CBSE 10th Biology | Life Processes | Nutrition

The various basic functions performed by living organisms to maintain their life on this earth are called life processes. The basic life processes common to all living organisms are as follows :

Nutrition:

• Nutrition is derived from the word ‘nutrient’. Nutrient is an organic or inorganic substance like proteins, carbohydrates, fats, vitamins and mineral salts, which provides energy for various metabolic processes.
• The process of obtaining food from the surroundings and using it for various metabolic activities by an organism is called nutrition.
  
• Energy is needed to maintain a state of order and balance in our body called homeostasis. We also need materials from outside to grow, develop, synthesise protein and other substances needed in the body. This source of energy and materials is the food we eat.
• Since, life on earth depends on carbon-based molecules most of these food sources are also carbon-based. Depending upon the complexity of these carbon-sources, different organisms can then use different kinds of nutritional processes.

Modes of Nutrition

It is defined as the method or mode of obtaining food by an organism. These are of two types.

Autotrophic Nutrition

Green plants are capable of manufacturing their own food in presence of light by using water and carbon-dioxide, this process is called photosynthesis. Such mode of nutrition is termed as autotrophic nutrition.

(i) Photosynthesis : It is the process by which green parts of the plant synthesise organic food in the form of carbohydrates from CO₂ and water in the presence of sunlight.

Green plants make their own food by photosynthesis.

(a)    Steps of photosynthesis :     During the process of photosynthesis, the following events occur :

• Absorption of light energy by chlorophyll.
• Conversion of light energy to chemical energy and splitting of water molecules into Hydrogen and oxygen.

  H₂O ® 2H⁺ + 2e^– + 1/2 O₂

  The above processes are considered as light reaction.

• Reduction of carbon-dioxide to carbohydrates. This is also known as dark reaction.

(b)    Conditions necessary for photosynthesis.

• Sunlight
• Chlorophyll
• Carbon-dioxide
• Water

These conditions are needed for autotrophic mode of nutrition.

(c)    Chloroplast : Chlorophyll containing organelles (i.e. plastid) which are found in large numbers in plant and algal cells undergoing photosynthesis are called chloroplast.

The structure of a leaf to show chloroplasts in it.

(The small circles in the above diagram are all chloroplasts).

The chloroplasts are, lens shaped and bounded by a double membrane. They are the main site of photosynthesis and occur in mesophyll cells of the leaf.

Internal Structure of Chloroplast

(d)    Raw materials for photosynthesis

• Carbon dioxide : It is a gas, which is released into the atmosphere during respiration by all living organisms. This gas is utilized by autotrophic plants which enters the leaf through the stomata present on its surface during the process of photosynthesis.
• Water : It is another requirement for photosynthesis which is transported upward through xylem tissues to the leaves, from where it reaches the photo-synthetic cells. This water then splits in the presence of sunlight and chlorophyll.
• Chlorophyll : It is a green pigment in plants which act as a catalyst. It is responsible for absorption of sun’s energy. The chlorophyll pigments are photoreceptor molecules which play a key role in the photosynthetic process. The different types of chlorophyll molecules are chlorophyll a, b, c, d and bacteriochlorophyll; of which chlorophyll a and b are most common.
• Light : It affects the rate of photosynthesis by its intensity, quality and duration. In green light, the rate of photosynthesis is minimum, while in red and blue lights the rate of photosynthesis is maximum. Rate of photosynthesis is higher in plants getting average light of 10-12 hrs a day.

(e) Structure of Stomata :     

They are tiny pores present on the surfaces of the leaves. Stomata function in gas exchange between the plant and the atmosphere. Each stoma is bordered by two bean / dumbbell shaped guard cells in dicots and monocots respectively.

Opening and Closing of Stomatal Pore :     The opening and closing of the pore is the function of guard cells. The guard cells swell when water flows into them causing the stomatal pore to open. Similarly the pore closes if the guard cells shrink. As large amount of water is lost through stomata, the plant closes these pores.

(a) Open and (b) closed stomatal pore

Elements such as N, P, Fe and Mg are required by the plant to build their body is taken up from the soil by roots. Nitrogen is the most important constituent of amino acid and nitrogenous bases.

Heterotrophic Nutrition

In multicellular organisms all the cells may not be in direct contact with the surrounding environment. Therefore, simple diffusion will not meet the requirement of all the cells.

The type of nutrition in which organisms derive their food (nutrients) from other living organism is called heterotrophic nutrition. In heterotrophic nutrition the energy is derived from the intake, digestion and oxidation of the organic substances, normally of plant or animal origin. Heterotrophic mode of nutrition is of different types :

(i) Saprotrophic Nutrition : It refers to the mode of nutrition in which organisms obtain nutrients from the dead and decaying organic matter e.g. fungi, yeast and bacteria. These organisms are called saprophytes.

