Class 7 Science Lesson 4

1. Tick (✔) the correct answer:

a. Which of the following is a renewable resource?
Ans: Solar energy

b. Which gas is mainly responsible for global warming?
Ans: Carbon dioxide

c. What is the main cause of water pollution?
Ans: Industrial waste

d. Which of the following animals is an indicator of wetland health?
Ans: Frog

e. What is the process of converting waste into reusable materials called?
Ans: Recycling

2. Fill in the blanks:

a. The variety of different species in an ecosystem is called ____________.
Ans: Biodiversity

b. Cutting down trees in a large area is known as ____________.
Ans: Deforestation

c. ____________ helps improve soil fertility by decomposing organic matter.
Ans: Composting

d. The layer of gases surrounding the Earth is called the ____________.
Ans: Atmosphere

e. Using pesticides excessively can harm ____________, which are beneficial insects.
Ans: Pollinators

3. Match the following:

Ans:

a. What are the effects of global warming on biodiversity?
Ans: Global warming causes habitat loss, alters migration patterns, disrupts breeding seasons, and increases the risk of extinction for many species.

b. How can individuals contribute to biodiversity conservation?
Ans: Individuals can plant native trees, reduce waste, avoid using harmful chemicals, support conservation organizations, and spread awareness about protecting nature.

c. Why is soil erosion harmful to the environment?
Ans: Soil erosion removes fertile topsoil, reduces agricultural productivity, causes sedimentation in water bodies, and leads to habitat destruction.

d. What is the role of national parks in biodiversity conservation?
Ans: National parks protect natural habitats, provide safe areas for wildlife, support research and education, and help preserve endangered species.

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Questions and Answers

a. Write the importance of biodiversity:

Ans: Biodiversity is critically important for maintaining the balance and health of ecosystems on Earth. It supports ecosystem stability and resilience by enabling systems to recover from environmental changes and disasters. A variety of species ensures that ecological processes such as pollination, nutrient cycling, and decomposition continue smoothly. Biodiversity provides humans with essential resources such as food, medicine, fuel, and raw materials for industry and shelter. Many modern medicines have been developed from compounds found in plants and animals. It maintains ecological balance by regulating population sizes and interactions between species. Moreover, biodiversity has cultural, aesthetic, and recreational value, enriching human lives and inspiring art, religion, and tourism. Conservation of biodiversity also ensures the survival of future generations who will depend on these natural resources.

b. How can we maintain ecosystem balance?

Ans: Ecosystem balance can be maintained through various protective and sustainable practices. Protecting wildlife habitats from destruction and fragmentation is key because habitats provide shelter and food for species. Sustainable resource use means harvesting plants and animals at a rate that does not exceed their regeneration. Pollution control reduces harmful substances in air, water, and soil that damage living organisms and their habitats. Conservation programs, such as establishing protected areas, restoring degraded lands, and breeding endangered species, help maintain biodiversity. Public awareness and education encourage individuals and communities to reduce waste, plant native species, and avoid activities harmful to nature. Integrating traditional knowledge with modern conservation also plays an important role in preserving ecosystems.

c. What is a wetland?

Ans: A wetland is an area where water covers the soil or is present near the surface either permanently or seasonally. Wetlands include swamps, marshes, bogs, and mangrove forests. These ecosystems support unique plant and animal species adapted to saturated conditions. Wetlands act as natural water filters by trapping sediments and pollutants, improving water quality. They regulate floods by absorbing excess rainfall and slowly releasing it. Wetlands provide breeding and feeding grounds for many fish, birds, and amphibians. They also store large amounts of carbon, helping mitigate climate change. Despite their importance, wetlands are vulnerable to drainage and conversion for agriculture or urban development.

d. Why are water reservoirs important?

Ans: Water reservoirs are man-made or natural lakes that store water for various uses. They are important because they supply water for drinking, agriculture, and industries, especially during dry seasons or droughts. Reservoirs help control floods by capturing excess rainwater and releasing it gradually. They recharge groundwater supplies by allowing water to seep underground. Reservoirs support aquatic ecosystems, providing habitats for fish and other aquatic species. Many reservoirs generate hydroelectric power, which is renewable and reduces reliance on fossil fuels. They also offer recreational opportunities like fishing and boating. Proper management of reservoirs ensures sustainable water availability for humans and nature.

e. Mention major methods of solid waste management:

Ans: Effective solid waste management reduces pollution and conserves resources. The 3Rs—Reduce, Reuse, and Recycle—are the foundation of waste management. Reducing waste means using fewer disposable products and packaging. Reusing involves using items multiple times before disposal. Recycling converts waste materials into new products, saving energy and raw materials. Composting transforms organic waste such as food scraps into nutrient-rich fertilizer, reducing landfill load and improving soil health. Landfilling is the controlled disposal of waste in designated sites engineered to prevent contamination. Incineration burns waste to reduce volume and sometimes generate energy but must be controlled to limit air pollution. Waste segregation at source—separating biodegradable and non-biodegradable materials—facilitates recycling and composting.

f. How does the extensive use of chemical fertilizers and insecticides deplete natural resources?

Ans: Extensive use of chemical fertilizers and insecticides damages natural resources in multiple ways. Overuse of fertilizers depletes soil nutrients and kills beneficial microbes, leading to soil degradation and erosion. Chemicals can leach into water bodies, causing pollution that kills aquatic life and contaminates drinking water. Insecticides do not only kill pests but also beneficial insects like pollinators and natural predators, reducing biodiversity and upsetting ecosystem balance. Air pollution results from volatilization of chemicals releasing harmful gases. Soil and water contamination reduce agricultural productivity over time, forcing farmers to apply more chemicals in a vicious cycle. Chemical residues also accumulate in food chains, posing health risks to animals and humans. Sustainable alternatives like organic farming, integrated pest management, and using biofertilizers are encouraged to reduce these impacts.

g. Explain the importance of wetlands:

Ans: Wetlands are among the most productive ecosystems, offering numerous ecological and economic benefits. They naturally filter pollutants, improving water quality and protecting downstream ecosystems. By absorbing floodwaters, wetlands reduce the severity and frequency of floods, protecting human settlements. They store large amounts of carbon in plant biomass and soil, helping mitigate global warming. Wetlands provide critical habitats for many endangered and migratory species, supporting biodiversity. They contribute to local economies through fisheries, agriculture, and ecotourism. Wetlands also help maintain groundwater levels by allowing water to percolate into aquifers. Their loss leads to increased flooding, water pollution, and biodiversity decline, making their conservation a priority.

h. “Nepal is rich in biodiversity.” Justify the statement:

Ans: Nepal is a biodiversity hotspot because of its unique geographical and climatic diversity. Its altitude ranges from the tropical lowlands of the Terai to the alpine and nival zones of the Himalayas, creating diverse habitats. Nepal’s ecosystems include dense tropical and temperate forests, alpine meadows, freshwater lakes, and wetlands. These varied environments support a wide range of plant and animal species, including rare and endemic species such as the red panda, snow leopard, one-horned rhinoceros, and various orchids. Nepal’s climate varies from subtropical to arctic, further supporting different species adapted to these zones. Protected areas like Chitwan National Park and Sagarmatha National Park conserve habitats and wildlife, promoting biodiversity. This richness has global significance for conservation and ecological research