Nutrition

Introduction

     All organisms require energy in order to stay alive. Energy is utilised to do the various bodily functions such as breathing, ingesting and digesting food, excreting, reproducing, locomotion, etc. Energy is obtained from food. Thus the process of intake of food is vital for the survival of an organism as it provides energy. This intake of food is called nutrition.

Nutrients

     Food contains various organic and inorganic substances. Those which are required by the organisms to carry out life functions are called nutrients. Nutrients are of various types - carbohydrates, fats, proteins, vitamins and minerals.

Modes of Nutrition

     The mechanism by which organisms obtain food are referred to as modes of nutrition. The organisms either synthesize their own food or obtain food prepared by other organisms in various ways. There are basically two modes of nutrition - autotrophic and heterotrophic.

Types of Heterotrophic Nutrition - Holozoic Nutrition

     This type of nutrition involves the taking in of solid particles of food which have to be further broken down into simpler particles inside the organism (there are exceptions which are called fluid feeders. Think of at least two of them. Look for answers in the Q & A section). These particles may be big or small.

Types of Heterotrophic Nutrition - Saprophytic

     'Sapros' refers to rotten and 'trophic' refers to food. Saprotrophic nutrition is the process by which the organisms feed on dead and decaying matter. The food is digested outside the cells or even the body of the organism - extracellular digestion. The organism secretes digestive juices that contain enzymes directly on to the food. The digestion makes the food soluble and it is then absorbed by the organism.

Types of Heterotrophic Nutrition - Parasitic

     In ancient Greece, the person getting free meals for entertaining others by his amusing converstions was called a parasite - 'para' refers to beside and 'sitos' refers to grains. Thus, parasitism is defined as an association between individuals of two different species which is beneficial to one and generally harmful to another.

Nutrition in Plants

     Most plants are autotrophic. They synthesize their own food. The green plants, also called the producers, trap the solar energy and convert it into chemical energy of the food. The biochemical reactions in the body which result in the formation of chemical compounds are collectively called anabolic reactions. Food is required to provide energy. The compound that can be easily broken down in order to yield energy is glucose.

Photosynthesis

     'Photo' refers to light and 'synthesis' means preparation. Thus, photosynthesis is the process by which the green plants use light energy of the sun to synthesize carbohydrates. Carbohydrates like the simple sugars (glucose) can be stored as starch.

Photosynthesis - Reactants

     During photosynthesis, carbon dioxide is converted into carbohydrates and this is called fixing of carbon dioxide. Many processes like respiration, combustion, volcanic activity, etc. release carbon dioxide into the atmosphere. This carbon dioxide of the atmosphere is used by the terrestrial plants while hydrophytes use the carbon dioxide dissolved in the water.

Photosynthetic Apparatus

     The photosynthetic pigments chlorophylls are present in the leaves because of which the leaves are green in colour and are called the photosynthetic organs.

Steps Involved in Photosynthesis

     It is so called as it takes place only in the presence of sunlight and hence is a light-dependent reaction. Robin Hill, an English biochemist conducted studies on isolated chloroplasts to understand the mechanism of light reactions.

Summary of Photosynthesis

     During photosynthesis, carbon dioxide and water are used to synthesize sugars. It occurs with the help of the radiant energy of the sun which is absorbed by the chlorophyll of the green plants.

Factors Affecting Photosynthesis

     The concentration of chlorophyll affects the rate of reaction as they absorb the light energy without which the reactions cannot proceed. Lack of chlorophyll or deficiency of chlorophyll results in chlorosis or yellowing of leaves. It can occur due to disease, mineral deficiency or the natural process of aging (senescence). Lack of iron, magnesium, nitrogen and light affect the formation of chlorophyll and thereby causes chlorosis.

Photosynthesis - Some Activities

     The leaf is first decolourised by treating it in 90% ethanol (alcohol) solution. It is then rinsed in hot water to remove all alcohol and to soften the tissue.

Nutrition in Animals

     All animals are heterotrophic (there are exceptions like Euglena, which has chlorophyll). The different modes of heterotrophic nutrition have already been dealt with in the earlier part of the chapter. Of all the methods of heterotrophism, holozoic is the most commonly found.

Nutrition in Amoeba

     Nutrition in amoeba is holozoic. Thus, solid food particles are ingested which are then acted upon by enzymes and digested. It is an omnivore, feeding on both plants and animals. Its diet includes bacteria, microscopic plants like the diatoms, minute algae, microscopic animals like other protozoa, nematodes and even dead organic matter.

Digestion in Amoeba

     Digestion in amoeba is intracellular taking place within the cell. The food taken in remains in a food vacuole or gastric vacuole formed by the cell membrane and small part of the cytoplasm. The vacuoles are transported deeper into the cells by cytoplasmic movements. Here they fuse with lysosomes that contain enzymes. Two enzymes amylase and proteinase have been reported.

Nutrition in Grasshopper

     Nutrition in grasshopper (Poecilocerus pictus) is holozoic and as the name indicates is a herbivore, feeding on different kinds of vegetation like the grasses, germinating grains, leafy vegetation, etc.

Mouthparts of Grasshopper

     A pair of hard, horny, heavy, large, with jagged inner edges and dark coloured triangular structures found one on either side. The two mandibles move in horizontal motion and crush food between them.

Digestive System of Grasshopper

     It consists of the mouth surrounded by the mouthparts. The mouth cavity is called the pharynx. It continues as the oesophagus that is short, narrow and thin-walled. The canal then enlarges into crop which is also thin-walled. The crop opens into short, muscular organ, the gizzard or the proventriculus. A pair of Salivaryglands lie outside and below the crop.

Human Digestive System

     Man is omnivorous - feeding on different kinds of food. Thus, the structure of the digestive system should be adapted to this diet. The human digestive system consists of an alimentary canal, which is approximately 8metres long.

Human Digestive System - contd...

     It is a sac-like organ which is connected to the oesophagus at the anterior by a cardiac sphincter and to the small intestine at the posterior end by a pyloric sphincter.

Gastric Glands and Their Secretions

     Liver is the largest gland and is found in the upper part of the abdomen on the right side of the body just below the diaphragm. Its secretion is called bile juice. It is alkaline and rich in organic salts called the bile salts. The alkaline nature serves to neutralize the acidic pH of the gastric juice and creates the right environment for the intestinal enzymes to function.

Other Digestive Juices

     It is secreted by the secretory glands of the stomach wall. It is highly acidic as it contains hydrochloric acid (HCl). It also contains enzymes like pepsin and renin. Both act on proteins. However, renin is present only in young children. It digests the milk proteins. Pepsin is secreted in its inactive form pepsinogen which becomes activated in acidic conditions.

Mechanism of Digestion

     Once the food is ingested into the mouth the action of the upper and the lower jaw crushes and grinds the food. This also stimulates the production of saliva. Saliva is thoroughly mixed with the food with the action of the jaws, teeth, inner walls of cheeks and tongue. The food is formed into bolus (a soft ball). Due to salivary amylase, partial digestion of starch takes place here.

Summary

     Nutrition can be defined as the process by which an organism obtains food that is used to provide energy and materials for its life sustaining activities.