Question

How many trophic levels human beings function in a food chain?

Answer 1

Food chain may be a sequence of living organisms which involves transfer of food energy from producers, through many steps of different organisms with repeated eating and being eaten is called a food chain. Each level or step that helps to make a food chain where transfer of energy takes place is called trophic level.

Complete answer:
All living organisms including plants, animals and microorganisms present in the environment make up the biotic components of the ecosystem. On the ability of their role in the ecosystem, these can be made to exist into three main groups:

Producers: They are green photosynthetic plants that entrap solar energy through chlorophyll to synthesize organic food from inorganic raw materials. So, they are called autotrophs (self-nourishing).
In the aquatic ecosystem, phytoplankton, algae and the floating, submerged and marginal plants found at the edges are the primary or chief producers.

Consumers: They are the animals that are not in the state of synthesizing the food materials. They are dependent and reliable on producers directly or indirectly for their survival. Thus, they are called heterotrophs.

Consumers are of following types:
- Primary Consumers (PC) or First Order Consumers: These animals directly are dependent on producers by obtaining food from them. They are also called herbivores or the main industry animals. (Convert plant matter and products into animal matter) Aquatic ecosystem: Common herbivores are molluscs, tadpole and mosquito larvae. Humans are also included in the same category as they are also dependent on plant sources for food.

- Secondary Consumers (SC) or Primary Carnivores: They are animals which feed on herbivores. Aquatic ecosystem: Hydra, frog, and zooplanktons constitute mainly the secondary consumers.

- Tertiary Consumers (TC) or Secondary Carnivores: Carnivores which feed and eat upon secondary consumers e.g., large fishes (aquatic ecosystem), snake (terrestrial ecosystem). There may be quaternary or fourth order consumers which feed and act as predators upon secondary carnivores.

The energy transfer takes place from one trophic level to another and only 10% energy is transferred. The law was proposed by Lindeman in 1942. The transfer of energy from one trophic level to another trophic level usually occurs by loss of energy at each level or step. Therefore, at each transfer only 10% of the total energy is actually transferred to the next trophic level. It is called 10% law. So, there are maximum 4-5 trophic levels in a food chain and human beings can be on third as well as fourth level because they eat both plants and animals.

Note: So when a primary consumer like humans or herbivore animals eat plants, about 10% of their energy from food is fixed whereas 90% energy is consumed in various metabolic activities. Similarly, when that herbivore is eaten by the secondary consumer or carnivore animal, again about 10% of energy is fixed and this carnivore can then be eaten by humans, suggesting that there is some loss of energy at each trophic level.