(a) The differences between Grazing Food Chain (GFC) and Detritus Food Chain (DFC) are as follows

(b) The Detritus Food Chain (DFC) may be connected to the Grazing Food Chain (GFC) at same level in an ecosystem. It can be supported by the fact that certain organisms of the GFC are predators to certain animals of DFC.
For example, earthworms which are detritivores are eaten by small birds (DFC) which becomes prey to predators like vulture/kites or even small animals of the GFC.

(a) Primary productivity is the rate at which solar energy is converted into organic substances through the process of photosynthetic and chemosynthetic autotrophs. It is also referred as the production of organic compounds through the biological process of photosynthesis. Its unit is gm^-2yr^-1 or (k cal m^-2) yr^-1.
(b) Primary productivity depends on the plant species inhabiting a particular area, environmental factors, availability of nutrients and photosynthetic capacity of plants.
Primary productivity of a place in Rajasthan, i.e. an arid (dry) region has low primary productivity because of some unfavourable environmental conditions, like absence of water, high temperature and lack of vegetation. On the other hand, Kerala, i.e., a coastal area has more primary productivity because of favourable environmental conditions like availability of water, moderate temperature and moderate amount of vegetation.

(a)

(b)

(c)

(d)

(e)

(f)

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.

1. Sun is the ultimate source of energy for all ecosystems on the earth.
2. Only about 50% of the incident solar radiation is photosynthetically active radiation (PAR).
3. Plants capture only 2-10% of the PAR and all organisms are dependent for their food on producers, either directly or indirectly. 
4. The flow of energy from the sun to producers and then to consumers is unidirectional and is keeping with the first law of thermodynamics.
5. Ecosystems need a continuous supply of energy for the synthesis of molecules needed and to counteract the tendency towards increasing disorderliness, i.e. energy flow follows the second law of thermodynamics too.

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.

(ii) Out of the total solar energy PAR is only 50%.

Zooplankton: They are primary consumers in an aquatic food chain who feeds upon phytoplanktons.

None of these - Plants are autotrophic and are called primary producers because they are self-sufficient to synthesise their own food. Also, there is nothing like secondary producers. 

1. Trophic level is a step or division of food chain. It is characterized by the method of obtaining food.
2. The number of trophic level is equal to number of steps in the food chain.
3. The two fundamental trophic levels are producers and consumers.
4. Producers are autotrophic organisms found in ecosystem which synthesise food from raw materials.
5.Consumers are heterotrophic organisms. Herbivores are primary consumers. In a pond ecosystem many crustaceaus, larvae of insects constitute this trophic level.

(a) Productivity is the rate of production of biomass (amount of living matter).
(b) Gross Prim y Productivity (GPP) is total amount of organic food synthesized by the producers per unit area and per unit time.
(c) Net Primary Productivity (NPP) is the total amount of biomass produced by the producers per unit area and per unit. It is GPP minus losses by way of respiration and decomposition. So NPP is represented as GPP-R.
(d) Secondary Productivity is the rate of biomass production by the consumers of per unit area per unit time. 'On average it is 10% for all the consumers.

(a) autotrophs
(b) upright
(c) light
(d) earthworms and soil microbes.
(e) ocean