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Q1. A single cell capable of forming all cell types is needed for:
ReproductionIn asexual reproduction (e.g., budding, fragmentation, or regeneration), specialized cells called stem cells or regenerative cells must be capable of dividing and differentiating into all the different cell types required to form a complete new organism. Without such a cell, reproduction of the whole body from a part is impossible.
Q2. In budding, a new individual develops as a:
Small outgrowthBudding is a form of asexual reproduction where a small protrusion (bud) forms on the parent organism. The bud grows, develops into a miniature version of the parent, and eventually detaches to live independently. This is commonly seen in yeast and Hydra.
Q3. Plasmodium reproduces by:
Multiple fissionPlasmodium, the malarial parasite, reproduces by multiple fission (also called schizogony). The nucleus divides multiple times rapidly without cytokinesis, then the cytoplasm divides simultaneously, producing many daughter cells at once. This allows rapid multiplication inside the host’s liver and red blood cells.
Q4. Bread mould observation is done over a period of:
One weekBread mould (Rhizopus) requires several days to grow, sporulate, and become visible to the naked eye. Over a week, fungal hyphae spread, and sporangia develop, producing black spores. Observing for shorter periods (one day or one hour) shows little to no visible growth.
Q5. Variation mainly arises due to:
DNA copying errorsDuring DNA replication, occasional mistakes occur in base pairing, insertion, deletion, or repair. These mutations introduce genetic variation. While environment and nutrition influence gene expression, the primary source of heritable variation is errors in DNA copying.
Q6. Fission is common in:
Unicellular organismsFission (binary or multiple) is the primary mode of reproduction in unicellular organisms like bacteria, Amoeba, Paramecium, and Plasmodium. These organisms have a simple body plan where one cell splits into two or more new individuals. Multicellular organisms cannot reproduce by simple fission due to tissue organization.
Q7. Fragmentation is not suitable for complex multicellular organisms because:
Tissues and organs are organisedComplex multicellular organisms have specialized tissues and organs arranged in a specific body plan. A fragment would lack the organizational structure (e.g., nervous system, circulatory system) needed to regenerate a complete, functional organism. Only organisms with simple body organization (like Spirogyra) can reproduce by fragmentation.
Q8. Fragmentation occurs mostly in organisms with:
Simple body organisationFragmentation requires that each fragment contains enough undifferentiated cells to grow into a complete organism. Simple organisms like filamentous algae (Spirogyra) and some flatworms lack complex organ systems, making fragmentation feasible. Complex organisms cannot regenerate entire bodies from arbitrary fragments.
Q9. Which organism shows fission in a definite orientation?
LeishmaniaLeishmania, a protozoan parasite, reproduces by binary fission in a fixed orientation. The flagellum (whip-like structure) determines the plane of division, ensuring that each daughter cell receives one flagellum. In contrast, Amoeba divides in any random plane.
Q10. Multiple fission occurs when:
Conditions are unfavourableMultiple fission is often a survival strategy under adverse conditions (e.g., lack of food, desiccation, or extreme temperature). The organism encysts and divides repeatedly to produce many daughter cells simultaneously. When conditions improve, the cyst ruptures, releasing numerous offspring to colonize the environment.
Q11. Regeneration is seen in:
Fully differentiated organismsRegeneration occurs in some fully differentiated organisms like Hydra, planarians (flatworms), and starfish. These organisms retain populations of undifferentiated stem cells capable of proliferating and differentiating to replace lost body parts or form complete organisms from fragments. Contrary to the distractor, regeneration is not limited to bacteria, plants, or unicellular organisms.
Q12. Tissues are further organised into:
OrgansIn multicellular organisms, cells with similar functions group together to form tissues (e.g., muscle tissue, nervous tissue). Different tissues then combine and organize into organs (e.g., heart, liver, kidney), which perform specific physiological functions.
Q13. Complex organisms require complex reproduction because:
Their body design is organisedComplex organisms have specialized tissues, organs, and organ systems arranged in a precise body plan. Simple methods like fragmentation or binary fission would disrupt this organization. Therefore, they require complex reproductive mechanisms (sexual reproduction involving specialized gametes) to produce offspring with the same organized body design.
