(a) Name the group of organisms which form in the first trophic level of all food chains. Why are they called so? (b) Why are the human beings most adversely affected by bio-magnification? (c) State one ill-effect of the absence of decomposers from a natural ecosystem.

(a) First Trophic Level:

• Group: Autotrophs or producers (all green plants and certain photosynthetic bacteria).
• Reason: They are called producers because they capture solar energy and convert it into chemical energy, producing organic compounds like sugar and starch from simple inorganic substances using chlorophyll in the presence of sunlight.

(b) Bio-magnification in Humans:

• Pesticides and other crop-protecting chemicals are non-biodegradable. These chemicals enter the food chain through soil or water and accumulate progressively at each trophic level.
• Since human beings occupy the top level in almost all food chains, the maximum concentration of these harmful chemicals gets accumulated in our bodies over time.

(c) Ill-effect of the Absence of Decomposers:

• In the absence of decomposers (bacteria and fungi), the dead remains of plants and animals and their waste products would pile up in the environment.
• The natural replenishment of the soil with simple inorganic nutrients would stop, halting nutrient cycling and eventually leading to the collapse of the ecosystem.