduction strategy.
Answer:
Case Deconstruction

Parthenogenesis in bees creates haploid drones via meiotic division. Our textbook confirms this maintains colony genetic diversity.

Theoretical Application
  • Drones ensure diploid queen production.
  • Limits mutation accumulation compared to mitosis.
Critical Evaluation

Example: This balances reproductive efficiency and adaptability, unlike obligate asexual species like water fleas.

Question 4:
Coral reefs exhibit both fragmentation and broadcast spawning. Compare these modes using evolutionary trade-offs and current climate change impacts.
Answer:
Case Deconstruction

Fragmentation ensures local adaptation but reduces diversity, while broadcast spawning disperses genes widely. Our textbook notes coral symbiont dependence.

Theoretical Application
  • Fragmentation thrives in stable reefs (Example: Great Barrier Reef).
  • Spawning fails with ocean acidification.
Critical Evaluation

Recent studies show 50% reduced spawning success due to warming, favoring fragmentation.

Question 5:
Researchers noted pre-fertilization barriers in wind-pollinated grasses but not in animal-pollinated flowers. Justify this observation with selection pressure evidence.
Answer:
Case Deconstruction

Wind pollination lacks pollinator specificity, increasing interspecies hybridization risk. Our textbook describes pollen-pistil interaction mechanisms.

Theoretical Application
  • Grasses evolve temporal isolation (Example: Bamboo flowering cycles).
  • Animal-pollinated plants use morphological barriers (Example: Orchid pollinia).
Critical Evaluation

This aligns with Darwin’s co-evolution theory, as seen in hawkmoth-pollinated flowers.

Question 6:
A farmer observed that some plants in his field reproduced through vegetative propagation while others relied on sexual reproduction. Compare these two modes of reproduction, highlighting their advantages and disadvantages.
Answer:
Case Deconstruction

Vegetative propagation involves asexual reproduction where new plants arise from vegetative parts like roots, stems, or leaves. Sexual reproduction involves fusion of gametes.

Theoretical Application
  • Advantages of vegetative propagation: Faster, maintains genetic purity (e.g., sugarcane).
  • Disadvantages: No genetic variation, prone to diseases.
  • Advantages of sexual reproduction: Genetic diversity (e.g., wheat).
  • Disadvantages: Slower, dependent on pollinators.
Critical Evaluation

Our textbook shows vegetative propagation is useful for crop uniformity, while sexual reproduction ensures adaptability.

Question 7:
In a lab experiment, students observed binary fission in Amoeba and multiple fission in Plasmodium. Explain these processes with labeled diagrams and their significance in disease spread.
Answer:
Case Deconstruction

Binary fission divides a parent cell into two identical daughter cells (e.g., Amoeba). Multiple fission produces many offspring simultaneously (e.g., Plasmodium).

Theoretical Application
  • Binary fission: [Diagram: Amoeba splitting into two]. Ensures rapid reproduction.
  • Multiple fission: [Diagram: Plasmodium releasing spores]. Allows survival in harsh conditions.
Critical Evaluation

Our textbook shows Plasmodium's multiple fission aids malaria transmission, while Amoeba's binary fission supports population growth.

Question 8:
A researcher found that parthenogenesis occurs in honeybees, producing drones. Analyze how this impacts the colony's genetic diversity and survival strategies.
Answer:
Case Deconstruction

Parthenogenesis is asexual reproduction where females produce offspring without fertilization. In honeybees, drones develop from unfertilized eggs.

Theoretical Application
  • Genetic diversity: Reduced due to haploid drones.
  • Survival strategy: Ensures rapid drone production for mating.
Critical Evaluation

Our textbook shows this limits adaptability but optimizes reproductive efficiency, balancing colony needs.

Question 9:
Students debated whether external fertilization (e.g., frogs) or internal fertilization (e.g., humans) is more evolutionarily advantageous. Present evidence-based arguments for both.
Answer:
Case Deconstruction

External fertilization occurs outside the body (e.g., frogs), while internal fertilization happens inside (e.g., humans).

Theoretical Application
  • External fertilization: High offspring numbers but vulnerable to predators.
  • Internal fertilization: Fewer offspring but higher survival rates.
Critical Evaluation

Our textbook shows internal fertilization is advantageous in terrestrial environments, while external fertilization suits aquatic habitats.

Question 10:
A farmer observed that some plants in his field reproduced through vegetative propagation while others relied on sexual reproduction. Compare these two modes of reproduction with two examples each, highlighting their advantages.
Answer:
Case Deconstruction

Vegetative propagation (e.g., potato tubers, banana rhizomes) produces genetically identical offspring, ensuring trait preservation. Sexual reproduction (e.g., mango seeds, wheat flowers) introduces genetic diversity.

