NCERT Solutions for Class 10 Science Chapter 15: Our Environment

Trophic levels refer to the hierarchical levels in a food chain through which energy flows in an ecosystem. Each position in a food chain represents a trophic level.

Example of a food chain:

Grass Grasshopper Frog Snake Hawk

In this food chain:

1. First trophic level: Grass (Producer)
2. Second trophic level: Grasshopper (Primary consumer/Herbivore)
3. Third trophic level: Frog (Secondary consumer)
4. Fourth trophic level: Snake (Tertiary consumer)
5. Fifth trophic level: Hawk (Quaternary consumer/Apex predator)

Decomposers play a crucial role in ecosystems by:

• Breaking down dead organic matter and waste products
• Recycling nutrients back into the soil
• Converting complex organic substances into simpler inorganic forms
• Maintaining the balance of nutrients in the environment
• Cleaning the ecosystem by removing dead organisms
• Examples of decomposers include bacteria and fungi

Ozone (O) is a molecule made up of three oxygen atoms. It exists in two forms:

• At the ground level: It's a harmful pollutant and a major component of smog
• In the upper atmosphere (stratosphere): It forms the ozone layer, which protects Earth from harmful ultraviolet (UV) radiation

Effects of ozone on ecosystems:

• The stratospheric ozone layer shields living organisms from harmful UV radiation that can cause skin cancer, cataracts, and immune system damage
• It protects plants from UV damage, allowing photosynthesis to continue properly
• It protects aquatic ecosystems, particularly phytoplankton, which form the base of marine food chains
• Ground-level ozone damages plant tissues, reduces growth, and affects biodiversity

Substances are classified as biodegradable or non-biodegradable based on their chemical nature and ability to be broken down by natural processes:

Biodegradable substances:

• Can be broken down by decomposers like microorganisms (bacteria, fungi)
• Have simpler chemical structures that microorganisms can decompose
• Examples: Paper, vegetable waste, cotton, wool, etc.

Non-biodegradable substances:

• Cannot be broken down by natural biological processes
• Have complex chemical structures that resist decomposition
• Remain in the environment for long periods, causing pollution
• Examples: Plastics, glass, metals, synthetic fibers, etc.

Biodegradable substances affect the environment in the following ways:

• Nutrient cycling: When biodegradable waste decomposes, it releases essential nutrients back into the soil, enriching it and supporting plant growth.
• Methane production: In anaerobic conditions (like in landfills), biodegradable waste produces methane, a potent greenhouse gas that contributes to global warming when released into the atmosphere.

Non-biodegradable substances affect the environment in the following ways:

• Land pollution: These substances accumulate in landfills and persist in the environment for hundreds or thousands of years, occupying large areas and reducing land available for other purposes.
• Water pollution: When non-biodegradable waste enters water bodies, it harms aquatic life, disrupts ecosystems, and can enter the food chain, eventually affecting human health through bioaccumulation.

Composting offers several advantages:

• Converts organic waste into nutrient-rich manure for plants
• Reduces the amount of waste going to landfills
• Doesn't produce harmful greenhouse gases like methane if done properly
• Improves soil structure, water retention, and aeration
• Reduces the need for chemical fertilizers
• Is a cost-effective and environmentally friendly waste management method
• Helps in reducing soil erosion

Non-biodegradable wastes cause numerous environmental problems:

• Pollution: They pollute air, water, and soil due to their inability to break down
• Harm to wildlife: Animals can ingest or get entangled in plastic waste, leading to injury or death
• Bioaccumulation: Toxic chemicals from non-biodegradable waste can accumulate in organisms and magnify up the food chain
• Disruption of ecosystems: They alter natural habitats and ecological balance
• Landfill space: They occupy significant space in landfills for indefinite periods
• Resource depletion: Most non-biodegradable materials are derived from non-renewable resources

If all decomposers are removed from the ecosystem, the following consequences would occur:

• Dead plants and animals would accumulate without decomposition
• Nutrient recycling would stop, as nutrients would remain trapped in dead matter
• Soil fertility would decrease due to lack of nutrient replenishment
• The space available for living organisms would be reduced
• All biogeochemical cycles would be disrupted
• Eventually, the ecosystem would collapse due to the absence of material flow

Banning plastic bags is necessary due to their harmful environmental impact:

• Plastic bags are non-biodegradable and persist in the environment for hundreds of years
• They pollute soil and water bodies, harming terrestrial and marine life
• Many animals mistakenly eat plastic bags or get entangled in them, leading to injury or death
• They block drainage systems, causing floods during heavy rains
• Their production consumes fossil fuels and releases harmful chemicals
• Microplastics from their degradation can enter the food chain and affect human health
• Alternatives like cloth, jute, or paper bags are more environmentally friendly