Ecosystem, Pollution and Biodiversity
Ecosystem, Pollution and Biodiversity MCQ Questions
7.
A tiger feeding on a deer that grazed on grass is an example of a:
ANSWER :
B. Secondary consumer
Approach
This question asks us to identify the trophic level of a tiger in a specific food chain: grass \(\rightarrow\) deer \(\rightarrow\) tiger. Understanding the definitions of different consumer levels is key to answering this.
Step-by-step
- Identify the producers: In any ecosystem, producers are organisms that create their own food, usually through photosynthesis. In this case, grass is the producer.
- Identify the primary consumer: Primary consumers (herbivores) feed directly on producers. Here, the deer grazes on grass, making it the primary consumer.
- Identify the secondary consumer: Secondary consumers (carnivores or omnivores) feed on primary consumers. The tiger feeds on the deer, which is a primary consumer. Therefore, the tiger is a secondary consumer.
- Identify the tertiary consumer (if applicable): Tertiary consumers feed on secondary consumers. In this specific food chain, there is no organism mentioned that feeds on the tiger, so we stop at the secondary consumer level for the tiger.
Correct Option:
B) A tiger feeding on a deer that grazed on grass is an example of a secondary consumer because it consumes a primary consumer (the deer).
Incorrect Options
- A) Primary consumer — A primary consumer feeds directly on producers (e.g., the deer eating grass). The tiger does not eat grass.
- C) Tertiary consumer — A tertiary consumer feeds on secondary consumers. In this food chain, the tiger is the secondary consumer, not a tertiary one.
- D) Decomposer — Decomposers (like bacteria and fungi) break down dead organic matter. The tiger is a living predator, not a decomposer.
8.
Which of the following correctly classifies humans in a typical food chain?
Approach
The question asks for the correct classification of humans in a typical food chain. To answer this, we need to understand the definitions of different trophic levels and feeding habits within an ecosystem.
Step-by-step
- Understand Food Chains: A food chain describes how energy and nutrients move through an ecosystem, from one organism to another.
- Define Trophic Levels: Organisms are classified into different trophic levels based on how they obtain energy.
- Producers (Autotrophs): Organisms that produce their own food, usually through photosynthesis (e.g., plants).
- Consumers (Heterotrophs): Organisms that obtain energy by consuming other organisms. Consumers are further divided into:
- Primary Consumers (Herbivores): Eat producers.
- Secondary Consumers (Carnivores/Omnivores): Eat primary consumers.
- Tertiary Consumers (Carnivores/Omnivores): Eat secondary consumers.
- Decomposers: Organisms that break down dead organic matter (e.g., bacteria, fungi).
- Classify Humans: Humans consume both plants (e.g., vegetables, fruits, grains) and animals (e.g., meat, fish, poultry). This feeding habit, where an organism consumes both plant and animal matter, defines an omnivore.
Correct Option:
C) Omnivores — Humans consume both plants (producers) and animals (consumers), placing them in the category of omnivores. This means they can act as primary, secondary, or even tertiary consumers depending on what they eat.
Incorrect Options
- A) Producers — Producers are organisms that create their own food, primarily through photosynthesis (e.g., plants). Humans cannot produce their own food; they must consume other organisms.
- B) Decomposers — Decomposers break down dead organic matter and waste products, returning nutrients to the ecosystem (e.g., bacteria, fungi). Humans do not perform this role.
- D) Autotrophs — Autotrophs are synonymous with producers; they are organisms that can produce their own food, typically using light or chemical energy. Humans are heterotrophs, meaning they must consume other organisms for energy.
9.
Consumers in an ecosystem are also known as:
Approach
The question asks to identify the term used for consumers in an ecosystem. This requires understanding the basic classification of organisms based on their mode of nutrition within an ecosystem.
Step-by-step
- Define Consumers: Consumers are organisms that obtain energy by feeding on other organisms or organic matter. They cannot produce their own food.
- Evaluate Option A (Autotrophs): Autotrophs are producers; they synthesize their own food using light or chemical energy (e.g., plants, algae). This is the opposite of consumers.
- Evaluate Option B (Heterotrophs): Heterotrophs are organisms that obtain energy by consuming organic substances produced by other organisms. This definition perfectly matches that of consumers.
- Evaluate Option C (Saprotrophs): Saprotrophs are a specific type of heterotroph (decomposers) that obtain nutrients by secreting digestive enzymes onto dead organic matter and absorbing the digested material. While they consume organic matter, the term "consumers" is broader and heterotrophs is the overarching category.
- Evaluate Option D (Photoautotrophs): Photoautotrophs are a specific type of autotroph that use light energy to synthesize food (e.g., green plants). This is a subset of producers, not consumers.
Based on these definitions, consumers are broadly classified as heterotrophs because they rely on other organisms for their food and energy.
Correct Option: B) Heterotrophs are organisms that cannot produce their own food and must obtain energy by consuming other organisms or organic matter. This is the definition of a consumer in an ecosystem.
Incorrect Options
- A) Autotrophs — Autotrophs are producers, meaning they can synthesize their own food, typically through photosynthesis (e.g., plants). They are not consumers.
- C) Saprotrophs — Saprotrophs are decomposers (a type of heterotroph) that feed on dead organic matter. While they consume, the term "heterotrophs" is the broader and more accurate classification for all consumers.
- D) Photoautotrophs — Photoautotrophs are a specific type of autotroph that uses light as an energy source to produce food (e.g., plants). They are producers, not consumers.
10.
Which one of the following is an example of a tertiary consumer?
ANSWER :
C. Wolf eating a fox
Approach
To identify a tertiary consumer, we need to understand the concept of trophic levels in an ecosystem. We will define producers, primary consumers, secondary consumers, and tertiary consumers, then evaluate each option based on these definitions.
