Life processes

All the processes such as respiration, nutrition, circulation, excretion etc. that are necessary for the survival of the living organisms are known as life processes.


Nutrition is a process of intake of nutrients (like carbohydrates, fats, proteins, minerals, vitamins and water) by an organism as well as the utilisation of these nutrients by the organism.

Modes of Nutrition

The two most common type of nutrition is autotrophic nutrition and heterotrophic nutrition.

Autotrophic Nutrition

It is a type of nutrition in which inorganic materials such as carbon-dioxide, is used up to synthesize organic food by a process known as photosynthesis. For example, green plants use the autotrophic mode of nutrition. Organisms which uses the autotrophic mode of nutrition are known as autotrophs.

Now the question arises how autotrophic nutrition occurs in plants using photosynthesis?

For the photosynthesis to occur, carbon-dioxide, water, sunlight and chlorophyll are the required raw materials. Sunlight provides energy, chlorophyll is used to absorb the sunlight, carbon-dioxide is reduced to carbohydrates and water is oxidized to release the oxygen. Water is taken up from the soil through the roots.

The site where the photosynthesis occurs in known as chloroplast. They contain a green colour pigment known as chlorophyll that traps sunlight for photosynthesis.

Steps of the photosynthesis are as follows-

  • Absorption of light by chlorophyll.
  • Conversion of light energy into chemical energy.
  • Splitting of water into hydrogen and oxygen.
  • Finally, the reduction of carbon-dioxide into carbohydrates.

Leaves contain small openings known as stomata which helps in the exchange of gases. Stomata/stoma is surrounded by guard cell which guards the opening and closing of stomata. Guard cells also contain chloroplast.

The opening and closing of stomatal pores are controlled by the guard cells. When water flows into the guard cells, they swell, become curved and cause the pore to open. On the other hand, when the guard cells lose water, they shrink, become straight and close the stomatal pore. A large amount of water is also lost from the cells of the plant leaves through open stomatal pores. So, when the plant does not need carbon dioxide and wants to conserve water, the stomatal pores are closed.

Structure of Stomata

Overall Equation of Photosynthesis


Heterotrophic Nutrition

In this mode of nutrition, an organism is unable to synthesize its own food. It is of following types-

  1. Holozoic nutrition is a type of nutrition where an organism takes in whole food and break it inside the body. For example, Amoeba, man, cat, dog, giraffe, frog, etc.
  2. Saprophytic nutrition is nutrition in which organisms feed on dead and decaying matter. For example, fungi, most of the bacteria.
  3. Parasitic nutrition is nutrition in which organism feed on a living host. For example, Cuscuta, plasmodium and roundworms. 


Nutrition in Amoeba

 Mode of nutrition in Amoeba is holozoic. The process of obtaining food by Amoeba is called phagocytosis. The various steps involved are:

Ingestion: Amoeba ingests food by using its pseudopodia. It ingests food by forming temporary finger-like projection called pseudopodia around it.

Digestion: Food is digested in the food vacuole by the digestive enzyme.

Absorption: the digested food present in the food vacuole is directly absorbed into the cytoplasm by diffusion.

Assimilation: a part of food is used to obtain energy through respiration and the remaining part is used to make parts of amoeba which lead to the growth of the cell.

Egestion: there is no fixed part for egestion. When some amount of undigested food collects inside the cell membrane suddenly ruptures at any place and the food is thrown out.


In the case of paramecium, ingestion is carried through hair-like structures called cilia to sweep the food particles from the water and put them into its mouth.

Ingestion is followed by other steps such as digestion, absorption, assimilation and egestion as in case of amoeba.



Humans consist of the alimentary canal which starts from the mouth and ends at the anus. The parts of the alimentary canal are as follows-

  1. Mouth
  2. Pharynx
  3. Oesophagus/food pipe
  4. Stomach
  5. Small intestine
  6. Large intestine
  7. Rectum
  8. Anus

Human Digestive System

Various steps of nutrition in human beings

  1. Ingestion

The mouth is the first portion of the alimentary canal. Food is ingested through the mouth.

