About this quiz
Ecosystem types, components, food chain, energy flow and biogeochemical cycles.
This Lok Sewa practice set has 50 multiple-choice questions (Subject: Environment · For: Nayab Subba, Kharidar, Section Officer · Level: Medium). Take the quiz above first; after that, use the study list below to revise every question with its correct answer and a short explanation.
Study list: all 50 questions with answers and explanations
In Nepali, ecosystem is:
- A) पारिस्थितिक प्रणाली ✔
- B) जलवायु परिवर्तन
- C) जैविक विविधता
- D) वातावरण प्रदूषण
Why: Ecosystem is पारिस्थितिक प्रणाली (also पारिस्थितिकीय प्रणाली) in Nepali: living things and their non-living surroundings working together as one system.
The term ecosystem was coined by:
- A) A. G. Tansley ✔
- B) Charles Darwin
- C) Mendel
- D) Lindeman
Why: British ecologist Arthur G. Tansley coined the term 'ecosystem' in 1935.
The term ecosystem was coined in:
- A) 1935 ✔
- B) 1859
- C) 1942
- D) 1972
Why: Tansley introduced the word 'ecosystem' in 1935.
Sunlight, water and soil are:
- A) Abiotic components ✔
- B) Producers
- C) Consumers
- D) Decomposers
Why: Sunlight, water, soil, air and temperature are abiotic (non-living) components. Plants, animals and microbes are the biotic (living) components.
Green plants are:
- A) Producers ✔
- B) Consumers
- C) Decomposers
- D) Abiotic
Why: Green plants are producers (autotrophs): they make their own food from sunlight, water and carbon dioxide by photosynthesis.
Herbivores are:
- A) Primary consumers ✔
- B) Producers
- C) Decomposers
- D) Tertiary consumers
Why: Herbivores such as deer, goats and rabbits eat plants directly, so they are primary consumers (second trophic level).
Bacteria and fungi are mainly:
- A) Decomposers ✔
- B) Producers
- C) Herbivores
- D) Abiotic factors
Why: Bacteria and fungi are decomposers: they break down dead plants and animals into simple substances.
Decomposers help by:
- A) Returning nutrients to the soil ✔
- B) Making sunlight
- C) Eating only living animals
- D) Producing oxygen only
Why: Decomposers break down dead matter and return nutrients such as nitrogen and phosphorus to the soil, where plants can use them again.
A pond is a:
- A) Freshwater aquatic ecosystem ✔
- B) Marine ecosystem
- C) Desert ecosystem
- D) Artificial city
Why: A pond is a freshwater aquatic ecosystem, with producers (algae, water plants), consumers (insects, fish, frogs) and decomposers.
A crop field is an example of:
- A) Artificial (man-made) ecosystem ✔
- B) Marine ecosystem
- C) Natural desert
- D) Ocean
Why: A crop field is an artificial (man-made) ecosystem: humans choose the plants, add water and fertiliser and remove weeds.
Which is a Ramsar wetland of Nepal?
- A) Koshi Tappu ✔
- B) Kathmandu Durbar Square
- C) Sagarmatha base camp
- D) Lumbini garden
Why: Koshi Tappu was Nepal's first Ramsar site (1987), important for migratory birds and wild water buffalo (arna).
Grass → deer → tiger is a:
- A) Food chain ✔
- B) Food web
- C) Nitrogen cycle
- D) Water cycle
Why: This is a food chain: energy passes in a straight line from grass (producer) to deer (herbivore) to tiger (carnivore).
Many interconnected food chains form a:
- A) Food web ✔
- B) Trophic level
- C) Biome
- D) Pyramid only
Why: Food chains in nature link together because most animals eat more than one food, forming a food web.
Each step in a food chain is a:
- A) Trophic level ✔
- B) Habitat
- C) Species
- D) Cycle
Why: Each feeding step is a trophic level: producers (1st), herbivores (2nd), carnivores (3rd) and top carnivores (4th).
Producers occupy which trophic level?
- A) First ✔
- B) Second
- C) Third
- D) Fourth
Why: Producers (green plants) are always at the first trophic level, because all other organisms depend on the food they make.
A food chain starting from dead organic matter is a:
- A) Detritus food chain ✔
- B) Grazing food chain
- C) Water cycle
- D) Food pyramid
Why: A detritus food chain starts from dead organic matter (detritus), such as fallen leaves → earthworms → birds.
