Every living organism needs energy to survive, grow, repair its body and respond to its surroundings. But where does this energy come from? How does food reach every cell of the body? How do humans obtain oxygen, and how are carbon dioxide and other wastes removed?

These questions are explained through Life Processes, an important chapter in Class 10 Science. It connects everyday activities such as eating, breathing and removing waste with the biological processes that keep an organism alive.

In these notes, you will learn the four major life processes—nutrition, respiration, transportation and excretion—along with their mechanisms, important diagrams to practise, differences, scientific explanations and concept-based MCQs. The explanations follow the core concepts of the NCERT Class 10 Science chapter and use standard biological terminology.

1. What Are Life Processes?

Life processes are the basic activities that living organisms perform to maintain life. These activities obtain energy and materials, distribute them throughout the body, and remove harmful waste products.

A living organism is not simply an object that moves. Many living organisms, such as plants, remain fixed in one place but continuously carry out essential internal activities.

Major life processes

Life process	Meaning	Example
Nutrition	Obtaining food and using it for energy, growth and repair	Plants prepare glucose by photosynthesis
Respiration	Releasing usable energy from food through chemical reactions	Cells break down glucose
Transportation	Moving essential substances from one part of an organism to another	Blood carries oxygen in humans
Excretion	Removing metabolic waste products from the body	Kidneys remove urea from blood

These processes are interconnected. Nutrition supplies food, respiration releases usable energy from it, transportation distributes necessary materials, and excretion removes certain waste products formed during metabolism.

1.1 Why do organisms need life processes?

Organisms need life processes for several reasons:

1. Energy supply: Cells need energy to perform their activities.
2. Growth: New cellular material is required for an organism to grow.
3. Repair: Damaged cells and tissues need to be repaired or replaced.
4. Maintenance: Cells must maintain suitable internal conditions for chemical reactions.
5. Waste removal: Metabolic reactions produce waste products that may become harmful if they accumulate.
6. Survival: Organisms must obtain resources and maintain their internal functions even when environmental conditions change.

1.2 What is metabolism?

Metabolism is the sum of all chemical reactions taking place inside a living organism.

It includes two broad categories:

• Anabolism: Reactions that build complex substances from simpler ones. For example, the formation of proteins from amino acids.
• Catabolism: Reactions that break down complex substances into simpler ones. For example, the breakdown of glucose during cellular respiration.

Anabolism generally requires energy, whereas catabolic reactions often release energy that can be captured and used by cells.

1.3 Why is movement alone not enough to identify life?

A change in position is not a complete test of whether something is alive. Plants may not move from one place to another, but their cells carry out respiration, growth and other essential processes.

Similarly, a moving machine is not a living organism because its movement does not arise from the integrated biological activities of living cells.

Important examination point: The maintenance activities of an organism are supported by continuous cellular processes, even when no obvious external movement is visible.

2. Nutrition

Nutrition is the process by which an organism obtains food or nutrients and uses them for energy, growth, repair and maintenance.

Food contains substances such as carbohydrates, proteins, fats, vitamins and minerals. Water is also essential for normal cellular functioning. Different nutrients have different roles in the body.

2.1 Types of nutrition

Nutrition is broadly classified into two major types: autotrophic nutrition and heterotrophic nutrition.

Basis	Autotrophic nutrition	Heterotrophic nutrition
Meaning	Organisms produce organic food from simpler inorganic substances	Organisms obtain organic food from other organisms or organic matter
Main source of carbon	Usually carbon dioxide	Organic compounds
Energy source	Light or chemical energy, depending on the organism	Energy stored in organic substances
Examples	Green plants and algae during photosynthesis	Humans, animals and fungi

2.2 Autotrophic nutrition

In autotrophic nutrition, organisms produce organic food from simpler substances.

Green plants carry out this process mainly through photosynthesis, using sunlight as the energy source. They use carbon dioxide and water to produce carbohydrates, releasing oxygen in the overall process.

Photosynthesis

Photosynthesis is the process by which green plants, algae and certain bacteria use light energy to produce organic substances from inorganic materials.

The overall simplified equation for oxygen-releasing photosynthesis is:

Here:

• CO₂ = carbon dioxide
• H₂O = water
• C₆H₁₂O₆ = glucose, a simple sugar
• O₂ = oxygen

This equation represents the overall process. It does not show all the intermediate chemical reactions.

2.3 Essential requirements for photosynthesis

1. Sunlight

Light supplies the energy required to drive photosynthesis. The absorbed energy is converted into chemical energy.

2. Chlorophyll

Chlorophyll is a green pigment that absorbs light energy. It is located in the chloroplasts of plant cells.

3. Water

Roots absorb water from the soil. It is transported to the leaves through the xylem.

4. Carbon dioxide

Carbon dioxide enters leaves mainly through small pores called stomata.

These requirements work together. Light provides energy, chlorophyll absorbs it, water supplies electrons and hydrogen in the photosynthetic process, and carbon dioxide supplies the carbon used to form organic molecules.

2.4 Where does photosynthesis occur?

Photosynthesis takes place in chloroplasts, which contain chlorophyll.

A typical leaf is well suited for photosynthesis because:

• Its broad, flat surface can capture light efficiently.
• Its thin structure allows gases to move over relatively short distances.
• Its internal air spaces help carbon dioxide reach photosynthetic cells.
• Its stomata permit gas exchange.
• Its veins contain xylem and phloem for transport.

The cells containing many chloroplasts in the leaf’s internal tissue are particularly important for photosynthesis.

2.5 Main events of photosynthesis

The major events can be understood in three broad stages:

1. Absorption of light: Chlorophyll absorbs light energy.
2. Conversion of energy and splitting of water: Light energy drives reactions that convert energy into chemical forms; water is split, releasing oxygen.
3. Formation of carbohydrates: Carbon dioxide is incorporated into organic molecules, using the energy and reducing power produced by the light-dependent reactions.