Step-by-step
- Understand Trophic Levels: In an ecosystem, organisms are categorized into different trophic levels based on their feeding position.
- Producers: Organisms that produce their own food, usually through photosynthesis (e.g., plants, algae).
- Primary Consumers (Herbivores): Organisms that feed on producers.
- Secondary Consumers (Carnivores/Omnivores): Organisms that feed on primary consumers.
- Tertiary Consumers (Top Carnivores/Omnivores): Organisms that feed on secondary consumers.
- Analyze the Food Chain Implied in Option C:
A wolf eating a fox implies the following food chain:
- Grass/Plants (Producer)
- Rabbit/Rodent (Primary Consumer, eats grass)
- Fox (Secondary Consumer, eats rabbit/rodent)
- Wolf (Tertiary Consumer, eats fox)
In this scenario, the fox is a secondary consumer, and the wolf, by preying on the fox, acts as a tertiary consumer.
- Evaluate the Options: We will apply the definitions to each given option.
Correct Option: C) Wolf eating a fox
This is an example of a tertiary consumer because the wolf (tertiary consumer) is preying on the fox (secondary consumer), which in turn would have preyed on a primary consumer (like a rabbit or rodent), which would have eaten producers (like grass).
Incorrect Options
- A) Grass — Grass is a producer, as it produces its own food through photosynthesis.
- B) Goat — A goat is a primary consumer (herbivore) because it feeds directly on producers like grass and plants.
- D) Earthworm — An earthworm is a detritivore or decomposer. It feeds on dead organic matter (detritus), playing a crucial role in nutrient cycling, but it does not fit into the typical producer-consumer trophic levels in the same way.
11.
Parasites in an ecosystem are categorised as:
Approach
The question asks to categorize parasites within an ecosystem. To answer this, we need to understand the definitions of different trophic levels and ecological roles: producers, consumers, decomposers, and detritivores.
Step-by-step
- Understand Parasitism: A parasite is an organism that lives on or in a host organism and gets its food from or at the expense of its host. This relationship is typically detrimental to the host.
- Relate to Trophic Levels: In an ecosystem, organisms are categorized based on how they obtain energy.
- Producers: These are organisms (like plants) that produce their own food, usually through photosynthesis. Parasites do not produce their own food.
- Consumers: These are organisms that obtain energy by feeding on other organisms. This category includes herbivores (eat plants), carnivores (eat animals), and omnivores (eat both). Parasites feed on living hosts, thus consuming them in a broad sense.
- Decomposers: These are organisms (like bacteria and fungi) that break down dead organic matter. Parasites feed on living hosts, not dead matter.
- Detritivores: These are organisms that feed on detritus (dead organic material). Similar to decomposers, parasites do not feed on dead matter.
- Conclusion: Since parasites obtain their nutrition by feeding on other living organisms (their hosts), they fit the definition of consumers. They are a specific type of consumer that lives in a close, often long-term, relationship with their host, deriving nutrients from them.
Correct Option: B) Consumers. Parasites obtain their nutrition by feeding on living host organisms, which classifies them as consumers in an ecosystem's trophic structure.
Incorrect Options
- A) Producers — Producers are autotrophs that create their own food (e.g., plants via photosynthesis). Parasites are heterotrophs and cannot produce their own food.
- C) Decomposers — Decomposers break down dead organic matter (e.g., bacteria, fungi). Parasites feed on living organisms.
- D) Detritivores — Detritivores feed on detritus (dead organic material). Parasites feed on living hosts.
12.
Decomposers in an ecosystem primarily include:
ANSWER :
C. Bacteria and fungi
Approach
The question asks to identify the primary decomposers in an ecosystem. Decomposers are organisms that break down dead organic matter, returning nutrients to the soil. We need to evaluate each option based on this definition.
Step-by-step
- Understand the role of decomposers: Decomposers are crucial for nutrient cycling in an ecosystem. They break down dead plants and animals, as well as waste products, into simpler substances that can be reused by producers.
- Evaluate Option A (Plants and algae): Plants and algae are primarily producers. They create their own food through photosynthesis and form the base of most food chains. They do not primarily decompose dead organic matter.
- Evaluate Option B (Insects and reptiles): Insects and reptiles are consumers. Some insects, like detritivores (e.g., dung beetles, some ants), do feed on dead organic matter, but they are not the primary microscopic agents responsible for the complete breakdown of complex organic molecules. Reptiles are typically predators or herbivores.
- Evaluate Option C (Bacteria and fungi): Bacteria and fungi are the principal decomposers in most ecosystems. They secrete enzymes that break down complex organic compounds in dead organisms and waste into simpler inorganic nutrients, which are then absorbed by plants. This process is essential for nutrient recycling.
- Evaluate Option D (Birds and mammals): Birds and mammals are consumers. They occupy various trophic levels (herbivores, carnivores, omnivores) but do not primarily function as decomposers. While some scavengers (a type of consumer) might eat dead animals, they don't break down organic matter at the cellular level like bacteria and fungi.
Correct Option: C) Bacteria and fungi are the primary decomposers in an ecosystem. They play a vital role in breaking down dead organic material and recycling nutrients back into the environment.
Incorrect Options
- A) Plants and algae — These are producers, forming the base of the food chain by converting light energy into chemical energy.
- B) Insects and reptiles — These are consumers. While some insects are detritivores, they are not the primary decomposers responsible for the complete chemical breakdown of organic matter. Reptiles are generally predators or herbivores.
- D) Birds and mammals — These are consumers, occupying various trophic levels (herbivores, carnivores, omnivores). They do not primarily decompose organic matter.
