Ecology Archives

31. Which of the following are the necessary conditions for the growth of

Which of the following are the necessary conditions for the growth of coral reefs?

1. Photic conditions
2. Clean and sediment free water
3. Sea salinity of 6%
4. Tropical sea water with temperature of 20°C to 21°C

Select the correct answer using the code given below :

1, 2 and 4 only

2 and 4 only

1 and 3 only

1, 2, 3 and 4

This question was previously asked in

UPSC CAPF – 2017

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The correct answer is A) 1, 2 and 4 only.

Coral reefs are complex ecosystems built by tiny marine animals called coral polyps. Their growth depends on specific environmental conditions:
1. **Photic conditions:** Corals have a symbiotic relationship with photosynthetic algae called zooxanthellae living in their tissues. These algae require sunlight for photosynthesis, which provides energy to the coral. Therefore, coral reefs are typically found in shallow, clear waters within the photic zone.
2. **Clean and sediment free water:** Sediments suspended in water can block sunlight needed by zooxanthellae and can also smother coral polyps. Pollution can also harm corals. Clean water is essential.
3. **Sea salinity of 6%:** This is incorrect. Coral reefs typically require stable salinity levels found in normal seawater, which is usually around 30-40 parts per thousand (ppt), or 3-4%. A salinity of 6% (60 ppt) is significantly higher than optimal and is not conducive to coral growth.
4. **Tropical sea water with temperature of 20°C to 21°C:** Corals thrive in warm tropical and subtropical waters. The ideal temperature range for most reef-building corals is generally between 20°C and 28°C (68°F to 82°F). The range 20-21°C falls within this suitable range.

Other conditions necessary for coral reef growth include adequate water circulation to bring nutrients and remove waste, and a hard substrate for larvae to settle on. Coral bleaching, a major threat to reefs, occurs when corals expel their symbiotic algae, often due to increased water temperature.

32. The trees of tropical rainforest have buttress roots because :

The trees of tropical rainforest have buttress roots because :

they help to provide aeration to soils

the organisms found in the buttresses have a symbiotic relationship

the trees belong to gramineae family

the buttresses have to bear the mechanical load of hardwoods

This question was previously asked in

UPSC CAPF – 2015

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The correct answer is D. Buttress roots provide structural support to large trees in unstable tropical rainforest soils, helping them bear their mechanical load and resist toppling.

Tropical rainforest soils are typically shallow, nutrient-poor, and sometimes waterlogged. Trees in these environments often do not develop deep taproots for stability. Instead, they rely on widespreading, shallow root systems and buttress roots at the base of the trunk. Buttress roots are large, triangular supports that spread horizontally and vertically, increasing the tree’s base area and providing stability against strong winds and the weight of the canopy and epiphytes.

While roots are involved in aeration (A), buttress roots’ primary function is structural support. Symbiotic relationships (B), such as mycorrhizae, occur on the roots for nutrient uptake, but the buttress structure itself is not defined by this. The Gramineae family (C) refers to grasses, not the large hardwood trees typical of tropical rainforests. The mechanical load (D) refers to the considerable weight and size of the trees which the buttresses help to support in the face of challenging soil conditions.

33. Consider the following statements: 1. Creepers or climbers are commo

Consider the following statements:

1. Creepers or climbers are commonly found in the tropical rain forest.
2. The epiphytes, which do not have their roots on the ground, survive on the trees in the tropical rain forest.
3. All epiphytes are not creepers.

Which of the statements given above is/are correct?

1, 2 and 3

2 and 3 only

1 and 2 only

3 only

This question was previously asked in

UPSC CAPF – 2012

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Statements 1, 2, and 3 are all correct.

Tropical rainforests are characterized by high biodiversity and a multi-layered structure. Plants adapt in various ways to compete for light and resources in this dense environment. Creepers, climbers (lianas), and epiphytes are common plant forms that utilize existing trees for support or growth medium. Epiphytes, unlike parasitic plants, do not draw nutrients directly from their host plant but obtain them from the air, rain, and debris. Epiphytes are a diverse group and include various plant types like orchids, ferns, bromeliads, etc., and not all of them are climbers or creepers in the traditional sense of growing along a surface.

