NEET Biology: Ecosystem questions with solutions

Q1. A river/ lake with an inflow of domestic sewage rich in organic waste may result in

1. Death of fish due to lack of oxygen
2. Drying of the river/ake very soon due to algal bloom
3. Increase population of aquatic food web organisms
4. An increased production of fish due to biodegradable nutrients

Answer: Death of fish due to lack of oxygen

Domestic sewage rich in organic matter increases the load of biodegradable waste. Decomposer bacteria use up dissolved oxygen while breaking it down, causing oxygen depletion that can kill fish.

Q2. What are the components of the common food chain of a pond ecosystem?

1. Phytoplanktons, zooplanktons, aquatic plants, small aquatic animals
2. Phytoplanktons, zooplanktons, aquatic plants, small aquatic animals, small fishes, big fishes, birds
3. Phytoplanktons, zooplanktons
4. None of the above

Answer: Phytoplanktons, zooplanktons, aquatic plants, small aquatic animals, small fishes, big fishes, birds

A common pond food chain starts with phytoplanktons as producers, then zooplanktons and other small aquatic organisms, followed by small fishes, big fishes, and finally birds. The correct choice is the one that includes this complete sequence.

Q3. Which of the following pairs is a sedimentary type of biogeochemical cycle?

1. oxygen and nitrogen
2. phosphorus and sulphur
3. phosphorus and nitrogen
4. phosphorus and carbon dioxide

Answer: phosphorus and sulphur

Phosphorus is a classic sedimentary cycle because it lacks a major atmospheric phase and cycles through rocks, soil, and water. Sulphur is also commonly treated as sedimentary in this context because it is largely stored in rocks and marine sediments, even though it can have some atmospheric movement.

Q4. In an ecosystem, which one shows one-way passage

1. free energy
2. carbon
3. nitrogen
4. potassium

Answer: free energy

Free energy moves through an ecosystem in a single direction: it enters mainly as sunlight, is transferred between trophic levels, and is ultimately dissipated as heat. In contrast, carbon, nitrogen, and potassium are recycled through biogeochemical cycles.

Q5. The main role of bacteria in the carbon cycle involves

1. photosynthesis
2. chemosynthesis
3. digestion or breakdown of organic compounds
4. assimilation of nitrogenous compounds

Answer: digestion or breakdown of organic compounds

Bacteria are key decomposers in the carbon cycle. They digest dead organisms and waste, converting organic carbon into simpler compounds and releasing carbon back into the environment.

Q6. A very efficient converter of solar energy with net productivity of 2-4 kg/m² or more is the crop of

1. wheat
2. sugarcane
3. rice
4. bajra

Answer: sugarcane

Sugarcane is one of the most efficient solar energy converters because it has a high photosynthetic rate and produces a large amount of biomass per square meter. Its net productivity can reach 2–4 kg/m² or more, which is much higher than the other listed crops.

Q7. Presence of plants arranged into well-defined vertical layers depending on their height can be seen best in:

1. Tropical Rain Forest
2. Grassland
3. Temperate Forest
4. Tropical Savannah

Answer: Tropical Rain Forest

Tropical rain forests exhibit a well-defined vertical stratification of plants due to their high biodiversity and dense vegetation, with layers like emergent, canopy, understory, and forest floor.

Q8. Which one of the following statements is correct for secondary succession?

1. (a) It begins on a bare rock.
2. (b) It occurs on a deforested site.
3. (c) It follows primary succession.
4. (d) It is similar to primary succession except that it has a relatively fast pace.

Answer: (b) It occurs on a deforested site.

Secondary succession occurs in areas where a disturbance has cleared an existing community but left the soil intact, such as a deforested site. This distinguishes it from primary succession, which begins on bare surfaces like rocks.

Q9. In relation to Gross primary productivity and Net primary productivity of an ecosystem, which one of the following statements is correct?