These stages are connected, but the complete process involves many intermediate reactions.

2.6 How do plants obtain the raw materials?

• Carbon dioxide: Enters through stomata in leaves.
• Water: Absorbed by roots from the soil and carried upward through xylem.
• Light: Reaches the leaf surface from the Sun or another suitable light source.
• Minerals: Absorbed from the soil and used for growth and normal cellular functioning. They are not a substitute for carbon dioxide or water in the photosynthesis equation.

2.7 Role of stomata

Stomata are small pores in the epidermis of leaves and some other plant organs. Each typical stoma is surrounded by two guard cells.

Their main functions are:

• Allowing carbon dioxide to enter for photosynthesis.
• Allowing oxygen to leave or enter, depending on the conditions and direction of gas exchange.
• Permitting water vapour to escape during transpiration.

When guard cells change their turgidity, the stomatal opening changes. This helps plants balance carbon dioxide uptake with water conservation.

2.8 How do we know that sunlight is necessary for photosynthesis?

A classic school experiment uses a destarched plant.

Procedure:

1. Keep a healthy potted plant in darkness for a sufficient period to reduce previously stored starch in its leaves.
2. Cover part of a leaf with opaque black paper.
3. Place the plant in sunlight for several hours.
4. Remove the leaf and test it for starch using iodine solution, following appropriate laboratory safety instructions.

Observation: The exposed region turns blue-black, while the covered region does not show the same starch-positive result.

Conclusion: Light is necessary for starch formation in the tested leaf under these conditions.

This experiment demonstrates the importance of light; it does not mean that starch is the only substance produced during photosynthesis.

2.9 How do we know that carbon dioxide is necessary?

In a standard school experiment, two destarched potted plants are placed under comparable conditions. One is placed in an airtight arrangement with a suitable carbon dioxide absorber, such as potassium hydroxide, while the other serves as a control with carbon dioxide available.

After exposure to light, the leaves are tested for starch.

The leaf in the carbon-dioxide-depleted arrangement does not show the same starch formation as the control.

Conclusion: Carbon dioxide is necessary for normal photosynthesis. Such experiments must be performed with appropriate laboratory supervision because some carbon dioxide absorbers are hazardous.

2.10 Heterotrophic nutrition

In heterotrophic nutrition, organisms obtain organic substances from other organisms or organic matter.

Different organisms obtain food in different ways.

Type	Explanation	Example
Holozoic nutrition	Food is taken into the body and processed internally	Humans, Amoeba
Saprotrophic nutrition	Organisms secrete digestive enzymes onto dead or decaying material and absorb soluble products	Many fungi
Parasitic nutrition	An organism obtains nutrients from a living host, often harming it	Tapeworm, Cuscuta

These categories describe different nutritional strategies. Some organisms have more specialised or mixed nutritional modes.

2.11 Nutrition in Amoeba

Amoeba is a unicellular organism that obtains food by holozoic nutrition.

The process occurs in the following stages:

1. Ingestion: Amoeba extends temporary projections called pseudopodia around a food particle.
2. Digestion: The food becomes enclosed in a food vacuole, where enzymes break it down.
3. Absorption: The soluble products of digestion pass into the cytoplasm.
4. Assimilation: The absorbed nutrients are used for energy, growth and other cellular activities.
5. Egestion: Undigested material is expelled from the cell.

This example shows that a single cell can carry out all essential nutritional steps without a specialised digestive system.

2.12 Human digestive system

Humans obtain nutrients through holozoic nutrition. Food is processed along the alimentary canal, with the help of digestive glands.

The major stages are ingestion, digestion, absorption, assimilation and egestion.

Main organs and their functions

Organ	Important function
Mouth	Chews food and mixes it with saliva
Salivary glands	Secrete saliva containing salivary amylase
Oesophagus	Moves food toward the stomach by peristalsis
Stomach	Stores and churns food; gastric juice begins substantial protein digestion
Liver	Produces bile
Gallbladder	Stores and concentrates bile
Pancreas	Releases digestive enzymes and bicarbonate-rich fluid into the small intestine
Small intestine	Completes much digestion and absorbs most nutrients
Large intestine	Absorbs water and electrolytes and helps form faeces
Rectum	Temporarily stores faeces
Anus	Allows faeces to leave the body

2.13 Digestion in the mouth

Digestion begins in the mouth through mechanical and chemical processes.

• Teeth break food into smaller pieces.
• The tongue helps mix food with saliva and form a bolus for swallowing.
• Saliva moistens food and contains salivary amylase, which begins the digestion of starch.

Chewing increases the surface area of food exposed to digestive enzymes.

2.14 Digestion in the stomach

The stomach is a muscular organ that temporarily stores food and mixes it with gastric juice.

Gastric juice contains:

• Hydrochloric acid (HCl): Creates an acidic environment and helps activate pepsin from its inactive precursor.
• Pepsin: Begins the digestion of proteins into smaller peptides.
• Mucus: Helps protect the stomach lining from acid and digestive enzymes.

The stomach does not complete all digestion. Most digestion and nutrient absorption occur in the small intestine.

2.15 Digestion in the small intestine

The small intestine is the principal site of chemical digestion and nutrient absorption in humans.

It receives bile from the liver and digestive secretions from the pancreas, as well as intestinal secretions.

Role of bile:

• Bile helps neutralise acidic material arriving from the stomach.
• Bile salts emulsify fats, breaking large fat droplets into smaller droplets. This increases the surface area available to lipase.
• Bile itself does not contain the main digestive enzymes that break down fats.

Role of pancreatic juice:

• Pancreatic amylase digests starch.
• Proteases digest proteins and peptides.
• Pancreatic lipase digests fats.
• Bicarbonate helps neutralise acidic contents entering from the stomach.

The products of digestion include simple sugars, amino acids, fatty acids and monoglycerides.