The main source of energy for ecosystems is the:
- A) Sun ✔
- B) Moon
- C) Soil
- D) Wind only
Why: The Sun is the main source of energy. Plants capture sunlight in photosynthesis and pass the energy on through food chains.
Energy flow in an ecosystem is:
- A) Unidirectional ✔
- B) Cyclic
- C) Random
- D) Reversible
Why: Energy flows one way (unidirectional): Sun → producers → consumers. At each step some is lost as heat, so it is not recycled.
The 10% law of energy transfer was given by:
- A) Raymond Lindeman ✔
- B) Tansley
- C) Darwin
- D) Odum
Why: Raymond Lindeman gave the 10% law in 1942: only about 10% of energy at one trophic level passes to the next.
According to the 10% law, how much energy passes to the next level?
- A) About 10% ✔
- B) 50%
- C) 90%
- D) 100%
Why: Only about 10% passes on. Example: if plants have 1,000 units, herbivores get about 100 and carnivores about 10.
Food chains are usually short because:
- A) Energy is lost at each level ✔
- B) Animals are lazy
- C) Plants are few
- D) Water is scarce
Why: So much energy is lost at each level that little is left after four or five steps, so food chains are usually short.
Which ecological pyramid is always upright?
- A) Pyramid of energy ✔
- B) Pyramid of numbers
- C) Pyramid of biomass in all cases
- D) None
Why: The pyramid of energy is always upright, because energy always decreases from one level to the next. Pyramids of number or biomass can be inverted.
Nutrients in an ecosystem move:
- A) In cycles ✔
- B) In one direction only
- C) Out of earth forever
- D) Only to the sun
Why: Unlike energy, nutrients such as carbon, nitrogen and water move in cycles between living things and the environment (biogeochemical cycles).
Water vapour released from plant leaves is:
- A) Transpiration ✔
- B) Condensation
- C) Precipitation
- D) Infiltration
Why: Transpiration is the loss of water vapour from plant leaves through tiny pores (stomata). It is part of the water cycle.
Formation of clouds from vapour is:
- A) Condensation ✔
- B) Evaporation
- C) Runoff
- D) Transpiration
Why: Condensation turns water vapour into tiny droplets as air cools, which form clouds.
Rain and snow are forms of:
- A) Precipitation ✔
- B) Evaporation
- C) Condensation
- D) Infiltration
Why: Precipitation is water falling from clouds as rain, snow, sleet or hail.
Water soaking into the ground is:
- A) Infiltration ✔
- B) Evaporation
- C) Transpiration
- D) Condensation
Why: Infiltration is water soaking into the soil. It recharges groundwater, which feeds springs and wells.
Plants take carbon dioxide from the air through:
- A) Photosynthesis ✔
- B) Respiration
- C) Decomposition
- D) Combustion
Why: In photosynthesis, plants take in carbon dioxide and, using sunlight and water, make glucose and release oxygen.
Carbon dioxide returns to the air by:
- A) Respiration, decomposition and burning ✔
- B) Photosynthesis
- C) Nitrogen fixation
- D) Condensation
Why: Respiration by living things, decomposition of dead matter and burning of fuel all release carbon dioxide back into the air.
Burning fossil fuels mainly increases:
- A) Carbon dioxide in the air ✔
- B) Nitrogen fixation
- C) Oxygen levels
- D) Ozone
Why: Burning coal, oil and gas releases carbon stored for millions of years as carbon dioxide, the main cause of global warming.
About how much of the air is nitrogen?
- A) 78% ✔
- B) 21%
- C) 50%
- D) 1%
Why: Nitrogen makes up about 78% of air, oxygen about 21%, and argon, carbon dioxide and other gases the remaining 1%.
Rhizobium bacteria are found in:
- A) Root nodules of legumes ✔
- B) Leaves of pine
- C) Human stomach only
- D) Rocks
Why: Rhizobium bacteria live in root nodules of legumes such as peas, beans and lentils, and fix nitrogen from the air.
Converting atmospheric nitrogen into usable forms is:
- A) Nitrogen fixation ✔
- B) Denitrification
- C) Transpiration
- D) Respiration
Why: Nitrogen fixation turns nitrogen gas (N₂), which plants cannot use, into ammonia or nitrates that they can use.
Ammonia → nitrites → nitrates is called:
- A) Nitrification ✔
- B) Denitrification
- C) Fixation by lightning
- D) Photosynthesis
Why: Nitrification is done by nitrifying bacteria: Nitrosomonas change ammonia to nitrites and Nitrobacter change nitrites to nitrates.
