Diversity in Living Organisms – Case-based Questions with Answers

20 Case-Based Questions — Class 9 Biology Chapter 13: Diversity in Living Organisms

Content Bank Snapshot:

Topics: Need for classification, five-kingdom system, plant groups, animal phyla, viruses, bacteria, lichens, distinguishing characters, ecological roles, and practical observations.

Case-Based Questions

Case 1: While observing pond water under a microscope, Riya notes many tiny, green, single-celled organisms moving slowly and containing chloroplasts.

Q1: Which group do these organisms most likely belong to?

A: Algae (often classified under Protista or in some contexts with simple plants); unicellular photosynthetic organisms (e.g., Chlorella).

Case 2: A gardener notices some plants dying due to a fungal infection. The affected plants show white fuzzy growth on stems.

Q2: Name the kingdom and one characteristic that places these organisms there.

A: Kingdom Fungi — absorbative heterotrophic nutrition and cell walls made of chitin; reproduce by spores.

Case 3: During a field trip, students find a mossy patch on a damp rock and nearby a small fern growing in soil.

Q3: Identify the plant groups and one key difference between them.

A: Mosses are bryophytes (non-vascular) and ferns are pteridophytes (vascular). Key difference: bryophytes lack true vascular tissue, while pteridophytes have xylem and phloem.

Case 4: A sample contains a rod-shaped cell with no membrane-bound nucleus and a cell wall. It multiplies rapidly by binary fission.

Q4: To which kingdom does it belong and what term describes its cell organisation?

A: Kingdom Monera (bacteria); it is prokaryotic — lacks membrane-bound nucleus and organelles.

Case 5: While classifying two flowering plants, a student finds one with parallel leaf venation and another with net-like venation.

Q5: Which are monocot and dicot? Give one more distinguishing feature.

A: Parallel venation = Monocot (e.g., grass); Net-like venation = Dicot (e.g., hibiscus). Another feature: monocots have one cotyledon; dicots have two.

Case 6: A biology teacher shows images of organisms: a sponge and a jellyfish. Students note one has pores while the other has tentacles with stinging cells.

Q6: Classify both into respective phyla and state one characteristic of each.

A: Sponge = Phylum Porifera — porous body and filter feeding. Jellyfish = Phylum Cnidaria — radial symmetry and cnidocytes (stinging cells).

Case 7: A student isolates a tiny organism that can photosynthesise but is not multicellular and lacks true roots or leaves.

Q7: Suggest the likely group and mention whether it would be found more in aquatic or terrestrial habitats.

A: Likely an alga (unicellular or simple multicellular); commonly found in aquatic habitats (ponds, lakes) though some algae live on moist terrestrial surfaces.

Case 8: An angiosperm produces flowers with petals in multiples of three and narrow leaves with parallel veins.

Q8: What class of angiosperms does it belong to and name one common feature of that class?

A: Monocots — feature: floral parts often in multiples of three and parallel leaf venation.

Case 9: During a lab, students observe a unicellular eukaryote that moves using pseudopodia and engulfs food particles.

Q9: Identify the organism type and name the mode of nutrition.

A: Protist (e.g., Amoeba); mode of nutrition is holozoic (ingestion/phagocytosis of food particles).

Case 10: A farmer finds tiny spherical structures on leaves that appear to be fungal spores; crop yield is affected.

Q10: Explain how fungi spread and one practical control measure.

A: Fungi spread via spores dispersed by wind, water or animals. Control measure: remove infected plant parts and apply appropriate fungicides or practice crop rotation to reduce inoculum.

Case 11: A seawater sample shows multicellular green strands attached to rocks forming dense mats.

Q11: What are these likely to be and list two ecological roles they perform.

A: Likely multicellular algae (seaweeds). Roles: primary producers supplying oxygen and food for aquatic food webs; provide habitat and shelter for marine organisms.

Case 12: In a school garden, students notice lichens on bark and conclude the air is relatively clean in that area.

Q12: Explain why lichens are considered bioindicators of air quality.

A: Lichens are sensitive to air pollutants (like sulfur dioxide); they thrive in clean air but decline in polluted environments, so their presence indicates good air quality.

Case 13: A zoology question shows an animal with segmented body rings and bristles used for movement.

Q13: Which phylum does it belong to and give one example.

A: Phylum Annelida — segmented worms; example: Earthworm (Pheretima/Octochaetona).

Case 14: A student finds a plant that bears cones instead of flowers and has needle-like leaves.

Q14: Classify the plant group and state one adaptive advantage of its leaf type.

A: Gymnosperm (e.g., Pinus). Needle-like leaves reduce water loss and are adapted to cold or dry conditions by reducing surface area and having thick cuticles.

Case 15: In a microbiology practical, students observe bacteria that can perform photosynthesis using sunlight but lack chloroplasts.

Q15: What group are these and how do they photosynthesise without chloroplasts?

A: Cyanobacteria (blue-green algae) in Monera. They have photosynthetic pigments (like chlorophyll) in thylakoid membranes within the cytoplasm, enabling photosynthesis without chloroplasts.

Case 16: A biology student classifies two animals: one with a notochord and dorsal nerve cord; another without these features.

Q16: Which major groups do they belong to and what is the importance of a notochord?

A: The animal with notochord belongs to Phylum Chordata (vertebrates); the other is an invertebrate (various phyla). Notochord provides axial support and is a precursor to the vertebral column in higher chordates.

Case 17: A botanist examines seeds: one is dust-like and dispersed by wind, another is fleshy within fruit eaten by animals.

Q17: Explain the dispersal strategies and which plant groups typically show them.

A: Dust-like seeds = wind dispersal (anemochory), common in some gymnosperms and some angiosperms (e.g., orchids with tiny seeds). Fleshy seeds in fruits = animal dispersal (endozoochory), typical of many angiosperms (e.g., mango).

Case 18: During an ecology project, students note decomposing leaves being rapidly broken down in one patch while another patch remains littered.

Q18: Suggest a biological reason for the difference and name organisms involved.

A: Faster decomposition likely due to presence of decomposers (bacteria and fungi) and detritivores (earthworms, insects) which break down organic matter. Environmental factors (moisture, temperature) also affect decomposition rate.

Case 19: A student is told that two animals have similar limb structures used for different functions (e.g., bat wing and human arm).

Q19: Identify whether these organs are homologous or analogous and justify briefly.

A: Homologous — same structural origin (forelimb bones) but modified for different functions, indicating common ancestry (divergent evolution).

Case 20: In a classification exercise, a student is given an organism that cannot be placed in any kingdom of the five-kingdom system due to acellular nature.

Q20: Which entity fits this description and how is it treated in biological study?

A: Viruses — acellular infectious agents containing nucleic acid and protein coat. They are studied separately in virology and are not placed within the five-kingdom classification.

Diversity in Living Organisms – Case-based Questions with Answers

20 Case-Based Questions — NCERT-aligned

Case-Based Questions

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