Test: Our Environment- 3 - Class 10 MCQ

The biotic components of an ecosystem include all living organisms within it, such as plants, animals, microorganisms, and human beings. These organisms interact with each other and with the abiotic components of the ecosystem to maintain a balance in nature.

• Assertion: In this scenario, the Assertion is correct as it highlights the interaction and balance maintenance in nature by various organisms.
• Reason: The Reason is also accurate, explaining the components of an ecosystem. However, the Reason is not a direct explanation of the Assertion; rather, it provides additional information about what constitutes an ecosystem. Hence, the correct answer is Option B.

• Option A: Biotic Components - Temperature, Rainfall
  • Biotic components refer to the living organisms within an ecosystem, such as plants, animals, and microorganisms.
  • Temperature and Rainfall are physical factors and thus classified as abiotic components.
  • Therefore, Option A is incorrectly matched.
• Option B: Abiotic Components - Wind, Soil, Minerals
  • Abiotic components include non-living physical factors that impact an ecosystem, such as Wind, Soil, and Minerals.
  • Therefore, this option is correctly matched.
• Option C: Natural Ecosystem - Garden, Crop-fields
  • Natural ecosystems occur naturally without human intervention and include forests, ponds, and lakes.
  • Gardens and crop-fields, on the other hand, are created and maintained by humans, making them human-made (artificial) ecosystems.
  • Therefore, Option C is incorrectly matched.
• Option D: Human-made Ecosystem - Forests, Ponds
  • Forests and ponds are examples of natural ecosystems.
  • Human-made ecosystems include those altered or created by human activity, such as gardens and crop-fields.
  • Therefore, Option D is incorrectly matched.
• Thus, the correctly matched pair is Option B: Abiotic Components - Wind, Soil, Minerals.

Autotrophs or producers, which include green plants capturing solar energy, form the first trophic level in a food chain. They convert sunlight into chemical energy, initiating the flow of energy through the ecosystem.

Autotrophs or producers occupy the first trophic level in a food chain, as they are the primary energy converters that transform sunlight into chemical energy, initiating the flow of energy through the ecosystem.

• The assertion is correct. Autotrophs, such as green plants, occupy the first trophic level in an ecosystem as they are capable of converting solar energy into chemical energy through photosynthesis.
• The reason is also correct. Autotrophs play a fundamental role in capturing solar energy and converting it into a form that can be utilized by heterotrophs (consumers) and decomposers within the ecosystem.
• Therefore, in this context, Option A is the correct answer as both the Assertion and Reason are true, and the Reason provides a valid explanation for the Assertion.

 The correct answer is C: Biomagnification.

• Biomagnification refers to the process where the concentration of harmful chemicals increases in organisms as they move up the food chain.
• This occurs because predators consume prey containing these chemicals, leading to higher concentrations at each trophic level.
•  Examples include mercury in fish or pesticides like DDT in birds.
• Unlike simple accumulation, biomagnification highlights the amplified impact on top predators, often affecting their health and survival.

The energy available at each trophic level gets diminished progressively due to loss of energy at each trophic level. This phenomenon is a key concept in understanding energy flow within ecosystems.

• The Assertion is true.

  It is a fundamental concept in ecology that energy diminishes at each trophic level in a food chain. This is due to the loss of energy during metabolism, heat loss, and other inefficiencies in energy transfer.

• The Reason is also true.

  Food chains are limited in length due to the significant energy loss that occurs at each trophic level. This limitation is a result of the inefficiency of energy transfer between trophic levels.

• However, the Reason is not the correct explanation of the Assertion.

  While both statements are true, the fact that energy diminishes at each trophic level does not directly explain why food chains generally consist of only three or four steps. The length of food chains is influenced by various factors beyond just energy loss.

• Option A: 10% Rule - Energy transferred to the next trophic level: Explanation: The 10% Rule indicates that only about 10% of the energy from one trophic level is transferred to the next level. The rest is lost as heat, used in metabolism, or remains unassimilated.
• Option B: Biological Magnification - Decrease in chemical concentration at higher trophic levels - Incorrect: Biological Magnification refers to the increase in concentration of harmful chemicals at higher trophic levels, not a decrease.
• Option C: Food Web - Linear sequence of organisms - Incorrect: A food web represents a complex network of feeding relationships, not a linear sequence. A linear sequence is referred to as a food chain.
• Option D: Unidirectional Energy Flow - Energy flows back to autotrophs - Incorrect: Unidirectional Energy Flow means that energy flows in one direction—from the sun to autotrophs (producers) to various levels of consumers and does not flow back.

• Ozone at the higher levels of the atmosphere plays a critical role in shielding the Earth's surface from ultraviolet (UV) radiation. This protective function is essential for maintaining life on Earth as it helps prevent harmful UV rays from reaching the surface, thus safeguarding living organisms from the detrimental effects of excessive UV exposure.

Ozone shields the surface of the earth from ultraviolet (UV) radiation from the Sun. UV radiation can be harmful to organisms, and ozone plays a crucial role in protecting life on Earth from its adverse effects.

• The assertion that biodegradable substances have a positive impact on the environment is true. Biodegradable substances can decompose naturally through the action of microorganisms, returning essential nutrients to the soil and contributing to the ecosystem's balance.
• The reason that biodegradable substances break down into harmless compounds is also true. When biodegradable materials decompose, they do not leave harmful residues behind, unlike non-biodegradable materials that can persist in the environment for long periods and cause pollution.
• Therefore, the reason provided is a correct explanation for the assertion.

• Option A: Ozone - Greenhouse Gas Ozone is not primarily categorized as a greenhouse gas. While it does have some greenhouse properties, its main environmental significance lies in its role in the stratosphere, where it protects Earth from harmful ultraviolet (UV) radiation. Thus, this pair is incorrectly matched.
• Option B: Plastic - Biodegradable Most plastics are non-biodegradable, meaning they do not break down easily by natural processes. This characteristic leads to long-term environmental pollution. Thus, this pair is incorrectly matched.
• Option C: Chlorofluorocarbons (CFCs) - Ozone Depletion Chlorofluorocarbons (CFCs) are synthetic chemicals that have been shown to deplete the ozone layer in the stratosphere. They release chlorine atoms when exposed to UV radiation, which then break down ozone molecules, leading to ozone layer thinning. This pair is correctly matched.
• Option D: Ultraviolet (UV) Radiation - Harmless to Humans Ultraviolet (UV) radiation is harmful to humans and can cause skin cancer, cataracts, and other health issues. It is precisely because of this harm that the ozone layer's protective role is so crucial. Thus, this pair is incorrectly matched.