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Life Processes

What are Life Processes?

Movements over very small scale are invisible to us. Molecular activity that takes place in our body cannot be seen by naked eye. But these movements are necessary for creation of new cells and repairing and maintenance of the existing or damaged cells in our body. The maintenance of any living tissue requires energy which is obtained by molecular movements in the bodies of various organisms which make life possible. These 4 processes are interconnected and essential for a life form to exist.

The 4 processes that are essential for life to exist, namely:

1. Nutrition

2. Respiration

3. Transportation

4. Excretion

1. Nutrition (Intake of Carbon based compounds - Why?)

A process to transfer a source of energy from outside the body of the organism, which we call food, to the inside, a process we commonly call nutrition.

Since life on earth depends on carbon- based molecules, most of these food sources are also carbon-based. Depending on the complexity of these carbon sources, different organisms can then use different kinds of nutritional processes.

2. Respiration (Exchange of Gases - Why?)

The food must be finally converted to a uniform source of energy that can be used for the various molecular movements needed for maintaining living structures, as well as to the kind of molecules the body needs to grow. Oxidizing-reducing (Redox) reactions are some of the most common chemical means to break-down molecules. 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 what we call respiration.

3. Transportation (Transportation of Energy to various parts of the body)

In multi-cellular organisms, all the cells may not be in direct contact with the surrounding environment. Thus, simple diffusion will not meet the requirements of all the cells. This poses a problem, since the food and oxygen are now taken up at one place in the body of the organisms, while all parts of the body need them. This situation creates a need for a transportation system for carrying food and oxygen from one place to another in the body.

4. Excretion (Removal of waste products from the body)

When chemical reactions use the carbon source and the oxygen for energy generation, they create by-products that are not only useless for the cells of the body, but could even be harmful. These waste by- products are therefore needed to be removed from the body and discarded outside by a process called excretion.


We need energy to maintain a state of order in our body. We also need materials from outside in order to grow, develop, synthesize protein and other substances needed in the body. This source of energy and materials is the food we eat.

Modes (Types) of Nutrition:

1) Autotrophic Nutrition

Some organisms use simple food material obtained from inorganic sources in the form of carbon dioxide and water.

Examples: Green plants and some bacteria.

2) Heterotrophic Nutrition

Other organisms utilize complex substances. These complex substances have to be broken down into simpler ones before they can be used for the upkeep and growth of the body. To achieve this, organisms use biocatalysts called enzymes.

3) Saprophytic Nutrition

Some organisms break-down the food material outside the body and then absorb it.

Examples: Fungi like bread moulds, yeast and mushrooms.

4) Holozoic Nutrition

Organism takes in whole material and break it down inside their bodies. What can be taken in and broken down depends on the body design and functioning.

Examples: Humans, Bear, Pigs, Cows, Lion

5) Parasitic Nutrition

Organisms derive nutrition from plants or animals without killing them.

Examples: Cuscuta (amar-bel), ticks, lice, leeches and tape-worms.

- Heterotrophs survival depends directly or indirectly on autotrophs.

Autotrophic Nutrition

Energy requirements of the autotrophic organism are fulfilled by photosynthesis. Carbon dioxide and water which is converted into carbohydrates in the presence of the sunlight and the chlorophyll. The green dots are cell organelles called chloroplasts which contain the chlorophyll.

Water used in the photosynthesis is taken up from the soil by the roots in the terrestrial plants. Other materials like nitrogen, phosphorus, iron and magnesium are taken up from the soil.

Nitrogen is an essential element used in the synthesis of proteins and the other compounds. This is taken up in the form of inorganic nitrates or nitrites. Or it is taken up as organic compounds which have been prepared by bacteria from the atmospheric nitrogen. (Nitrogen Fixation)

Carbohydrates are utilized for providing energy to the plant. The carbohydrates which are not used immediately are stored in the form of starch, which serves as the internal energy reserve to be used as and when required by the plant.

Steps of Photosynthesis

(i) Absorption of light energy by chlorophyll.

(ii) Conversion of light energy to chemical energy and splitting of water molecules

into hydrogen and oxygen.

(iii) Reduction of carbon dioxide to carbohydrates.

In humans, food we eat is stored in our body in the form of glycogen.

What is Stomata? How does it function?

Pores through which massive gaseous exchange takes place in the leaves. Large amounts of water can also be lost through these stomata, in order to retain water the plant closes these pores when it does not need carbon dioxide for photosynthesis.

