Nutrition and Respiration

Life Processes

  • The processes that maintain homeostasis and proper functioning of the body are called life processes. For Example Respiration, Excretion, Nutrition and Transportation.
  • In unicellular organisms, all these processes are carried out by a single cell.
  • In multicellular organisms, well-developed systems are present to carry out the processes.


  • Nutrition is the process of an organism acquiring the food which is needed for its nourishment and for the sustenance.
  • Nutrients: Materials which provide nutrition to organisms are called nutrients. Carbohydrates, proteins and fats are the main nutrients and are called macronutrients. Minerals and vitamins are required in small amounts and hence are called micronutrients.
  • Autotrophic and heterotrophic are two main modes of nutrition.


Autotrophic Nutrition

  • The mode of nutrition in which organisms synthesize their food from simple inorganic substances like carbon dioxide and water in the presence of sunlight is called autotrophic nutrition. Example- Green plants and some bacteria.
  • Plants synthesize their food for by using light energy, they are called photoautotrophs.
  • Bacteria synthesize their food by using chemical energy, they are called chemoautotrophs.
  • Carbon and energy requirements of the autotrophic organism are fulfilled by photosynthesis.


  • The process by which green plants make their own food with the help of CO2 and H2 O in the presence of chlorophyll and sunlight is also called photosynthesis.
  • Chlorophyll present in the green parts absorbs light energy.
  • This light energy is used to split water into hydrogen and oxygen.
  • Hydrogen is then used to reduce carbon dioxide into carbohydrates, typically glucose.
  • The carbohydrates which are not used immediately are stored in the form of starch.
  • Chlorophyll is essential for photosynthesis and stomata to facilitate the intake of carbon dioxide.
  • It involves the given reaction:

6CO2 + 6H2O → C6H 12O 6+ 6O2


  • Chloroplasts are the organelles found in the cells of green plants that contain chlorophyll.
  • They are the site of photosynthesis, as they have chlorophyll pigment.
  • Stomata are the tiny pores present on the surface of the leaves. Large amounts of gaseous exchange take place in the leaves through these pores for the purpose of photosynthesis.


  • Stomata are pores on the leaves that help in the exchange of gases.
  • They are mostly present on the underside of the leaf.
  • Stomata are covered with guard cells which regulate the opening and closing of the pore.
  • As the water concentration increase in the guard cell, it results in the opening of the stomata.
  • The water content of the guard cells is responsible for their function.

Heterotrophic Nutrition

  • The mode of nutrition in which an organism cannot prepare their own food and takes food from another organism is called heterotrophic nutrition. For example human beings, animals, non-green plants, etc.
  • Heterotrophic nutrition can be further divided into three types saprophytic nutrition, holozoic nutrition, and parasitic. 
  • Holozoic nutrition is a type of heterotrophic nutrition that is characterized by the internalization (ingestion) and internal processing of liquids or solid food particles.e.g. Amoeba, cow, dog, etc.
  • Saprotrophic nutrition is the mode of nutrition in organisms feed on dead and decaying organic matter.Example fungi.
  • Parasitic nutrition is nutrition in which an organism derives its food from the body of another living organism called its host without killing it. Example: Leech is an ectoparasite while Ascaris is an endoparasite. Cuscuta is a parasitic plant.

Nutrition in Amoeba

  • Amoeba gets its food by Holozoic mode of nutrition.
  • It engulfs the food particle using pseudopodia, the process is called phagocytosis.The engulfed food gets enclosed in a food vacuole.
  • Then it involves the ingestion, digestion, and egestion of food material.
  • The remaining undigested material is moved to the surface of the cell and thrown out.

Nutrition in Paramoecium

  • Paramoecium gets its food by Holozoic mode of nutrition.
  • Cilia present on their food surface help them to engulf the food through the oral groove.
  • The food vacuole contains the entire food particle which moves around the cytoplasm known as cyclosis.
  • Food digested in the food vacuole is absorbed by the cytoplasm.
  •  Waste food is then excreted out from the body through minute pores or cytopyge.

Nutrition in Human Beings

  • In human beings, the process of intake of essential nutrients in the form of food takes place through an entire system known as the digestive system.
  • The digestive system has an alimentary canal and associated digestive glands, which together function to nourish the body.
  • There are five stages in human nutrition; Ingestion, Digestion, Absorption, Assimilation and Egestion.
  • Four stages i.e. ingestion, digestion, absorption and egestion, take place in the alimentary canal, while assimilation of food takes place in the whole body.

