Class 10 Science Chapter 13: Our Environment — Important Questions & Sample Paper

Excessive use of chlorofluorocarbons (CFCs)

Paper

Sunlight

Bacteria and fungi

A is true but R is false.

An ecosystem is a self-sustaining unit where living organisms interact with each other and with the non-living environment. Its two main components are biotic (living) and abiotic (non-living).

A possible web: grass → grasshopper → frog → snake → hawk; grass → rabbit → hawk. If one species declines, predators can switch to alternative prey. This redundancy prevents collapse, unlike a single chain where loss of one link breaks the whole chain.

Short-term: Rabbit population will increase due to lack of predation, leading to overgrazing of grass. Long-term: Grass cover depletes, causing starvation and eventual decline in rabbit population, leading to an unbalanced ecosystem with loss of vegetation and possibly soil erosion.

An ecosystem is a self-sustaining unit where living organisms interact with each other and with the non-living environment. The two major components are biotic factors (e.g., plants) and abiotic factors (e.g., sunlight).

According to the 10% law, only about 10% of the energy at one trophic level is transferred to the next level. Given 10,000 J of energy at the producer level (grass), the energy at the primary consumer (grasshopper) = 10% of 10,000 J = 1,000 J. At the secondary consumer (frog) = 10% of 1,000 J = 100 J. This frog is the third trophic level (producers as first). So energy available at third trophic level is 100 J. The number of trophic levels is limited because energy decreases drastically at each level; after 4-5 levels, very little energy remains to support another level. For example, at the fifth level, only 0.01% of original energy remains, insufficient to sustain a population. Removing all cows (primary consumers) from a grassland ecosystem would have cascading effects: Producers (grass) would grow unchecked, possibly leading to overgrowth and later depletion of soil nutrients. Predators depending on cows (if any, like wolves or parasites) would lose a food source, causing their population to decline. Decomposers would initially face a decrease in cow dung, altering nutrient cycling. Biodiversity would decrease, and the ecosystem might shift to a different stable state dominated by shrubs or invasive species due to changes in grazing pressure. Thus, energy flow and population dynamics would be disrupted.

Biodegradable substances (e.g., paper, wood, vegetable peels) can be broken down by decomposers into simpler, harmless substances, recycling nutrients. Non-biodegradable substances (e.g., plastic, DDT, glass) cannot be decomposed by microbes and persist in the environment, causing pollution. They accumulate in ecosystems. Biomagnification occurs when non-biodegradable toxic substances (e.g., DDT, mercury) enter a food chain at the producer level and become concentrated at successive trophic levels. In an aquatic food chain: DDT in water → absorbed by phytoplankton (producer) → zooplankton (primary consumer) accumulates it → small fish → large fish → fish-eating birds (top consumer). Since DDT is not metabolized or excreted, its concentration increases with each trophic level, reaching harmful levels in top predators, affecting reproduction. Eco-friendly practices: (1) Use of biodegradable packaging materials like jute or paper instead of plastic. (2) Proper waste segregation and recycling of non-biodegradable materials like plastics and e-waste. Reducing consumption and promoting circular economy techniques can minimize waste.

Invasive plant reduces native plants, leading to herbivore and carnivore decline. Producers are affected first. Biological control: introduce a specific herbivore, but it may become invasive.