2.16 How are digested nutrients absorbed?

The inner lining of the small intestine contains numerous finger-like projections called villi. Cells on these projections also possess microscopic projections called microvilli.

These structures greatly increase the surface area available for absorption.

• Simple sugars and amino acids enter blood capillaries.
• Most long-chain dietary fats are packaged into particles that enter lymphatic vessels called lacteals before eventually reaching the bloodstream.
• Absorbed nutrients are transported to tissues and used by cells.

Assimilation is the use of absorbed nutrients by cells. For example, glucose may be used in respiration, amino acids may be used to build proteins, and some excess energy may be stored.

2.17 Nutrition: important differences

Process	Meaning
Ingestion	Taking food into the body
Digestion	Breaking complex food into simpler substances
Absorption	Moving digested nutrients across the intestinal lining into blood or lymph
Assimilation	Using absorbed nutrients in cells
Egestion	Removing undigested food from the digestive tract

Remember: Egestion and excretion are different. Egestion removes undigested food, whereas excretion removes metabolic waste products produced by the body’s chemical activities.

3. Respiration

Have you noticed that your breathing becomes faster after running or climbing stairs? During physical activity, muscle cells need more energy. To meet this demand, the body increases oxygen delivery and removes carbon dioxide more rapidly.

Respiration is the set of cellular chemical reactions through which organisms release usable energy from food. In Class 10, the main focus is on how glucose is broken down to release energy.

It is important to distinguish breathing from cellular respiration. Breathing moves air into and out of the lungs, whereas cellular respiration involves chemical reactions inside cells.

3.1 Why is energy necessary?

Energy is needed for:

• Muscle contraction and body movement.
• Growth and repair of cells.
• Transport of substances across cell membranes.
• Synthesis of proteins and other cellular materials.
• Maintaining the internal organisation of cells.

Much of the energy released during respiration is captured in the form of ATP (Adenosine Triphosphate).

3.2 What is ATP?

ATP is a molecule that transfers usable chemical energy within cells. When ATP is converted into ADP and inorganic phosphate, usable energy can be released for cellular activities.

This is a simplified representation of ATP hydrolysis. The actual energy available depends on the conditions and reactions involved.

ATP is often called the energy currency of the cell because cells use it to couple energy-releasing reactions with energy-requiring activities.

3.3 Breakdown of glucose

The first major step in the breakdown of glucose occurs in the cytoplasm.

During this process, a six-carbon glucose molecule is converted into two three-carbon pyruvate molecules. A small amount of ATP is produced, and reduced electron carriers are also formed.

The subsequent breakdown of pyruvate depends on oxygen availability and the organism or cell type.

3.4 Aerobic respiration

Aerobic respiration is the breakdown of food using oxygen, with carbon dioxide and water formed as the overall end products when glucose is completely oxidised.

The simplified overall equation is:

The released energy is captured partly in ATP, while some is dissipated as heat.

In human cells, the initial breakdown of glucose occurs in the cytoplasm. Subsequent major stages of aerobic respiration take place in the mitochondria.

3.5 Anaerobic respiration and fermentation

When oxygen is unavailable or insufficient for a particular metabolic pathway, some cells and microorganisms can obtain energy through anaerobic pathways.

In the Class 10 context, two important examples are:

In yeast:

Glucose is converted into ethanol and carbon dioxide, releasing a small amount of energy.

This process is a form of alcoholic fermentation and is used in baking and certain fermentation industries.

In human muscle cells:

During intense activity, when the rate of energy demand exceeds the capacity of aerobic metabolism to meet it, lactate can accumulate as a result of anaerobic glycolysis.

The simplified equation represents the overall conversion; the pathway includes several intermediate reactions.

Lactate production does not mean that muscle cells stop using oxygen entirely. Aerobic and anaerobic energy pathways can contribute simultaneously to energy production.

3.6 Aerobic versus anaerobic respiration

Basis	Aerobic respiration	Anaerobic pathways
Oxygen	Uses oxygen in the overall pathway	Do not require oxygen for the pathway being described
Breakdown of glucose	Can be complete	Partial breakdown in the examples discussed
Main products	Carbon dioxide and water in complete oxidation	Ethanol and carbon dioxide in yeast fermentation, or lactate in human muscle cells
Energy yield	Much higher ATP yield per glucose molecule	Much lower ATP yield per glucose molecule
Location in eukaryotic cells	Cytoplasm and mitochondria	The pathways discussed occur in the cytoplasm
Example	Most energy production in human cells under ordinary conditions	Yeast fermentation and lactate production in exercising muscles

3.7 Fate of pyruvate

After glucose is converted into pyruvate, its further breakdown can follow different routes.

Glucose (6-carbon molecule)

Glycolysis in the cytoplasm

Pyruvate (3-carbon molecules)

Sufficient oxygen

Further oxidation in mitochondria

CO₂ + H₂O

Yeast fermentation

Anaerobic pathway

Ethanol + CO₂

Intense muscle activity

Anaerobic glycolysis

Lactate

3.8 Breathing and respiration are not the same

Breathing	Cellular respiration
Physical process of moving air	Chemical process of releasing energy from food
Involves respiratory organs and muscles	Occurs inside cells
Supplies oxygen and removes carbon dioxide in humans	Produces usable energy, often captured as ATP
Does not itself release energy from glucose through cellular chemical reactions	Involves enzyme-controlled chemical reactions

3.9 Human respiratory system

The human respiratory system brings oxygen into the body and removes carbon dioxide.

Its main parts are:

1. Nostrils and nasal cavity: Air enters and is filtered, warmed and humidified.
2. Pharynx: A shared passage for air and food.
3. Larynx: Contains the vocal cords and directs air into the lower respiratory tract.
4. Trachea: The windpipe, supported by cartilage rings that help prevent collapse.
5. Bronchi: Two main branches that carry air into the lungs.
6. Bronchioles: Smaller branching air passages.
7. Alveoli: Tiny air sacs where oxygen and carbon dioxide are exchanged.
8. Diaphragm and intercostal muscles: Help change the volume of the chest cavity during breathing.

