Plant Nutrition, Nutrition in Plants || Autotrophic and Heterotrophic Nutrition || Parasitism, Mutualism & Insectivorous Plants

In this article we are going to discuss about the Chemosynthetic Nutrition Chemolithotrophs / Chemo-organotrophs Heterotrophic  Autotrophic Nutrition / Photosynthetic Organisms: Photolithotrophs/ Photo-organotrophs Nutrition: Holozoic Nutrition/ Saprobiontic Nutrition / Parasitism/ Mutualism/ Insectivorous Plants the all topic are provided by our live learns team full of free. 

Diverse forms of organisms have made earth their abode. There are tall trees, massive trees, very small plants etc. Despite the variety in forms and structure, all require energy for sustenance that comes from food in the form of organic compounds. This is absolutely necessary for their growth, development and metabolism. These processes contribute to the continuance of their life. Each of these activities requires energy in a specific form. The energy comes from burning food. Plants store food in various forms, generally as complex organic compounds. Compounds like starch, fats and proteins are energy rich and when broken yield energy. Two types of reactions occur in cells (metabolism) all the time-anabolic or energy requiring and catabolic or energy releasing.

One important difference between them is that anabolic (synthetic) reactions generally require…energy (endothermic), whereas catabolic reactions generally produce it (exothermic). In fact, one important function of catabolic reactions is to liberate energy.

Energy is required for three main purposes

(1) To drive the cell’s anabolic reactions, e.g., synthesis of proteins, storage compounds, etc, 

(2) For work; e.g contraction muscle transmission of nerve impulses, secretion by glands, etc.

(3) Maintenance and preservation of a constant  internal environment and of the tissues and organs in a state of health and functional efficiency.

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Energy is, therefore, of vital importance to an organism and much of metabolism is concerned with its production. All animals are dependent on plants for their nutrition. Plants manufacture the food material since they do not produce their food. On the contrary animals depend on plant requirements. This is called their food for autotrophic nutrition or autotrophism (auto = self, trophic = feeding). Animals are heterotrophs (hetero = other) since these to not produce their food. Hence, animals depend on plants for their food requirements. Since plants use light energy to make complex compounds; they are also called photo(auto)trophs. Some bacteria use energy from other chemical compounds (instead of sun) and are called chemo(auto)trophs.

The term photosynthesis means building up or assembly (synthesis) by using light (photo). The major chemical pathway of photosynthesis is the conversion of carbon dioxide (CO2) and water (H20) to carbohydrates [CHOH and oxygen (O2).

The reaction can be represented by following equation

CO2 + H0 (+ green plants) [CH2O] + O2

This (and any other similar equation) is a representation of the summary of the processThe carbohydrates thus formed possess more energy than the starting materials CO2 and H20. By inputting the sun’s energy, the energy-poor reactants are converted to energy-rich products. Photosynthesis can be regarded as a process of converting the radiant energy of the sun into chemical energy in plant tissues. (Remember the first law of thermodynamics

which states that energy cannot be created or destroyed but may be converted from one form to another). Most of the plants have in-built mechanisms for the synthesis of complex chemical compounds known as food. The compounds are synthesized by using solar energy. The other organisms derive energy from substances synthesized by plants as they do not have their own mechanism of production of food.

On this basis living organisms are divided into two groups

(1) The organisms which manufacture their own foods are called autotrophs. Most of the plants are autotrophs. They possess green pigment chlorophyll which is called instrumental in conversion of light energy into chemical energy.

(2) The organisms which obtain food from other sources since they can not manufacture their The own required food are called heterotrophs. These organisms either depend on plants or other living organisms to obtain their food (parasites) or derive their food from organic matter available from dead and decaying organisms (saprophytes).


Autotrophic organisms could either be  photosynthetic or chemosynthetic.

Photosynthetic Organisms

Most of the plants are autotrophs. These l can synthesize their own food material. It has been possible due to the presence of a special tvn e of pigment known as chlorophyll. This s green pign hectic organism is always present in all photosynthetic

The light energy from the sun 1s absorbed by chlorophyll. Using water from the soil and carbon dioxide from the air, starch 1S synthesized in the plants. This process in called photosynthesis

In higher plants with organized chloroplast. water serves as hydrogen donor in photosynthesis

This is a normal process of photosynthesi common to most autotrophic plants. However bacteria water is not used in photosynthesis Instead inorganic or organic substances acta hydrogen donors. On this basis, two types have been recognized.

1. Photolithotrophs. These bacteria use inorganic substances such as H,S, etc., as Bacterioviridin (chlorobium hydrogen source. chlorophyll) and bacteriochlorophyll are the pigments which take part in the conversion of chemical energy, e.g., Chlorobium, Chromatium etc.

2. Photo-organotrophs. These bacteria use non-sulphur organic compounds like organic acids, alcohol, etc., as hydrogen donors. The pigments like bacterioviridin and bacteriochlorophyll are also involved, e.g., Rhodospirillum.

