(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.

(i) Chemical composition of detritus:
1. Decomposition is faster when detritus is rich in nitrogen and water-soluble substances like sugars.
2. Decomposition is slow when detritus is rich in lignin and chitin.
(ii) Oxygen
1. Decomposition is an oxygen-consuming process.
2. Anaerobic conditions inhibit decomposition.

Carbon cycle is significantly influenced by the following human activities:
(i) Rapid deforestation
- By massive felling of forest trees, there is an increase in the concentration of carbon dioxide in the atmosphere, because the trees which could hold a lot of carbon in their biomass are lost.
- The increased concentration of CO₂ could lead to global warming, because CO₂ is a greenhouse gas.
(ii) Massive burning of fossil fuels for energy and transport (automobiles) has increased the rate of release of carbon dioxide into the atmosphere.

All energy of sun trapped by green plants ultimately returns to the environment.

Recycling of phosphorus: Phosphorus is a major constitutent of biological membranes, nucleic acids and cellular energy transfer system. The natural reservoir of phosphorus is rock, which, contains phosphorus in the form of phosphates. When rocks are weathered, minute amount of these phosphates dissolve in soil solution and are absorbed by the roots of the plants. Herbivores and other animals obtain this element from plants. Herbivores and other animals obtain this element from plants. The waste products and the dead organisms are decomposed by phosphate-solubilizing bacteria releasing phosphorus. Unlike carbon cycle, there is no respiratory release of phosphorus into atmosphere.
Differences between carbon and phosphorus cycle: The major and important differences between carbon and phosphorus cycle are, firstly, atmospheric inputs of phosphorus through rainfall are much smaller than carbon inputs, and secondly, gaseous exchanges of phophorus between organisms and environment are negligible.

Many organisms occupy different positions in different food chains, several food chains get interconnected to form the food web.

Man can be a primary as well as secondary consumer because man eats plants as well as meat of other animals. So, man is herbivores as well as carnivores.

Biomass in terms of fresh weight shows variations in weight due to seasonal moisture defferences whereas the biomass in terms of dry weight remains unaffected by such seasonal moisture variations. Therefore, the measurement of biomass in terms of dry weight is considered more accurate than fresh weight.

(a)

(b)

(c)

(d)

(e)

(f)

(i) The species that invade a bare area called pioneer species.
(ii) In a xeric succession the pioneer species are usually lichens then bryophytes, which are succeeded by ferns and some other bigger plants.
Lichen produces lichen acid and carbonic acid which corrode rock surface and release minerals required for growth. The corroded rock accumulates soil particle by wind and provides substrate for bryophytes and ferns.

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.

(i) Lichens are the pioneer species on a bare rock. They are resistant to desiccation and temperature extremes. They produce organic acids which corrode the rock surface. This produces depressions and releases minerals which facilitate their further growth. The dead lichens add organic matter to the forming soil. The next community develops on thismeagre soil formed.
(ii) The climax community will be trees.

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.

The movement of nutrient elements through the living and the nonliving components of the biosphere, or of any particular ecosystem, is called biogeochemical cycle.
Two types of biogeochemical cycle are:
(a) Gaseous cycle (e.g., oxygen cycle, carbon cycle, nitrogen cycle, water cycle).
(b) Sedimentary cycles (e.g., phosphorus cycle, sulphur cycle, calcium cycle, potassium cycle).

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.

(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.

A climax community is the community that gets established at the terminal stage of succession and remains in equilibrium with the environment.
Difference:

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