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Life Processes

Chapter: Life Processes



Although living things look different from each other they have certain things in common which are as follows: 1. All the living things move, 2. They reproduce, 3. they need nutrition, 4. they are sensitive, 5. they excrete, 6. they respire, 7. they grow.

What are Life Processes?

  1. Different types of functions are carried out in an organism to keep it in a living state. These functions continue to happen even when the organism is in resting period i.e. when the organism is asleep or just sitting idle. These processes which are performed in a living organism to keep it living are called as life processes.
  2. The life processes need energy to maintain the health and growth of an organism and this energy comes from the food we take. Since life on earth depends on carbon-based molecules, most of these food sources are also carbon- based. So, the process of obtaining the food necessary to carry out the life processes for maintaining the health and growth of an organism is called nutrition.
  3. The outside sources of energy could be quite varied. so, they need to be broken down and converted into a uniform source of energy that can be used by living organisms. This process requires a series of chemical reactions like the oxidation-reduction reactions which need oxygen. The oxygen used in these chemical reactions is obtained from outside environment, the process of acquiring oxygen from outside the body, and to use it in the process of break-down of food sources for cellular needs, is called as respiration.
  4. Multicellular organisms have different organs each having a specialized function to perform. Therefore the uptake of food and oxygen will also be the function of specialized tissues. Since the food and oxygen are now taken up at one place in the body of the organisms there is need of a special transportation system to transport food and oxygen to all the parts of the body.
  5. During the process of energy generation where carbon source and oxygen are utilized a lot of by- products are generated which are not useful to the body while some could be harmful to the body.  So, these by-products need to be eliminated out of the body by a process called excretion.

Let us look in detail about various processes essential to maintain life:


Living organisms require energy for their growth, development and for synthesis of important substances like proteins. They get energy through food. Food contains all the essential nutrients required for the growth and development of an organism. The process of obtaining the food is called as nutrition.

How do living things get their food?

  1. Some organism obtain their food from inorganic sources in the form of carbon dioxide and water, these organisms are called autotrophs. Examples: green plants and bacteria.
  2. Organisms which obtain their food from complex substances are called heterotrophs. These organisms break the complex substances into simple substances using biocatalysts called enzymes and obtain their energy.

Autotrophic nutrition

It is the mode of nutrition in which the organisms carry out photosynthesis to meet their energy requirement. Photosynthesis is a process in which the plants convert carbon dioxide and water into carbohydrates in the presence of sunlight. Carbohydrate that is produced is converted and stored in the form of starch, which serves as an internal energy reserve. Water used in the process of photosynthesis is taken up from soil. Along with water soil also supplies some essential elements like nitrogen, iron, phosphorus and magnesium.  Nitrogen is taken up in the form of inorganic nitrates or nitrites or as organic compounds which are prepared by bacteria from atmospheric nitrogen. Nitrogen is essentially used for the synthesis of proteins and other important compounds.

Heterotrophic nutrition

Each and every organism is adapted to its own environment. Their mode of nutrition depends on the type and availability of food material and also on how it is obtained by that organism. Here are a few examples:

  1. Some organisms break-down food material outside the body and then absorb it. eg: Fungi like bread moulds, yeast and mushrooms.
  2. Some of the organisms take up the food and then break it down into simpler substances inside the body. e.g. human beings.
  3. Organisms like tapeworm, ticks, lice, leeches, cuscuta obtain their nutrition from plants and animals but without killing them.

How do organisms obtain their nutrition?

The digestive system varies from organism to organism. In single-celled organisms food may be taken in by the entire surface. But as the complexity increases the digestive system also becomes complex. Let us look at few examples of digestion in single celled organisms:

  1. Amoeba has finger like projections on its surface which fuse over the food particles forming food vacuole. Inside the food vacuole the complex food material is broken down into simpler substances which then diffuse into cytoplasm. The remaining undigested material is moved to the surface of the cell and thrown out.
  2. In case of paramecium which is also a unicellular organism the cell has a definite shape and food is taken in at a specific spot. Food is moved to this spot by the movement of cilia which cover the entire surface

Nutrition in human beings:

The alimentary canal is basically a long tube extending from the mouth to the anus. The tube has different parts. Various regions are specialized to perform different functions. The process of digestion is accomplished by mechanical and chemical processes.