3.10 Mechanism of breathing

Breathing has two main phases: inhalation and exhalation.

During inhalation:

• The diaphragm contracts and flattens.
• The external intercostal muscles raise the ribs.
• The volume of the chest cavity increases.
• Pressure inside the lungs falls below atmospheric pressure.
• Air flows into the lungs.

During exhalation at rest:

• The diaphragm relaxes and becomes dome-shaped.
• The rib cage moves down and inward.
• The volume of the chest cavity decreases.
• Pressure inside the lungs rises above atmospheric pressure.
• Air flows out.

During forceful breathing, additional muscles help with inhalation or exhalation.

3.11 How does gaseous exchange occur?

Alveoli are specialised structures for gas exchange. Their features include:

• Very thin walls that reduce the diffusion distance.
• A moist surface that allows gases to dissolve.
• A rich network of blood capillaries.
• A large combined surface area for exchange.

Oxygen moves from alveolar air into the blood because of a difference in oxygen partial pressure. Carbon dioxide moves in the opposite direction from blood into alveoli.

These gases move by diffusion, the net movement of particles from a region of higher partial pressure to lower partial pressure for each gas.

3.12 Transport of oxygen and carbon dioxide

• Oxygen: Most oxygen in human blood is carried bound to haemoglobin inside red blood cells. A small amount is dissolved in plasma.
• Carbon dioxide: Most is transported in the blood as bicarbonate ions. Some is bound to proteins, including haemoglobin, and a smaller amount is dissolved in plasma.

The blood delivers oxygen to tissues, where cells use it for aerobic respiration. Carbon dioxide produced by cellular metabolism is carried back toward the lungs for removal.

3.13 Why does breathing rate increase during exercise?

Working muscles require more ATP. As energy demand rises, the body increases ventilation and blood flow to help supply oxygen and remove carbon dioxide. Breathing rate and depth are adjusted through nervous and chemical control mechanisms.

Important distinction: Breathing rate is not the same as cellular respiration rate, although they are closely related under many conditions.

4. Transportation in Human Beings

In a large multicellular organism, most cells are not in direct contact with the external environment. Diffusion alone cannot deliver oxygen and nutrients quickly enough to every cell.

A specialised transportation system moves essential substances between organs and tissues.

In humans, the circulatory system consists mainly of the heart, blood and blood vessels.

4.1 Blood and its components

Blood is a fluid connective tissue that transports substances throughout the body.

Component	Main function
Plasma	Carries dissolved nutrients, hormones, wastes, proteins and electrolytes
Red blood cells (RBCs)	Carry most oxygen using haemoglobin
White blood cells (WBCs)	Help defend the body against pathogens
Platelets	Participate in blood clotting

Plasma is the liquid portion of blood. It contains mostly water along with dissolved substances.

Red blood cells in humans lack a nucleus when mature, which provides more space for haemoglobin. White blood cells have nuclei and include different types with different immune functions.

4.2 Structure of the human heart

The human heart is a muscular organ that pumps blood through two connected circuits.

The heart has four chambers:

• Right atrium: Receives oxygen-poor blood returning from the body.
• Right ventricle: Pumps oxygen-poor blood toward the lungs.
• Left atrium: Receives oxygen-rich blood returning from the lungs.
• Left ventricle: Pumps oxygen-rich blood to the body.

A muscular wall called the septum separates the right and left sides of the heart and prevents direct mixing of the blood in the two sides.

The left ventricle has a thicker muscular wall than the right ventricle because it must generate sufficient pressure to send blood throughout the body.

4.3 Blood vessels

The three main types of blood vessels are arteries, veins and capillaries.

Feature	Arteries	Veins	Capillaries
Main direction	Away from the heart	Toward the heart	Connect small arteries and veins
Wall	Thick and elastic	Generally thinner	Extremely thin
Pressure	Generally high	Generally low	Low compared with arteries
Valves	Generally absent along most arteries	Present in many veins, especially in the limbs	Absent
Main role	Carry blood away from the heart	Return blood to the heart	Exchange gases, nutrients and wastes with tissues

Important: Arteries are defined by the direction in which blood flows, not by whether the blood is oxygen-rich.

For example, the pulmonary artery carries oxygen-poor blood from the right ventricle to the lungs, while the pulmonary veins carry oxygen-rich blood from the lungs to the left atrium.

4.4 Double circulation

Humans have double circulation, meaning blood passes through the heart twice during one complete circuit of the body.

It consists of two main pathways.

Pulmonary circulation:

Right ventricle → pulmonary artery → lungs → pulmonary veins → left atrium.

This circuit carries blood between the heart and lungs for gaseous exchange.

Systemic circulation:

Left ventricle → aorta → body tissues → venae cavae → right atrium.

This circuit delivers oxygen and nutrients to the body and returns oxygen-poor blood to the heart.

Lungs

Gaseous exchange

Left side of heart

Receives oxygen-rich blood and pumps it to the body

Body tissues

Oxygen delivery and carbon dioxide collection

Right side of heart

Receives oxygen-poor blood and pumps it to the lungs

The two circuits operate continuously as part of one closed circulatory system.

4.5 Why is double circulation important?

1. Prevents direct mixing: The right and left sides of the heart are separated.
2. Efficient oxygen supply: Oxygen-rich blood can be pumped to the body at an appropriate pressure.
3. Supports high energy demands: It helps supply oxygen to tissues that require substantial energy.
4. Separates the circuits: Blood pressure can be maintained at different levels in pulmonary and systemic circulation.

4.6 Blood pressure and pulse

Blood pressure is the pressure exerted by circulating blood on the walls of blood vessels, commonly measured in an artery.

