Class 10 Science Notes

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Life Processes Class 10 Notes

Life Processes is the first chapter of Unit II and the largest biological chapter in the syllabus. It opens with the one question that divides the living from the non-living, then takes the four processes that every living organism must perform, nutrition, respiration, transport and excretion, one at a time, showing for each how a plant does it and how an animal does it.

Class:10Subject:ScienceUnit:IICovers:CBSE 2024-25

6 Key Formulas

DWritten byDeep Narayan

UpdatedSeptember 2026

Key Concept Summary

What are the characteristics that distinguish a living organism from a non-living thing?

Living organisms show growth, reproduction, metabolism, a response to stimuli, the ability to self-regulate their internal environment, and movement. The single most reliable of these is metabolism, since it means chemical reactions are going on inside the body all the time. Growth by accretion, such as a mountain or a swelling crystal, is not life, and a mule which cannot reproduce is still alive, so neither test is enough on its own.

What Makes Something Living

The opening question of Unit II is not descriptive. It asks what separates a living organism from a non-living thing, and the answer is a list of characteristics that any living thing must show. The examiner usually wants them in a fixed set, so learn the list and be ready to add one example to each.Metabolism is the most important of them and the one that decides the argument. Growth by accretion, in which a substance simply piles up on the outside as in a mountain or a crystal, is not life, whereas growth in a living organism happens from within as a result of metabolic activity. That single distinction is the answer to most variations of the question.

Growth: a living organism increases in size and mass from within, as a seedling becomes a tree.
Reproduction: living organisms produce offspring, so a mule, which is sterile, is alive even though it cannot reproduce.
Metabolism: the sum of all the chemical reactions taking place in the body, and the most reliable single sign of life.
Response to stimuli: a living organism reacts to a change around it, as the shoot of a plant bends towards light or a human hand withdraws from a hot object.
Self-regulation and movement: the organism maintains a steady internal environment, and it also carries out movement of its own or of its parts, as in ciliary movement and the movement of plant leaves.

The two counter-examples that always appear

A moving object such as a moving bus is not alive, because the movement is not generated from within, and a growing mountain is not alive, because the growth is by accretion from outside. Quote both when the question asks for a difference, and remember that a sterile mule is still living while a growing crystal is not.

Nutrition: Autotrophic and Heterotrophic

Nutrition is the process by which an organism obtains food, and it is the first of the four life processes. The two types are autotrophic, where the organism makes its own food, and heterotrophic, where the organism takes in food made by others. Every green plant is autotrophic, and every animal is heterotrophic.Autotrophic nutrition in green plants is photosynthesis, and the board expects the equation, the raw materials, the by-product, the conditions and the site. The compensation point is the extra idea that appears in the two-mark questions: it is the light intensity at which the rate of photosynthesis exactly equals the rate of respiration.

Photosynthesis: the process by which green plants make food in the presence of sunlight and chlorophyll, using carbon dioxide and water and giving out oxygen.
Raw materials and by-products: carbon dioxide and water are the raw materials, glucose is the food produced, and oxygen is the by-product released through the stomata.
Conditions and site: chlorophyll and sunlight are necessary, and the process takes place in the chloroplasts of the leaf cells.
Heterotrophic nutrition: animals, non-green plants, fungi and bacteria cannot make their own food and depend on others for it.
Holozoic, saprophytic and symbiotic: holozoic nutrition is the taking in of solid food, saprophytic nutrition is feeding on dead and decaying matter, and symbiotic nutrition is the mutually beneficial arrangement such as Rhizobium in the root nodules of a legume.

Photosynthesis

6 C O_{2} + 6 H_{2} O sunlight chlorophyll C_{6} H_{12} O_{6} + 6 O_{2}

Above the compensation point the plant gains, below it the plant loses

The compensation point is the light intensity at which the rate of photosynthesis equals the rate of respiration, so there is no net gain and no net loss of food. Above the compensation point the plant makes more food than it consumes and stores the excess as starch, and below it the plant consumes more food than it makes. Writing both halves of that sentence is worth a full mark on its own.

Respiration

Respiration is a chemical reaction in which the energy stored in food is released and made available for use by the organism. It happens in every living cell, in plants and in animals, and it happens in the light and in the dark just as photosynthesis does. A plant therefore respires at night when it cannot photosynthesise at all.Aerobic respiration needs oxygen and takes place mainly in the mitochondria, and it is far more efficient than anaerobic respiration. Anaerobic respiration works without oxygen and gives much less energy, and in the human body it produces lactic acid, which is the cause of the cramp a runner feels in the muscles.