Creepers and climbers use trees to reach sunlight in the upper canopy. Epiphytes grow on other plants (typically trees) without being rooted in the ground, allowing them to access sunlight higher in the forest. Examples of epiphytes include many species of orchids, bromeliads, and ferns. A climber ascends, while a creeper spreads along the ground; epiphytes grow *on* other plants. Thus, not all epiphytes are necessarily creepers or climbers, although some epiphytes might also exhibit climbing behaviour.

34. Which one among the following phenomena includes processes, such as pr

Which one among the following phenomena includes processes, such as production, predation, nutrient transformation, and the influx and efflux of energy and materials ?

Ecological function

Ecosystem function

Ecosystem structure

Biogeochemical cycles

This question was previously asked in

UPSC CAPF – 2011

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The phenomenon that includes processes like production, predation, nutrient transformation, and the influx and efflux of energy and materials is known as ecosystem function.

Ecosystem functions are the physical, chemical, and biological processes that take place within an ecosystem. These include primary production (conversion of light energy into organic matter, ‘production’), consumption (herbivory, predation), decomposition (breakdown of organic matter, leading to ‘nutrient transformation’), and the overall flow of energy and cycling of materials (‘influx and efflux of energy and materials’). These processes describe how an ecosystem works and maintains itself.

Ecological function is a broader term that could refer to the role of an organism or a process within an ecosystem, but “ecosystem function” specifically describes the sum of processes within the ecosystem itself. Ecosystem structure refers to the composition of the ecosystem (species, biomass, etc.). Biogeochemical cycles are specific pathways of elemental cycling, which are *part* of ecosystem functions but do not encompass all the processes listed (like production and predation as energy flow components).

35. The green plants in a terrestrial eco- system absorbs sunlight that fa

The green plants in a terrestrial eco- system absorbs sunlight that falls on their leaves and convert it into food energy. The percentage of solar radia- tion absorbed by all green plants for the process of photosynthesis is about

10%

This question was previously asked in

UPSC NDA-2 – 2023

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The percentage of solar radiation absorbed by all green plants for the process of photosynthesis is about 1%.

Ecological studies show that only a small fraction of the total solar energy incident on the Earth’s surface is captured by producers (green plants) and converted into chemical energy through photosynthesis. This efficiency is typically stated as being around 1%. This absorbed energy forms the base of most ecosystems, supporting all subsequent trophic levels.

While plants absorb some portion of the sunlight (especially in the red and blue wavelengths), much of the incident light is reflected or transmitted. Furthermore, not all absorbed energy is converted into biomass; a significant portion is lost as heat or used by the plant for its own metabolic processes (respiration). The 1% value refers to the efficiency of conversion of incident solar energy into net primary production.

36. The following six (6) items consist of two statements, Statement I and

The following six (6) items consist of two statements, Statement I and Statement II. Examine these two statements carefully and select the correct answer using the code given below.
Statement I :
Phytoplankton produce most of the organic carbon in the ocean.
Statement II :
Algae are produced in the cold water biome.

Both the statements are individually true and Statement II is the correct explanation of Statement I

Both the statements are individually true but Statement II is not the correct explanation of Statement I

Statement I is true but Statement II is false

Statement I is false but Statement II is true

This question was previously asked in

UPSC NDA-2 – 2018

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Statement I is true: Phytoplankton are microscopic marine algae and cyanobacteria that perform photosynthesis. They are the primary producers in the ocean and are responsible for producing a vast majority of the organic carbon through photosynthesis, forming the base of the marine food web. Statement II is false: While algae exist and are productive in cold water biomes (like polar oceans during spring blooms), they are also abundant and diverse in temperate and tropical waters. Algae are found in virtually all aquatic and moist terrestrial environments globally, not exclusively in cold water biomes.

– Phytoplankton are crucial for marine ecosystems and the global carbon cycle.
– They contribute significantly to atmospheric oxygen production.
– Algae are a diverse group of photosynthetic organisms found in a wide range of habitats with varying temperatures.

Estimates suggest that phytoplankton photosynthesis accounts for about half of the total global primary production. Different species of algae are adapted to different temperature ranges, from hot springs to polar seas.

37. Which one of the following is the correct sequence about various level

Which one of the following is the correct sequence about various levels of organization of Biosphere?