• Systolic pressure: Arterial pressure during ventricular contraction.
• Diastolic pressure: Arterial pressure during ventricular relaxation.

Blood pressure is commonly expressed in millimetres of mercury (mmHg).

The pulse is the pressure wave felt in an artery as the heart pumps blood. Pulse rate usually corresponds closely to heart rate under ordinary conditions.

Blood pressure and pulse rate are related to circulation, but they measure different things.

4.7 Lymphatic system

The lymphatic system collects excess tissue fluid and returns it to the bloodstream. It also supports immune defence and helps absorb dietary fats through specialised lymphatic vessels in the small intestine.

The fluid circulating through these vessels is called lymph.

5. Transportation in Plants

Plants do not have a heart or a blood circulatory system. Instead, they use specialised conducting tissues to transport water, minerals and organic food.

The two principal vascular tissues are xylem and phloem.

5.1 Xylem

Xylem transports water and dissolved mineral ions from roots toward the stem and leaves. It also contributes to mechanical support.

The main water-conducting elements in flowering plants are vessels and tracheids. These cells are generally dead at maturity and form hollow pathways for water movement.

Water enters root cells from the soil, moves into the xylem and travels toward the leaves.

5.2 How does water move upward?

Several processes contribute to the movement of water in plants:

• Root pressure: Pressure that may develop in roots due to the movement of water into them. It can contribute to water movement under certain conditions.
• Capillary action: Water can rise in narrow tubes because of adhesion to the walls and cohesion among water molecules, although this alone cannot explain water movement in tall trees.
• Transpiration pull: Evaporation of water from leaf surfaces creates tension that pulls water upward through continuous water columns in the xylem.
• Cohesion and adhesion: Water molecules cohere to one another, while adhesion helps them interact with the xylem walls.

The cohesion-tension mechanism is the main explanation for long-distance water transport in tall plants.

5.3 Transpiration

Transpiration is the loss of water vapour from the aerial parts of a plant, especially through stomata.

Its importance includes:

1. Helping create the pull that moves water upward.
2. Supporting the transport of dissolved mineral ions.
3. Contributing to temperature regulation by evaporative cooling.
4. Maintaining the movement of water through plant tissues.

However, excessive transpiration can cause water stress if water loss exceeds the plant’s ability to absorb and transport water.

5.4 Phloem

Phloem transports sugars and other organic substances from sources to sinks.

• A source is a region where sugars are produced or released into transport, such as a photosynthesising mature leaf.
• A sink is a region where sugars are used or stored, such as a growing root, developing fruit or storage organ.

Phloem transport is called translocation.

Unlike the simple idea that food always travels downward, phloem can transport materials in different directions in different sieve tubes, depending on source-sink relationships.

Phloem tissue contains living conducting cells, including sieve-tube elements and their associated companion cells in flowering plants.

5.5 Xylem versus phloem

Basis	Xylem	Phloem
Main transported substances	Water and mineral ions	Sugars and other organic substances
Principal function	Supplies water and minerals to aerial parts	Distributes organic nutrients
Main conducting cells	Vessels and tracheids	Sieve-tube elements in flowering plants
Living or dead	Main conducting elements generally dead at maturity	Main conducting elements living
Direction	Net movement is generally from roots toward aerial parts	Movement depends on sources and sinks

Exam point: Xylem and phloem perform different but complementary functions. Water transport supports photosynthesis and other cellular processes, while phloem distributes the organic food made by plants.

6. Excretion

Metabolic reactions produce substances that the body must remove or manage. The biological process of removing metabolic waste products is called excretion.

Examples include carbon dioxide from cellular respiration and nitrogenous wastes such as urea in humans.

Excretion is different from egestion, which removes undigested food from the digestive tract.

6.1 Why is excretion necessary?

• Some metabolic waste products can be harmful if they accumulate.
• Excess water and ions must be regulated to maintain internal balance.
• Removing nitrogenous waste helps maintain normal cellular functioning.
• Excretion contributes to homeostasis, the maintenance of relatively stable internal conditions.

6.2 Human excretory system

The main organs of the human urinary system are:

1. A pair of kidneys.
2. A pair of ureters.
3. The urinary bladder.
4. The urethra.

Functions of the organs:

• Kidneys: Filter blood, regulate water and electrolyte balance, and form urine.
• Ureters: Carry urine from the kidneys to the urinary bladder.
• Urinary bladder: Temporarily stores urine.
• Urethra: Carries urine out of the body.

The kidneys also help regulate blood pressure and acid-base balance and release hormones involved in red blood cell production and mineral balance.

6.3 Why do humans remove urea?

The breakdown of amino acids can produce ammonia, which is toxic at elevated concentrations. In humans, the liver converts much of this nitrogenous waste into urea, which is less toxic than ammonia.

Urea is carried by the blood to the kidneys and removed in urine.

The kidneys also remove other waste products and regulate the composition of body fluids.

6.4 Nephron: the functional unit of the kidney

A nephron is the microscopic functional unit of a kidney. It filters blood and modifies the resulting filtrate to form urine.

The main parts include:

• Glomerulus: A cluster of capillaries where blood filtration begins.
• Bowman’s capsule: A cup-shaped structure that collects the filtrate.
• Renal tubule: A series of tubular regions in which water and useful substances are reabsorbed and additional substances may be secreted.
• Collecting duct: Receives fluid from multiple nephrons and contributes to the final concentration of urine.

6.5 How is urine formed?

Urine formation can be understood through three key processes.

1. Ultrafiltration

Blood enters the glomerulus under pressure. Water and many small dissolved substances pass through the filtration barrier into Bowman’s capsule.

Blood cells and most large plasma proteins normally remain in the blood.

The initial filtrate contains water, salts, glucose, amino acids and nitrogenous waste.

2. Selective reabsorption

As the filtrate passes through the renal tubule, useful substances are returned to the blood.

