Life on the Earth (Biosphere and Ecosystems) — Practice

Question 1

A grassland food chain is: Grass → Grasshopper → Frog → Snake → Eagle. If the grass contains 10,000 kcal of energy, (a) how much energy does the grasshopper receive? (b) How much does the eagle receive? (c) Why is it inefficient for humans to eat meat instead of grain?

Accepted Answer

(a) Grasshopper receives 10% of grass energy = 10% × 10,000 = **1,000 kcal**.

(b) Energy transfer at each level: Grasshopper 1,000 → Frog 100 → Snake 10 → Eagle **1 kcal**. The eagle receives only 1/10,000th (0.01%) of the energy stored in the original grass.

(c) Human inefficiency of meat-eating: If humans eat grain (T1→T2 = 10% efficiency), 1,000 kcal of grain gives 100 kcal to humans. If humans eat beef raised on grain (T1→T2→T3), 1,000 kcal of grain → 100 kcal beef → 10 kcal to humans. Eating meat requires 10× more grain for the same caloric benefit. This is why the same land can feed 10× more vegetarians than meat-eaters — directly relevant to India's food security and land use policy.

Question 2

Match each biome to its climate conditions and give ONE specific location and ONE characteristic plant or animal adaptation:
(a) Tropical Rainforest  (b) Taiga/Boreal Forest  (c) Desert  (d) Tundra

Accepted Answer

(a) **Tropical Rainforest**: Climate — high temperature (24–27°C year-round) + high rainfall (200cm+). Location: Amazon Basin (Brazil), Congo Basin (Africa), Western Ghats (India). Adaptation: Emergent trees with buttress roots (shallow soil, so roots spread wide for support and nutrient absorption); thick bark not needed (no freezing); canopy stratification maximises light capture in dense vegetation.

(b) **Taiga (Boreal Forest)**: Climate — short, cool summer (3–5 months) + cold, long winter (−30°C) + moderate precipitation (40–100cm, mostly snow). Location: Siberia, Canada, Scandinavia; parts of Himachal Pradesh at high altitudes. Adaptation: Conical shape of conifers (pine, fir, spruce) — snow slides off instead of accumulating and breaking branches; needle-shaped leaves with waxy coating prevent water loss in frozen winters (physiological drought).

(c) **Desert**: Climate — high temperature (40–50°C by day, near 0°C at night) + very low rainfall (<250mm/year). Location: Sahara, Thar (India), Arabian Desert. Adaptation: Cacti — shallow but wide-spreading roots absorb rare rainfall quickly; succulent stems store water; thorns instead of leaves (reduce transpiration; deter grazers).

(d) **Tundra**: Climate — permanently frozen subsoil (permafrost), extremely cold (−30°C to −10°C), very short growing season (60 days), low precipitation. Location: Arctic regions, high Himalayas (Ladakh). Adaptation: Cushion plants — grow low (avoid freezing wind); long roots reach deep nutrients; mosses and lichens dominate (most flowering plants can't survive).

Question 3

The Sariska Tiger Reserve in Rajasthan lost ALL its tigers by 2005 due to poaching, despite being a protected area. Using the concepts of food chain, food web, and ecosystem stability, explain: (a) what happens to the ecosystem when apex predators are removed, (b) why food webs are more stable than simple food chains, and (c) what conservation strategy can restore apex predator populations.

Accepted Answer

(a) **Removing apex predators — Trophic Cascade**:
Tigers (top predators) control deer and nilgai (herbivore) populations. Without tigers:
→ Deer/nilgai populations explode (no predation pressure)
→ Herbivores overgraze the forest understory and grass layer
→ Grasses, shrubs, and tree seedlings are consumed faster than they regenerate
→ Forest cover declines → soil erosion increases → water bodies silt up
→ Secondary consumers (wolves, leopards) that depended on the same prey may also decline
This is a **trophic cascade** — removing one species at the top restructures the entire ecosystem below. Yellowstone's wolf reintroduction (1995) demonstrated this: without wolves, elk had overgrazed riverbanks, causing erosion; with wolves restored, vegetation recovered and rivers became more stable.

(b) **Food web stability**:
In a simple food chain (grass → deer → tiger), if deer disease kills 80% of deer, tigers starve immediately. In a food WEB, tigers also eat wild boar, peacock, and smaller mammals. If deer decline, tigers shift prey. The redundancy of multiple connections buffers against species loss — this is called **functional redundancy**. Ecosystems with complex food webs (high biodiversity) are more resilient to disturbance than simple chains.

(c) **Conservation strategy — source-sink reintroduction**:
Sariska used **translocation from Ranthambore** — tigers were relocated from a healthy 'source' population to the depleted 'sink' reserve. Key steps:
(i) Eliminate poaching: patrol density increased; villages near core zone relocated with compensation.
(ii) Restore prey base: herbivore numbers monitored; vegetation managed to support deer.
(iii) Reduce human-wildlife conflict: livestock loss compensated immediately — removes incentive for retaliatory killing.
(iv) Genetic diversity: bring tigers from different source populations to prevent inbreeding in small populations.
By 2024, Sariska has ~30 tigers — a conservation success demonstrating that ecosystem restoration is possible with sustained effort.

Practice — Life on the Earth (Biosphere and Ecosystems)

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