1. Gross primary productivity is always more than net primary productivity
2. Gross primary productivity and Net primary productivity are one and same
3. There is no relationship between Gross primary productivity and Net primary productivity
4. Gross primary productivity is always less than net primary productivity

Answer: Gross primary productivity is always more than net primary productivity

Gross primary productivity (GPP) refers to the total energy or biomass produced by autotrophs in an ecosystem, while net primary productivity (NPP) is the energy remaining after autotrophs use some for respiration. Thus, GPP is always greater than NPP.

Q10. Most animals that live in deep oceanic waters are:

1. secondary consumers
2. tertiary consumers
3. detritivores
4. primary consumers

Answer: detritivores

Most animals in deep oceanic waters rely on detritus, organic matter that sinks from upper layers, as their primary food source, making them detritivores.

Q11. The term ecosystem was coined by

1. E.P. Odum
2. A.G. Tansley
3. E. Haeckel
4. E. Warming

Answer: A.G. Tansley

The term 'ecosystem' was coined by A.G. Tansley in 1935 to describe the interaction between living organisms and their physical environment.

Q12. In an ecosystem the rate of production of organic matter during photosynthesis is termed as:

1. Gross primary productivity
2. Secondary productivity
3. Net productivity
4. Net primary productivity

Answer: Gross primary productivity

Gross primary productivity (GPP) refers to the total rate at which plants in an ecosystem produce organic matter through photosynthesis, without accounting for the energy used in respiration.

Q13. The mass of living material at a trophic level at a particular time is called:

1. Standing state
2. Net primary productivity
3. Standing crop
4. Gross primary productivity

Answer: Standing crop

The mass of living material at a trophic level at a specific time is referred to as the standing crop. It represents the biomass present in organisms at that level.

Q14. Which one of the following processes during decomposition is correctly described?

1. Humification-Leads to the accumulation of a dark coloured substance humus which undergoes microbial action at every fast rate
2. Catabolism-Last step decomposition under fully anaerobic condition
3. Leaching-Water soluble inorganic nutrients rise to the top layers of soil
4. Fragmentation-Carried out by organisms such as earthworm

Answer: Fragmentation-Carried out by organisms such as earthworm

Fragmentation is the process where detritivores like earthworms break down detritus into smaller particles, aiding decomposition.

Q15. Secondary productivity is rate of formation of new organic matter by

1. Parasite
2. Consumer
3. Decomposer
4. Producer

Answer: Consumer

Secondary productivity refers to the rate at which consumers (heterotrophs) convert the organic matter they consume into their own biomass. It is distinct from primary productivity, which is associated with producers.

Q16. The breakdown of detritus into smaller particles by earthworm is a process called

1. humification
2. fragmentation
3. mineralisation
4. catabolism

Answer: fragmentation

Fragmentation is the process by which detritus is broken down into smaller particles, and earthworms play a key role in this by physically breaking down organic matter.

Q17. The biomass available for consumption by the herbivores and the decomposers is called:

1. net primary productivity
2. secondary productivity
3. standing crop
4. gross primary productivity

Answer: net primary productivity

Net primary productivity (NPP) is the energy or biomass remaining after plants use some of the gross primary productivity (GPP) for their own respiration. This NPP is available for herbivores and decomposers to consume.

Q18. The rate of formation of new organic matter by rabbit in a grassland, is called

1. net productivity
2. secondary productivity
3. net primary productivity
4. gross primary productivity

Answer: secondary productivity

Secondary productivity refers to the rate at which consumers, like rabbits, convert the organic matter they consume into their own biomass.

Q19. Which one of the following ecosystem types has the highest annual net primary productivity?

1. tropical deciduous forest
2. temperate evergreen forest
3. temperate deciduous forest
4. tropical rain forest

Answer: tropical rain forest

Tropical rain forests have the highest annual net primary productivity due to their warm climate, abundant sunlight, and consistent rainfall, which support rapid plant growth and biomass accumulation.

Q20. About 70% of total global carbon is found in

1. grasslands
2. agroecosystems
3. oceans
4. forests

Answer: oceans

Oceans hold about 70% of the global carbon due to their vast size and the ability of water to dissolve carbon dioxide, as well as the presence of marine organisms and sediments that store carbon.