These include:

• Glucose, which is normally reabsorbed almost completely under healthy conditions.
• Amino acids.
• Required ions.
• A large proportion of filtered water.

The amount of each substance reabsorbed depends on the body’s needs and the properties of the nephron.

3. Tubular secretion

Certain substances are transferred from the blood into the tubular fluid. These can include hydrogen ions, potassium ions and some waste products or drugs.

Secretion helps regulate electrolyte balance, acid-base balance and waste removal.

The fluid remaining after these processes becomes urine.

6.6 Path of urine

The pathway is:

Kidneys → Ureters → Urinary bladder → Urethra → Outside the body

Do not confuse the ureter with the urethra. The ureter carries urine from a kidney to the bladder, whereas the urethra carries urine from the bladder out of the body.

6.7 Regulation of urine production

The quantity and concentration of urine vary with water intake, sweating, dissolved waste production and the body’s need to conserve water.

The hormone antidiuretic hormone (ADH) increases water reabsorption in the kidneys under appropriate conditions, reducing water loss in urine.

When the body has excess water, urine generally becomes more dilute. When water must be conserved, urine generally becomes more concentrated.

6.8 Dialysis and artificial kidneys

When kidneys fail to remove sufficient waste or regulate body fluids, dialysis may be used to perform some of their functions.

In haemodialysis, blood passes through a dialyser separated from dialysis fluid by a semipermeable membrane. Certain wastes and excess electrolytes move across the membrane, and excess water can be removed under controlled conditions.

Dialysis supports waste removal and fluid balance but does not replace every function of healthy kidneys.

6.9 Excretion in plants

Plants do not possess kidneys or a specialised urinary system. They use several methods to manage waste products.

• Gas exchange: Oxygen generated during photosynthesis and carbon dioxide produced during respiration can diffuse through stomata and other surfaces, depending on conditions.
• Transpiration: Excess water can leave as water vapour.
• Storage: Certain waste substances are stored in vacuoles or other tissues.
• Leaf fall: Some stored substances are removed when leaves or other plant parts are shed.
• Gums and resins: Certain waste or secondary products accumulate in tissues such as older xylem.
• Release into surroundings: Some substances can be released into the surrounding soil.

These strategies vary among plant species and environmental conditions.

7. Important Diagrams to Practise

Diagrams are useful for understanding the chapter and preparing for questions that require labelling or explanation.

1. Photosynthesis

Practise labelling sunlight, carbon dioxide, water, glucose and oxygen. Understand the role of chlorophyll and stomata.

2. Human digestive system

Identify the oesophagus, stomach, liver, pancreas, small intestine and large intestine. Explain where digestion and absorption occur.

3. Human respiratory system

Label the trachea, bronchi, lungs, bronchioles, alveoli and diaphragm. Explain inhalation and gas exchange.

4. Human heart

Label the four chambers, major blood vessels and septum. Trace the route of blood during double circulation.

5. Xylem and phloem

Identify the conducting tissues and explain their roles in transporting water, minerals and food.

6. Nephron

Label the glomerulus, Bowman’s capsule, renal tubule and collecting duct. Explain filtration, reabsorption and secretion.

8. Common Misconceptions and Important Corrections

Misconception	Correct understanding
Plants do not respire.	Plants respire continuously, both during the day and at night.
Photosynthesis and respiration are the same process.	Photosynthesis stores energy in organic substances; respiration releases usable energy from them.
Breathing and respiration mean the same thing.	Breathing moves air; cellular respiration involves chemical reactions that release energy.
All arteries carry oxygen-rich blood.	The pulmonary artery carries oxygen-poor blood toward the lungs.
All veins carry oxygen-poor blood.	Pulmonary veins carry oxygen-rich blood toward the heart.
Bile digests fat using enzymes.	Bile salts emulsify fat; lipase enzymes digest it chemically.
Digestion and absorption occur only in the stomach.	Digestion begins in the mouth, and most digestion and nutrient absorption occur in the small intestine.
Excretion means passing stool.	Passing undigested food is egestion; removing metabolic wastes is excretion.
Xylem and phloem perform identical functions.	Xylem mainly transports water and minerals; phloem transports organic nutrients.
Urine is formed only by filtration.	Urine formation involves filtration, selective reabsorption and tubular secretion.

9. Quick Revision Notes

1. Life processes are essential activities that maintain the life of an organism.
2. The four major processes studied in this chapter are nutrition, respiration, transportation and excretion.
3. Metabolism includes all chemical reactions in the body; anabolism builds substances and catabolism breaks them down.
4. Autotrophic nutrition involves producing organic food from simpler substances. Green plants mainly use photosynthesis.
5. Photosynthesis requires light, chlorophyll, carbon dioxide and water under suitable conditions.
6. Stomata enable gas exchange and regulate water loss.
7. Heterotrophic nutrition includes holozoic, saprotrophic and parasitic strategies.
8. Human digestion involves ingestion, digestion, absorption, assimilation and egestion.
9. Salivary amylase begins starch digestion. Pepsin begins protein digestion in the stomach.
10. Bile emulsifies fats; it is not a digestive enzyme.
11. The small intestine is the main site of digestion and nutrient absorption.
12. Respiration releases usable energy from food; ATP transfers usable energy within cells.
13. Glycolysis converts glucose into pyruvate in the cytoplasm.
14. Aerobic respiration uses oxygen in the overall pathway and yields much more ATP per glucose molecule than fermentation.
15. Alveoli provide a large, thin-walled surface for gas exchange.
16. Haemoglobin carries most oxygen in human blood; most carbon dioxide is transported as bicarbonate.
17. The human heart has four chambers, and humans have double circulation.
18. Xylem transports water and mineral ions; phloem transports sugars and other organic substances.
19. Transpiration pull is the main mechanism driving long-distance upward water transport in plants.
20. Nephrons filter blood and modify the filtrate through reabsorption and secretion to form urine.
21. The urinary pathway is kidneys → ureters → urinary bladder → urethra.
22. Plants manage wastes through gas exchange, water loss, storage and shedding of tissues, among other mechanisms.