Alimentary Canal

  • In humans it is a long tube of varying diameter which starts with the mouth and ends with the anus.
  • It comprises of mouth, oesophagus, stomach, small intestine and large intestine.


  • The mouth has teeth and tongue. Salivary glands are also present in the mouth.
  • Saliva is secreted by the salivary glands.The saliva contains an enzyme called salivary amylase that breaks down starch which is a complex molecule to give simple sugar.
  • The tongue has gustatory receptors which perceive the sense of taste.
  • The tongue helps in turning over the food so that saliva can be properly mixed in it.
  • Teeth help in breaking down the food into smaller particles so that, swallowing of food becomes easier.


  • It is a thin and long muscular tube that leads into the stomach.
  • Its function is to transport food and fluid, after being swallowed, from the mouth to the stomach.
  • Food is pushed down by peristaltic movements.

Peristaltic movement

  • Rhythmic contraction of muscles of the lining of the alimentary canal to push the food forward.
  • Muscles present in the wall of the alimentary canal are responsible for peristalsis.


  • It is a large organ that expands when food enters it.
  • It receives food from the oesophagus at one end and opens into the small intestine at the other end.
  • The stomach's inner lining secretes digestive fluids, hydrochloric acid, and mucus.
  • In the stomach, food is turned into chyme, a semi-solid substance.
  • Gastric juice contains enzymes that help break down the food.
  • In addition to killing harmful bacteria, hydrochloric acid helps in the partial digestion of proteins.
  • The mucus secreted by the wall of the stomach resists the action of HCl on itself.

Small Intestine

  • It is the longest part of the alimentary canal. It is the site of the complete digestion of food into different components.
  • It has regions, the duodenum, the region which follows the stomach; the jejunum is the middle part; and the ileum is the later region which continues further into the large intestine.
  • The bile salts emulsify fat by acting on large fat globules to break them into smaller globules. This increases the efficiency of pancreatic enzymes.
  • The food entering the small intestine is acidic. It is made alkaline by the action of bile juice so as to facilitate the action of pancreatic enzymes.
  • Pancreatic juice contains enzymes like trypsin for digesting proteins and lipase for breaking down emulsified fats.
  • The walls of the small intestine contain glands that secrete intestinal juice.
  • The enzymes present in it finally convert the proteins to amino acids, complex carbohydrates into glucose and fats into fatty acids and glycerol.
  • The internal surface of the small intestine is folded into finger-like projections called villi.
  • Villi increase the surface area for absorption.
  • The villi are richly supplied with blood vessels that take the absorbed food to each and every cell of the body.
  • The unabsorbed food is sent into the large intestine where its wall absorbs more water from this material.
  • A common pancreatic duct from the pancreas and liver opens into the duodenum.
  • Most of the chemical digestion and absorption takes place in the small intestine.

Large Intestine

  • Although shorter, it is a large intestine because it is wider in diameter than the small intestine.
  • The region of the large intestine after the ileum is called the colon, while the last part is called the rectum.
  • Colon has three regions, ascending colon, transverse colon and descending colon.
  • It houses many useful bacteria required for the digestion of food.
  • Rectum: It is the last and broad chamber-like structure.
  • Anus: It is the end point of the alimentary canal.

Physiology of Digestion

  • Food is mechanically digested in the buccal cavity, where teeth masticate it and saliva mixes with it to form a bolus.
  • Salivary amylase, which is found in saliva, begins the process of digestion of starch in the buccal cavity itself, turning it into the sugar maltose.
  • In the stomach, the churning of food takes place due to the muscular contraction and relaxation of its wall. It breaks down the food into simpler substances.
  • Pepsin's activity in the stomach causes the digestion of proteins to begin. Pepsin works by dissolving proteins into smaller pieces known as peptides.
  • The bolus, after mixing with gastric juice, turns into a fine soluble form known as chyme.
  • Chyme enters the small intestine, where complete digestion takes place due to the action of various enzymes present in the pancreatic juice, bile and intestinal juice.
  • The digested food is completely absorbed by the villi and microvilli of the small intestine.
  • Undigested food then enters the large intestine.
  • The colon is responsible for the absorption of water and salts, whereas the rectum stores the undigested food temporarily before defaecation.