Returning nitrogen gas to the air is:
- A) Denitrification ✔
- B) Nitrification
- C) Fixation
- D) Condensation
Why: Denitrification by denitrifying bacteria changes nitrates back into nitrogen gas, which returns to the air and completes the cycle.
Lightning helps in:
- A) Nitrogen fixation ✔
- B) Carbon storage
- C) Phosphorus release
- D) Transpiration
Why: Lightning's energy makes nitrogen and oxygen combine into nitrogen oxides, which rain carries to the soil as nitrates. This is natural nitrogen fixation.
Oxygen is released into the air mainly by:
- A) Photosynthesis ✔
- B) Burning
- C) Respiration
- D) Decomposition
Why: Photosynthesis by plants and algae (including ocean phytoplankton) releases oxygen into the air.
The phosphorus cycle is a:
- A) Sedimentary cycle ✔
- B) Gaseous cycle
- C) Energy cycle
- D) Food web
Why: The phosphorus cycle is sedimentary: phosphorus comes mainly from rocks and soil and has no important gaseous stage.
Which is a gaseous cycle?
- A) Nitrogen cycle ✔
- B) Phosphorus cycle
- C) Sulphur from rocks only
- D) Calcium cycle
Why: The nitrogen cycle is a gaseous cycle because its main reservoir is the atmosphere (78% nitrogen).
Fertiliser overuse disturbs nutrient cycles and causes:
- A) Eutrophication ✔
- B) Ozone formation
- C) Earthquakes
- D) Volcanoes
Why: Extra nitrogen and phosphorus wash into lakes and rivers, causing eutrophication: algae bloom, then oxygen falls and fish die.
Deforestation disturbs the carbon cycle by:
- A) Reducing CO₂ absorption ✔
- B) Increasing photosynthesis
- C) Cooling the earth
- D) Adding nitrogen
Why: Trees absorb and store carbon dioxide, so cutting forests means less carbon is absorbed, and burning them releases more.
Ecosystem services include:
- A) Clean air, water, food and flood control ✔
- B) Only tourism
- C) Only mining
- D) Only roads
Why: Ecosystem services are nature's benefits to people, such as clean air and water, food, medicine, pollination and flood control.
Carnivores that eat herbivores are:
- A) Secondary consumers ✔
- B) Producers
- C) Primary consumers
- D) Decomposers
Why: Carnivores that eat herbivores, such as a fox eating a rabbit, are secondary consumers (third trophic level).
An animal that eats both plants and animals is a(n):
- A) Omnivore ✔
- B) Herbivore
- C) Producer
- D) Decomposer
Why: An omnivore eats both plants and animals, such as humans, bears and crows.
Phytoplankton in a lake are:
- A) Producers ✔
- B) Decomposers
- C) Tertiary consumers
- D) Abiotic factors
Why: Phytoplankton are tiny floating plants and algae that photosynthesise, so they are producers in water ecosystems.
Alpine meadows in the Himalaya are a:
- A) Mountain (terrestrial) ecosystem ✔
- B) Marine ecosystem
- C) Desert ecosystem
- D) Artificial ecosystem
Why: Alpine meadows (लेक, खर्क) above the treeline are mountain terrestrial ecosystems, used for summer grazing.
Rara Lake is a:
- A) Freshwater wetland (Ramsar site) ✔
- B) Marine ecosystem
- C) Desert
- D) Man-made reservoir only
Why: Rara Lake in Mugu, Nepal's largest lake, is a freshwater wetland listed as a Ramsar site in 2007, inside Rara National Park.
Which organism converts dead leaves into humus?
- A) Fungi ✔
- B) Tigers
- C) Deer
- D) Eagles
Why: Fungi (along with bacteria) break down dead leaves into humus, the dark organic part of soil that improves fertility.
Oceans act in the carbon cycle as a:
- A) Carbon store (sink) ✔
- B) Nitrogen source only
- C) Energy source
- D) Producer of nitrogen gas
Why: Oceans absorb large amounts of carbon dioxide from the air and store carbon, so they act as a major carbon sink.
Energy lost at each trophic level is mainly lost as:
- A) Heat ✔
- B) Light
- C) Sound
- D) Electricity
Why: Most energy at each level is used for respiration and life processes and is lost as heat, so only about 10% passes on.