Saturday, July 20, 2024

 Our Environment

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This chapter focuses on the importance of our environment and the potential threats it faces. Here are the key takeaways:

  • Environment: It’s everything around us, including living (biotic) and non-living (abiotic) factors. Examples include air, water, land, plants, animals, and humans.
  • Components of the Environment:
    • Biotic: Living organisms like plants, animals, and microorganisms.
    • Abiotic: Non-living components like air, water, soil, rocks, and minerals.
  • Ecosystems: A self-contained unit where living organisms interact with each other and their non-living environment.
    • Producers: Plants that capture sunlight and produce food (organic matter) through photosynthesis.
    • Consumers: Animals that depend on producers or other consumers for food. They can be herbivores (plant-eaters), carnivores (meat-eaters), or omnivores (eat both plants and animals).
    • Decomposers: Organisms like bacteria and fungi that break down dead organic matter, returning nutrients to the environment.
  • Waste Management:
    • Biodegradable Waste: Materials that can be decomposed by living organisms like bacteria (e.g., food scraps, leaves).
    • Non-biodegradable Waste: Materials that take very long to decompose naturally (e.g., plastic, glass, metal).
    • Importance of Proper Waste Disposal: Improper waste disposal can pollute our environment.
  • Threats to the Environment:
    • Pollution: Contamination of air, water, and land by harmful substances. This can be caused by human activities like burning fossil fuels, industrial waste, and improper waste disposal.
    • Ozone Depletion: The thinning of the ozone layer in the stratosphere, which protects us from harmful ultraviolet radiation from the sun.
  • Importance of Environmental Protection: It’s crucial to conserve our environment for a healthy planet and a sustainable future. This involves practices like reducing our carbon footprint, recycling, and using resources wisely.

Questions (Page 212)

1. What are trophic levels ? Give an example of food chain and state the different trophic levels in it.

Ans : Trophic levels refer to the feeding positions of organisms within a food chain or web. They represent the flow of energy and nutrients through an ecosystem. Here’s a breakdown:


  • Food Chain: A linear sequence of organisms where one organism eats another, transferring energy. It represents a simplified pathway of who eats whom.

Example of a Food Chain:

  • Grass (producer) –> Grasshopper (herbivore) –> Frog (carnivore) –> Snake (apex predator)

Trophic Levels in the Example:

  1. Producer (First Level): Organisms that can produce their own food, like plants through photosynthesis (grass in this case).
  2. Primary Consumer (Second Level): Herbivores that eat producers (grasshopper eating grass).
  3. Secondary Consumer (Third Level): Carnivores that eat herbivores (frog eating grasshopper).
  4. Apex Predator (Top Level): Carnivores that have no natural predators (snake eating frog).

2. What is the role of decomposers in the ecosystem ?

Ans : Decomposers play a vital role in ecosystems by acting as nature’s cleanup crew and recyclers.

  • Breakdown of Dead Matter: Decomposers, primarily bacteria and fungi, break down dead plants, animals, and other organic matter. This process, called decomposition, helps return nutrients like nitrogen, phosphorus, and carbon back into the soil.
  • Nutrient Recycling: By breaking down dead organisms, decomposers release essential nutrients trapped in these materials. These recycled nutrients become available again for producers (plants) to absorb and use for growth. This maintains a healthy cycle of nutrient flow within the ecosystem.
  • Making Space for New Life: Decomposition clears away dead organic matter, preventing an accumulation that would hinder the growth of new organisms. This creates space and resources for new life to flourish.
  • Maintaining Ecosystem Balance: Decomposers are crucial for maintaining the balance of organic matter in the ecosystem. Without them, dead matter would pile up, disrupting the natural nutrient cycle and hindering the overall health of the environment.

Questions (Page 214)

1. Why are some substances biodegradable and some non-biodegradable ?

Ans : 

Biodegradable Materials:

  • Made up of complex organic molecules, often containing carbon chains.
  • Decomposers can recognize and break down these complex molecules using enzymes.
  • Examples: food scraps, leaves, paper (made from cellulose, a plant fiber).

Non-biodegradable Materials:

  • Made up of complex synthetic molecules or very stable natural materials.
  • Decomposers lack the necessary enzymes to break down these complex structures.
  • Examples: plastic (synthetic polymers), glass (silicon dioxide), metal (elements like iron or aluminum).

2. Give any two ways in which biodegradable substances would affect the environment.

Ans : 

  1. Release nutrients:  Good for plants, but too much can cause imbalances in water or soil.
  2. Produce methane:  Natural process, but methane is a greenhouse gas.

3. Give any two ways in which non-biodegradable substances would effect the environment.

Ans : 

  1. Pollutes environment: Doesn’t break down, fills landfills and oceans (plastic pollution).
  2. Harms wildlife: Animals get entangled or eat it, causing injury or death.

Questions (Page 216)

1. What is ozone and how does it affect any ecosystem ?

Ans : Ozone (O3) is a gas molecule made up of three oxygen atoms. It exists in two regions of the atmosphere:

  1. Tropospheric Ozone (Ground-Level Ozone): This is a harmful pollutant found in the lower atmosphere near the Earth’s surface. It’s created by chemical reactions involving sunlight and pollutants like nitrogen oxides.
  2. Stratospheric Ozone (Ozone Layer): This beneficial layer resides in the upper atmosphere (stratosphere). It acts as a shield, absorbing harmful ultraviolet (UV) radiation from the sun. This protects life on Earth from the damaging effects of UV radiation, which can cause skin cancer, cataracts, and harm ecosystems.