10. Life Processes – Practice Quiz (20 MCQs)

Question 1. Which of the following best describes a life process?

A. Any movement from one place to another

B. An activity that helps maintain the life of an organism

C. A change in the colour of an object

D. A process that occurs only in animals

Correct Answer: B. An activity that helps maintain the life of an organism

Explanation: Life processes include nutrition, respiration, transportation and excretion. Plants carry out these processes even though they generally remain fixed in one place.

Question 2. Which combination is essential for photosynthesis in green plants?

A. Oxygen, glucose and darkness

B. Nitrogen, oxygen and protein

C. Glucose, minerals and oxygen only

D. Carbon dioxide, water, light and chlorophyll

Correct Answer: D. Carbon dioxide, water, light and chlorophyll

Explanation: Photosynthesis uses light energy to produce organic substances from carbon dioxide and water. Chlorophyll absorbs the light energy required for the process.

Question 3. What is the main function of bile salts during digestion?

A. Emulsifying fats into smaller droplets

B. Converting proteins directly into amino acids

C. Digesting starch into simple sugars

D. Absorbing glucose into the bloodstream

Correct Answer: A. Emulsifying fats into smaller droplets

Explanation: Bile salts increase the surface area of fat droplets, allowing lipase to act more effectively. Bile does not itself contain the main fat-digesting enzyme.

Question 4. Which process converts glucose into two pyruvate molecules?

A. Ultrafiltration

B. Transpiration

C. Glycolysis

D. Emulsification

Correct Answer: C. Glycolysis

Explanation: Glycolysis occurs in the cytoplasm and converts one six-carbon glucose molecule into two three-carbon pyruvate molecules. It also produces a small amount of ATP.

Question 5. Why are alveoli suitable for gaseous exchange?

A. They have thick walls that prevent gas movement.

B. They contain digestive enzymes.

C. They store urine before it leaves the body.

D. They have thin walls, a rich blood supply and a large surface area.

Correct Answer: D. They have thin walls, a rich blood supply and a large surface area.

Explanation: These features support rapid diffusion of oxygen and carbon dioxide between alveolar air and blood.

Question 6. Which blood vessel carries oxygen-poor blood from the heart to the lungs?

A. Aorta

B. Pulmonary artery

C. Pulmonary vein

D. Vena cava

Correct Answer: B. Pulmonary artery

Explanation: The pulmonary artery carries blood from the right ventricle to the lungs. Arteries are defined by their direction of blood flow away from the heart, not by their oxygen content.

Question 7. What is the main role of the small intestine’s villi?

A. Producing red blood cells

B. Storing undigested food

C. Increasing the surface area for nutrient absorption

D. Pumping blood to the liver

Correct Answer: C. Increasing the surface area for nutrient absorption

Explanation: Villi and their cellular microvilli increase the surface available for absorption of digested nutrients.

Question 8. Which statement about phloem is correct?

A. It transports only water from roots to leaves.

B. It is the main site of urine formation.

C. Its only function is to provide mechanical support.

D. It transports sugars and other organic substances between sources and sinks.

Correct Answer: D. It transports sugars and other organic substances between sources and sinks.

Explanation: Phloem distributes organic nutrients from regions where they are produced or released to regions where they are used or stored.

Question 9. What is the primary function of haemoglobin in red blood cells?

A. Carrying most oxygen in the blood

B. Producing digestive enzymes

C. Filtering urine

D. Breaking down starch in the mouth

Correct Answer: A. Carrying most oxygen in the blood

Explanation: Haemoglobin binds oxygen in the lungs and releases it in tissues according to local conditions.

Question 10. Which sequence correctly represents the path of urine through the human urinary system?

A. Urethra → Kidneys → Ureters → Bladder

B. Kidneys → Ureters → Urinary bladder → Urethra

C. Bladder → Kidneys → Urethra → Ureters

D. Kidneys → Urethra → Ureters → Bladder

Correct Answer: B. Kidneys → Ureters → Urinary bladder → Urethra

Explanation: Urine forms in the kidneys, travels through the ureters to the bladder for storage, and leaves through the urethra.

Question 11. Which process is directly responsible for the upward movement of water through tall plants under ordinary transpiring conditions?

A. Digestion

B. Fermentation

C. Transpiration pull

D. Blood circulation

Correct Answer: C. Transpiration pull

Explanation: Water evaporating from leaves creates tension in the xylem water column. Cohesion between water molecules helps transmit this pull downward toward the roots.

Question 12. What is the major role of hydrochloric acid in the stomach?

A. Emulsifying fats

B. Absorbing all digested nutrients

C. Producing bile salts

D. Creating an acidic environment that helps activate pepsin and supports protein digestion

Correct Answer: D. Creating an acidic environment that helps activate pepsin and supports protein digestion

Explanation: Hydrochloric acid creates the acidic conditions needed for pepsin activity and helps denature proteins. The stomach also churns food and protects itself with mucus.

Question 13. Which statement correctly distinguishes excretion from egestion?

A. Excretion removes metabolic wastes, while egestion removes undigested food.

B. Excretion occurs only in plants, while egestion occurs only in humans.

C. Excretion means absorbing nutrients, while egestion means digesting them.

D. Both terms refer only to the removal of carbon dioxide.

Correct Answer: A. Excretion removes metabolic wastes, while egestion removes undigested food.

Explanation: Urea is an excretory waste product. Undigested food leaves the digestive tract through egestion.

Question 14. Which component of blood is mainly responsible for helping it clot?

A. Plasma water alone

B. Platelets

C. Red blood cells

D. Haemoglobin alone

Correct Answer: B. Platelets

Explanation: Platelets participate in the processes that form blood clots. Clotting also requires plasma proteins and a coordinated sequence of chemical reactions.