(ii) Parasitic Nutrition : It refers to the mode of obtaining food synthesized by other animals and effecting them badly. The organism which obtains food is called the parasite and the organism from which the food is obtained is called ‘host’. This nutrition is observed in fungi, bacteria, few plants like Cuscuta and some animals like Plasmodium and roundworm, orchids, ticks, lick, leeches etc.

Parasite can be further classified as follows

(iii) Holozoic Nutrition : it refers to the mode of nutrition in which the complex organic matter in the form of solid food is ingested, digested and then absorbed into the cells and utilized e.g. Amoeba, frog, human being etc.

(a)    Nutrition in Amoeba

Nutrition in Amoeba

• The mode of nutrition in Amoeba is holozoic and it is omnivorous.
• It feeds on unicellular plants or animals such as Paramecium, Oscillatoria etc.
• The various steps of nutrition are ingestion, digestion, absorption, assimilation and egestion.
• When Amoeba comes in contact with food particles, it sends out temporary finger-like extensions of the cell surface called pseudopodia which engulf the prey by forming a food cup. This process is ingestion.
• When the tips of encircling pseudopodia touch each other, the food is encaptured into a bag called food vacuole. This step is digestion.
• The food vacuole serves as a temporary stomach secreting digestive juice.
• The digested food gets absorbed and diffuses into the cytoplasm and then assimilated. This process is called assimilation.
• The process of elimination of undigested food is called egestion. Egestion of undigested food takes place at any point on the surface of the body i.e. there is no fixed anus

(b) Nutrition in Human Beings : The organs which are responsible for ingestion, digestion absorption, assimilation and egestion constitute the digestive system. The digestive system comprises of alimentary canal and associated digestive glands.

    Mouth ® Buccal Cavity ® Pharynx ® Oesophagus ® Stomach ® Small Intestine ® Large Intestine ® Rectum ® Anus

    Process of nutrition : the digestive system consist of long alimentary canal extending from mouth to the anus.

The human digestive system.

Ingestion : Process of taking food inside the body.

Digestion : The food is crushed to smaller particles which are smaller and of same texture by teeth and mixed with saliva secreted by salivary glands.

• Saliva contains an enzyme called salivary amylase that breaks starch into sugar. Thus digestion of starch (carbohydrates) begins in mouth itself. Since the food remains in mouth only for a short time, so the digestion of food remains incomplete in mouth.
• The food is swallowed with the help of tongue and goes down the food pipe called oesophagus which carries it to the stomach by the rhythmic contraction of muscles produced by lining of alimentary canal. These movements are called peristaltic movements.
• Stomach is a large organ which expands when food enters it. The muscular walls of the stomach help in mincing the food thoroughly with more digestive juices.
• These digestive functions are taken care of by the gastric glands present in the wall of the stomach. These glands release hydrochloric acid, a protein digesting enzyme called pepsin and mucus.
• HCl (hydrochloric acid) facilitates the action of enzyme pepsin as this enzyme works in acidic medium. HCl also prevents fermentation of food and kills harmful micro-organisms present in food.
• Pepsin, the protein diagesting enzyme converts proteins into peptones and proteoses.
• Mucus protects the lining of stomach from the action of HCl.
• From stomach, the food enters the small intestine. The exit of food from the stomach is regulated by a sphincter muscle which releases it in small amounts into the small intestine.
• The length of the small intestine is different in various animals depending on the food they eat.
• Herbivores eating grass need a longer small intestine to allow cellulose to be digested. Meat is easier to digest, hence carnivores like tigers have a shorter small intestine.
• The small intestine is the site of complete digestion of carbohydrates, proteins and fats.
• The food coming from the stomach is acidic and has to be made alkaline for the pancreatic enzyme to act. Bile juice from the liver accomplishes this in addition to acting on fats.
• Fats are present in the form of large globules in small intestine which makes it difficult for enzymes to act on them.
• Bile salts break fats into smaller globules and thus increase the efficiency of enzyme action. This is called emulsification of fat.
• The pancreas secretes following enzymes :
  • Trypsin which digest proteins.
  • Lipase which digests fats.
  • Amylase which digests carbohydrates.
• The walls of small intestine contain glands which secrete intestinal juice. The enzymes present in it, finally convert the proteins into amino acids, complex carbohydrates into glucose and fats into fatty acids and glycerol.

Absorption and Assimilation : The inner lining of the small intestine has numerous finger – like projections called villi which increase the surface area for the absorption of digested food. The villi are richly supplied with blood vessels which take the absorbed food to each and every cell of the body, where it is utilized for obtaining energy, building up new tissues and the repair of the old ones.

Egestion : The undigested food is sent into the large intestine where more villi absorb water from this material. The rest of the materials are removed from the body via anus. The exit of this waste material is regulated by anal sphincter. This is called egestion.

Summary of Digestive enzymes of various glands with their secretion and end products of

Digestion in Man