Aerobic respiration: with oxygen and in the presence of mitochondria, glucose is broken down to carbon dioxide and water with the release of energy.
Anaerobic respiration: without oxygen, glucose is broken down to alcohol and carbon dioxide in yeast and to lactic acid in muscle cells, and far less energy is released.
Why plants and animals respire the same way: the chemical breakdown of glucose is identical in both, which is one reason life is treated as one subject and not two.
Breathing is not respiration: breathing is the physical movement of air in and out of the lungs, while respiration is the chemical release of energy inside the cells.
In human beings, inhalation happens when the diaphragm contracts and flattens, and exhalation happens when it relaxes and returns to its dome shape, so air is pushed out.

Aerobic respiration

C_{6} H_{12} O_{6} + 6 O_{2} \to 6 C O_{2} + 6 H_{2} O + energy

Anaerobic respiration

C_{6} H_{12} O_{6} \to 2 C_{2} H_{5} O H + 2 C O_{2} (yeast) C_{6} H_{12} O_{6} \to 2 C H_{3} C H (O H) C O O H (muscle)

Three pairs students routinely interchange

Photosynthesis is not respiration: one builds up food in light and uses carbon dioxide, while the other breaks down food at all times and gives out carbon dioxide. Respiration is not breathing: one is chemical and happens in the cells, while the other is physical and happens in the lungs. And in anaerobic respiration, yeast gives alcohol while muscle gives lactic acid, so the two products are never interchanged.

Transport in Plants

Plants have no moving circulatory fluid like an animal, so transport is handled by two specialised tissues that work in completely different ways. Xylem carries water and dissolved minerals from the roots upward, while phloem carries the food made in the leaves to every part of the plant, in either direction.The two are compared along three axes in the board questions: the direction of movement, whether the process is passive or active, and whether energy is used. Xylem moves water only upward and does so passively, while phloem moves food in both directions and does so by an active process that consumes energy.

Xylem: the tissue that carries water and mineral salts upward from the roots to the leaves, and its movement is unidirectional.
Transpiration pull: water evaporates from the leaves through the stomata and the resulting suction pulls a continuous column of water up the xylem, and this is the main driving force.
Root pressure: the water pushed up from the roots by their own osmotic action helps, but it is a weak force and it is not what pulls water to the top of a tall tree.
Phloem: the tissue that carries food, mainly as sucrose, from a source where it is made to a sink where it is used or stored, and the movement can be upwards or downwards.
Translocation: the process by which phloem carries food from a source to a sink, and it is an active process which therefore needs energy from ATP.

Transpiration pull is the answer to why water rises at all

Water does not climb a tree because the roots push it, because root pressure is far too weak for a tall plant. It climbs because water evaporating from the leaves through the stomata creates a pull, and a continuous column of water is dragged up the xylem against gravity. In a long answer, name transpiration, name the stomata, and then explain that the pull is generated by the evaporation.

Transport in Animals: The Human Circulatory System

Animals move materials with a circulating fluid. In human beings this is the blood, pumped by the heart through a closed system of arteries, veins and capillaries. The heart has four chambers, two atria that receive blood and two ventricles that pump it out, and the wall of a ventricle is thicker than that of an atrium because the ventricle has to send blood to the whole body.The blood makes two circuits in one complete round trip, which is called double circulation, and this arrangement is what keeps oxygenated and deoxygenated blood from mixing. The blood is also joined by a second fluid, the lymph, which collects the fluid left behind in the tissues and returns it to the bloodstream.

The heart: four chambers, the right atrium and left atrium above and the right ventricle and left ventricle below, with a muscular septum separating the two sides.
Arteries: blood vessels carrying blood away from the heart, with thick elastic walls, and pulmonary artery is the exception, since it carries deoxygenated blood.
Veins: blood vessels carrying blood back to the heart, with thin walls and valves that prevent the backflow of blood, and pulmonary vein is the exception, since it carries oxygenated blood.
Capillaries: vessels one cell thick that connect the arteries to the veins, and their thin walls are the site where gases, nutrients and wastes are exchanged with the tissues.
Double circulation: the pulmonary circuit runs from the right ventricle to the lungs and back to the left atrium, and the systemic circuit runs from the left ventricle to the body and back to the right atrium.

