Plants are divided into broad categories in terms of their mode of nutrition. The first category consists of green plants which make their own food by the common process called photosynthesis. Such plants are classified as autotrophic.

Self-dependence for nutritional requirements of these plants is based on their ability to use water from the soil and carbon dioxide from the environment and prepare glucose sugar as a result of chemical reaction in the presence of chlorophyll (the green matter present in the leaves and the sun). Subsequently, glucose is converted into different types of sugars (fructose, xylose, etc.), vegetable oils, proteins and starches. Photosynthesis is one of the most important chemical reactions due to which life is sustained on our planet earth. Oxygen evolved in the process of photosynthesis is a by-product necessary for respiration and human health.

The second category comprises the non-green plants which obtain their food from external sources. They get their nutrition by decomposed dead organic matters, including foodstuffs like cooked food, bread, meat, etc. Such plants include mainly fungi and bacteria and some of them may also cause different disease in plants and animals, including man. The second category, as described here is classified as heterotrophic.

This category of plants also includes some very special plants called insectivorous plants, which can eat insects and flesh. However, under normal conditions photosynthesis also takes place in these plants.

Insectivorous plants grow in humid environment and soil of poor quality that is deficient in nitrogen and minerals. Other plants can hardly compete with these plants because they can also use insects as food and survive in the most difficult times. Like other green plants, insectivorous plants can be grown in the house as a hobby. Since the desired insects may not be easily available, small pieces of meat could be substituted. Their morphological adaptation and the mechanism by which the insects are trapped are interestingly different. In all the cases, the leaves have been modified into traps to catch the insects. Some varieties of insectivorous plants are briefly discussed hereunder.

Pitcher plants: They are found in tropical and temperate zones. These plants possess tubular or pitcher-shaped leaves provided with a colourful lid. These pitchers contain digestive enzymes in the form of a liquid. The insects are attracted to the pitcher by their colourful leaves and/or their odour.

Once an insect gets into the pitcher it cannot come out because of the downward directed hairs inside the pitcher. The insects are killed and the insect-protein is digested for the nitrogen requirements of the plant. On completion of the process, the stalk of the pitcher twists downwards and the remains of the insect are blown out by the jerks of the air current.

Sundews: These constitute another interesting group of carnivorous plants. In these the leaf blades are flattened and possess numerous glandular hairs which secrete sticky fluid containing digestive juices. Whenever an insect alights on the leaf, it is smeared with the mucilaginous substance, the secretion of the glands at the hair tips. Simultaneously, some of the hairs which are sensitive to contact bend inwards and trap the insect. As usual, the body of the insect is digested and the remains of the insect thrown out by the straightening of the glandular hairs and the jerks of the wind.

Venus (flytrap): The morphology of these plants is more like leaves with 12-20 marginal spines about one inch long. The hairs at the upper surface of the blades are sensitive. The touch of the insects cause two halves of the blade to move together and the marginal spines get interlocked. The insect thus interlocked gets killed and digested. The leaf reopens to discard the remains.

Bladderworts: These are submerged rootless water plants. The bladders have valves which open only on the inner side. When a water insect strikes the sensitive hairs on the outside of the lid, it opens inside and the insect enters the bladder. After its entry, the lid is tightly closed. The insect dies due to exhaustion and it is then digested. Now the valve opens again and the remains of the insect are swept out by water currents.

In many of the insectivorous species, there are no highly specialised leaves. In these the leaf surfaces are covered with sticky hairs to which the insects are glued, killed and digested. There are between 400 to 500 species of insectivorous plants.