(a) Healthy ecosystems are the base for a wide range of economic, environmental and aesthetic goods and services. The products of ecosystem processes are named as ecosystem services. For examples, healthy forest ecosystem purifies air and water, minimize droughts and floods, cycle nutrients, generates fertile soils, provides wildlife habitat, maintains biodiversity, pollinate crops, provid storage site for carbon and also provide aesthetic,cultural and spiritual values. Though value of such services of biodiversity is difficult to determine, it seems reasonable to think that biodiversity should carry a healthy price tag.
(b) Based on the nature of the habitat - whether it is water (or very wet areas) or it is on very dry areas- succession of plants is called hydrarch or xerarch, respectively.
Differences: Hydrarch succession takes place in wetter areas and the successional series progress from hydric to mesic conditions. As against this, xerarch succession takes place in dry areas and the series progress from xeric to mesic conditions.
Similarity: Both hydrarch and xerarch successions lead to medium water conditions (mesic), neither too dry (xeric) nor too wet (hydric).

Function: To meet the deficit which occurs due to imbalance in the rate of influx and efflux.

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.

Grazing food chain:
Autotrophs ---> herbivores ---> primary carnivores ---> secondary carnivores
Detritus food chain:
Decay and ---> decomposer ---> soil animal
Excretory organism which consume Materials other soil from the organisms. grazing food.

Transfer of energy from one trophic level to the next, keeps the prey population under control, biological control, helps maintain species diversity.

Gradual/predictable change in the species composition of given area. Rate of succession would be faster in a forest destroyed by a forest fire. Such disturbances create new conditions that encourage some species and discourage or eliminate other species/since after a forest fire some soil is already present. So, succession is faster than primary succession.

(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.

(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.

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.

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.