Blood and lymph in four lines

Blood is a fluid connective tissue made of plasma, red blood cells containing haemoglobin that carry oxygen, white blood cells that fight germs, and platelets that make the blood clot. Lymph is the colourless fluid that collects from the spaces between the cells, carries digested fat from the intestine, and contains lymphocytes that help in immunity. The composition of blood is a three-mark question that appears almost every year, so it is worth learning as four items and not as a paragraph.

Excretion in Plants and Animals

Excretion is the removal of the metabolic waste produced inside the body, and it is the fourth life process. Plants do it by a set of different routes rather than by a single organ, whereas human beings do it mainly through the kidneys, with help from the lungs, the skin and the liver.In human beings the functional unit of the kidney is the nephron, and the process has three stages that the board likes to separate: filtration at the glomerulus into Bowman's capsule, selective reabsorption in the tubule, and the formation of urine. The most asked detail is the composition of the filtrate and the composition of the urine, and the difference between the two is where the marks are.

In plants, by shedding: leaves, bark, flowers and fruits fall and carry the waste away with them.
In plants, by storage: the waste is stored in the vacuoles of the cells, which isolate harmful substances from the cytoplasm.
Transpiration and guttation: water vapour is lost through the stomata as transpiration, and droplets of water are forced out of the hydathodes at the leaf tips as guttation on a humid night.
In human beings: the kidneys remove urea and other nitrogenous waste, the lungs remove carbon dioxide and water vapour, the skin removes salts and urea in sweat, and the liver produces urea from the breakdown of excess amino acids.
The nephron: filtration at the glomerulus into Bowman's capsule, selective reabsorption in the convoluted tubule, and the formation of urine in the collecting duct, which is then carried by the ureter to the bladder and out through the urethra.

Glucose in the filtrate, but not in the urine

The filtrate inside Bowman's capsule contains glucose, amino acids, urea, salts and a large amount of water, but the healthy body reabsorbs all the glucose and the amino acids back into the blood in the tubule. Urine therefore contains urea, uric acid, creatinine, excess water and excess salts, but no glucose and no protein. If glucose appears in the urine, that is a sign of disease, and saying so is the mark that distinguishes a full answer from a partial one.

How the Questions Are Asked

The questions in this chapter are almost all of two kinds: a long question asking for the same process in a plant and in an animal, and a short question asking for a definition or a labelled diagram. The long question is won by writing both sides under clear headings rather than by mixing them together.The diagrams asked in the examination are the human heart, the nephron, the respiratory system, the stomata in a leaf, and the water-conducting xylem pathway. Each one is a standard figure with a fixed set of labels, and those labels are the vocabulary the same question then uses in its written part.

Define autotrophic and heterotrophic nutrition, and give one example of each.
What are the raw materials, the conditions and the by-products of photosynthesis, and where does the process take place?
What is the difference between aerobic and anaerobic respiration, and what causes a cramp during exercise?
How are water and food transported in a plant, and which of the two needs energy?
What is double circulation, and why is it necessary in human beings?
How is urine formed in the human kidney, and what does urine contain?

Answer plant-and-animal questions as two labelled halves

When the question says explain the process in plants and animals, write one short paragraph for the plant and one for the animal under separate headings, and close with one sentence comparing them. A single mixed paragraph is the commonest way to lose the comparison mark, because the examiner cannot see both sides stated. The four headings to use are nutrition, respiration, transport and excretion.

Quick Revision

Key formulas at a glance

Memorise these equations — direct application numericals and derivations in CBSE & JEE frequently hinge on these.

Photosynthesis

6 C O_{2} + 6 H_{2} O sunlight chlorophyll C_{6} H_{12} O_{6} + 6 O_{2}

The food-making process of green plants; oxygen is the by-product.

Aerobic respiration

C_{6} H_{12} O_{6} + 6 O_{2} \to 6 C O_{2} + 6 H_{2} O + energy

The breakdown of food with oxygen, in the mitochondria of the cell.

Anaerobic respiration in yeast

C_{6} H_{12} O_{6} \to 2 C_{2} H_{5} O H + 2 C O_{2}

Fermentation in yeast; used for making bread and alcohol.

Anaerobic respiration in muscle

C_{6} H_{12} O_{6} \to 2 C H_{3} C H (O H) C O O H

Lactic acid during vigorous exercise, which is the cause of a cramp.

Transpiration

H_{2} O (l) sunlight, stomata H_{2} O (g)

The loss of water vapour that creates the pull carrying water up the xylem.