Chemosynthetic Nutrition

There is another group of organisms which which synthesize their own food material like photosynthetic organisms but without using sunlight. These organisms use chemical energy for the synthesis of complex food materials. The energy comes from oxidation of inorganic or organic substances and is used in the synthesis of carbohydrates. These organisms are known as chemoautotrophs. Chemosynthesis occurs mostly in bacteria. On the basis of chemical compounds involved in energy supplying reactions, following two types have been recognized

1. Chemolithotrophs. The energy used By these organisms comes from the oxidation o inorganic substances. For example, nitrifying bacteria Oxidize ammonia into nitrite and then nitrite into nitrate (e.g Nitrosomonas, Nitrobacter), iron bacteria which convert ferrous compounds into ferric compounds (e.g.. bacillus), sulphur bacteria which change H,S into sulphur (c.g, Thiobacillus) are Some into free examples of chemolithotrophs.

2. Chemo-organotrophs. These are bacteria which oxidize organic compounds like methane to free carbon dioxide and water. The energy used to liberate is synthesized food. Methanococcus, Acetobacter, Lactobacillus, etc.. are some of the examples of this type of bacteria.


Heterotrophic organisms can not produce the food they require and, therefore, it is obtained from other sources including other living organisms and dead and decaying organic matter. The complex organic food forms the source of energy required for metabolic Heterotrophic activities. Their nutrition can be classified into following groups.

Holozoic Nutrition

Organisms with holozoic nutrition consume complete food which is broken down into simple molecules inside the organism. These molecules are then absorbed. This is the mode of nutrition in animals which have a specially developed digestive system for this purpose. Insectivorous plants, despite their autotrophic nature due to the subsequent presence of chlorophyll and photosynthesis, are partly holozoic.

Saprobiontic nutrition (Saprotrophic or Saprophytic Nutrition) Saprophytes obtain their food from complex organic compounds from the bodies of decaying plants and animals. The food occurs either in a Soluble form or it is digested externally into simple molecules which then diffuse into the saprophyte, Sometimes by special structures such as haustora

in fungi. Some bacteria and fungi are common examples of saprophytes. However, only a few higher plants are saprophytes. Monotropa and Neottia are saprophytic angiosperms.

Monotropa, commonly known as Indian Pipe lacks chlorophyll It is generally found in the forest litter of Shimla and Khasi hills. Fungal supplies mycelium that surrounds the roots nourishment to these plants. Neottia, which is an orchid, similarly lacks root hairs and depends on mycorrhizal fungus for absorption of nutrients.


These organisms derive their food from other living organisms in the form of complex organic substances. The parasites are always in close association with their host. It is the beneficiary while the host is harmed. The food is usually obtained

in soluble form. Plants do not have any special system for the absorption and digestion of food. This is generally carried out by enzymes. Many fungi and bacteria are total parasites and thus cause harmful diseases. Parasites are classified as semi-parasites or partial parasites and total parasites.

1. Total parasites. These plants always lack chlorophyll and, therefore, depend totally on other living organisms for their nutrition. Cuscuta known as dodder, is the best example of total stem parasite. It sends haustoria into the host plant which make contact with the vascular tissues of the host. The water as well as food is thus absorbed. Rafflesia, also called stinking corpse lily, is a total root parasite It derives its food from the roots of Cissus and figs. Balanophora and Orobanche are other common total root parasites.

2. Partial parasites. These plants possess chlorophyll and thus manufacture their own food material. However, partial parasites have to depend on the host for mineral and water requirements. Cassytha, Loranthus and Viscum are some of the common partial stem parasites. Santalum album (sandalwood) is a partial root parasite.


It is a close relationship between members of two different species. Both the organisms derive mutual benefit. Such association can be between algae and fungi to form lichens, between roots of legumes and bacteria (Rhizobium) and roots of higher plants and fungi (mycorrhiza). The phenomenon is also known as symbiosis.

Insectivorous Plants

This is a special group of chlorophyllous plants which catch and kill insects to obtain nitrogen which is otherwise deficient in habitat in which these plants live. The plants thus are autotrophic with a partly holozoic mode. There are a large number of insectivorous plants. These have specially developed structures to help catch insects. Some of the modifications are listed below  Plants thus follow many different processes so that the metabolic activities are carried out and life continues. Whether plants are autotrophic or heterotrophic, energy needed for their life-sustaining activities is always made available. In plants, chlorophyll being present, photosynthesis is carried out using light energy.

The organic food thus synthesized is useful for the sustenance of the plants as well as other organisms which lack the ability to manufacture food for themselves.


short notes

1 Chemosynthesis, 

2. Mutualism, 

3. Parasitism, 

4. Autotropism, 

5. Insectivorous plants.

Differentiate between

1. Autotroph and heterotroph

2. Parasite and saprophyte

3. Photosynthetic and chemosynthetic organisms

4. Autotrophs and Insectivorous plants

5. Total parasites and partial parasites.

Very short answer type questions

1. Name the most common end product of photosynthesis.

2. What are the raw materials for photosynthesis ?

3. Where does the energy come from in chemosynthesis?

4. Name the three main examples of mutualism.

5. Which mineral is obtained by insectivorous plants by digesting insects?

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