The Living Organisms — Characteristics and Habitats

Why this chapter matters for UPSC: Habitat, adaptation, biotic and abiotic factors, food chains and the 10% rule are the vocabulary of GS3 ecology, and Prelims loves the traps: acclimatisation is not adaptation, whales breathe air, the energy pyramid is never inverted. This chapter is where that vocabulary begins. The 2020-21 and 2023-24 books title it "The Living Organisms — Characteristics and Habitats"; in NCERT's rationalised 2023-24 edition it is Chapter 6, with the text essentially unchanged.

🧠 First Principles — Read This First

Paheli and Boojho travel from the cold Himalaya (oaks, pines, deodars) to the hot Rajasthan desert (camels, cacti) and the sea beach at Puri (casuarina trees, crabs, fish). Every place, however hot, cold or humid, has living things; Boojho even finds a tiny spider in a cupboard, and Paheli reads of tiny organisms living in the openings of volcanoes.

The chapter builds two ideas from this:

1. Habitat and adaptation. The place where an organism lives is its habitat; the features or habits that let it live there naturally are its adaptations. A fish cannot live out of water and a camel cannot live in the sea.
2. What makes something living. Living things need food, grow, respire, respond to stimuli, excrete, reproduce, move and die. Non-living things may show some of these, but not all together.

PART 1 — Quick Reference

Key Terms (NCERT)

Adaptations in Different Habitats (NCERT)

PART 2 — Concepts & Narrative

Abiotic Factors and Seeds (NCERT Activity)

Soak moong seeds and keep sets of them in five conditions: dry, fully under water, in a sunny room, in a dark cupboard and in the cold of a refrigerator. Germination differs, showing that air, water, light and heat, all abiotic factors, matter for plants, and for all living organisms. NCERT asks whether sunlight and heat are biotic or abiotic: they are abiotic.

Adaptation versus Acclimatisation

If we go from the plains to a high mountain, we struggle to breathe and exercise for some days and breathe faster; after a while the body adjusts. Such small changes in one organism over a short period are acclimatisation. Adaptation is different: it takes thousands of years, because abiotic factors change slowly; organisms that cannot adapt die, and only the adapted survive. This is why habitats hold such a variety of organisms.

Characteristics of Living Things

Paheli enjoys Edward Lear's Complete Nonsense rhyme in which a Table asks a Chair to go for a walk: funny, because chairs and tables are not alive. But deciding what is living is not always easy: plants do not walk, yet a bus moves; clouds seem to grow. NCERT's list:

From Habitat to Ecosystem (NCERT Class X)

All the interacting organisms in an area, together with the non-living parts of their environment, form an ecosystem: a garden, a forest, a pond, a lake. Gardens and crop fields are human-made ecosystems; so is an aquarium with a few plants and animals added.

• Producers: all green plants and certain bacteria, which make food by photosynthesis.
• Consumers: herbivores, carnivores, omnivores and parasites, which depend on producers directly or indirectly.
• Decomposers: bacteria and fungi that break down dead remains into simple substances that return to the soil for plants.

PART 3 — UPSC Integration

Habitat, adaptation and the characteristics of life lead directly into ecology. The biotic-abiotic distinction becomes the ecosystem; who eats whom becomes the food chain and the trophic level; the 10% rule explains why top predators are few and why food chains are short, and why eating lower on the food chain feeds more people. Adaptations explain distributions: why cacti suit the Thar, conifers the Himalaya, and why migratory birds crowd Bharatpur in winter. Biological magnification explains why pesticides worry ecologists, and hotspots explain why the Western Ghats and the north-east matter so much in conservation questions. Mains answers should name the ecological principle, then the Indian example.

Exam Strategy

Prelims traps:

• Acclimatisation = short-term, one organism (breathing faster on a mountain); adaptation = over thousands of years.
• Sunlight and heat are abiotic.
• Dolphins and whales have no gills; they breathe air through blowholes.
• Cactus "leaves" are stems; the leaves are spines.
• Plants respire day and night; seeds respire (a sack of wheat is warm inside).
• Trophic level depends on position in the chain; in grass → grasshopper → frog → snake → eagle, the snake is the tertiary consumer.
• 10% is an average; energy flow is one-way; the energy pyramid is always upright; biomass pyramids in the sea are inverted.
• Hotspots: 34 worldwide in NCERT XII; India has parts of 3 (Western Ghats-Sri Lanka, Indo-Burma, Himalaya).
• Hibernation (winter, bears) vs aestivation (summer, snails and fish).

Mains angle: Explain why food chains rarely exceed four links, or how desert and mountain organisms are adapted to their habitats, with Indian examples.

Practice Questions

Practice (UPSC-pattern, not past papers).

Prelims:

1. Which of the following is an abiotic component of a habitat?
   (a) Grass
   (b) Bacteria in the soil
   (c) Sunlight
   (d) Insects

2. A person from the plains breathes faster for a few days after reaching a high mountain, and then adjusts. This is an example of:
   (a) Adaptation
   (b) Acclimatisation
   (c) Migration
   (d) Hibernation

3. Which of the following sea animals breathe air through blowholes rather than using gills?
   

   1. Dolphin
      
   2. Whale
      
   3. Octopus
      Select the correct answer using the code below:
      (a) 1 and 2 only
      (b) 2 and 3 only
      (c) 1 and 3 only
      (d) 1, 2 and 3

4. In the food chain grass → grasshopper → frog → snake → eagle, the tertiary consumer is the:
   (a) Grasshopper
   (b) Frog
   (c) Snake
   (d) Eagle

5. Which ecological pyramid can never be inverted?
   (a) Pyramid of numbers
   (b) Pyramid of biomass
   (c) Pyramid of energy
   (d) All three can be inverted

6. Consider the following statements:
   

   1. On average, about 10% of the food eaten at one trophic level is available to the next.
      
   2. Energy can flow back from herbivores to producers.
      
   3. Food chains usually have only three or four steps.
      Which of the statements given above are correct?
      (a) 1 and 2 only
      (b) 1 and 3 only
      (c) 2 and 3 only
      (d) 1, 2 and 3

7. Which of the following biodiversity hotspots, as listed in NCERT, cover parts of India?
   

   1. Western Ghats and Sri Lanka
      
   2. Indo-Burma
      
   3. Himalaya
      Select the correct answer using the code below:
      (a) 1 and 2 only
      (b) 2 and 3 only
      (c) 1 and 3 only
      (d) 1, 2 and 3

Mains (UPSC-pattern):

1. "Food chains are short because energy is lost at every step." Explain with reference to the 10% rule and ecological pyramids. (150 words)
2. Distinguish between adaptation and acclimatisation, and illustrate how desert and mountain organisms are adapted to their habitats. (150 words)

📦 Revision Capsule

Sources

Sources

• NCERT, Science (Class VI), ch. 9 "The Living Organisms — Characteristics and Habitats" (2020-21 print) and ch. 6 in the Rationalised 2023-24 edition: NCERT's book archives as captured by the Wayback Machine, 2020 copy and 2023-24 copy.
• NCERT, Science (Class X), ch. 13 "Our Environment", Reprint 2025-26: book archive.
• NCERT, Biology (Class XII), ch. 12 "Ecosystem" and ch. 13 "Biodiversity and Conservation", Reprint 2025-26 (book archive); ch. 13 "Organisms and Populations", 2021-22 print (adaptations).