Double circulation

Right ventricle \to Lungs \to Left atrium \to Left ventricle \to Body \to Right atrium

The blood makes two circuits in one complete round trip.

Exam Strategy

How this chapter is asked

High-yield question patterns observed across CBSE boards, JEE Main & Advanced, and NEET.

Metabolism is the most reliable single sign of life, and growth by accretion such as a mountain or a crystal is not growth in the living sense.
A mule cannot reproduce but is alive, so reproduction alone cannot be used to define a living organism, and this counter-example is asked regularly.
Photosynthesis builds up food in light and uses carbon dioxide, while respiration breaks down food at all times and gives out carbon dioxide, and the two are never the same process.
Breathing is the physical movement of air; respiration is the chemical release of energy inside the cells, and using the words for each other is a standard penalty.
In anaerobic respiration yeast gives alcohol and muscle gives lactic acid, and the cramp felt by a runner is caused by the lactic acid.
Water rises in a plant because of the transpiration pull created by evaporation from the leaves, not because of root pressure, which is too weak for a tall tree.
Xylem carries water upward and passively, while phloem carries food in either direction by translocation, which is an active process needing energy from ATP.
The filtrate inside Bowman's capsule contains glucose, but the healthy body reabsorbs it, so urine contains urea, uric acid, excess water and salts and no glucose.
Pulmonary artery is the only artery that carries deoxygenated blood and pulmonary vein is the only vein that carries oxygenated blood, and both are asked by name.

FAQ

Frequently asked questions

What are the characteristics of a living organism?

A living organism shows growth, reproduction, metabolism, a response to stimuli, the ability to regulate its internal environment, and movement. Metabolism, meaning the sum of all the chemical reactions going on in the body, is the most reliable of these characteristics. Growth by accretion, as in a mountain or a crystal, is not life because the growth happens from outside, and a sterile mule is alive even though it cannot reproduce.

What is the difference between autotrophic and heterotrophic nutrition?

Autotrophic organisms make their own food, and green plants do this by photosynthesis using carbon dioxide, water, sunlight and chlorophyll, and giving out oxygen. Heterotrophic organisms cannot make their own food and depend on other organisms, and this includes all animals, non-green plants, fungi and most bacteria. Heterotrophic nutrition is of three kinds: holozoic, saprophytic and symbiotic, and the symbiotic example the board expects is the Rhizobium bacteria in the root nodules of a legume.

What is the difference between aerobic and anaerobic respiration?

Aerobic respiration takes place in the presence of oxygen, mainly in the mitochondria, and it breaks glucose down completely to carbon dioxide and water with the release of a large amount of energy. Anaerobic respiration takes place without oxygen and gives much less energy, producing alcohol and carbon dioxide in yeast and lactic acid in muscle cells. The lactic acid produced during vigorous exercise is what causes a cramp, and the fermentation in yeast is used in making bread and alcohol.

How is water and food transported in a plant?

Water and mineral salts are transported through the xylem, from the roots upward to the leaves, and the movement is unidirectional. The main force is the transpiration pull created when water evaporates from the leaves through the stomata, while root pressure plays only a small part. Food is transported through the phloem from a source where it is made to a sink where it is used or stored, and this process is called translocation and is an active one requiring energy.

What is double circulation, and how does the human circulatory system work?

Double circulation is the arrangement in which the blood makes two circuits in one complete round trip of the body. The pulmonary or smaller circuit carries deoxygenated blood from the right ventricle to the lungs and returns oxygenated blood to the left atrium. The systemic or larger circuit carries oxygenated blood from the left ventricle to the whole body and returns deoxygenated blood to the right atrium. The arrangement keeps oxygenated and deoxygenated blood separate and allows a faster flow of blood.

How is urine formed in the human kidney?

The functional unit of the kidney is the nephron, and the process has three stages. Blood is filtered at the glomerulus into Bowman's capsule, producing a filtrate containing glucose, amino acids, urea, salts and water. In the convoluted tubule, all the glucose and the amino acids and most of the water are selectively reabsorbed back into the blood. The remaining fluid, containing urea, uric acid, creatinine, excess water and excess salts, leaves the body as urine, and in a healthy person it contains no glucose.

Next Chapters

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Class 10 Science Notes Control and Coordination Class 10 Notes How do Organisms Reproduce Class 10 Notes Acids, Bases and Salts Class 10 Notes

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