The opening and closing of the pore is a function of the 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.

Travel Deep Inside a Leaf

Heterotrophic Nutrition

In single-celled organisms, the food may be taken in by the entire surface. But as the complexity of the organism increases, different parts become specialized to perform different functions.

Amoeba takes in food using temporary finger-like extensions of the cell surface which fuse over the food particle forming a food-vacuole. Inside the food- vacuole, complex substances are broken down into simpler ones which then diffuse into the cytoplasm. The remaining undigested material is moved to the surface of the cell and thrown out.

In Paramoecium, 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 of the cell.

Nutrition in Human Beings

The alimentary canal is basically a long tube extending from the mouth to the anus.


- Crushing the food with our teeth to generate particles which are small and of the same texture.

- Saliva secreted by the salivary glands to make the food wet for easy transport. It also contains an enzyme called ‘Salivary Amylase’ that starts digestion of starch and breaks it down into smaller molecules of simple sugar.

The muscular tongue helps in movement of food inside the mouth and mixing of

saliva with the food.

Food Pipe/ Oesophagus

- Peristaltic movements occur all along the gut that contract muscles rhythmically in order to push the food forward.

- The food is taken to the stomach through the food-pipe or Oesophagus.


- The stomach is flexible and expands when food enters it. The glands on stomach walls secrete digestive juices, mucus and release hydrochloric acid. The muscles on the stomach walls also help in mixing of food and the juices.

- The enzyme released that helps in digestion of proteins which are called pepsin. It works in an acidic medium which is provided by the HCl in the stomach.

- The mucus protects the internal lining of our stomach.

- The food is then released in small quantities into the small intestine through a sphincter muscle.

Small Intestine

- Small Intestine is the ‘longest part of the alimentary canal’ which is fitted into a compact space because of extensive coiling. The length of the small intestine differs in various animals depending on the food they eat.

- Herbivores eating grass need a longer small intestine to allow the cellulose to be digested. Meat is easier to digest, hence carnivores like tigers have a shorter small intestine.

- Complete digestion of carbohydrates, proteins and fats takes place in the small intestine.

- The small intestine receives enzymes from Liver and Pancreas.

- The bile juice from liver is basic in nature and helps in making the acidic food coming from stomach basic. It also provides the basic medium for the pancreatic enzyme to work.

-The bile juice is also responsible for digestion of fat globules by the action of bile salts. It breaks the globules into smaller units for easier action of enzymes.

- The pancreas secretes pancreatic juice which contains enzymes like trypsin for digesting proteins and lipase for breaking down emulsified fats.

- The walls of the small intestine contain glands which 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.

- Small intestine has finger like projections called ‘villi’ that help in absorption of food on its walls by increasing the surface area available.

- The villi are richly supplied with blood vessels that help in transportation of the absorbed food to each and every cell of the body, where it is utilized for obtaining the energy, the building up new tissues and the repair of old tissues.

- The unabsorbed food is sent into the large intestine where its wall absorb more water from this material.

- The rest of the material is removed from the body via the anus. The exit of this waste material is regulated by the anal sphincter.

How the Digestion of Food occurs?


Diverse organisms breakdown the food taken during nutrition into energy in different ways:

1. Some use oxygen to break-down glucose completely into carbon dioxide

2. Some use other pathways that do not involve oxygen

The process of conversion of glucose into energy and by products:

1. In cytoplasm of the cell the break-down of glucose, a six-carbon molecule starts. It is converted into a three-carbon molecule called pyruvate.

2. The pyruvate may be converted into different products depending upon availability of oxygen.

Anaerobic Respiration

The process of breakdown of glucose/pyruvate in absence of oxygen to give Ethanol and Carbon Dioxide.

It also takes place in yeast during fermentation.

Lesser energy is released compared to Aerobic Respiration.

Aerobic Respiration

The process of breakdown of glucose/pyruvate in presence of oxygen to give Carbon Dioxide and Water.

Break- down of pyruvate using oxygen takes place in the mitochondria. Energy released is higher than in anaerobic respiration.

- Sometimes, when there is a lack of oxygen in our muscle cells, another pathway for the break-down of pyruvate is taken. Here the pyruvate is converted into lactic acid which is also a three-carbon molecule. This build-up of lactic acid in our muscles during sudden activity causes cramps.