Q14. The main advantage of asexual reproduction is:
Rapid multiplicationAsexual reproduction (binary fission, budding, fragmentation) allows a single parent to produce many offspring quickly without needing a mate. This rapid multiplication is advantageous in stable, favourable environments, enabling a population to exploit resources efficiently. However, it produces little genetic variation.
Q15. Sugar solution is used in Activity 11.1 mainly to:
Provide nutrientsIn experiments growing yeast, sugar (sucrose or glucose) serves as an energy and carbon source. Yeast cells metabolize sugar through fermentation or aerobic respiration, obtaining energy for growth and reproduction. Without sugar, yeast would have no nutrient source and would not multiply visibly.
Q16. Specialized reproductive cells are necessary because:
All cells cannot reproduceIn complex multicellular organisms, most cells are differentiated (e.g., neurons, muscle cells) and have lost the ability to divide. Only specialized germ cells (sperm and egg in animals; gametes in plants) retain the capacity for meiosis and fertilization, ensuring genetic continuity across generations.
Q17. Yeast and mould differ mainly in their:
Growth patternYeast is a unicellular fungus that reproduces by budding and forms smooth, moist colonies. Mould (e.g., Rhizopus, Penicillium) is multicellular, growing as filamentous hyphae that form fuzzy, cottony colonies with visible spores. Both are fungi with similar nutrition (heterotrophic, absorbing nutrients), so growth pattern is the key difference.
Q18. Multicellular organisms cannot reproduce by cell-by-cell division because:
Body organisation is complexIn multicellular organisms, cells are specialized and organized into tissues and organs. If each cell divided independently, it would destroy the structural and functional organization. Instead, reproduction occurs through specialized reproductive cells or structures, not by random cell-by-cell division.
Q19. Variation is useful because it helps in:
Long-term survival of speciesVariation provides the raw material for natural selection. When environmental conditions change (e.g., climate shift, new predator, disease), individuals with advantageous variations are more likely to survive and reproduce. This ensures the species adapts over generations, preventing extinction. Variation does not guarantee immediate survival of all individuals.
Q20. Yeast growth in Activity 11.1 is best observed after:
1–2 hoursYeast reproduces rapidly by budding under optimal conditions (warm temperature, sugar solution). Within 1–2 hours, a visible increase in cell count can be observed under a microscope. A few minutes is too short for significant division; one week or one month would lead to overgrowth, nutrient depletion, and possibly cell death.
Q21. Spirogyra is a:
Filamentous algaSpirogyra is a green alga that forms long, unbranched filaments of cylindrical cells arranged end to end. It is multicellular (but with simple organization), contains spiral-shaped chloroplasts, and reproduces by fragmentation and conjugation. It is not a protozoan, bacterium, or unicellular organism.
Q22. Which mode involves growth of a body part into a complete organism?
RegenerationRegeneration refers to the ability of an organism to regrow lost body parts or, in some cases, develop a complete new organism from a small body part (e.g., planaria fragment regenerating into a whole worm). While fragmentation also produces new individuals from parts, regeneration specifically emphasizes the growth process from a body part.
Q23. Yeast reproduces mainly by:
BuddingYeast (Saccharomyces cerevisiae) primarily reproduces asexually by budding. A small protrusion (bud) forms on the parent cell, receives a nucleus, grows, and eventually detaches. Under favourable conditions, multiple buds may form. Binary fission is more common in bacteria, not yeast.
Q24. Bread mould grows best in a place that is:
Cool, moist and darkBread mould (Rhizopus) thrives in cool temperatures (20–25°C), high humidity (moisture is essential for spore germination and hyphal growth), and darkness (light inhibits sporulation). Cold and dry conditions slow growth; hot and dry or bright conditions kill spores or prevent germination.
Q25. Bacteria that survive increased temperature are those that are:
Heat resistant variantsWithin a bacterial population, genetic variation exists. Some bacteria may have mutations that confer heat resistance (e.g., heat-stable enzymes, altered membrane lipids, or spore-forming ability). When temperature increases, these heat-resistant variants survive while others die. This illustrates natural selection.