  1. Digestion
  • The food digestion process begins in the mouth. Food is complex in nature.
  • To breakdown food and absorb it, we need a biological catalyst known as enzymes.
  • The mouth contains salivary glands that secrete saliva. Saliva contains an important enzyme known as salivary enzymes that breaks down starch into simple sugars.
  • The food then passes via oesophagus into the stomach. The movement of the food inside the oesophagus occurs via rhythmic contraction of muscles, this is known as peristalsis.
  • The stomach contains gastric glands that secrete mucus, hydrochloric acid and pepsin. Pepsin is a protein-digesting enzyme. It digests the protein present in food to form smaller molecules.
  • Pepsin is active only in the presence of hydrochloric acid.
  • Mucus helps to protect the stomach wall from its own secretion of HCl. If the mucus is not secreted, hydrochloric acid will cause the erosion of the inner lining of the stomach leading to the formation of an ulcer in the stomach.
  • After the stomach, food then enters into the small intestine. The small intestine is larger in herbivores due to cellulose digestion compared to carnivores.
  • Complete digestion of carbohydrates, proteins and fats occurs in the small intestine.
  • The small intestine receives secretions from the pancreas and bile from the liver. Bile helps in emulsification of fats.
  • The pancreas secretes digestive enzymes such as pancreatic amylase, trypsin and lipase. Amylase breaks down the starch into simpler sugars, trypsin digests the protein and lipase breaks down the fats.
  • Intestinal wall also contains glands that secrete intestinal juice. These juices complete the digestion of complex carbohydrates into glucose, protein into amino acids and fats into fatty acids and glycerol.
  1. Absorption

The small intestine has villi that increase the surface area for the absorption of food. The digested food which is absorbed through the walls of the small intestine goes into our blood.

  1. Assimilation

The blood carries digested and dissolved food to all the parts of the body where it becomes assimilated as parts of the cells. This assimilated food is used by the body cells for obtaining energy as well as for growth and repair of the body. This energy is released by the oxidation during the respiration.

  1. Egestion

The unabsorbed food is then transferred to the large intestine where water is absorbed.

Undigested food is then expelled out from the anus.


  • It is a metabolic process which involves the breakdown of food to release energy is known as respiration.
  • Respiration involves:
  • Intake of oxygen from the surrounding
  • Oxidation of food
  • Release of energy
  • Elimination of carbon dioxide produced as a by-product.

Breakdown of glucose by different pathways


Types of respiration

Aerobic respiration

  • The respiration which uses oxygen is called as aerobic respiration. In this process food is completely broken down into carbon dioxide and water by oxidation. Glucose is converted into pyruvate and it is broken down in carbon-dioxide and water in presence of oxygen it is known as aerobic respiration. It produces a considerable amount of energy for the use by an organism which gets stored in the ATP molecules.




Anaerobic respiration

The respiration which takes place without oxygen is called anaerobic respiration.

  • The breakdown of pyruvate into ethanol and carbon-dioxide is the absence of oxygen is known as fermentation. As this process occurs in the absence of oxygen, it is known as anaerobic respiration.
  • When respiration takes place in human muscle then glucose is converted into lactic acid with the release of a small amount of energy.
  • The energy released during the process is used up to synthesize the ATP (adenosine triphosphate).
  • Compared to animals, plants used stomata to exchange carbon-dioxide and oxygen. This exchange occurs through 





Respiration in Human Beings

Human respiratory system starts consists of nostrils, nasal cavity, pharynx, trachea, bronchi, bronchioles and then lungs. In the lungs, alveoli are present, where an exchange between the oxygen and carbon-dioxide takes place.

Passage of air in Humans

Humans have a respiratory pigment known as haemoglobin to carry the oxygen to different parts of the body and to remove carbon-dioxide from the body. Compared to oxygen, carbon-dioxide is more soluble in water, so it is usually transported in dissolved form.

Respiration in animals

  • In amoeba, respiration takes place by simple diffusion of gases through the cell membrane.
  • Earthworm which lives in the soil uses its skin to absorb oxygen from the air and remove carbon dioxide. The respiratory organ is skin.
  • In aquatic animals like fish, prawns have gills as the respiratory organs extract oxygen dissolved in water and take away carbon dioxide from the body.
  • In insects like grasshopper, cockroach, housefly, the mosquito has tiny holes called spiracles on their body and the air tubes called tracheae as the respiratory organs.
  • The respiratory organs of the land animals such as birds, humans, dog have lungs. (frogs have both lungs and skin)

All the respiratory organs have three common features:

  • Have a large surface area.
  • Have thin walls for easy diffusion and exchange of gases.
  • Have a rich blood supply for transporting gases.



Blood is a fluid connective tissue that transport food, oxygen, carbon-dioxide, nitrogenous waste etc. Blood contains plasma and blood cells. Red blood cells carry oxygen throughout the body. The heart is the pumping organ in the body.

  • The human heart is 4 chambered, with two atrium and two ventricles.
  • The left atrium receives the oxygen-rich blood from the lungs. While receiving the blood it relaxes.
  • The left ventricle pumps oxygen-rich blood throughout the body.
  • De-oxygenated blood comes from the body to the upper right atrium. It contracts to pump the blood to the right ventricle.
  • The right ventricle pumps the blood to the lungs for oxygenation.

Structure of the Human Heart

Note: Fishes have two-chambered heart, amphibians and reptiles have three-chambered heart except crocodile which possess 4 chambered heart. Birds and mammals have 4 chambered heart.