Question 15. Why is double circulation advantageous in humans?

A. It eliminates the need for lungs.

B. It allows all blood to bypass the heart.

C. It supports efficient oxygen delivery and keeps the pulmonary and systemic circuits distinct.

D. It prevents blood from entering capillaries.

Correct Answer: C. It supports efficient oxygen delivery and keeps the pulmonary and systemic circuits distinct.

Explanation: The right side of the heart pumps blood to the lungs, while the left side pumps blood to the body. Separation supports effective circulation.

Question 16. Which of the following is a product of alcoholic fermentation in yeast?

A. Urea and oxygen

B. Lactic acid only, under all conditions

C. Water and large amounts of ATP from complete glucose oxidation

D. Ethanol and carbon dioxide

Correct Answer: D. Ethanol and carbon dioxide

Explanation: Yeast can convert sugars into ethanol and carbon dioxide through alcoholic fermentation, releasing a small amount of energy.

Question 17. Which process returns useful substances such as glucose from the nephron filtrate to the blood?

A. Selective reabsorption

B. Egestion

C. Inhalation

D. Translocation

Correct Answer: A. Selective reabsorption

Explanation: During selective reabsorption, useful substances and the required amounts of water and ions are returned to the blood. Under healthy conditions, filtered glucose is normally almost completely reabsorbed.

Question 18. Which statement about plant respiration is correct?

A. Plants respire only at night.

B. Plants respire during both day and night.

C. Plants respire only when they are flowering.

D. Plants do not require energy for cellular activities.

Correct Answer: B. Plants respire during both day and night.

Explanation: Respiration supplies energy for plant cells continuously. Photosynthesis requires suitable light conditions, but respiration is not restricted to daylight or darkness.

Question 19. What would most directly happen if the walls of the alveoli became much thicker?

A. The blood would stop containing plasma.

B. The kidneys would produce more bile.

C. Diffusion of oxygen and carbon dioxide would become less efficient.

D. The small intestine would stop absorbing all nutrients immediately.

Correct Answer: C. Diffusion of oxygen and carbon dioxide would become less efficient.

Explanation: Increasing the diffusion distance reduces the rate of gas exchange, all else being equal. Thin alveolar walls help oxygen and carbon dioxide diffuse efficiently.

Question 20. A plant transports water through xylem and sugars through phloem. Which statement best explains why both tissues are necessary?

A. Both tissues perform exactly the same function.

B. Xylem produces glucose, while phloem absorbs sunlight.

C. Phloem removes all water from the leaves.

D. Xylem supplies water and minerals, while phloem distributes organic nutrients.

Correct Answer: D. Xylem supplies water and minerals, while phloem distributes organic nutrients.

Explanation: Plants need water and mineral ions for cellular activities and photosynthesis, while sugars produced by photosynthesis must be distributed to growing and storage tissues.

11. Frequently Asked Questions (FAQs)

1. What are the four main life processes in Class 10 Science?

The four major processes covered in this chapter are nutrition, respiration, transportation and excretion. Together, they help organisms obtain nutrients, release usable energy, distribute materials and remove metabolic wastes.

2. What is the difference between photosynthesis and respiration?

Photosynthesis uses light energy to produce organic substances from carbon dioxide and water. Cellular respiration breaks down organic substances to release usable energy, much of which is captured in ATP. The two processes have different roles, even though their overall chemical equations are related.

3. Why do plants need respiration if they make their own food?

Plants produce sugars through photosynthesis when conditions are suitable, but those sugars must be broken down to supply energy for cellular activities. Respiration supports growth, repair, transport and maintenance in plant cells.

4. Why does the small intestine have villi?

Villi increase the inner surface area of the small intestine, allowing digested nutrients to be absorbed efficiently. Their blood capillaries and lymphatic vessels carry absorbed materials away for distribution throughout the body.

5. Why is the left ventricle thicker than the right ventricle?

The left ventricle pumps blood through the systemic circulation to the entire body and must generate relatively high pressure. The right ventricle pumps blood to the nearby lungs through the pulmonary circulation, which operates at lower pressure.

6. What is the difference between an artery and a vein?

An artery carries blood away from the heart, whereas a vein carries blood toward the heart. Oxygen content does not define these vessels: the pulmonary artery carries oxygen-poor blood, and pulmonary veins carry oxygen-rich blood.

7. What is the difference between xylem and phloem?

Xylem mainly carries water and dissolved mineral ions from roots toward the aerial parts of a plant. Phloem transports sugars and other organic substances from sources to sinks, depending on the plant’s needs.

8. What is the functional unit of the kidney?

The nephron is the functional unit of the kidney. It filters blood, reabsorbs useful substances and water, and secretes certain substances into the tubular fluid. These processes help form urine and maintain the body’s internal balance.

9. How do plants remove their waste products?

Plants manage wastes through several mechanisms, including gas exchange, transpiration, storage in vacuoles or tissues, accumulation of gums and resins, shedding leaves and releasing some substances into the surroundings. They do not have a specialised urinary system like humans.

10. How should students revise Life Processes effectively?

Study each process by linking its purpose, structures, mechanism and products. Practise labelled diagrams of the digestive system, respiratory system, heart and nephron. Then compare similar terms, such as breathing versus respiration and excretion versus egestion, before attempting conceptual MCQs.

Conclusion

Life Processes explains how living organisms maintain life through coordinated biological activities. Nutrition provides the materials needed by cells, respiration releases usable energy, transportation moves essential substances, and excretion removes metabolic wastes.

The most important step in mastering this chapter is to understand how each structure supports its function: why alveoli have thin walls, why the heart has four chambers, why leaves contain stomata, how xylem and phloem differ, and how nephrons form urine. Once these connections are clear, diagrams, short answers and conceptual questions become much easier to understand and revise.

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