Assertion & Reason Test: Our Environment - Class 10 MCQ

Explanation:
The given assertion and reason are related to the role of green plants in the ecosystem. Let's break down the explanation into headings and bullet points for better understanding:
Assertion: Green plants of the ecosystem are the transducers.
- This statement asserts that green plants play the role of transducers in the ecosystem.
Reason: Producers trap the radiant energy of the sun and change it into chemical energy.
- This statement provides a reason for the assertion by stating that producers (green plants) convert the radiant energy of the sun into chemical energy.
Now, let's analyze the given options:
A: Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
- This option states that both the assertion and reason are true, and the reason correctly explains the assertion. This option is correct because it aligns with the given statements.
B: Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
- This option states that both the assertion and reason are true, but the reason does not correctly explain the assertion. However, this option is incorrect because the reason does explain the assertion.
C: Assertion (A) is true but reason (R) is false.
- This option states that the assertion is true, but the reason is false. However, this option is incorrect because both the assertion and reason are true.
D: Assertion (A) is false but reason (R) is true.
- This option states that the assertion is false, but the reason is true. However, this option is incorrect because both the assertion and reason are true.
E: Both Assertion and Reason are false.
- This option states that both the assertion and reason are false. However, this option is incorrect because both the assertion and reason are true.
Therefore, the correct answer is option A: Both assertion (A) and reason (R) are true, and reason (R) is the correct explanation of assertion (A).

The Correct Answer is Option B.

1. Why Assertion (A) is true:

   • In a food chain, energy travels in one direction — from the Sun → autotrophs (producers) → herbivores → carnivores → decomposers.

   • At each step (trophic level), only a fraction (~10%) of the energy is passed on; the rest is lost as heat. Because of this loss, energy cannot cycle back up to an earlier level.

2. Why Reason (R) is true:

   • Autotrophs (like green plants) capture solar energy through photosynthesis.

   • They convert it into chemical energy in their tissues, which then becomes available to herbivores.

   • None of that stored energy returns directly to the Sun.

3. Why (R) does not explain (A):

   • The fact that autotrophs don’t send energy back to the Sun is a statement of direction, but it doesn’t explain why flow is strictly one-way.

The Correct Answer is Option A. Here is the detailed explanation: 

• Assertion (A) is true

  • In nature, every animal uses special methods—like hiding, speed, or protective colours—to survive when predators or harsh conditions threaten them.

• Reason (R) is true

  • The praying mantis has a green body that looks just like leaves. This camouflage makes it hard for both predators and prey to spot it.

• Why (R) explains (A):

  • Being green and blending into foliage is one of the many survival strategies animals use.

  • Since camouflage helps the mantis avoid enemies and catch food, it is a direct example of the general idea stated in the assertion.

Because both statements are correct and the reason gives a concrete example of the assertion, the correct choice is A.

The Correct Answer is Option B

1. Assertion (A) is true:

   • CFCs (chlorofluorocarbons) released into the air eventually reach the stratosphere.

   • There, UV rays break CFC molecules, freeing chlorine atoms.

   • Each chlorine atom can destroy thousands of ozone (O₃) molecules, thinning the ozone layer.

2. Reason (R) is true:

   • CFCs have been widely used as refrigerant gases and in fire-extinguishing foams.

3. Why (R) does not explain (A):

   • Knowing where CFCs are used (refrigerators, extinguishers) does not tell us how they destroy ozone.

   • The correct explanation involves the chemical reaction in the stratosphere (UV-driven release of chlorine radicals), which is not stated in (R).

Because both statements are correct but the Reason given is not the explanation for ozone depletion, the right choice is B.

Crown files are most destructive. These destroy the canopies of trees and entire vegetational cover of that particular area. Due to this fire, the temperature rises upto 700°C and may adversely affect the vegetation.

The assertion is correct because plants can synthesize food due to the presence of abiotic components like carbon dioxide and sunlight, due to which energy is produced. This energy is transferred at each trophic level.

The reason is correct because due to energy obtained, organisms at each trophic level sustain.

Man is an example of an omnivorous animal because Omni means all and vore means eater. An organism which can feed on the plant, as well as the meat of the animal, are called omnivorous.

Man consumes plants (fruit vegetables) and also eats the meat of animals like goat, chicken etc thus man is considered as the Omnivorous animal.

A trophic level is the position of an organism in a food chain. A food chain starts with producers which are green plants and occupy the lowest trophic level. The highest trophic level is occupied by carnivores which feed on lower trophic levels for energy. A simple food chain is represented as

Plant ---> Herbivore ---> Carnivore

Hence, trophic levels are formed by different organisms linked in a food chain.

The Correct Answer is Option B.

1. Assertion (A) is true:

   • Ecology indeed studies how organisms (plants, animals, microbes) interact with each other and with factors like temperature, soil, water, and sunlight.

2. Reason (R) is true:

   • An ecosystem is exactly that: all the living (biotic) parts plus the non-living (abiotic) parts working together.

3. Why (R) does not explain (A):

   • While (R) defines an ecosystem, it does not explain what ecology studies or how those relationships are examined.

   • Ecology is broader: it looks at energy flow, nutrient cycling, population dynamics, and so on within that ecosystem.

Because both statements are correct but the Reason does not directly explain the Assertion, the correct choice is B.

The Correct Answer is Option D.

1. Why Assertion (A) is false

   • The first trophic level in any food chain is made up of autotrophs (producers), such as green plants and algae.

   • Consumers (heterotrophs) occupy the second or higher levels, because they feed on those autotrophs or on other consumers.