  1. The buccal cavity performs two major functions, mastication of food and facilitation of swallowing. The teeth and tongue with the help of saliva masticate and mix up the food thoroughly.
  2. The saliva secreted into the oral cavity contains electrolytes and enzymes like salivary amylase and lysozyme which help in the breakdown of food. Mucus in the saliva helps in lubricating and adhering the masticated food particles into a bolus.
  3. The bolus is then conveyed into the pharynx and then into oesophagus by swallowing.
  4. The bolus further passes down through the oesophagus by successive waves of muscular contractions called peristalasis.
  5. The gastro-oesophagal sphinchter controls the passage of food into the stomach.
  6. The stomach stores the food for 4-5 hours. The food mixes thoroughly with the acidic gastric juice of the stomach by the churning movements of its muscular wall and is called the chyme.
  7. The proenzyme pepsinogen on exposure to hydrochloric acid gets converted into the active enzyme pepsin, the proteolytic enzyme of the stomach.
  8. Pepsin converts proteins into proteases and peptones. The mucus and bicarbonates present in the gastric juice play an important role in lubrication and protection of the mucosal epithelium from excoriation by the highly concentrated HCl.
  9. Lipases are the enzymes used for the digestion of lipids and small amounts of this enzyme are secreted by the gastric glands.
  10. Various types of movements are generated by the muscularis layer of small intestine which helps in thorough mixing of food with various secretions in the intestine thereby facilitating digestion.
  11. The bile, pancreatic juice and the intestinal juice are the secretions released in small intestine.
  12. The pancreatic juice contains inactive enzymes like trypsin, chymotripsinogen, procarboxypeptidase, amylases, lipases, and nucleases. trypsinogen is activated by an enzyme called enterokinase, secreted by the intestinal mucosa into active trypsin, which inturn activates other enzymes in the pancreatic juice.
  13. Bile released into the duodenum contains bile salts, cholesterol and phospholipids which help in emulsification of fats.
  14. The enzymes present in the intestinal juices secreted by small intestine convert the proteins to amino acids, carbohydrates to glucose and fats into fatty acids and glycerol.
  15. The digested food is absorbed by the walls of small intestine, the inner lining of which has a number of fingers like projection called villi which increase the surface area of absorption.
  16. The villi are richly supplies 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 repairing of the old tissues.
  17. The unabsorbed food is taken up by large intestine where more villi absorb water from this material. The rest of the material is removed from the body through anus. The removal of wate material from anus is regulated by anal spinchter.


  1. The food material taken in during the process of nutrition is used in cells to provide energy for various life processes.
  2. The glucose that is produced after digestion process is broken down into carbon dioxide and water. In some organisms this step requires oxygen and in some organisms oxygen is not required.
  3. But the first step i.e. break down of glucose into 3 carbon compound pyruvate is a common step for all the organisms.
  4. In some organisms like yeast pyruvate is converted into ethanol and carbon dioxide in the absence of oxygen and hence it is called anaerobic respiration.
  5. In other organisms like human beings for example, pyruvate is broken down into three molecules of carbon dioxide and water in the presence of oxygen and hence it is called aerobic respiration. Aerobic respiration takes place in mitochondria.
  6. The energy released during aerobic respiration is a lot higher than the energy released during anaerobic respiration.
  7. In muscle cells where there is lack of oxygen the pyruvate is converted into lactic acid.
  8. The energy released during cellular respiration is used for the production of ATP molecule which is used to fuel other activities in the cell.
  9. ATP is broken down giving rise to a fixed amount of energy which can drive the endothermic reactions taking place in the cell.
  10. Organisms in which aerobic respiration takes place, they need to ensure that there is sufficient intake of oxygen.
  11. Plants exchange their gases with the environment through stomatal openings.
  12. Animals have evolved different organs for the uptake of oxygen from the environment and for getting rid of the carbon dioxide produced.
  13. Terrestrial animals can breathe the oxygen in the atmosphere, but animals that live in water need to use the oxygen dissolved in water.
  14. The rate of breathing in aquatic animals is high since the amount of dissolved oxygen is fairly low compared to the oxygen in the air.
  15. Organs used for absorption of air in terrestrial animals vary from organism to organism.
  16. All the organs used for absorption of air have a structure that increases the surface area which is in contact  with the oxygen rich atmosphere.
  17. The organs involved in respiration have a very fine and delicate surface for the exchange of oxygen and carbon dioxide.

