1. Why are humans at the top of most food chains? Humans are
omnivores and can eat at multiple trophic levels. We have no natural predators due to our intelligence and
technology.
2. What would happen if all decomposers disappeared? Dead
matter would accumulate indefinitely. Nutrients would be locked in dead bodies. Eventually, producers would
die due to nutrient depletion, collapsing the entire ecosystem.
3. Why is ozone harmful at ground level but beneficial in
stratosphere? Ground level O₃ is a pollutant (causes breathing problems). Stratospheric O₃
absorbs harmful UV radiation, protecting life below.
4. Can we create an artificial ecosystem? Difficult to
replicate natural balance. Biosphere 2 experiment showed challenges in maintaining gas balance, water cycle,
and food production. Natural ecosystems are self-regulating.
5. DDT Story: DDT was widely used as pesticide. It's
fat-soluble and persistent (non-biodegradable). Entered water → absorbed by plankton → small fish → large
fish → birds. Concentration increased at each level.
6. Effect on Birds: High DDT levels caused thin eggshells.
Eggs broke before hatching. Populations of eagles, pelicans declined drastically. Led to DDT ban in many
countries.
7. Lesson: Chemicals that don't break down can accumulate in
food chains. Top predators (including humans) are most affected. We need to use biodegradable alternatives.
8. Causes: Burning fossil fuels, deforestation, industrial
processes release CO₂, CH₄, N₂O. These greenhouse gases trap heat, causing global warming.
9. Effects: Rising sea levels (ice melting), extreme weather
(floods, droughts), coral bleaching, ecosystem disruption, species extinction, food insecurity.
10. Solutions: Renewable energy (solar, wind), electric
vehicles, afforestation, energy efficiency, international agreements (Paris Agreement), individual actions
(reduce, reuse, recycle).
11. Assertion: A food web is more stable than a food
chain.
Reason: In a food web, organisms have multiple food sources. If one species disappears,
predators can switch to alternatives. Food chains have no backup.
Both A and R are True, R is correct explanation of A.
12. What is the 3R principle? Reduce (use less), Reuse (use
again), Recycle (convert waste to new products). Priority: Reduce > Reuse > Recycle. Prevents waste at
source rather than managing it after creation.
