NEET Biology Ecosystem MCQs Set 15

Answer: (c) Marsh meadow stage

Explanation:
1. The hydrarch sequence is phytoplankton, submerged plants, submerged free floating plants, reed swamp, marsh meadow, scrub and forest.
2. So the reed swamp stage is followed by the marsh meadow stage.

Teacher's Note:
1. Hydrarch succession starts in water and ends in a mesic forest.
2. Learn the sequence as one chain.

Answer: (b) 10 kg

Explanation:
1. Grass biomass is 1000 kg.
2. Deer get 10% of it, which is 100 kg, and the tiger gets 10% of that, which is 10 kg.

Teacher's Note:
1. Only about ten percent of the energy or biomass passes to the next trophic level.
2. Apply the factor once for each step.

Answer: (d) both (b) and (c)

Explanation:
1. Decomposers break down dead organic matter and release the minerals back to the soil.
2. Without them the mineral cycle stops, and the energy locked in dead matter cannot flow further, so both (b) and (c) are correct.

Teacher's Note:
1. Decomposers close the nutrient cycle.
2. Without decomposition producers would run out of minerals.

Answer: (a) I-A, II-B, III-C, IV-D

Explanation:
1. Gross primary productivity is the total fixation of energy by producers.
2. Consumers (secondary producers) are mobile, green plants are transducers of solar energy, and a food web is an interlocking pattern of food chains.

Teacher's Note:
1. Green plants convert (transduce) light energy into chemical energy.
2. A food web is a network of many food chains.

Answer: (b) the second law of thermodynamics

Explanation:
1. At each transfer some energy is lost as heat in respiration and becomes unavailable.
2. This degradation of energy into heat follows the second law of thermodynamics.

Teacher's Note:
1. Energy flow is unidirectional and loses quality at every step.
2. That is why food chains are short.

Answer: (b) deer and bees

Explanation:
1. Deer feed on plants and bees feed on nectar and pollen, so both are primary consumers.
2. The other pairs combine a herbivore with a carnivore or an omnivore, so they are at different levels.

Teacher's Note:
1. Trophic level depends on what the organism eats.
2. Herbivores are always at the second trophic level.

Answer: (b) lichens

Explanation:
1. On bare rock the first colonisers (pioneer species) are lichens.
2. They secrete acids that weather the rock and form soil, so they are called farmers of nature.

Teacher's Note:
1. Pioneer species on rock are lichens, and on water they are phytoplankton.
2. Mosses come after lichens.

Answer: (a) primary producers are more than primary consumers

Explanation:
1. By the ten percent law, energy and usually the biomass and numbers decrease at higher levels.
2. So primary producers are more than primary consumers.

Teacher's Note:
1. Most pyramids are upright.
2. Exceptions are the pyramid of numbers in a tree ecosystem and the pyramid of biomass in the sea.

Answer: (a) Producers

Explanation:
1. Energy decreases at each successive trophic level.
2. The producers, at the lowest level, hold the maximum energy.

Teacher's Note:
1. The pyramid of energy is always upright.
2. It can never be inverted.

Answer: (b) different communities of plants, animals and microbes together with their physico-chemical environment

Explanation:
1. An ecosystem includes all the living communities (plants, animals and microbes) and the non-living physico-chemical environment.
2. Only option (b) includes all of these.

Teacher's Note:
1. An ecosystem has both biotic and abiotic components.
2. Option (c) leaves out the animals.

Answer: (c) both the above

Explanation:
1. An ecosystem works through the unidirectional flow of energy and the cyclic movement of nutrients.
2. Both are important, so the answer is (c).

Teacher's Note:
1. Energy flows in one direction while nutrients cycle.
2. Together they keep the ecosystem running.

Answer: (c) biogeochemical cycle

Explanation:
1. The movement of nutrient elements through the biotic and abiotic parts of an ecosystem is nutrient cycling.
2. It is also called a biogeochemical cycle.

Teacher's Note:
1. Gaseous and sedimentary cycles are the two types of biogeochemical cycles.
2. Their reservoirs are the atmosphere and the earth's crust.

Answer: (a) tropical rain forest

Explanation:
1. A tropical rain forest has several vertical layers of vegetation, from the herbs on the ground to the tall emergent trees.
2. This vertical stratification is best developed there.

Teacher's Note:
1. More species and more layers are found in tropical rain forests.
2. Savannah is mostly grassland with scattered trees.

Answer: (a) lichen, moss, herbs, shrubs

Explanation:
1. This is xerarch succession on bare rock.
2. Lichens come first and are followed by mosses, herbs, shrubs and finally trees.

Teacher's Note:
1. The order is lichen, moss, herbs, shrubs, trees.
2. Each stage prepares the soil for the next.

Answer: (a) d, c, e, b and a

Explanation:
1. The hydrarch sequence is phytoplankton, submerged plants, submerged free floating plants, reed swamp and marsh meadow.
2. This is d, c, e, b and a.

Teacher's Note:
1. Water gets shallower as silt and organic matter accumulate.
2. The vegetation changes from aquatic to terrestrial.

Answer: (c) producers

Explanation:
1. Producers fix solar energy during photosynthesis.
2. This is how energy enters the living part of the ecosystem.

Teacher's Note:
1. The sun is the only source of energy for most ecosystems.
2. Producers are the only organisms able to capture it.

Answer: (d) None of these

Explanation:
1. Consumers that feed on herbivores are called primary carnivores, so (a) is correct.
2. The detritus food chain starts with dead organic matter, and the position of an organism in the food chain is its trophic level, so (b) and (c) are also correct.
3. No statement is wrong.

Teacher's Note:
1. Herbivores are primary consumers and the carnivores that eat them are primary carnivores.
2. The grazing food chain starts with producers and the detritus food chain with dead matter.

Answer: (d) Diagram D

Explanation:
1. In a forest the producers are large trees, so their total biomass is far greater than that of the consumers.
2. The biomass pyramid is therefore upright, with a broad base of producers and narrower bars for primary and then secondary consumers.
3. Only diagram D shows this.

Teacher's Note:
1. The number of individuals does not decide the biomass pyramid.
2. Large trees carry a huge biomass even when their number is small.

Answer: (d) standing crop

Explanation:
1. The mass of living organisms at each trophic level at a particular time is the standing crop.
2. It is measured as fresh or dry weight per unit area.

Teacher's Note:
1. Standing state refers to the amount of nutrients in the soil at a given time.
2. Standing crop refers to living material.

Answer: (b) 10 J

Explanation:
1. Energy fixed at T1 is 1% of 10,000 J, which is 100 J.
2. By the ten percent law T2 receives 10% of 100 J, which is 10 J.

Teacher's Note:
1. Apply the ten percent law once for each step up the food chain.
2. Do not apply it to the incident energy directly.

Answer: (d) more than one option is correct

Explanation:
1. Xerarch succession begins on dry areas and ends in mesic conditions.
2. Hydrarch succession begins in water and also ends in mesic conditions, so both (a) and (b) are correct.

Teacher's Note:
1. Both kinds of succession converge to a mesic climax.
2. The climax is the stable final community.