Respiration in human beings:

  1. In human beings, air enters the body through nostrils. The air passing through nostrils is filtered by fine hairs lining that passage.
  2. From nostrils air passes through the throat and then to the lungs. Rings of cartilage present in the throat ensure that the air passage does not collapse.
  3. Inside the lungs the passage divides into smaller tubes which terminate into balloon like structures called alveoli which serves as a surface for the exchange of gases. Alveoli contain an extensive network of blood vessels.
  4. When we breathe in air we lift our ribs and flatten our diaphragm as a result of which the chest cavity becomes larger.
  5. As the chest cavity enlarges the air is sucked into the lungs and fills the expanded alveoli.
  6. The blood brings carbon dioxide from the rest of the body and releases into the alveoli and the oxygen in the alveolar air is taken up by blood in the alveolar blood vessels to be transported to all the cells in the body.
  7. During the breathing cycle, the lungs always contain residual volume of air so that there is sufficient time for oxygen to be absorbed and for the carbon dioxide to be released.
  8. In animals with large size, the diffusion pressure alone cannot deliver oxygen to all the body parts instead respiratory pigments help in delivering oxygen. In humans the respiratory pigment haemoglobin has high affinity for oxygen and this pigment is present in red blood corpuscles.

Transportation in human beings:

Blood transports food, oxygen and waste materials in our body. Blood consist of a fluid medium called plasma which transports food, carbon dioxide and nitrogenous wastes in dissolved form. Oxygen and many other substances like salts are transported by the blood. We thus need of a pumping organ to push blood around body, a network of tubes to reach the tissues and a system to ensure that this network can be repaired if damaged.

Our pump — the heart

  1. The heart is a muscular organ which has the size of our closed fist. Since both oxygen and carbon dioxide have to be transported by blood, our heart has four chambers which prevents the mixing of oxygen rich blood with the blood containing carbon dioxide.
  2. The carbon dioxide rich blood has to be transported to lungs and the oxygenated blood from lungs has to be brought back to the heart.
  3. The oxygen rich blood is then pumped to the rest of the body.
  4. Oxygen rich blood from the lungs comes to the left atrium. The left atrium relaxes when it is collecting the blood and then contracts while the blood is transferred to left ventricle as it expands. When the left ventricle contracts the blood is pumped out of the body.
  5. De-oxygenated blood comes from the body to the upper chamber on the right side, i.e. the right atrium as it expands.
  6. As the right atrium contracts, the corresponding lower chamber, the right ventricle dilates, this transfers blood to right ventricle, which in turn pumps it to lungs for oxygenation.

Oxygen enters the blood in the lungs:

  1. The separation of right and left side of the heart prevents the mixing of oxygenated blood with the deoxygenated blood. The separation of the heart into four chambers also allows the efficient supply of oxygen to the body.
  2. This kind of a separation of heart is useful in most of the animals and birds which need high amounts of energy to maintain their body temperatures.
  3. Animals like amphibians and reptiles have a three chambered heart where there is a slight mixing of oxygenated blood with the deoxygenated blood.
  4. Fishes on the other hand have a two chambered heart, the blood is pumped to gills and is oxygenated there and then passes to the rest of the body. Thus, blood goes only once
  5. Through the heart in the fish during one cycle of passage through the body.
  6. In case of vertebrates the blood goes twice to the heart during each cycle and this is called double circulation.

The tubes- blood vessels

  1. Arteries and vessels carry blood away from the heart to various organs in the body and arteries have thick, elastic walls since the blood they collect from the heart is under high pressure.
  2. Veins on the other hand collect the blood from different organs and bring it back to heart. Veins do not have thick walls because the blood they collect from the organs is not under pressure.
  3. Veins have valves to ensure that the blood flow is only in one direction.
  4. The arteries divide into smaller vessels once they reach the organ in order to bring the blood in contact with all the individual cells.
  5. The smallest vessels are called capillaries; their walls are about one cell thick. Exchange of material between blood and surrounding cells takes place across this thin wall.
  6. Capillaries join to form veins which convey blood from organs to heart.

