[Biology Class Notes] on Heterotroph Pdf for EXAM

We do a lot of activities on our daily basis, to perform these activities we require energy and the energy can be obtained from the food we eat. Hence nutrients are the main source of energy that is necessary for our body. All the living organisms require energy and they get it in various forms. 

Depending on how they obtain their energy and nutrients these are further classified into two types they are:

1. Autotrophs

2. Heterotrophs

Autotrophs and Heterotrophs

Autotrophs have the capability to produce their own energy and food from the required raw materials. Hence they are called producers. Examples include plants, algae, and some types of bacteria. 

Heterotrophs are called consumers, as dependent on producers or other consumers. Examples include humans, dogs, fishes, birds, etc.

Heterotroph Definition

The organisms that depend on other organisms for nutrients and energy are considered heterotrophs. The heterotrophic meaning in Greek is as follows, the term “hetero” means “other” and “trophe” means “nourishment”.

In the food chain, heterotrophs are present on the second and the third level. Whereas each of the food chains consists of three trophic levels that help to describe the role of an organism in the ecosystem. The first trophic level is occupied by autotrophs such as algae, plants, etc. Herbivores occupy the second trophic level and the carnivores occupy the third trophic level. Here both the herbivores and carnivores are considered heterotrophic organisms.

Types of Heterotrophs

Heterotrophs are further divided into two types:

1. Photoheterotrophs: The organisms that obtain energy from light are called photoheterotrophs, but they cannot get the carbon dioxide directly from the air thus they depend on other organisms for carbon dioxide consumption. 

2. Chemoheterotrophs: These organisms get both energy and carbon dioxide from other organisms. Heterotrophic microbes are the best examples of chemoheterotrophs that include fungi and protozoa, as they require carbon dioxide and energy from other organisms. 

Plant and Animal Heterotrophs

Some of the plants cannot produce their own food and they have to obtain their food from others, such plants are heterotrophs. It occurs in plants that are parasitic or saprophytic. In these cases, the parasitic plant depends on the host for survival whereas the saprophytic one depends on the dead and decayed matter for food. 

Animals are heterotrophs according to the definition since they cannot prepare their food as that of plants by the process of photosynthesis. 

The other type of heterotrophs are detrivores, that obtain nutrients from the decaying plant and animals. Saprophytes are the organisms that consume decayed organic matter. Another way of dividing the heterotrophs is, they can be organotrophs or lithotrophs. Organotrophs are the ones that use reduced carbon compounds as the source of electrons from plants and animals. Whereas the lithotrophs use inorganic compounds such as sulfur, nitrate, or ammonium.