The energy released is used to create/synthesize ATP (Adenine Tri-Phosphate) from ADP (Adenine Di-Phosphate) and inorganic phosphate . ATP is used for all cell activities and all endothermic reactions.

Endothermic reactions are those which require energy from an external source.

Since Aerobic Respiration is dependent on oxygen, the aerobic organisms require regular uptake of oxygen.

Respiration in Plants

- In plants, the exchange of gases takes place through stomata by the process of diffusion of gases namely carbon dioxide and oxygen.

- The direction of diffusion depends on environmental conditions and requirements of the plant.

- What would happen at Night in plants? Does it need CO2 at night?

Respiration in Plants (at day time and at night time)

Respiration in Animals

- Animals have different and specific organs for exchange of gases.

- Terrestrial animals breathe through lungs while the aquatic and amphibians breathe either through gills or their skin.

Who breathes faster?

- Since the amount of oxygen dissolved in water is less, the rate of breathing of

aquatic animals is much faster than the terrestrial ones.

- Fishes take in water through their mouth and force them through gills where oxygen is absorbed in the blood. In terrestrial animals this process happens at lungs which have greater surface area for exchange of gases.

-These organs are delicate and have to be protected. Their surface is very thin and helps in exchange of gases.

- Oxygen has to be sent to these organs placed inside the body through a mechanism.

How other animals respire?

Respiration in Humans

- Air is taken into the body through the nostrils. The air passing through the nostrils is filtered by fine hairs that line the passage.

- The passage is also lined with mucus which helps in this process of filtration.

- Air passes through throat and ring cartilages help in supporting the pressure inside the air pipe and prevent it from collapsing. This part of the system is called trachea.

- Air then enters bronchi allowing air to flow into each lung which further divided into tree branch like structures called bronchioles.

- The bronchioles terminate into balloon like structure called alveoli which contain excessive network of blood vessels which help in exchange of gases by the process of diffusion.

The process of Inhaling and Exhaling

- When we breathe the lung capacity is increased by flattening of the diaphragm and lifting of ribs. This allows the air from the surrounds to rush into the nasal cavity and then ultimately to the alveoli.

- This brings in the oxygen rich air into our bodies for exchange. This oxygen is carried into various parts of the body in blood with help of hemoglobin that dissolves oxygen to form oxy-hemoglobin.

- Hemoglobin is found in RBCs (Red Blood Cells)

- The deoxygenated blood containing molecules of carbon dioxide are also brought near the alveoli through the blood capillaries. It is here that exchange of gases takes place by process of diffusion.

- The lungs now containing carbon dioxide need to exhale it out. This is done by contraction of the diaphragm which pushes the air out of the lungs.

During the breathing cycle, when air is taken in and let out, the lungs always contain a residual volume of air so that there is sufficient time for oxygen to be absorbed and for the carbon dioxide to be released.

Respiration in Human Beings


We need a pumping organ and a network of tubes to pump the blood throughout the body. This pump is the heart. Humans have a 4 chambered heart.

- The fluid component of blood called plasma carries dissolved food, carbon dioxide, nitrogenous wastes in the dissolved form.

The oxygen is carried by _________________ in the blood.

Human Heart

- It is a muscular organ and it is as big as our fist. It is located in the center of our chest.

- Vertebrates have double circulation mechanism since blood goes through the heart twice.

Fishes, on the other hand, have only two chambers to their hearts, and the blood is pumped to the gills, is oxygenated there, and passes directly to the rest of the body. Thus, blood goes only once through the heart in the fish during one cycle of passage through the body.

-It has chambers to prevent the mixing of oxygenated and deoxygenated blood.

-This separation allows a highly efficient supply of oxygen to the body. This is useful in animals that have high energy needs, such as birds and mammals, which constantly use energy to maintain their body temperature.

- In animals that do not use energy for this purpose, the body temperature depends on the temperature in the environment. Such animals, like amphibians or many reptiles have three-chambered hearts, and tolerate some mixing of the oxygenated and de-oxygenated blood streams.

The Process of Pumping

- The carbon dioxide-rich blood has to reach the lungs for the carbon dioxide to be removed, and the oxygenated blood from the lungs has to be brought back to the heart.

- This oxygen-rich blood is then pumped to the rest of the body.

OXYGENATED BLOOD: Oxygen-rich blood from the lungs comes to the thin walled upper chamber of the heart on the left, the left atrium.

