Question 51:
Which type of ecological succession occurs when an area previously devoid of life becomes colonized by living organisms?
(A) Secondary succession
(B) Primary succession
(C) Autogenic succession
(D) Allogenic succession
Answer: (B) Primary succession
Explanation:
Primary succession occurs in areas where no life previously existed, such as newly formed volcanic islands or regions exposed after a glacier retreats. It begins with the colonization of pioneer species like lichens and mosses.
Question 52:
In a food chain, the amount of energy available to the top predator is usually:
(A) Greater than that of primary producers
(B) Equal to that of primary producers
(C) Less than that of primary producers
(D) Equal to that of herbivores
Answer: (C) Less than that of primary producers
Explanation:
The amount of energy available to top predators is significantly less than that available to primary producers due to the loss of energy at each trophic level, as per the 10% law. Most energy is lost as heat, with only about 10% being passed on to the next level.
Question 53:
Which of the following is a consequence of deforestation on the carbon cycle?
(A) Increase in carbon sequestration
(B) Increase in CO₂ release into the atmosphere
(C) Decrease in atmospheric CO₂
(D) Stabilization of carbon levels
Answer: (B) Increase in CO₂ release into the atmosphere
Explanation:
Deforestation leads to the release of stored carbon from trees and plants into the atmosphere as CO₂. This contributes to an increase in atmospheric CO₂ levels, exacerbating the greenhouse effect and climate change.
Question 54:
Which of the following correctly represents a detritus food chain?
(A) Grass → Cow → Lion
(B) Algae → Small fish → Large fish
(C) Dead leaves → Earthworms → Birds
(D) Grass → Insect → Frog
Answer: (C) Dead leaves → Earthworms → Birds
Explanation:
The detritus food chain involves the breakdown of dead organic matter (detritus) by decomposers and detritivores. In this example, dead leaves (detritus) are consumed by earthworms (detritivores), which are then eaten by birds (secondary consumers).
Question 55:
Which of the following organisms is a primary consumer?
(A) Snake
(B) Lion
(C) Rabbit
(D) Fungi
Answer: (C) Rabbit
Explanation:
Primary consumers are herbivores that feed on plants (producers). A rabbit, which feeds on grass and other plants, is a primary consumer. Snakes and lions are secondary and tertiary consumers, respectively, and fungi are decomposers.
Question 56:
Which of the following ecosystems is known for its high net primary productivity (NPP)?
(A) Arctic tundra
(B) Open ocean
(C) Estuaries
(D) Desert
Answer: (C) Estuaries
Explanation:
Estuaries are highly productive ecosystems where freshwater meets saltwater, providing nutrients that support high levels of primary productivity. This makes them among the most productive ecosystems, along with tropical rainforests and coral reefs.
Question 57:
Which gas is the primary cause of the “greenhouse effect”?
(A) Oxygen
(B) Nitrogen
(C) Carbon dioxide
(D) Sulfur dioxide
Answer: (C) Carbon dioxide
Explanation:
Carbon dioxide (CO₂) is the primary greenhouse gas responsible for trapping heat in the Earth’s atmosphere, leading to the greenhouse effect and contributing to global warming.
Question 58:
The term “keystone species” refers to:
(A) A species that is the most abundant in an ecosystem
(B) A species that plays a crucial role in maintaining the structure of an ecosystem
(C) A species that is at the top of the food chain
(D) A species that reproduces rapidly
Answer: (B) A species that plays a crucial role in maintaining the structure of an ecosystem
Explanation:
A keystone species is one whose presence and role within an ecosystem have a disproportionately large effect on the other organisms in the system. The removal of a keystone species can lead to significant changes in the ecosystem structure and function.
Question 59:
In which biome would you expect to find the greatest annual temperature fluctuations?
(A) Tropical rainforest
(B) Desert
(C) Tundra
(D) Temperate forest
Answer: (B) Desert
Explanation:
Deserts experience extreme temperature fluctuations, with very hot days and cold nights due to the lack of moisture in the air to moderate temperatures. Tropical rainforests have stable temperatures, while tundras and temperate forests have more moderate fluctuations.
Question 60:
What is the role of nitrogen-fixing bacteria in the nitrogen cycle?
(A) Converting nitrates into nitrogen gas
(B) Converting nitrogen gas into ammonia
(C) Decomposing organic matter
(D) Converting ammonia into nitrates
Answer: (B) Converting nitrogen gas into ammonia
Explanation:
Nitrogen-fixing bacteria convert atmospheric nitrogen (N₂) into ammonia (NH₃), which plants can use. This process is essential for making nitrogen available to living organisms, as most cannot directly use atmospheric nitrogen.
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