Ecosystem—Biosphere — Community — Population

Population — Organism — Eco system — Biosphere

Organism — Community — Population — Biosphere

Organism — Population — Eco system — Biosphere

This question was previously asked in

UPSC NDA-2 – 2015

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The correct sequence of organization in the biosphere, from smallest to largest functional level typically starts with individual organisms, then populations of the same species, communities of different species interacting, ecosystems where the community interacts with its environment, and finally the biosphere encompassing all ecosystems. Option D, Organism — Population — Eco system — Biosphere, follows this logical progression, although it skips the ‘Community’ level, which is often included between Population and Ecosystem. Among the given options, it presents the most accurate relative ordering.

Understanding the hierarchical levels of organization in ecology, from individual organisms to the entire biosphere, is fundamental.

The typical hierarchy is Organism -> Population -> Community -> Ecosystem -> Biome -> Biosphere. An ecosystem includes both the living (biotic community) and non-living (abiotic) components of an area.

38. Identify the land biome on the basis of the given characteristics: 1

Identify the land biome on the basis of the given characteristics:

1. Their climates are characterised by high rainfall and temperatures that vary from cold to mild.
2. These forests contain primarily deciduous trees – including maple, oak, hickory and beechwood.
3. Raccoons, opossums, bats and squirrels are found in the trees.

Select the correct land biome from the options given below:

Tropical forest

Temperate forest

Boreal forest

Mediterranean forest

This question was previously asked in

UPSC NDA-1 – 2024

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The described land biome is the Temperate forest.

Temperate forests are characterized by moderate to high rainfall and distinct seasons, leading to temperature variations from cold in winter to mild in other seasons. They are predominantly composed of deciduous trees (trees that shed their leaves seasonally) like maple, oak, hickory, and beechwood. The fauna described, such as raccoons, opossums, bats, and squirrels, are commonly found in these forests.

Tropical forests have high rainfall and consistently high temperatures with evergreen trees. Boreal forests (Taiga) are found in colder regions with coniferous trees and lower rainfall. Mediterranean forests are characterized by hot, dry summers and mild, wet winters, often featuring evergreen shrubs and trees adapted to drought.

39. Keppel Island is completely bleached mainly due to the expansion of

Keppel Island is completely bleached mainly due to the expansion of

Starfish.

Blue whale.

Octopus.

Sea horse.

This question was previously asked in

UPSC NDA-1 – 2021

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The correct answer is A) Starfish.

Coral bleaching is primarily caused by environmental stress, most notably elevated sea temperatures. However, biological factors can also contribute. Outbreaks of predatory starfish, specifically the Crown-of-Thorns starfish (*Acanthaster planci*), are known to cause significant damage to coral reefs by feeding on polyps. Severe predation can weaken the coral, making it more susceptible to bleaching, or cause direct mortality that appears as whitening (tissue loss revealing the white skeleton). Keppel Island, being part of the Great Barrier Reef ecosystem which experiences COTS outbreaks, is susceptible to such damage. While climate change and rising temperatures are the main driver of widespread bleaching events, localised stress from predators like starfish can exacerbate or cause bleaching in specific areas. Given the options, Starfish (Crown-of-Thorns) is the only organism listed that is a known significant predator of coral and contributes to coral damage and bleaching.

Blue whales, octopuses, and sea horses do not feed on coral and are not associated with causing coral bleaching. While other factors like pollution or disease can cause bleaching, the question points to “expansion” of a species, and Crown-of-Thorns starfish populations can undergo periodic outbreaks or expansions, leading to increased predation pressure on reefs.

40. What is ‘pyrophilous organism’?

What is ‘pyrophilous organism’?

Fresh grass growing after ground fire

Fungi growing in soils of burnt terrains

Seeds germinating after clear felling of forest

Organisms with capacity to regenerate the tail after it was lost due to damage

This question was previously asked in

UPSC Geoscientist – 2023

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The correct answer is Fungi growing in soils of burnt terrains.

‘Pyrophilous’ means ‘fire-loving’. Pyrophilous organisms are those that are either dependent on fire for part of their life cycle or thrive in environments recently affected by fire. Fungi that specifically colonize or grow best on burnt organic matter or in fire-affected soil are classic examples of pyrophilous organisms.

While fresh grass might grow rapidly after a fire (due to nutrient release and reduced competition), the term pyrophilous specifically describes organisms that are *favored* *by* the fire itself. Some seeds are pyrophilous because heat from fire breaks dormancy. Option D describes regeneration after injury, not fire dependency.