31 Years NEET Previous Year Questions: Ecosystem - 2

Therophytes are those plants which survive the adverse season like winter as a seed and complete their life cycle between spring and autumn.

The rate at which organic molecules are formed in a green plant is called gross productivity.

50% of the solar energy incident over earth is present in PAR (photosynthetically active reaction). About 1-5% of total incident solar energy or 2-10% of PAR is captured by the photosynthetic organisms for photosynthesis.

Plankton → Organisms passively floating in upper water.
Nekton → Actively swimming Benthos → Lead sedentary life upon the sea bottom

In an ecosystem producers (green plants) are always more than consumers (herbivores, carnivores etc.)

Energy f low takes place only in one direction i.e., producers → herbivores → carnivores whereas, nutrients use carbon, nitrogen and potassium shows cyclic flow.

Organic pollutants provide nutrients for stimulating growth of algae and other plants. Algal bloom reduces availability of light to submerged plants which get killed. The dead submerged plants consume more oxygen in decomposition. This reduces availability of oxygen to other life forms leading to death of organisms. This is known as eutrophication.

Some plants growing in salty  marshes develop special roots for respiration, called  pneumatophores. They are (–) vely geotropic.

The greatest biomass of autotrophs in the oceans is that of free floating microalgae, cyanobacteria and nanoplankton.

First trophic level is occupied by producers. Second trophic level is occupied by primary consumers. Third trophic level is occupied by the secondary consumers.

Grasslands will have highest value of gross production. Net production is obtained after subtracting the respiratory utilization from gross production. Secondary and tertiary production is related with secondary and tertiary consumers respectively.

Nitrogenase is an enzyme involved in biological nitrogen fixation. Enzyme nitrate reductase is involved in conversion of nitrate to nitrite. Conversion of ammonia to nitrate is carried out by Nitrosomonas and Nitrobacter.  

An ecosystem having low stability can be easily damaged. An ecosystem having high resilience will take less time to recover. 

Barophiles are bacteria which live in high pressure environments. They are generally found on ocean floors, where pressure generally exceeds 380 atm (38 MPa). Some have been found at the bottom of the Pacific Ocean where the maximum pressure is roughly 117 MPa.

Three fourth surface of earth is covered by oceans which contain 97.5% of total water. It is marine water with about 3.5% salt content only 2.5% is fresh water which occurs on land. Most of this water (1.97%) occurs as frozen ice caps and glaciers,  0.5% fresh water occurs as ground water. Rivers and lakes contain 0.02%, soil 0.01% while atmosphere possesses 0.001% of water as vapours.

Fresh weight is not used for the construction of ecological pyramids because the total fresh weight does not change into energy. Hence we can say that fresh weight is not continuous in the tropic levels.

They are found in the equatorial regions  rainfall exceeds 140 cm. The warm humid climate supports broad leaved evergreen plants. Productivity is very high (12000 k. cal/m²/ year). The vegetation show stratification into two or more well defined layers. 

About 70% oftotal global carbon is found in oceans. This oceanic reservoir regulates the amount of carbon dioxide in the atmosphere. Atmosphere contains only about one percent of total global carbon. 

The microorganisms breakdown the complex compounds of dead protoplasm of producers and consumers absorb some of the decomposition products and release simple substances. 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.

Food chain is the transfer of energy from green plants (Primary producers), through a sequence of organisms occupies in a food chain is known as its trophic level. Therefore, statements b and c are correct.

The cor rect sequence of plants in a hydrosere is Volvox, Hydrilla, Pistia, Scirpus, Lanatana and Oak. A hydrosere is a plant succession which occurs in a fresh water lake. In time, an area of open fresh water such as a lake will naturally dry out, ultimately becoming woodland. During this change, a range of different landtypes such as swamp and marsh will succeed each other. The succession from open water to climax woodland is likely to take at least two hundred years.

A pond ecosystem is a delicate balance of fish, plants and other animals. Fish occupy more than one tropic level in pond ecosystem. Small fishes act as secondary consumer. They feed on primary consumer. Large fishes act as tertiary consumer. They feed on smaller fish. 

The statement (i) and (ii) are correct. The statement (iii) is incorrect because predators cannot lead to the extinction of prey species. Predator and prey evolve together. The statement (iv) is incorrect because chemical such as nicotine and strychnine produced by the plants are not metabolic disorders but are metabolic wastes.

The biomass available for consumption by the herbivores and the decomposers is called net primary productivity. It is equal to the rate of organic matter created by photosynthesis minus the rate of respiration and other losses.

A standing crop is the quantity or total weight or energy content of the organism, which are in a particular location at a particular time.