With the evolution of oxygen releasing photoautotrophic organisms, 20.95%.

Change of ammonium compounds, nitrites and nitrates into molecular nitrogen by certain bacteria and fugin is termed denitrification.

Upright, inverted and spindle-like pyramids.

Auroral animals are active at dawn, vesperal animals are active in the evening.

Each trophic level has a certain mass of living material at a particular time called as standing crop.
Biomass: The standing crop is measured as mass of living organisms or the number in a unit area. The biomass of a species is expressed in terms of fresh or dry weight. Measurement of biomass in terms of dry weight is more accurate as the moisture content of biomass fluctuates greatly.
Standing state: Organisms need a constant supply of nutrients to grow, reproduce and regulate various body functions. The amount of nutrients, such as carbon, nitrogen, phosphorus, calcium, etc. present in the soil at any given time, is referred to as the standing state.

Primary source of energy is sun.This solar energy is first trapped by the green plants, called producers, and is used to assimilate organic food by the process of photosynthesis. This food energy of the producers is transferred to the herbivores (primary consumers) and then to different types of carnivores because all the consumers are heterotrophs. The energy can not be transferred from consumers to producers and from the producers to sun. So there is producers and from the producers and from the producers and from the producers to sun. So there is always unidirectional flow of energy which is accompanied with decrease in usable energy.

Robert Constanza et al tried to put a price tag ecosystem services.
It is about 33 billion US dollars/years.

1. Detritus food chain on terrestrial ecosystem becomes connected with the grazing food chain because some of the organisms of DFC are prey to the animals of GFC.
2. IN nature, some animals that are omnivores occupy a trophic level in both DFC and GFC and form a food web.

(i) The process by which autotrophs convert inorganic materials into organic material with the help of solar energy is called photosynthesis.
\({ { 6CO }_{ 2 } }+12{ { H }_{ 2 }O }\quad \underrightarrow { Light } \quad C{ _{ 6 } }{ { H }_{ 12 } }{ O_{ 6 }+6{ { H }_{ 2 } } }O+6{ { { O } }_{ 2 } }\)
(ii) The green pigment which traps solar energy and converts light energy into chemical energy is chlorophyll.
(iii) The three pigments, i.e. chlorophyll, carotenoids and xenthophylls together form a complex of pigments in the thylakoid membrane. These complexes work for the absorption of light and its transfer to a reaction centre.These complexes are called photosynthetic unit of photosystem or pigment system.

(a)

(b)

(c)

(d)

(e)

(f)

Sun is the endless source of energy, but the chemical materials of the environment are exhaustible.The producers fix solar energy into the chemical energy of organic compounds by utilizing inorganic substance (i.e., CO₂ and water). This stored energy is passed to consumers by repeated eating and being eaten.Decomposers act on dead decaying organic matter and return the locked inorganic substance back to the environment for their reuse by producers.Without this, all life will ultimately cease to exist and earth will be full of dead organisms and waste organic substances.

In ecological succession, the climax community remains stable as long as the environment remains unchanged.

(b) Pyramid is inverted. It is because in pond ecosystem, producers are the smallest organisms while herbivores and carnivores are largest in size. Consequently, there is a gradual increase in biomass of organisms at successive trophic levels.

All the regions of the world (atmosphere, lithosphere ad hydrosphere) where living organisms occur together with their abiotic environments from a biosphere. Main subdivisions of biosphere are atmosphere, lithosphere and hydrosphere.

All organisms/animals which depend directly or indirectly on plants for their food are called consumers.
Consumers are of the following types:
(i) Primary consumers
They are the organisms/animals which depend directly on producers for their food;they are also called as herbivores,e.g. deer, rabbit, zooplanktons.
(ii)Secondary consumers
Secondary consumers are those animals which depend on the primary consumers for their food; they are primary carnivores, e.g frogs,hyena.
(iii)Tertiary consumers
Tertiary consumers are those animals which depend on the secondary consumers for their food;they are the secondary carnivores, e.g. lion, eagle, kite, etc.

(i) Grasslands,Forests.
(ii) Oceans, Ponds, Lakes.
(iii) Agricultural fields, Aquariums.

Primary productivity is defined as the amount  of biomass or organic matter produced per unit area over a time period by the plants during photosynthesis.
It is also defined as the amount of biomass or  organic matter produced per unit area over a time period by the plants during photosynthesis.
Primary productivity depends on:
(i)The plant species inhabiting a particular area.
(ii)The environmental factors.
(iii) Available of nutrient.
(iv) Photosynthetic capacity of plants.

Pond - an Ecosystem
1. Pond is a fairly self-sustainable unit that shows even complex interactions of an aquatic ecosystem.
2. It is a shallow water body in which all the major/basic components of an ecosystem are well exhibited.
3. The abiotic components ar:
(i) Water with all the dissolved inorganic substance.
(ii) The rich soil deposit at the bottom.
(iii) The solar input.
(iv) The cycle of temperature.
(v) day length.
(vi) Climatic factor.
1. The producers or autotrophic components include phytoplanktons, some algae, floating and submerged and marginal plants.
2. The consumers are represented by
(i) zooplanktons,
(ii) f ree-swimming animals,
(iii) bottom dwelling animals.
1. The decomposers are the bacteria and fungi that are found at the bottom.
2. This system performs all the function of an ecosystem.
(i) Conversion of inorganic materials into organic compounds with the help of radiant energy of sun.
(ii) Consumption of autotrophs  by heterotrophs, (food chain/food web), decomposition and mineralisation (nutrient cycling), etc.

Process of decomposition
(i) Fragmentation:
It is the process of breaking of the detritus into smaller particles by detritivores like earthworm.
(ii) Leaching: It is the process in which watersoluble inorganic substances run down into soil horizon and get precipitated as unavailable salts.
(iii) Catabolism:
1. The enzymatic conversion of the detritus into simple organic compounds and then into inorganic compounds is called catabolism.
2. The enzymes are secreted by the decomposers like bacteria and fungi
(iv) Humification:
Humification during decomposition leads to the accumulation of a dark coloured, amorphous substance, called humus.
(v) Mineralisation:
It is the process in which the humus is degraded by certain microbes and the inorganic nutrients are released.

Components of an Ecosystem:
The components are broadly classified into two categories:
(i) Biotic components
(ii) Abiotic components

Biotic components include the following:

Producers:
These are the green plants or other autotrophs, which prepare their own organic food and feed energy into the ecosystem.
Decomposers:
Decomposers are the organisms which degrade the dead and decaying organic matter and satisfy their energy requirement, e.g. bacteria and fungi.

Abiotic Components:
They include the factors like:
(i) Air
(ii) Water
(iii) Solar radiation
(iv) Temperature
(v) Soil with organic and inorganic compounds as nutrients to plants.