Class 10 Science Chapter 13 Question Answers - Our Environment

Q1: Differentiate between biodegradable and non-biodegradable substances with the help of one example each. List two changes in habit that people must adapt to dispose non-biodegradable waste for saving the environment.
Ans: 1. Biodegradable substances: Substances that can be slowly destroyed and broken down into very small parts by natural processes by bacteria, fungi, etc. For example, organics wastes like vegetables and fruit peels.
2. Non-biodegradable substances: Substances that cannot be broken down or decomposed into the soil by natural agents are called as non-biodegradable. For example, plastic.
Habits to dispose non-biodegradable waste are:

• Segregating and treating the non-biodegradable waste before putting in dustbins.
• Recycle the plastics or glass present in non-biodegradable wastes.
• Motivate people to use paper or jute bags instead of plastic bags.

Q2: Our food grains such as wheat and rice, vegetables and fruits, and even meat are found to contain varying amounts of pesticide residues. State the reason to explain how and why it happens?
Ans: The harmful pesticides like DDT enter the plant body on being absorbed from the soil. When these are eaten by animals they get accumulated in the animal’s body as they are neither metabolized nor excreted out of their body. The concentration of these harmful chemicals gets increased at successive levels and are thus found in food grains as well as meat.

Q3: How is ozone formed in the higher level of the atmosphere? “Damage to ozone layer is a cause of concern”. Justify this statement.
Ans: Ozone is formed due to action of UV rays on oxygen molecules to form free oxygen atom which subsequently combines with another molecule of oxygen to form ozone. The reaction is:

O + O₂ → O₃ (Ozone)
Ozone depletion is a cause of concern because it protects us from the harmful ultraviolet radiations of the Sun by absorbing them. The UV rays can cause skin cancer, ageing, cataract, etc. to human beings if they are not absorbed by ozone due to ozone depletion.

Q4: Explain phenomenon of “biological magnification”. How does it affect organisms belonging to different trophic levels particularly the tertiary consumers?
Ans: The levels of harmful toxicants/pesticides like DDT gets increased at successive trophic levels as they are neither metabolised nor excreted by the organism. They get accumulated in organism’s body with their higher concentrations at higher trophic levels. This is called as biological magnification.
Since, the tertiary consumers are at the top of the food chain, so a higher amount of these toxicants is present in them compared to the lower trophic levels.

Q5: The first trophic level in a food chain is always a green plant. Why?
Ans: Green plants contain a pigment called chlorophyll which traps the energy from the Sun and converts it into chemical energy to be utilised by the members of the next trophic level. So, the first trophic level in a food chain is always a green plant.

Q6: List two environment friendly practices or habits which need to be followed by every member of a family community. Explain how these practices will support the “save the environment” mission.
Ans:

• Use of paper bags or jute bags instead of plastic bags.
• Segregate biodegradable and non-biodegradable wastes in separate dustbins.
• Use fuels like CNG, unleaded petrol or other ecofriendly fuels in vehicles.
• Due to uses of environment friendly practices or habits we can save our environment.

Q7: Write the harmful effects of using plastic bags on the environment. Suggest alternatives to plastic bags.
Ans: Harmful effects of plastic bags:

• They clog the drainage system.
• They choke the alimentary canal of cattle when they get eaten by them.
• On burning they release toxic gases.
• They are non-biodegradable and do not decompose easily.

Alternative to plastic bags:

• Use of jute bags or paper bags.
• Reusable cloth bags.

Q8: Construct an aquatic food chain showing four trophic levels.
Ans: Phytoplankton → Zooplankton → Small fish → Bird.

Q9: Why is improper disposal of waste a curse to the environment?
Ans: The improper disposal of wastes pollutes our environment and can cause harm to living organisms.

Q10: What are the advantages of cloth bags over plastic bags during shopping?
Ans: Cloth bags are better than the plastic bags because they:

• can be used to carry many things
• can be reused
• are made of biodegradable materials
• do not pollute the environment.