- The left atrium relaxes when it is collecting this blood. It then contracts, while the next chamber, the left ventricle, relaxes, so that the blood is transferred to it.

- Left ventricle contracts in its turn, the blood is pumped out to the body.

DEOXYGENATED BLOOD: De-oxygenated blood comes from the body to the upper chamber on the right, the right atrium, as it relaxes.

- As the right atrium contracts, the corresponding lower chamber, the right ventricle, dilates.

- This transfers blood to the right ventricle, which in turn pumps it to the lungs for oxygenation.

Transportation of Blood in Human Heart.

Which has thicker walls? Ventricles or Atriums?

Since ventricles have to pump blood into various organs, they have thicker muscular walls than the atria do. Valves ensure that blood does not flow backwards when the atria or ventricles contract.



The metabolic processes in the body already discussed produce waste and they need to be removed from the body. These wastes are generally nitrogenous and need to be removed for the proper functioning of the body. The biological process of removal of these wastes from the body is called as Excretion.

Different organisms use different ways to remove the wastes:

- Simple Organisms such as unicellular animals use the process of diffusion to for removal of wastes from their bodies into the surroundings.

- Complex multi-cellular organisms use specialized organs and processes for the removal of these wastes.

Excretion in Human Beings:

The excretory system in humans include:

- A pair of Kidneys

- A pair of Ureters

- A Urinary Bladder

- A Urethra

Kidneys are located on both sides of the backbone in the abdomen.

Urine produced in the kidney after the filtration of blood is passed into the urinary bladder through the two ureters which connect the kidneys to the bladder.

The urine is stored in the urinary bladder till the time it is passed out of the body through urethra.

Excretion in Humans

Why and How is Urine Produced?

Urine is produced in the body for the removal of waste products from the blood.

Like CO2 is removed from the lungs, the nitrogenous wastes such as urea and uric acid from the blood are removed in the kidneys. The kidneys act as basic filtration units of the body.

Like other body parts, such as lungs and small intestine that have a large network of blood capillaries for exchange of material, kidneys too have a dense network of thin blood vessels called capillaries that to help in removal of waste products from the body.

These clusters of capillaries are associated with the cup-shaped end of a coiled tube called Bowman’s Capsule that collects the filtrate

Each kidney has large numbers of these filtration units called nephrons packed close together.

Substances such as glucose, amino acids, salts and a major amount of water, are selectively re-absorbed as the urine flows along the tube.

The amount of water reabsorbed depends on the amount of excess water in the body and the amount of waste material in the body.

The urine forming in each kidney eventually enters a long tube, the ureter, which connects the kidneys with the urinary bladder.

Urine is stored in the urinary bladder until the pressure of the expanded bladder leads to the urge to pass it out through the urethra.

The bladder is muscular, so it is under voluntary nervous control and as result, we can usually control the urge to urinate.

Structure of Kidneys and the Nephron

What is Hemodialysis?

When the functioning of kidneys reduce due to either infections or restricted blood flow to the kidneys, the waste material starts accumulating in the body.

If this wastes keep on accumulating in the body, then it may lead to many diseases and make the body really sick and may even lead to death due to kidney failure.

It is therefore necessary that these wastes are removed from the body by use of an artificial kidney.

An artificial kidney removes the wastes from the body through the process called as dialysis.

Artificial kidneys contain a number of tubes with a semi-permeable lining, suspended in a tank filled with dialyzing fluid.

This fluid has the same osmotic pressure as blood, except that it is devoid of nitrogenous wastes. The patient’s blood is passed through these tubes.

During this passage, the waste products from the blood pass into dialyzing fluid by diffusion. The purified blood is pumped back into the patient. But, there is no reabsorption involved as in the kidneys.

Normally, in a healthy adult, the initial filtrate in the kidneys is about 180 L daily. However, the volume actually excreted is only a liter or two a day, because the remaining filtrate is reabsorbed in the kidney tubules.

Process of Hemodialysis

Excretion in Plants

Oxygen is a waste product generated during photosynthesis. It is removed through stomata. They can get rid of excess water by transpiration.

For other wastes, plants use their tissues which consist of dead cells such as cork, and that they can even lose some parts such as leaves.

Waste products may be stored in leaves that fall off. Many plant waste products are stored in cellular vacuoles.

Other waste products are stored as resins and gums, especially in old xylem. Plants also excrete some waste substances into the soil around them

Transpiration in Plants

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