(a) Define ecosystem. Discuss the structure and functions of ecosystem. (20 marks) (b) What is apiculture? Describe the various…

(a) Ecosystem: structure and functions

An ecosystem is a functional unit of nature in which a living community interacts with its non-living environment through flow of energy and cycling of materials. The term was coined by A. G. Tansley (1935). Examples are a pond, a forest, a grassland or the Sundarbans mangroves.

Structure:

• Abiotic components: physical factors (light, temperature, water, soil, topography) and chemical factors (pH, salinity, oxygen, carbon dioxide, nutrients).
• Biotic components: producers (green plants, algae, cyanobacteria), consumers (primary herbivores, secondary and tertiary carnivores, omnivores) and decomposers (bacteria and fungi) which return nutrients to the soil.
• The community is arranged in species composition, stratification and trophic levels.

Functions:

• Energy flow. Solar energy is fixed by producers and flows one way through the food chain and food web, and about 10% passes to the next level (Lindeman's ten percent law); the rest is lost as heat. Gross and net primary productivity measure production.
• Nutrient (biogeochemical) cycling. Carbon, nitrogen, phosphorus and water move between organisms and the environment in cycles.
• Ecological pyramids show the trophic structure; the energy pyramid is always upright, while numbers and biomass pyramids may be inverted.
• Development and regulation: succession and homeostasis maintain stability.
• Services such as pollination, water regulation and carbon storage.

(b) Apiculture, methods of beekeeping and uses of honey

Apiculture is the rearing and management of honey bees in artificial hives for honey, wax, pollen, propolis, royal jelly and pollination. In India the species kept in hives are the Indian hive bee (Apis cerana indica) and the introduced European bee (Apis mellifera). The rock bee (Apis dorsata) and little bee (Apis florea) are wild; their honey is collected, but they are not kept in hives.

Methods of beekeeping:

• Traditional (fixed-comb) methods: colonies kept in log hives, clay pots, wall niches or boxes; the combs are fixed, so inspection is not possible and honey is got by cutting the combs, which destroys brood.
• Modern movable-frame hives (the Langstroth hive; in India the Newton hive for A. cerana): bees build comb on separate frames that can be lifted out. This allows inspection, control of diseases and swarming, honey extraction without destroying comb, and queen management. The hive has a brood chamber, queen excluder and honey supers.
• Migratory beekeeping: hives are moved to follow the flowering seasons.

Uses of honey: it is a food and energy source rich in sugars (glucose and fructose), enzymes, vitamins and minerals. It is used in traditional and modern medicine for coughs, wound healing and as an antimicrobial agent, as a preservative and sweetener in food, and in cosmetics. Bees also raise crop yield by pollination.

(c) Difference between SEM and TEM

The scanning electron microscope (SEM) and the transmission electron microscope (TEM) both use an electron beam focused by electromagnetic lenses in a vacuum, but they differ as follows.

• Principle: in SEM a fine beam scans the surface and the secondary and back-scattered electrons given off form the image. In TEM the beam passes through an ultrathin specimen and the transmitted electrons form the image.
• Image: SEM gives a three-dimensional-looking view of surface topography, with a large depth of field. TEM gives a flat two-dimensional view of the internal ultrastructure.
• Specimen: SEM takes thick, solid, dry specimens, coated with a thin layer of gold or other metal. TEM needs ultrathin sections (about 50–100 nm) cut with an ultramicrotome and stained with heavy metals such as lead or uranium.
• Resolution and magnification: TEM is better (about 0.1–0.5 nm and up to about a million times) than SEM (about 1–10 nm and up to a few hundred thousand times).
• Uses: SEM for insect cuticle, pollen, feathers and parasite surfaces; TEM for organelles, membranes, viruses and cell pathology.