An ecosystem comprises with biotic and abiotic component. A biotic component include light, air, water, temperature, humidity etc, while biotic factor comprises all living organism. Absence or limited availability of any component (either abiotic or biotic) makes an ecosystem incomplete like the profundal and benthic zone in an aquatic ecosystem.

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.

Atmosphere supplies CO₂ and O₂ to most organisms and moisture to some organisms; lithosphere provides water and minerals; and hydrosphere gives water and some dissolved minerals.

The upright pyramid and the inverted pyramid  are the two types of pyramids of biomass.

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

Humus is a dark-coloured, amorphous substance accumulated by the process of humification during decomposition of detritus.
Properties:
(i) It is highly resistant to microbial action and undergoes decomposition at an extremely slow rate.
(ii) Being colloidal in nature ,it serves as a reservoir of nutrient.
(iii) It improves the water-holding capacity of soil.

Green algae are not likely to be found in the deepest strata of sea because the environment is perpectually dark and sun as source of energy not available.

(i) The process of harvesting chemical energy for metabolic activities by oxidising the food molecules is called respiration.
(ii) The most common substrate used in the process is glucose.
(iii) ATP or Adenosine Triphosphate is also known as energy currency of the cell.

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 water-soluble inorganic substances run down into soil horizon and get precipitated as unavailable salts.
(iii) Catabolism:
The enzymatic conversion of the detritus into simple organic compounds and then into inorganic compounds, is called catabolism.
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.

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.