4. Nutrition in Living Organisms


Some life-processes go on continuously in living organisms. Substances which are digested and assimilated for obtaining energy and for the growth and health of our body are called foodstuffs. We get several types of nutrients from foodstuffs.

Nutrients can be classified into two types, namely, macro-nutrients and micro[1]nutrients. Nutrients like carbohydrates, proteins and fats are required in large quantity. These are macro-nutrients. Minerals and vitamins are required in very small quantity. They are called micro-nutrients.

Autotrophic plants

How do plants produce their own food? Plants also need food for their growth. They can produce their own food. With the help of sunlight and chlorophyll, plants make their food in their leaves, using water and nutrients from the soil and carbon dioxide from the air. This process is called as photosynthesis.

Plants convert light energy into chemical energy and store it in the form of food. Water, minerals and salts are absorbed by roots from the soil. The stem transports them up to the leaves. The leaves have microscopic openings called stomata through which they take in the CO2 from the air. The chloroplasts present in the leaves contain chlorophyll, which absorbs sunlight, helping to convert carbon dioxide and water into food. Oxygen is given out in this process. Besides leaves, photosynthesis takes place in some other parts like green stems, too, as they contain chlorophyll.

Transport system in plants

Take a pumpkin stem having 2-3 leaves. Cut it under water with a sharp blade. Take some water in a conical flask and add 7-8 drops of ink to it. Put the pumpkin stem vertically in that flask. Observe the changes that take place in it and discuss them in the classroom. The transport system of plants consists of the xylem and the phloem. The xylem transports minerals and water from the root to all aerial parts of the plant. The phloem transports the food (glucose, etc.) from the leaves to other parts of the plant where it is either consumed or stored. Though the plants have a transport system, they do not have a separate digestive or excretory system.

Plants produce carbohydrates by the process of photosynthesis. Carbohydrates are made from carbon, hydrogen and oxygen. Proteins are made from carbon, hydrogen, oxygen and nitrogen. How do plants obtain the nitrogen necessary for the synthesis of proteins ?

Air contains gaseous nitrogen. However, plants cannot utilize gaseous nitrogen. It needs to be fixed i.e. converted into compounds. Fixation of nitrogen occurs by biological and atmospheric methods.

Biological fixation of nitrogen

 Two different types of micro-organisms can bring about biological nitrogen fixation. Root-nodules of leguminous plants contain the rhizobium micro[1]organisms. These micro-organisms absorb atmospheric nitrogen and convert it into its nitrate, a compound. Micro-organisms like azotobacter are present in soil. They also convert atomspheric nitrogen into nitrates.

Symbiotic nutrition

In some cases, two or more than two different types of plants live together to fulfill their needs of nutrition, protection, support, etc. with each others’ help. This type of nutrition is called symbiotic nutrition. Some fungi grow around the roots of some other plants. These plants supply nutrients to the fungi and in turn, fungi supply minerals and water to the plants. Some fungi and algae live together. The fungi provides water, minerals as well as shelter to algae. In return, the algae provide food to the fungi. Lichen is an example of a symbiosis between algae and fungi.

Heterotrophic plants

 Heterotrophic plants do not contain chlorophyll. How do the heterotrophic plants live ? From where do they get food? Have you seen a yellow, wire-like, leafless climber plant growing on a big tree ? What is its name ? The plants that grow on the body of other plants to obtain food are called as parasitic plants, for example, loranthus, cuscuta, etc. Due to the absence of chlorophyll, the cuscuta is completely dependent on the host plant. Hence, it is said to be a completely parasitic plant. You must have also noticed loranthus that grows on trees.

Insectivorous plants

We have seen how some plants feed upon insects to obtain nutrients. These insectivorous plants generally grow in soil or water deficient in nitrogen compounds. The plant body of the Drosera burmanii has a flower[1]like appearance. It grows close to the ground. Its leaves are attractively pink or red in colour with hairs at the margin. Droplets of a sticky subtance found at the tips of the hairs attract insects. The scientist Johannes Burman identified this plant in Sri Lanka in 1737. Hence, the plant is named after him.

Saprophytic plants

 Plants which obtain the food from dead and decaying bodies of other organisms are called saprophytic plants. Various types of fungi like mushrooms and yeast are saprophytes. Fungi secrete digestive enzymes on the dead remains to digest or breakdown the carbon compounds they contain. The resulting solution is absorbed to obtain nutrients.

Nutrition in animals

 This concept refers to the body’s need for nutrients, mode of ingesting food and its use in the body.

Nutrients necessary for various activities of the body are obtained from food. They are supplied to the various parts of body through blood. The food that we consume does not mix with blood as it is. It needs to convert into soluble forms that can easily mix in blood. Nutrition in animals involves various steps from ingestion to egestion.

Types of nutrition in animals

(A) Holozoic nutrition

Amoeba does not have organs like hands and mouth. It is a unicellular animal. It can take in food through any part of the surface of its unicellular body. It surrounds the food particle from all sides to take it into the cell. After that, it digests the food with the help of different enzymes. Undigested food is left behind as the amoeba moves further with the help of pseudopodia. In unicellular animals like amoeba, euglena, paramoecium, etc. all the steps of nutrition occur within their unicellular body.

Insects have mouth-parts for ingestion of food. For example, insects like the cockroach and grasshopper which nibble have jaw-like mouth-parts. Butterflies suck food with a a tube-like proboscis. Mosquitoes and bedbugs use a needle-like mouth part to pierce and a tube-like mouth part to suck blood or other fluids.

According to the type of food, animals can be classified as –

  1. Herbivores : Herbivores use plants directly as their food. Example are grazing animals, granivores (seed-eaters), frugivores (fruit-eaters), etc.
    2. Carnivores : Animals that depend on other animals for their food are carnivores. Carnivores are indirectly dependent on plants for food. Examples are animals that feed on herbivores (predators), animals that feed on insects (insectivores).
    3. Omnivores : Animals that obtain their food from both plants and animals are called omnivores. Examples are monkey, chimpanzee, human, etc. Some of the organisms around us perform the function of cleaning and conserving the environment by the very act of feeding themselves. They are called scavengers and decomposers.
    4. Scavengers obtain their food from dead bodies of animals, for example, vulture, crow, hyena, etc. 5. Decomposers are some microbes which obtain their food by decomposing the dead bodies of organisms or other materials.

(B) Saprozoic nutrition

Some insects, unicellular animals, etc. obtain the nutrients by absorbing the liquid organic material from the dead bodies of other animals or from the environment. This is saprozoic nutrition. Example, houseflies, ants, spiders, etc.

(C) Parasitic nutrition

  1. Have you seen small animals on the bodies of animals like dogs and buffalloes ? Which are those small animals ?
  2. From where do these little animals obtain their food?
  3. From where do the worms in the intestine obtain their food? Some animals depend upon other animals for food. They can obtain the food only from animals on whom they are dependent. This is called as parasitic nutrition.

Some animals live on the body surface of other animals and obtain their food by sucking their blood. This is called ectoparasitic nutrition and such animals are called ectoparasites, for example, louse, bed-bug, tick, etc. Animals like tapeworm and roundworms live inside the body of other animals and obtain their food. This is endoparasitic nutrition and these animals are known as endoparasites.