(a) We do not clean ponds or lakes, but an aquarium needs to be cleaned regularly. Why?

(b) Why is ozone layer getting depleted at the higher levels of the atmosphere? Mention one harmful effect caused by its depletion.

Q: (a) We do not clean ponds or lakes, but an aquarium needs to be cleaned regularly. Why? (b) Why is ozone layer getting depleted at the higher levels of the atmosphere? Mention one harmful effect caused by its depletion.

(a) **Cleaning of Aquarium vs. Ponds/Lakes:** - A pond or lake is a **natural, self-sustaining ecosystem** containing a complete balance of producers, consumers, and decomposers (bacteria and fungi). The decomposers naturally break down dead organic matter and excreta into simple inorganic substances, keeping the water clean. - An aquarium is a **human-made (artificial) and incomplete ecosystem**. It usually lacks a sufficient population of decomposers. Consequently, metabolic wastes (like fish excreta) and uneaten food accumulate, turning into toxic substances that can kill the fish. Therefore, it must be cleaned regularly. (b) **Ozone Depletion and Harmful Effect:** - **Reason for depletion:** The ozone layer is getting depleted due to the release of synthetic chemicals like **chlorofluorocarbons (CFCs)**, which are widely used as refrigerants and in fire extinguishers. - **Harmful effect:** Depletion of the ozone layer allows harmful **ultraviolet (UV) radiation** from the Sun to reach the Earth's surface, which can cause **skin cancer** in human beings, damage eyes, and harm other organisms.

Our Environment

Ecosystem and Ozone Depletion

Official Answer

(a) Cleaning of Aquarium vs. Ponds/Lakes:

A pond or lake is a natural, self-sustaining ecosystem containing a complete balance of producers, consumers, and decomposers (bacteria and fungi). The decomposers naturally break down dead organic matter and excreta into simple inorganic substances, keeping the water clean.
An aquarium is a human-made (artificial) and incomplete ecosystem. It usually lacks a sufficient population of decomposers. Consequently, metabolic wastes (like fish excreta) and uneaten food accumulate, turning into toxic substances that can kill the fish. Therefore, it must be cleaned regularly.

(b) Ozone Depletion and Harmful Effect:

Reason for depletion: The ozone layer is getting depleted due to the release of synthetic chemicals like chlorofluorocarbons (CFCs), which are widely used as refrigerants and in fire extinguishers.
Harmful effect: Depletion of the ozone layer allows harmful ultraviolet (UV) radiation from the Sun to reach the Earth's surface, which can cause skin cancer in human beings, damage eyes, and harm other organisms.

natural ecosystemartificial ecosystemself-sustainingdecomposersaquariumchlorofluorocarbonsCFCsultraviolet radiationUVskin cancer

Marking Scheme

11.5 marks
21.5 marks

Hint

(a) Think about the role of decomposers in a natural ecosystem versus a small glass jar. (b) Recall the synthetic chemical used in refrigerators and the disease caused by UV rays.

Quick Oral Answer

Ponds are natural ecosystems with decomposers that clean up waste, while aquariums are artificial and lack enough decomposers, so we must clean them. Ozone is depleted by CFCs from refrigerators, and its depletion causes skin cancer due to increased UV radiation.

Analysis & Explanation

This question is divided into two parts. Part (a) tests the understanding of natural vs. artificial ecosystems. Natural ecosystems have self-cleaning mechanisms through decomposers, whereas artificial ones are incomplete and require human intervention. Part (b) focuses on the chemical cause of ozone depletion (CFCs) and its direct biological consequence (UV radiation causing skin cancer).

Common Mistakes

1Writing that ponds do not get dirty at all, rather than explaining the role of decomposers.
2Confusing ozone depletion with global warming or greenhouse effect.
3Attributing ozone depletion to carbon dioxide instead of CFCs.

Interesting Facts

The Montreal Protocol (1987) was a global agreement to freeze CFC production, which has successfully helped the ozone layer slowly recover over the decades.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2022?

This question carries 3 marks in the CBSE Class 10 Science 2022 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Our Environment" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Ecosystem and Ozone Depletion" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2022 paper?

This is a Short Answer question from Section Section B in the CBSE Class 10 Science 2022 paper.