About Autotrophs and Heterotrophs

Autotrophs 

                    Green plants and some primitive animals like Euglena prepare their own food from inorganic substances. These are called autotrophs. They are classified into two types. 

1. Photosynthetic autotrophs 

2. Chemosynthetic autotrophs. 

Photosynthetic autotrophs

               Those organisms which synthesize their food from carbon dioxide and water in the presence of sun light, are called photosynthetic autotrophs.

e.g. purple sulphur bacteria, green sulphur bacteria and animals like Euglena.

Chemosynthetic autotrophs 

               Some bacteria obtain energy by biological oxidation of certain inorganic substances for the preparation of food instead of sunlight. Such bacteria are called chemosynthetic bacteria.

e.g. Nitrifying bacteria, sulphur bacteria, iron bacteria and hydrogen bacteria.

Heterotrophs 

             The non-green plants and animals are not capable of preparing their own food. They depend on other plants and animals for their food. They are called heterotrophs. They are classified into three types. They are parasitic nutrition, saprophytic or saprozoic nutrition and holozoic nutrition( only in animals ).

Parasitic nutrition

             Parasitism is a one sided relationship, where one partner gets the benefit at the expense of the other. The other partner is harmed. The partner which gets benefit is the parasite and the other partner is the host. In plants, viscum album ( mistletoe ) is a stem parasite. It grows on the branches of oak and walnut trees. It absorbs minerals and water from the host with the help of haustoria.

The animal may be

1. Ectoparasites 

2. Endoparasites 

Ectoparasites 

          The parasites which are often found on the outer surface of the host are called ectoparasites e.g. Ticks, Leeches.

Endoparasites 

             If the parasites live inside the body of the host they are called endoparasites. e.g. tape worm and round worm.

Saprophytic/ Saprozoic nutrition 

              This is met with in plants and animals. the decompose the dead bodies of plants and animals into simpler compound and absorb the organic food passively through the body wall of the organisms.

e.g. Bacteria, fungi and some protozoans.

             Have you ever seen umbrella shaped structures appearing after rains on open grass land? These are mushrooms ( Agaricus ). They lead a saprophytic mode of nutrition. They depend on dead organic materials for their food. They secrete digestive enzyme into the medium and convert the food into simple soluble forms and absorb them through the root like structures, The rhizoids.

Holozoic nutrition

                Animals depend on plants or other animals for their food. The food thus taken is digested in the alimentary canal. Here, they are digested into simpler substances with the help of digestive enzymes. Residual products are removed. This type of nutrition is called holozoic nutrition e.g. all higher animals.