Ecosystem (Class XII)

Biological control through antagonism involves competition, parasitism and predation.

The limnetic zone is the well-lit, open surface waters in a lake, away from the shore.

Fusion of male and female gametes in plants, called as fertilization. It does not require sunlight.

Ecosystem development includes all of the above discussed options.

The functioning of an ecosystem mainly depends on the pattern of energy flow.

All of the above are biogeochemical cycles.

The greatest reservoirs of phosphate are the insoluble ferric and calcium phosphates in rocks (rock phosphate), in combination with calcium, iron and aluminium. Slow process of weathering releases phosphates into the soil.

An ecosystem can be defined as a structural and functional unit of biosphere or segment of nature consisting of community of living beings and the physical environment, both interacting and exchanging materials between them.

These are the microorganisms which feed on dead plants and animals and reduce their remains to minerals and gases again. Examples are fungi (like mushrooms) and bacteria. They occupy the last position in the food chain.

Dr. Odum has been dubbed as the <span style="font-family:" arial;="" font-size:="" small;="">“father of modern ecology” and is credited with pioneering the concept of ecosystem. 

Nitrogenase is the enzyme used by some organisms to fix atmospheric nitrogen gas (N₂). It is the only known family of enzymes, which accomplishes this process.

It is just the reverse statement as an ecosystem is considered to be stable in the ecological sense if its structure and functions remain more or less the same throughout the year.

Pyramid of biomass - Amount of living or organic matter present in an organism is called biomass. Pyramid of biomass is upright for terrestrial habitats; inverted or spindle-shaped in aquatic habitats.

Lindemann in 1942 put forth ten percent law for the transfer of energy from one trophic level to the next. According to the law, during the transfer of organic food from one trophic level to the next, only about ten percent of the organic matter is stored as flesh. The remaining is lost during transfer or broken down in respiration.

Joshua tree is one of the most characteristic plants of the Mojave desert and extends southwards to the Mohave-Sonoran desert ecotone. This species grows from Southern California, Mexico and Western Arizona eastwards into Southern Nevada and Southwestern Utah.

Elton is especially remembered for founding and for nearly twenty years editing the Journal of Animal Ecology. He is also known for his studies on animal community patterns (including the community-oriented concepts of the Eltonian niche and the pyramid of numbers) and for a number of contributions to economic biology and conservation studies.

Increase in soil fertility by promoting humus formation is an ecological importance of forests.

First tropic level in an energy pyramid represents producers which contain the highest amount of energy. Therefore, the first trophic level will transfer the highest amount of energy to the next trophic level. Since only 10% of the energy is transferred to the next trophic levels, the higher trophic levels will have less amount of energy as compared to the first trophic level. 

Forests maintain ecological balance. Forests help in maintaining the ecological balance in the following ways:

They absorb carbon dioxide and release oxygen.
They provide the soil with the necessary humus content.
They prevent soil erosion by binding the soil with tree roots.
They check floods by holding rain water in subsoil.
They increase moisture content of the air through transpiration.
They provide natural habitat for wildlife.

The concentration of heavy metals in the body of the organisms increases with the increase in trophic level. Since phytoplanktons are present at the lowermost trophic level, the concentration of heavy metals in phytoplanktons will be minimum, while the concentration of heavy metals in herring gull will be the highest as it is present at the highest trophic level. Hence, the correct order of organisms with increasing levels of heavy metals is option 2.