2. Why Reason (R) is true

   • Autotrophs (like plants) capture sunlight and convert it into chemical energy (glucose) via photosynthesis.

   • Consumers cannot perform photosynthesis and must obtain energy by eating other organisms.

Since (A) is false and (R) is true, the correct choice is D.

Decomposers keep the environment clean by decomposing or consuming the dead remains of other organisms.

Crop fields are man made and some biotic and abiotic components are manipulated by humans. Artificial ecosystems are those ecosystems which are modified and managed by human beings.

Crop fields are man-made, plants do not grow naturally; rather , most of the plants are grown by humans according to the season, type of soil, etc. Crop fields are not like wild forest areas which are left to the care of nature and can sustain themselves.

In crop fields, the land is managed, soil is prepared for sowing seeds, then irrigated and further progress is also kept under observation for getting good yield.

Thus, crop fields are known as artificial ecosystems.

An abiotic factor is a non-living part of an ecosystem that shapes its environment. In a terrestrial ecosystem, examples might include temperature, light, and water. In a marine ecosystem, abiotic factors would include salinity and ocean currents. Abiotic and biotic factors work together to create a unique ecosystem.

Organisms which break down the complex organic compounds present in dead and decaying matter are called decomposers, e.g., certain bacteria and fungi. Decomposers act as cleaning agents of the environment by decomposing the dead bodies of plants and animals. They also help in recycling of materials, replenishment of soil's nutrients etc. The consequence of their absence in an ecosystem can be disastrous as discussed below

(i) The dead bodies would keep lying, it would lead to their accumulation and thus, polluting the environment.

(ii) The elements by which bodies are made would never be returned to the environment. As a result, all the nutrients present in soil, air and water would soon be exhausted and the whole life cycle of organisms will be disrupted.

90% of naturally occurring atmospheric ozone occurs in the stratosphere. Stratospheric ozone is very important, it removes almost all incoming UVA, and 70% of the incoming UVB at equator, 90% at poles. All aircraft produce water, CO₂, CO etc. in exhaust gases. Most commercial flights are confined to the troposphere, but high-level supersonic aircraft inject pollutants into the stratosphere, which leads to the thinning of the ozone layer. Of these nitrogen oxides are especially harmful.

Ozone is damaging as it is a deadly poison. It is beneficial as it shields the surface of the earth from UV radiations of the Sun. We should stop the release of Chlorofluorocarbons (CFCs) to protect the ozone.

1. Assertion (A) is true.

   • An aquatic food chain takes place entirely in water—ponds, lakes, rivers, and oceans.

2. Reason (R) is true.

   • In that example, phytoplankton (tiny plants) are eaten by zooplankton (tiny animals), which are eaten by fish, which in turn are eaten by sharks.

3. Why (R) explains (A):

   • The listed sequence shows exactly how an aquatic food chain works—from producers in water up to top predators.

Because both statements are correct and the Reason directly illustrates the Assertion, the correct choice is A.

Substances like polythene bags and plastics are non- biodegradable because they cannot be broken down by micro-organisms into simpler harmless substances in nature. Substances that can be broken down by microorganisms in natural simple harmless substances are biodegradable substances.

Herbivores obtain their food from plants. Hence, they are known as first order carnivores. The carnivores like tigers cannot be preyed upon further, lie at the top of the food chain and hence termed as top carnivores.

The Correct Answer is Option D.

1. Assertion (A) is true

   • Producers (like green plants) take simple inorganic molecules (CO₂ and H₂O) and build complex organic molecules (sugars, proteins) in their bodies.

2. Reason (R) is true

   • Green plants capture sunlight and convert it into chemical energy (ATP, NADPH) during photosynthesis.

3. Why (R) explains (A):

   • The chemical energy produced by green plants is exactly what powers the assembly of inorganic molecules into organic ones.

   • Without converting solar energy into usable chemical energy, plants could not fix CO₂ into sugars.

Because both statements are correct and the Reason directly explains how producers perform the function described in the Assertion, the correct choice is D.

Green plants are producers. The first trophic level in a food chain is a producer i.e. those organisms which produce food by photosynthesis.

Tropical rain forests have disappeared mainly due to man’s activities. Due to overpopulation in countries like India, rain forests are cut to make space available for man to live and build houses. To build buildings and factories man has incessantly cut down trees. This has caused the depletion of rainforests.

Harmful chemicals accumulate progressively at each trophic level. Since man is at the apex of all the food chains, the concentration of harmful chemicals may be higher in human beings. The phenomenon involved is known as biomagnification.

The Correct Answer is Option C.

1. Assertion (A) is true.

   • In an ecosystem, many food chains overlap and interconnect, forming a food web.

2. Reason (R) is false.

   • A kite is a predatory bird (a secondary or tertiary consumer) that feeds on smaller animals.

   • It does belong to the food web, linking the chain from producers up to top predators.

Because the first statement is correct and the second is incorrect, the right choice is C.

The Correct Answer is Option A. 

1. Why Assertion (A) is true

   • Non-biodegradable toxicants (like DDT, mercury and certain plastics) cannot be broken down by bacteria or sunlight.

   • At each step in the food chain, a predator eats many contaminated prey, so the chemical concentration builds up (bio-magnifies).

2. Why Reason (R) is true

   • Top predators (e.g. eagles, large fish, humans) eat multiple organisms from lower levels.

   • Because each prey has already accumulated the toxicant, the predator ends up with the highest concentration.

3. Why (R) explains (A)

   • The inability of these chemicals to degrade plus repeated consumption directly causes higher and higher concentrations at each trophic step—peaking in top predators.

Since both statements are correct and the Reason gives the precise explanation for the Assertion, the answer is A.