Q26. Multiple fission results in:
Many daughter cells at onceIn multiple fission, the parent cell’s nucleus divides repeatedly without cytoplasmic division. Then, the cytoplasm divides simultaneously, producing numerous daughter cells (often dozens or hundreds) from a single parent. This differs from binary fission, which produces exactly two daughter cells.
Q27. In Amoeba, binary fission can occur:
In any planeAmoeba has no fixed body shape or polarity. Binary fission can occur in any plane because the cell constricts and divides without a predetermined orientation. This contrasts with Leishmania (fixed orientation due to flagellum) or Paramecium (transverse division).
Q28. Regeneration is the ability to:
Form a new organism from body partsRegeneration is the biological process by which an organism replaces lost or damaged body parts. In some species (e.g., planaria, Hydra), a small body fragment can regenerate into a complete new organism through cell proliferation and differentiation. This is a form of asexual reproduction.
Q29. Spirogyra reproduces asexually by:
FragmentationSpirogyra filaments break into smaller fragments due to mechanical action or decay. Each fragment (containing a few cells) grows into a new, complete filament through cell division and elongation. This is the primary asexual reproduction method in Spirogyra. (Spirogyra also reproduces sexually by conjugation.)
Q30. Which organism causes kala-azar?
LeishmaniaLeishmania donovani is a protozoan parasite transmitted by the bite of infected female sandflies. It causes visceral leishmaniasis (kala-azar), a disease characterized by fever, weight loss, anemia, and hepatosplenomegaly. Plasmodium causes malaria; Amoeba causes amoebic dysentery; yeast causes candidiasis (not kala-azar).
Q31. Budding produces offspring that are:
Genetically similarBudding is a form of asexual reproduction. The offspring (bud) is produced by mitosis from the parent cell, receiving an identical copy of the parent’s DNA. Therefore, the offspring is genetically similar (a clone) to the parent, though not absolutely identical due to possible rare mutations.
Q32. Which environmental factor is mentioned as affecting bacterial survival?
TemperatureTemperature is a critical environmental factor affecting bacterial survival, growth, and reproduction. Each bacterial species has an optimal temperature range. Extreme heat denatures enzymes and proteins; extreme cold slows metabolism. Variations in temperature can kill bacteria or allow heat-resistant variants to survive and multiply.
Q33. Cotton plug in the test tube allows:
Exchange of airA cotton plug is porous, allowing air (including oxygen) to enter the test tube while preventing dust, airborne bacteria, and insects from contaminating the culture. This is essential for aerobic organisms like yeast and mould, which require oxygen for growth and reproduction. Complete sealing would suffocate them.
Q34. The mould seen on bread belongs to:
FungiBread mould (commonly Rhizopus stolonifer) is a fungus, belonging to the division Zygomycota. Fungi are eukaryotic, heterotrophic organisms with cell walls containing chitin, growing as hyphae and reproducing via spores. Bacteria, algae, and protozoa are not responsible for typical fuzzy bread mould.
Q35. In fragmentation, each fragment:
Grows into a new individualIn fragmentation, the parent organism breaks into two or more fragments. Each fragment contains enough cells (often with regenerative capacity) to grow, develop, and differentiate into a complete new organism independent of the parent. This is a method of asexual reproduction in simple multicellular organisms like Spirogyra and some flatworms.
Q36. Modes of reproduction in organisms depend on:
Body designThe reproductive method an organism uses is largely determined by its body design (cellular organization, complexity, presence of specialized structures). Unicellular organisms use fission; simple multicellular organisms use budding or fragmentation; complex organisms require sexual reproduction with specialized reproductive organs. Habitat and food availability influence timing but not fundamental mode.
Q37. Species survival over time depends greatly on:
VariationGenetic variation within a species provides resilience against environmental changes, diseases, and predators. When conditions change, variants with advantageous traits survive and reproduce, ensuring species continuity. Uniformity (no variation) makes a population vulnerable to extinction if a single environmental challenge affects all individuals equally.