  • It is a process in living organisms involving the production of energy, typically with the intake of oxygen and the release of carbon dioxide from the oxidation of complex organic substances.
  •  It occurs in the presence of specific enzymes at optimum temperatures in the cells to release energy for various metabolic activities.
  • The process in a complete way can be written in the form of an equation:

Glucose + oxygen → Carbon dioxide + Water + Energy

  • Gaseous exchange: Intake of oxygen from the atmosphere and release of carbon dioxide.
  • Breakdown of simple food in order to release energy inside the Cellular Respiration.

Types of Respiration

  • Anaerobic respiration: The pyruvate may be converted into ethanol and carbon dioxide. This process takes place in yeast during fermentation. Since this process takes place in the absence of air (oxygen), it is called anaerobic respiration.
  • Aerobic respiration: The breakdown of pyruvate using oxygen takes place in the mitochondria. This process breaks up the three-carbon pyruvate molecule to give three molecules of carbon dioxide. The other product is water. Since this process takes place in the presence of air (oxygen), it is called aerobic respiration.


Aerobic respiration

Anaerobic respiration

Takes place in the presence of oxygen.

Takes place in the absence of oxygen.

Complete breakdown of food occurs in it.

Incomplete breakdown of food occurs in it.

It takes place in the cytoplasm and inside mitochondria.

It takes place in the cytoplasm only.

The end products are Carbon dioxide and water.

The end products are lactic acid or ethanol and Carbon dioxide.

More energy is released.

Less energy is released.


On the basis of products form, it is of two types:

  • Alcoholic Fermentation: An incomplete breakdown of sugar into ethanol and carbon dioxide to release energy is called as alcoholic fermentation.
  • Lactic Acid Fermentation: It is the process of the incomplete breakdown of sugar into lactic acid and energy in some bacteria, is called Lactic acid fermentation.

Human Respiratory System

  • The human respiratory system is more complex and involves breathing, the exchange of gases and cellular respiration.
  • Breathing involves the inhalation of oxygen and the exhalation of carbon dioxide.
  • The gaseous exchange takes place in the lungs, and oxygen is supplied to all cells of the body.
  • The human respiratory system involves the nose, nasal cavities, pharynx, larynx, trachea/windpipe, bronchi, bronchioles and alveoli.
  • Nostrils: Air is taken into the body through the nostrils.
  • Nasal passage: It is mainly the conducting zone for air.
  • Pharynx: Nasal chamber opens into the pharynx. It passes it to the larynx.
  • Larynx: is located in the neck region and in front of the trachea.
  • Trachea: The air passes from the pharynx and gets into the trachea.
  • Bronchi: The trachea divides into two smaller tubes called Bronchi.
  • Bronchioles: Bronchi are subdivided into two smaller tubes called Bronchioles.
  • Alveoli: These are balloon-like structures located inside the lungs.
  • Ribs: There are 12 pairs of bones that form a cage in the thoracic region.
  • Lungs: These are the primary organs for respiration.

Mechanism of Breathing

  • The internal and external intercostal muscles, which are connected to the ribs and the diaphragm, let humans respire.
  • The capacity of the lungs grows the pressure within decreases, and air from the outside gushes in as the dome-shaped diaphragm contracts and flattens, and the rib cage expands because of the activity of intercostal muscles. This is inhalation.
  • To exhale, the diaphragm relaxes and becomes dome-shaped again; the chest cavity contracts due to the action of intercostal muscles, the volume inside the lungs decreases, pressure increases and the air is forced out of the lungs.
  • Inhaled air increases the concentration of oxygen in the alveoli, so oxygen simply diffuses into the surrounding blood vessels.
  • Blood coming from cells has more concentration of carbon dioxide than outside air, and thus carbon dioxide simply diffuses out of the blood vessels into the alveoli.
  • Thus, breathing takes place due to the combined action of intercostal muscles and the diaphragm, while the exchange of gases takes place due to simple diffusion.

Respiration in Other Organisms

  • Terrestrial Organism – use atmospheric oxygen for respiration
  • Aquatic Organisms – use oxygen dissolved in water.
  • Respiration in Plants: Respiration in plants is simpler than the respiration in animals. Gaseous exchange occur through - Stomata in leaves, Lenticels in stems and General surface of the roots.