Theoretical Application
  • Advantage of vegetative propagation: Faster and independent of pollinators.
  • Advantage of sexual reproduction: Enhances adaptability to environmental changes.
Critical Evaluation

While vegetative propagation is efficient for crop uniformity, sexual reproduction ensures long-term species survival through variation, as per our NCERT examples.

Question 11:
In a lab experiment, students observed binary fission in Amoeba and multiple fission in Plasmodium. Tabulate the differences and explain their biological significance.
Answer:
Case Deconstruction
FeatureBinary FissionMultiple Fission
DivisionTwo equal cellsMany daughter cells
ExampleAmoebaPlasmodium
Theoretical Application

Binary fission ensures rapid multiplication in favorable conditions, while multiple fission (e.g., Plasmodium cysts) aids survival in harsh environments.

Critical Evaluation

Our textbook highlights how these strategies align with organismal habitat needs, demonstrating evolutionary adaptability.

Question 12:
A researcher noted that parthenogenesis occurs in honeybees (drones) and lizards (some species). Analyze why this phenomenon is ecologically advantageous but genetically restrictive.
Answer:
Case Deconstruction

Parthenogenesis allows rapid population growth (e.g., honeybee drones) without mates, crucial for colony survival. However, it limits genetic diversity (e.g., whiptail lizards).

Theoretical Application
  • Ecological advantage: Colonization of new habitats.
  • Genetic restriction: Vulnerability to diseases due to identical genes.
Critical Evaluation

As per NCERT, this trade-off exemplifies how reproductive strategies balance short-term survival and long-term resilience.

Question 13:
In hydra, both budding and regeneration were observed. Differentiate these processes with labeled diagrams and justify their role in asexual reproduction.
Answer:
Case Deconstruction

Budding in hydra forms a new organism from an outgrowth, while regeneration regrows lost parts. [Diagram: Hydra budding] [Diagram: Regeneration in hydra]

Theoretical Application
  • Budding: Efficient for rapid cloning.
  • Regeneration: Repairs damage, ensuring survival.
Critical Evaluation

Our textbook confirms these asexual methods optimize resource use in stable environments, as seen in hydra lab studies.

Question 14:

A farmer observed that some of his banana plants were producing fruits without seeds, while others had seeds. He was curious about the difference in reproduction methods. Explain the two types of reproduction observed in banana plants, highlighting the advantages of seedless fruit production.

Answer:

The banana plants exhibit both sexual and asexual reproduction. Seed-bearing bananas result from sexual reproduction, where fertilization occurs between male and female gametes, leading to genetic variation.

Seedless bananas are produced through vegetative propagation (a type of asexual reproduction), where new plants grow from vegetative parts like rhizomes or suckers. This method ensures:

  • Uniformity in fruit quality and traits.
  • Faster multiplication of desirable varieties.
  • No dependence on pollinators or seeds.
Farmers prefer seedless bananas as they are commercially more viable due to better texture and consumer preference.
Question 15:

In a pond ecosystem, a student noticed that some organisms like Hydra reproduce by budding, while others like frogs reproduce sexually. Compare these two modes of reproduction, emphasizing their significance in maintaining population stability.

Answer:

Asexual reproduction (e.g., budding in Hydra) involves a single parent producing genetically identical offspring. This method is advantageous because:

  • It allows rapid population growth in stable environments.
  • It requires less energy as no mate is needed.

Sexual reproduction (e.g., in frogs) involves two parents, leading to genetic variation. This is beneficial because:
  • It enhances adaptability to changing environments.
  • It increases disease resistance due to genetic diversity.

While asexual reproduction ensures quick colonization, sexual reproduction maintains long-term population stability through variation, crucial for survival in dynamic ecosystems.

Question 16:

In a botanical garden, two flowering plants Plant A and Plant B were observed. Plant A produces a large number of small, lightweight pollen grains, while Plant B produces fewer but larger pollen grains. Based on this observation:

  • Identify the mode of pollination in Plant A and Plant B.
  • Explain one adaptation each in these plants for their respective modes of pollination.
Answer:

Plant A exhibits anemophily (wind pollination), as indicated by the production of numerous small and lightweight pollen grains, which are easily carried by wind.
Plant B shows entomophily (insect pollination), as fewer but larger pollen grains are typically adapted for insect transfer.

Adaptations:

  • Plant A: The flowers are small, inconspicuous, and lack bright colors or nectar, reducing energy expenditure on attracting pollinators. The pollen grains are smooth and non-sticky for easy wind dispersal.
  • Plant B: The flowers are brightly colored, fragrant, and produce nectar to attract insects. The pollen grains are sticky or spiny to adhere to insect bodies.