Effects of Ozone on Ecosystems:

  • Ground-Level Ozone: This ozone is detrimental to ecosystems. It can damage plant tissues, reduce growth rates, and hinder photosynthesis. This can disrupt food webs and reduce overall plant productivity.
  • Stratospheric Ozone Depletion: The depletion of the ozone layer allows more UV radiation to reach the Earth’s surface.

2. How can you help in reducing the problem of waste disposal ? Give any two methods.

Ans : 

  1. Reduce and Reuse:
  • Reduce consumption: Buy only what you need and avoid impulse purchases. This minimizes the amount of waste generated in the first place.
  • Reuse items: Opt for reusable shopping bags, water bottles, and containers instead of disposables. You can also give old clothes or furniture a new life through repair or donation.
  1. Recycle and Compost:
  • Recycle properly: Learn about your local recycling program and separate recyclable materials like paper, plastic, glass, and metal for proper collection.
  • Compost food scraps and yard waste: This reduces the amount of organic waste going to landfills and creates nutrient-rich compost for your garden.


1. Which of the following groups contain only biodegradable item ?

(a) Grass, flowers and leather

(b) Grass, wood and plastic

(c) Fruit peels, cake and lime juice

(d) Cake, wood and grass

Ans : (c) Fruit peels, cake and lime juice

2. Which of the following constitutes a food-chain ?

(a) Grass, wheat and mango

(b) Grass, goat and human

(c) Goat, cow and elephant

(d) Grass, fish and goat

Ans : (b) Grass, goat and human

3. Which of the following are environment friendly practices ?

(a) Carrying cloth-bags to put purchases in while shopping

(b) Switching off unnecessary lights and fans

(c) Walking to school instead of getting your mother to drop on her scooter

(d) All of the above

Ans : (d) All of the above

4. What will happen if we kill all the organisms in one trophic level ?

Ans : Killing all organisms in one trophic level of an ecosystem would have a cascading effect, disrupting the entire food chain and leading to several imbalances:

  1. Population Explosion at the Previous Level: Without their natural predators, organisms in the previous trophic level would experience a population boom. Imagine all the grasshoppers thriving with no frogs to eat them!
  2. Resource Depletion: This population increase would rapidly deplete the food sources available at the previous level. The grasshoppers would eat all the grass, leaving them with nothing to sustain their growing numbers.
  3. Starvation and Population Crash:  As food resources become scarce, the herbivore population (grasshoppers in this example) would eventually face starvation and a population crash.
  4. Impact on Decomposers:  Since there wouldn’t be dead organisms from the consumed level (frogs) decomposers would have less organic matter to break down, affecting nutrient cycling in the ecosystem.
  5. Disruption of the Food Chain:  The entire food chain would be disrupted, impacting all remaining levels. Without herbivores, carnivores higher in the chain wouldn’t have food either.

5. Will the impact of removing all the organisms in a trophic level be different for different trophic levels ? Can the organisms of any trophic level be removed without causing any damage to the ecosystem ?

Ans : No, the impact of removing all organisms in a trophic level wouldn’t be significantly different across levels.  Here’s why:

  • Interdependence: All trophic levels are interconnected. Removing any level disrupts the flow of energy and nutrients within the food web.
  • Cascading Effect:  The consequences would ripple through the ecosystem. For example, removing herbivores (like removing all grasshoppers) would impact the plants they eat (grass) and the carnivores that rely on them (like frogs).

No level can be removed without causing damage.  Every level plays a crucial role:

  • Producers (Plants): They form the base of the food chain, capturing sunlight and producing energy for consumers.
  • Consumers (Herbivores, Carnivores): They transfer energy throughout the food chain by feeding on lower levels.
  • Decomposers (Bacteria, Fungi): They break down dead organic matter, returning nutrients to the soil for producers.

6. What is biological magnification ? Will the levels of this magnification be different at different levels of the ecosystem ?

Ans : Biological magnification is like poison building up in the food chain. Nasty chemicals don’t break down easily and get more concentrated as animals eat each other. Top predators end up with the most poison, making them sick.

7. What are the problems caused by the non-biodegradable wastes that we generate ?

Ans : Non-biodegradable wastes create a multitude of problems for our environment. Here are some of the most significant:

  • Pollution: Non-biodegradable waste like plastic bags and bottles can clog drains and pollute waterways, harming marine life and ecosystems. When burned, they release toxic fumes, polluting the air.
  • Landfill overflow:  As these wastes don’t decompose, they accumulate in landfills, taking up valuable space. Landfills can also leach harmful chemicals into the soil and groundwater.
  • Harm to wildlife: Animals can get entangled in plastic debris or mistake it for food, leading to injuries, starvation, and death.
  • Disrupted natural processes:  Non-degradable waste can block natural processes like soil formation and hinder plant growth.

8. If all the waste we generate is biodegradable, will this have no impact on the environment ? 

Ans : Even biodegradable waste can cause problems if not managed well. Too much waste can overwhelm decomposers, leading to slow breakdown, bad smells, and nutrient imbalances in soil or water. Composting and reducing waste are still important!

9. Why is damage to the ozone layer a cause for concern ? What steps are being taken to limit this damage ?

Ans : 

  • Ozone Layer: Protects us from harmful sunrays (UV).
  • Damage Concern: More UV rays reach Earth due to a damaged ozone layer, causing:
    • Increased Skin Cancer risk
    • Eye Damage
    • Harm to Ecosystems (plankton, plants)
  • Taking Action:
    • Montreal Protocol: Banned harmful chemicals (CFCs) that damage the ozone layer.
    • Alternatives Found: Replaced CFCs with safer options.
    • Monitoring Continues: Track healing and identify new threats.
  • The Takeaway: Ozone layer is healing, but we need to stay responsible for its full recovery.
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