Double Circulation

The right side and left side of the heart are separated to prevent the mixing of oxygenated and deoxygenated blood. Invertebrates, blood goes through the heart twice during each cycle. This is defined as double circulation. 

Double Circulation

Note: The force that the blood exerts against the wall of the vessel is known as blood pressure. The pressure of blood inside the artery during ventricular contraction is known as systolic pressure whereas the pressure in the artery during ventricular relaxation is known as diastolic pressure. The normal blood pressure is 120/80 mm of Hg.


Artery Capillary Vein
They carry blood away from the heart One cell thick smallest vessel They carry blood towards the heart
They carry oxygenated blood except for the pulmonary artery. Help in the exchange of the material between the blood and surrounding cells. They carry deoxygenated blood except for pulmonary vein.
They have thick walls and do not have valves. They do not have valves They have thin walls and also possess valves.
Exception: pulmonary artery- carry deoxygenated blood from the right ventricle to the lungs. Exception: pulmonary vein- carry oxygenated blood from lungs to the left ventricle.


  • Circulatory medium
  • Fluid connective tissue
  • Connects different systems of the body by transporting gases digested food, hormones and waste materials to different body parts.

Components of blood

Plasma – fluid matrix on which blood cells are embedded.

Red blood cells – small cells without a nucleus. Carry oxygen from the lungs to a different part of the body. It contains respiratory pigment, haemoglobin which has an affinity for oxygen. Because of the small size, they are able to travel through capillaries.

White blood cells – These are nucleated cells. It helps to fight infects and build the immune system. Live for 3-4 days in the human body.

Platelets – Platelets are blood cells that help in blood clotting.


Lymph known as interstitial fluid is a fluid that that leak out from the pores of the capillaries.

These are colourless, present in body tissue spaces. Unidirectional flow from tissue to the heart. Absorb fat from intestine to blood.

Lymph  lymphatic capillaries   lymph vessel vein  heart

Transport in Plants

Transportation water, food and minerals are carried through the vascular bundles known as xylem and phloem in the plant.


  • Plants have xylem for the transportation of water. Xylem transports water from the roots to different parts of the plants.
  • Xylem tissue consists of:
  • vessels and tracheids are non – living long tube, spindle-shaped cells with pits in their thick cell walls. Water and minerals are absorbed by the root hair from the soil by the process called diffusion and osmosis.
  • Xylem parenchyma- store food
  • Xylem fibres- dead cells, provide support.
  • Loss of water in the form of water vapour from the aerial parts of the plants is known as transpiration. The transpiration creates a suction which pulls the water up to the higher plants.


  • Similarly, transport of food in plants occurs via the phloem. It transports food from the leaves to different parts of the plants which is called as translocation.
  • Phloem is made up of
  • sieve tube – tubular cells with perforated walls. It helps in conduction of food along with the companion cell.
  • companion cell- regulates metabolic activities of the sieve tube.
  • phloem parenchyma- support sieve tube and also stores starch.
  • phloem fibres- dead cells, gives mechanical strength.

Transport in Plants



Excretion in plants

Photosynthesis:                   6CO2+12H2OC6H12O6+6H2O+6O2

  • The main waste product produced by the plants are carbon dioxide, water vapour and oxygen. The gaseous wastes of respiration and photosynthesis in plants are removed through stomata in leaves and lenticels in stems and released in air.
  • The plants also store some of the waste products in their body parts. The plants get rid of these wastes by shedding of the leaves, peeling of the bark and felling of fruits.
  • The plants get rid of wastes by secreting them in the form of gums and resins.
  • Plants also excrete some waste substances into the soil around them.


  • The process involved in the removal of nitrogenous waste from the body is known as excretion.
  • Excretory system of humans consists of a pair of kidneys, a pair of ureters, urinary bladder and urethra.
  • The basic filtration unit of the kidneys is known as nephrons.

Human Excretory System

Nephron are the structural and functional unit of kidneys.

  • They consist of bowman’s capsule and renal tubule.
  • The bowman’s capsule contains a bundle of blood capillaries which is called the glomerulus. One end of the glomerulus is attached to the renal artery which brings dirty blood containing wastes and the other end of glomerulus comes out of the capsule as a capillary and joins the renal vein.
  • The function of the glomerulus is to filter the blood passing through it.
  • For the formation of urine, some substances such as glucose, amino acids are selectively reabsorbed and the waste materials like urea, unwanted salts and excess water remain behind which is formed as urine.
  • The nephron carries this urine into the collecting duct of the kidney from where it is carried to the ureter.
  • Through ureter, it is stored in the urinary bladder which is a muscular structure and it is under nervous control.


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