Sunday, February 28, 2016


Unlike plants, animals cannot prepare their own food. Instead, they procure food by feeding on other organisms. 
Hence, they are called Heterotrophs. Heterotrophic nutrition is of two types. Saprozoic and Holozoic.

Saprozoic nutrition in very primitive animals, especially some protozoans, and parasites exhibit saprozoic mode of nutrition. They absorb food materials dissolved in water through their body surfaces. 

Some animals secrete enzymes into the external medium. These enzymes breakdown the complex organic molecutes into simple organic molecules. These are then absorbed by the animal through its body surface. As the food is already digested and in the form of small molecules, some of these animals may not have special digestive organs. Even if present, the digestive system in these animals is very simple.

Holozoic nutrition Majority of animals take solid particulate food or liquid food through special feeding mechanisms and digest them with the help of digestive enzymes. This mode of nutrition is know as holozoic nutrition

The size of food particles varies considerably ranging from microscopic organisms to large animals and plants. Depending on the size of the food, different mechanisms to capture the food. 

Some animals use pseudopodia (Amoeba), tentacles (Hydra) for capture the food. These animals do not cut the food into small pieces and swallow the entire food at one time. Other animals which feed on solid food have mechanisms to cut the food into small pieces before they consume it. 

For example, snails have snarp teeth like structures on their tongue called Radula with which they scrape the surface of food and swallow the food particles. 

Some animals, like lions and tigers, are equipped with organs to chase, seize (capture) kill, cut and cat the prey. 

Some animals feed only on liquid food. For example scorpions and spiders kill the prey and inject digestive enzymes into the body of the dead animal. These enzymes digest the food and convert it into liquid form which the animal will feed. 

Houseflies, butterflies, mosquitoes, aphids, leeches etc.,also feed on liquid food. Butterflies have long tube like proboscis which is inserted into the flowers and nectar is sucked. 

Mosquitoes have special organs to pierce through the skin and suck the blood. Blood sucking animals such as mosquitoes and leeches secrete substances into the blood to prevent blood from clothing while they are feeding. 

Animals like earth worms feed on soil containing decomposed organic material.

Thus,a variety of feeding mechanisms are seen in animal kingdom and the type of feeding mechanisms in the animal depends on the type and nature of the food. 

Mono and Polyphagous animals: 
Some animals feed on only one type of food material and these are called monophagous animals. 

A typical example for this is the caterpillar larva of silkworm which feeds only on mulberry leaves. 

Several animals feed on plant material are called herbivores while those feeding on other animals are called carnivores. Animals which eat both plants and animals are called omnivores. 

Diet of an animal may be different in different sexes or at different stages of its life. For example, male mosquito feeds on plant juices white female mosquito feeds on blood. Similarly, caterpillar larva feeds on leaves while the butterfly feeds on the nectar. 

Thus, there is a great variation in the type of food consumed and the method by which it is consumed in holozoic animals. 


The third type of nutrition is called mixotrophic nutrition. In this type of nutrition, there is an association of two different living organisms.

Nutrients may be obtained by both the organisms or only by one organism. In the former condition, both the organisms are benefited while in the latter case only once of the organisms is benefited of the association.

When two organisms live together, exchange nutrients and are benefited mutually. This nutrition is called symbiotic nutrition.

One of the organisms provide nutrients required for the other organism which the other provides shelter or nutrients or both.

Symbiotic mode of nutrition is seen in both plants and animals. Nitrogen fixing bacteria living in the root nodules of leguminous plants is a typical example for symbiotic nutrition.

Plant provides shelter and nutrients to the bacteria while bacteria provide nitrogenous compounds to the plant.

Similarly, symbiotic association is seen in lichens where algae supplies food to fungi, fungi provides protection to algae and live together.

In animal kingdom, the association of certain crabs with sea anemones is an example of symbiotic nutrition.

Sea anemones give protection to the animal while the small pieces of food particles are provided to sea anemones by the crab. 

Parasitism is the second type of mixotrophic nutrition – parasite is an organism which lives inside (called endoparasite) or outside (called ectoparasite) of another organism (called host ) and obtain the nutrients form the host organism.

In this mode of nutritiononly parasite is benefited. Body functions of the host are usually affected badly due to the invasion of the parasite and the host may even die.


Heterotrophs cannot synthesise their own nutrients. They depend on other sources for the supply of nutrients including those required for energy production. Most of the bacteria, all fungi and all animals are heterotrophs.

