Question
Which one of the following processes during decomposition is correctly described? [NEET 2013]
(a) Fragmentation-Carried out by organisms such as earthworm
(b) Humification-Leads to the accumulation of a dark coloured substance humus, which undergoes microbial action at a very fast rate
(c) Catabolism-Last step in the decomposition under fully anaerobic condition
(d) Leaching-Water soluble inorganic nutrients rise to the top layers of soil
Answer/Explanation
Ans. (a)
Fragmentation is one of the steps during decomposition, in which detritus is converted into small fragments. Humification leads to dark coloured amorphous substance called humus that is highly resistent to microbial action and undergoes decomposition at an extremely slow rate. Catabolism is the set of metabolic pathways that breaks down molecules into smaller units to release energy. Leaching refers to the loss of water soluble plant nutrients from the soil due to the rain and irrigation.
Question
Which ecosystem has the maximum biomass? [NEET 2017]
(a) Forest ecosystem
(b) Grassland ecosystem
(c) Pond ecosystem
(d) Lake ecosystem
Answer/Explanation
Ans. (a)
Biomass refers to the amount of living organic matter. Forest ecosystem have the maximum biomass, because it includes organisms of all trophic levels as compared to pond, lake or grassland ecosystem. In forest ecosystems productivity is also high that contributes to maximum biomass.
Question
Presence of plants arranged into well defined vertical layers depending on their height can best seen best in [NEET 2017]
(a) tropical savannah
(b) tropical rain forest
(c) grassland
(d) temperate forest
Answer/Explanation
Ans. (b)
Tropical rain forests show stratification. It can be defined as the grouping of plants into two or more well defined layers depending upon their height. These layers are called strata or storeys. There storeys consist of respectively very tall emergent trees, tall trees, small trees, a shrub layer and a ground layer of ferns, mosses and herbs.
Question
The term ecosystem was coined by [NEET 2016, Phase I]
(a) AG Tansley
(b) E Haeckel
(c) E Warming
(d) EP Odum
Answer/Explanation
Ans. (a)
The term ecosystem was coined by $A G$ Tansley in 1935. Ecosystem is a self regulated and self sustaining structural and functional unit of nature. It consists of living beings and their physical environment.
Question
Which one of the following is a characteristic feature of cropland ecosystem? [NEET 2016, Phase II]
(a) Least genetic diversity
(b) The absence of weeds
(c) Ecological succession
(d) The absence of soil organisms
Answer/Explanation
Ans. (a)
Cropland ecosystem is largest anthropogenic ecosystem characterised by less diversity and high productivity.
Question
The primary producers of the deep-sea hydrothermal vent ecosystem are [NEET 2016, Phase II]
(a) green algae
(b) chemosynthetic bacteria
(c) blue-green algae
(d) coral reefs
Answer/Explanation
Ans. (b)
The primary producers of the deep-sea hydrothermal vent ecosystem are archaebacteria.
These have chemosynthetic mode of nutrition. Thus option (b), i.e.
chemosynthetic bacteria is the correct option.
Question
Which one of the following is not a functional unit of an ecosystem? [CBSE AIPMT 2012]
(a) Energy flow
(b) Decomposition
(c) Productivity
(d) Stratification
Answer/Explanation
Ans. (d)
Stratification is not the functional unit of ecosystem. Vertical distribution of different species occupying different levels is called stratification. It represent the structural unit of an ecosystem. For example, trees occupy top vertical strata or layer of a forest, shrubs the second and herbs and grasses occupy the bottom layers.
Question
Quercus species are the dominant component in [CBSE AIPMT 2008]
(a) temperature deciduous forests
(b) alpine forests
(c) scrub forests
(d) tropical rain forests
Answer/Explanation
Ans. (a)
Temperate deciduous forests grow in continental climates with summer rainfall and severe winters. They are dominated by broad leaved deciduous trees like Quercus virginiana, magnolias, bays and hallies as well as such tropical species as Ficus aurea and Lysiloma.
Question
The slow rate of decomposition of fallen logs in nature is due to their [CBSE AIPMT 2008]
(a) low moisture content
(b) poor nitrogen content
(c) anaerobic environment around them
(d) low cellulose content
Answer/Explanation
Ans. (a)
The slow rate of decomposition of fallen logs in nature is due to their low moisture content. The cellulose is in high amount in fallen logs. The environment arround the fallen logs is aerobic, $\mathrm{i.e.} \mathrm{O}_2$ is present.
Question
An ecosystem which can be easily damaged but can recover after some time if damaging effect stops, will be having [CBSE AIPMT 2004]
(a) low stability and high resilience
(b) high stability and low resilience
(c) low stability and low resilience
(d) high stability and high resilience
Answer/Explanation
Ans. (a)
Stability is the power of a system to be in their state against unfavourable factor. Resilience is the capability of regaining its original shape or position after being deformed. Hence, it has low stability and high resilience.
Question
Which of the following is the most stable ecosystem? [CBSE AIPMT 1995]
(a) Forest
(b) Desert
(c) Mountain
(d) Ocean
Answer/Explanation
Ans. (d)
Oceanic biome or ecosystem occupies more than two-thirds of the earth’s surface. This is the most stable ecosystem.
Question
What is true of ecosystem? [CBSE AIPMT 1998]
(a) Primary consumers are least dependent upon producers
(b) Primary consumers out-number producers
(c) Producers are more than primary consumers
(d) Secondary consumers are the largest and most powerful
Answer/Explanation
Ans. (c)
In an ecosystem producers (green plants) are always more than primary consumers (herbivores).
Question
In an ecosystem, which one shows one-way passage [CBSE AIPMT 1998]
(a) free energy
(b) carbon
(c) nitrogen
(d) potassium
Answer/Explanation
Ans. (a)
The flow of energy in any ecosystem is unidirectional. The only source of energy is sunlight. It gets trapped by producers then it flows from herbivores to carnivores or consumers at different trophic level.
Question
Decomposers are organisms that [CBSE AIPMT 1994]
(a) Elaborate chemical substances, causing death of tissues
(b) operate in living body and simplifying organic substances of cells step by step
(c) attack and kill plants as well as animals
(d) operate in relay terms, simplifying step by step the organic constituents of dead body
Answer/Explanation
Ans. (d)
Decomposers are the organisms, normally a fungus or bacterium, that digest organic material by secreting digestive enzymes into the environment, in the process liberating nutrients into the environment. These are also known as microconsumers, reducers or scavengers, as converting complex organic constituents of dead bodies of plants, animals, human wastes into simple soluble forms.