Maintenance by platelets:

Platelets play a major role  in blood clot formation. When a person is injured he starts bleeding and if the bleeding is not controlled it leads to death. So the platelets which circulate around the body plug these leaks by a clot formation.


  1. Some amount of plasma, proteins and blood cells escape through the pores in the walls of capillaries into the intercellular spaces in the tissue to form tissue fluid called lymph.
  2. Lymph is another type of fluid involved in transportation. Lymph is similar to plasma but colorless and contains less amount of proteins.
  3. Lymph in the intercellular spaces of the tissue drains into lymphatic capillaries which join to form large lymph vessels that finally open into larger veins.
  4. Lymph carries digested and absorbed fat from intestine and drains excess fluid from extra cellular space back into the blood.

Transportation in plants:

  1. Plants make their food through the process of photosynthesis using CO2 and water in the presence of sunlight. Apart from these sources plants also require some raw materials for building up their body.
  2. Soil is the richest source of these raw materials. The raw materials include nitrogen, phosphorus and other minerals.
  3. Plants absorb these raw materials through roots. Since, root is the part of plant body which is in contact with the soil.
  4. If the distance between soil-containing organs and chlorophyll containing organs is small the raw materials can easily diffuse through all parts of the plant body. But in case if the distance is large plants need a special transport system for this purpose.
  5. Plant transport system will move energy store from leaves and raw material from roots.
  6. There are two transport systems in plants one is the xylem which conducts water and minerals from the soil and the other is phloem which transports products of photosynthesis to other parts of the plant.

Transport of water:

  1. In xylem tissues, vessels, tracheids of the roots, stems and leaves are interconnected to form a continuous system of water conducting channels reaching all the parts of the plant.
  2. Root cells in contact with the soil take up ions from the soil thereby creating a difference in the concentration of ions between soil and the root. In order to remove this difference water moves into the root and from the root the water is pushed upwards.

Transport of food and other substances:

  1. The products of photosynthesis formed in the leaves are transported to all the parts of the plant through a conducting tissue called phloem and this process is called translocation.
  2. Along with the products of photosynthesis phloem also transports amino acids and other substances.
  3. These substances are delivered to storage organs of roots, fruits, seeds and to growing organs.
  4. The translocation process takes place through sieve tubes with the help of adjacent companion cells both in upward and downward direction.
  5. The translocation process in phloem requires energy. Material like sucrose is transferred into phloem tissue using energy from ATP.
  6. This increases the osmotic pressure of the tissue causing water to move into it. This pressure moves the material in the phloem to tissues which have less pressure. This allows the phloem to
  7. Move material according to the plant’s needs.


The metabolic activities taking place in the body generate metabolic waste that need to be removed from the body. The biological process involved in the removal of harmful metabolic wastes is called excretion. The mode of excreting harmful substances varies among the organisms. Unicellular organisms remove wastes by simple diffusion from the body surface into the surrounding water. On the other hand multicellular organisms use specialized organs for the process of excretion.

Excretion in Human Beings:

  1. The excretory system of a human being includes a pair of kidneys, ureters, urinary bladder and urethra.
  2. Kidneys are located in the abdomen, on either side of the backbone.
  3. Urine produced in the kidneys passes through the ureters into the urinary bladder where it is stored until it is released through urethra.
  4. Urine is produced in the body for the elimination of nitrogenous wastes like urea or uric acid from the kidneys.
  5. A tuft of capillaries called glomerulus present in cup shaped structure called bowman’s capsule collect the filtered urine.
  6. As the urine passes along the tube some substances such as glucose, amino acids, salts and major amount of water are reabsorbed. The amount of water reabsorbed depends on the how much amount of excess water is present in the body.
  7. Urine forming in each kidney enters a long tube, the ureter which connects kidney with the urinary bladder.
  8. Urine is stored in the urinary bladder until until the pressure of the expanded bladder leads to the urge to pass it out through the urethra.
  9. The bladder is muscular, so it is under nervous control, as a result we can control the urge to urinate.

Excretion in Plants:

  1. Plants use completely different strategies for excretion. Oxygen is a waste product produced by plants during photosynthesis. They can get rid of water by transpiration.
  2. Many plant waste products are stored in cellular vacuoles. Waste products may be stored in leaves that fall off.
  3. Some of the waste products are stored as resins and gums, especially in old xylem.
  4. Plants secrete waste products into the soil around them.