Question 17:

A farmer observed that some of his papaya plants bore only male flowers, while others had female or bisexual flowers. He noticed that the plants with only male flowers did not produce fruits. Explain:

  • The significance of this observation in papaya plants.
  • How this reproductive feature can be advantageous in agricultural practices.
Answer:

Significance: Papaya exhibits dioecy, where male and female flowers are borne on separate plants. Only female or bisexual plants produce fruits, while male plants are essential for pollination but do not yield fruits.

Agricultural Advantage:

  • Farmers can selectively cultivate female or bisexual plants to maximize fruit production.
  • Male plants can be maintained in controlled ratios (e.g., 1 male per 10 females) to ensure pollination without wasting resources on non-fruit-bearing plants.
  • This feature allows for hybrid breeding by controlling cross-pollination between selected male and female plants.

Question 18:

A farmer observed that some of his banana plants were producing fruits without seeds, while others had seeds. He was curious about the reason behind this variation. Explain the biological process responsible for seedless banana production and compare it with the process that leads to seeded bananas. Also, mention one advantage of seedless bananas for commercial cultivation.

Answer:

The seedless bananas are produced through vegetative propagation, specifically by using suckers or rhizomes from a parent plant. This is a form of asexual reproduction where new plants are genetically identical to the parent.

In contrast, seeded bananas result from sexual reproduction, involving the fusion of male and female gametes, leading to seed formation.

One advantage of seedless bananas for commercial cultivation is uniformity in fruit quality, as all plants are clones of the parent, ensuring consistent taste, size, and yield. Additionally, seedless bananas are more appealing to consumers as they are easier to eat.

Question 19:

In a laboratory experiment, students observed that Hydra reproduces by forming small outgrowths that eventually detach to become new individuals. Identify the type of reproduction and describe the process. How does this method differ from fragmentation seen in organisms like Spirogyra?

Answer:

The type of reproduction observed in Hydra is budding, which is a form of asexual reproduction.

The process involves:

  • Formation of a small outgrowth (bud) on the parent body.
  • The bud grows and develops tentacles and a mouth.
  • Once mature, it detaches from the parent and becomes an independent organism.


In contrast, fragmentation (seen in Spirogyra) involves the breaking of the parent body into pieces, each of which grows into a new individual.

The key difference is that budding involves the formation of a specialized outgrowth, while fragmentation is a passive process where the organism breaks due to external forces or natural growth.

Question 20:

In a pond ecosystem, a student noticed that some organisms like Hydra reproduce by budding, while others like frogs undergo external fertilization. Compare these two modes of reproduction, emphasizing their suitability in aquatic environments.

Answer:

Budding in Hydra (asexual reproduction):

  • A small outgrowth (bud) develops on the parent body and detaches later.
  • Advantage: Rapid multiplication without a mate, useful in stable pond conditions.

External fertilization in frogs (sexual reproduction):
  • Eggs and sperm are released into water, where fertilization occurs.
  • Advantage: Increases genetic diversity, crucial for adaptation in changing environments.

Budding is efficient for quick colonization, while external fertilization ensures species survival through variation. Water supports both processes by providing a medium for gamete transfer and bud dispersal.

Question 21:

A farmer observed that some of his banana plants were producing fruits without seeds, while others had seeds. He was curious about the difference in reproduction methods. Explain the two types of reproduction observed in banana plants, highlighting their advantages and disadvantages.

Answer:

Banana plants exhibit both asexual and sexual reproduction.

Asexual Reproduction (Vegetative Propagation):
In seedless bananas, reproduction occurs through vegetative propagation, where new plants grow from suckers or rhizomes.

  • Advantages: Faster growth, identical genetic traits (clones), and no need for pollinators.
  • Disadvantages: Lack of genetic diversity makes them susceptible to diseases.

Sexual Reproduction:
Seeded bananas reproduce sexually via flowers and seeds.
  • Advantages: Genetic variation improves adaptability and disease resistance.
  • Disadvantages: Slower growth and dependency on pollinators.

Most cultivated bananas are seedless due to human preference, while wild bananas reproduce sexually.

Question 22:

In a pond ecosystem, a student noticed that Hydra reproduces both by budding and regeneration. Compare these two methods of reproduction in Hydra, explaining their significance in survival and population growth.

Answer:

Budding in Hydra:
Hydra reproduces asexually by forming a small outgrowth (bud) that detaches to become a new organism.

  • Significance: Rapid population increase under favorable conditions.
  • Process: No gamete formation; genetically identical offspring.

Regeneration in Hydra:
Hydra can regrow lost body parts or even an entire organism from a fragment.
  • Significance: Survival mechanism after injury or predation.
  • Process: Involves specialized cells like interstitial cells for tissue repair.

While budding aids in quick reproduction, regeneration ensures resilience. Both methods contribute to Hydra's adaptability in changing environments.

Chat on WhatsApp