Q38. During fission, a unicellular organism:
Divides to form new individualsFission is the process by which a single-celled organism divides into two (binary fission) or more (multiple fission) daughter cells, each becoming a new independent individual. The parent organism no longer exists as a separate entity. It does not become multicellular, form tissues, or die (rather, it replicates itself).
Q39. In multicellular organisms, reproduction is carried out by:
Specialised cellsIn complex multicellular organisms, most body cells (somatic cells) are differentiated and cannot reproduce. Only specialized reproductive cells (germ cells—sperm and egg in animals; gametes in plants) are capable of undergoing meiosis and fertilization to produce offspring. This ensures organized, controlled reproduction.
Q40. Variation may not always benefit the individual because:
It may be harmful to survivalWhile some variations are beneficial, many are neutral or harmful. Harmful mutations can disrupt essential functions, reduce fitness, cause developmental abnormalities, or lead to diseases that decrease survival chances. Variation is not inherently good—natural selection acts on the net effect.
Q41. The cell type capable of forming other cell types must be able to:
ProliferateStem cells or regenerative cells must be able to proliferate (divide repeatedly) to produce a population of cells that can then differentiate into various specialized cell types. Without the ability to proliferate, a single cell cannot generate enough cells to form tissues, organs, or a complete new organism.
Q42. If the temperature of temperate water increases, most bacteria will:
DieMost bacteria in temperate water are adapted to a specific temperature range (approximately 20–30°C). A significant temperature increase denatures essential enzymes and proteins, disrupts cell membranes, and inhibits metabolism, leading to widespread death. Only heat-resistant variants (thermophiles) may survive and multiply.
Q43. Which mode is fastest in increasing population size?
Multiple fissionMultiple fission produces numerous daughter cells (often hundreds or thousands) from a single parent in a short time. For example, Plasmodium can produce 8–24 daughter cells in one cycle. This exponential increase is faster than binary fission (2 cells), budding (1–2 buds), fragmentation, or sexual reproduction (which requires mating and gestation).
Q44. Binary fission produces:
Two daughter cellsBinary fission (binary = two) involves division of a single parent cell into exactly two daughter cells of roughly equal size. The parent cell replicates its DNA, elongates, and constricts in the middle, producing two separate individuals. This is common in bacteria, Amoeba, and Paramecium.
Q45. Reproduction in unicellular organisms mainly occurs by:
FissionUnicellular organisms reproduce primarily by fission—binary fission (e.g., Amoeba, bacteria, Paramecium) or multiple fission (e.g., Plasmodium). Regeneration, spore formation, and fragmentation are more common in multicellular or simple multicellular organisms, not the primary mode for unicellular organisms.
Q46. Binary fission means division into:
Two equal partsThe term “binary fission” literally means “division into two.” In this process, the parent cell divides into two approximately equal-sized daughter cells. In budding, by contrast, division is unequal (small bud forms on larger parent).
Q47. Yeast reproduction in Activity 11.1 is observed using a:
MicroscopeYeast cells are microscopic (approximately 3–10 micrometers in diameter). Their reproduction by budding cannot be seen with the naked eye, a hand lens, or a magnifying glass. A compound microscope (400x magnification or higher) is required to observe individual yeast cells, their buds, and the process of cell division.
Q48. Specialized cells are organised into:
TissuesIn multicellular organisms, cells with similar structure and function are grouped together to form tissues (e.g., epithelial tissue, muscle tissue, connective tissue). Tissues then combine to form organs, and organs form organ systems. This hierarchical organization enables specialized functions.
Q49. Fragmentation does not require:
Specialised reproductive organsFragmentation is a simple form of asexual reproduction. It does not involve the formation of specialized reproductive structures (e.g., flowers, testes, ovaries). Any body fragment that contains enough regenerative cells can grow into a new individual through ordinary growth and cell division. Maturation and cell division are still required.
Q50. The whip-like structure in Leishmania helps determine:
Orientation of fissionLeishmania has a single flagellum (whip-like structure) at one end. During binary fission, the plane of division is fixed relative to the flagellum, ensuring that each daughter cell inherits one flagellum. This is an example of definite orientation in fission. While the flagellum also aids movement, the question specifically asks about its role in reproduction.