You might have seen packets of mushrooms sold in the vegetable
market. You may have also seen fluffy umbrella-like patches growing on rotting wood during the rainy season. Let us find out what type of nutrients they need to survive and from where they get them.

These organisms are called fungi.They have a different mode of nutrition. They secrete digestive juices on the dead and decaying matter and convert it into a solution. Then they absorb the nutrients from it.

This mode of nutrition  in which organisms take in nutrients in solution form from dead and decaying matter is called saprotrophic nutrition.
Plants which use saprotrophic mode of nutrition are called saprotrophs.

The fungal spores are generally present in the air. When they land on wet and warm things they germinate and grow. Now, can you figure out how we can protect our things from getting spoiled?

Some organisms live together and share shelter and nutrients. This is called symbiotic relationship. For example, certain fungi live in the roots of trees. The tree provides nutrients to the fungus and, in return, receives help from it to take up water and nutrients from the soil. This association is very important for the tree.

Some of the bacteria and of fungi depend on other
dead organisms to obtain nutrients. Those which live on other organisms, decompose and degrade the complex molecules present in these organisms to simple molecules.

Bacteria and fungi absorb these molecules through their body surface. These are called saprophytes. In this process, they add several valuable nutrients to the medium in which they live(water or soil).


OMNIVORES: All the animals are heterotrophic in their nutrition. They cannot synthesise their own food material. Hence, they consume other organisms such as plants, animals and microorganisms.

Size and nature of food consumed is different in 

different animals.


They may consume either small microscopic or large plants or animals or both. Animals consuming plants as food are called herbivores. Those consuming other animals are called carnivores. Those which consume both animals and plants are called omnivores. Interestingly, some plants are also carnivorous especially insectivorous (feed on insects). They supplement their autotrophic nutrition by obtaining nitrogen rich nutrients from the insects.

Nepenthes, Dionea (Venus fly trap), Drosera (sun dew plant) and Utricularia ( bladder wort) are some of the examples for this type of plants. All these plants are autotrophic and can live by themselves without feeding on insects. However, their growth is stimulated when they feed on insects. 


Friday, February 26, 2016


Organisms which exhibit autotrophic nutrition are 
called Autotrophs. These organisms are able to synthesise their nutrients from simple inorganic compounds.

They require minerals, water and carbon dioxide for their growth. They are capable of converting carbon dioxide into various complex organic compounds.

However, they require energy for this purpose. Depending on how they obtain the energy for converting carbon dioxide to organic compounds, there are two types of autotrophs photoautotroph and chemoautotroph.

Several bacteria(such as green bacteria, purple bacteria and cyanobacterial) can use light as a source of energy and synthesise complex organic molecules.

Similarly, All the algae and higher plants use light as source of energy. These autotrophic organisms are called photoautotrophic organisms

These organisms have special pigments is their body to trap the light energy which drives other reactions.

Second group of autotrophs are chemoautotrophs. These organisms obtain energy by oxidizing simple inorganic compounds. 

Such as hydrogen, iron containing compounds, sulphur, hydrogen sulphide, ammonia, nitrite, and other nitrogen containingcompounds. However, all these organisms require carbon dioxide as a source of carbon atoms.


Autotrophic, Heterotrophic and Mixotrophic Nutrition -TEXT

All the living organisms require a continuous supply of carbon containing compounds(also called principal carbon) for growth and for building their body structures

Energy is also required to maintain their daily activities and it is derived by oxidizing either organic or inorganiccompounds. Chemical compounds required for body building and for energy production are called nutrients. Intake of nutrients into the body by an organism is called nutrition.

Nutrients may be very simple or very complexinorganic or organic compounds. Different organisms require different types of nutrients

For example, several bacteria can survive with a supply of few inorganic salts. Plants use water and carbon dioxide and synthesize carboncompounds like carbohydrates. 

They also use simple nitrogen and sulphur containing compounds to synthesize complex molecules required for their growth. In contrast, amino acids, fatty acids and vitamins for their survival.

They do not have the capacity to synthesise several chemical compounds required for their growth. They depend on other organisms for the supply of these nutrients.

All the nutrients required by an organism are usually obtained through the food they consume. Hence, several times, intake and utilization of food is considered to be similar to nutrition.

Differentorganisms use different methods to obtain their nutrients, especially of carbon source. Autotrophic, heterotrophic and mixotrophic nutrition are three modes by which organisms obtain their principal source of carbon.