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Life Processes

NCERT Class 10 · Science Based on NCERT Class 10 Science textbook · Free CBSE study kit

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Chapter Notes

Overview
This chapter explores the fundamental processes that define life, including nutrition, respiration, transport, and excretion. It explains how living organisms maintain their internal order by acquiring energy and materials from the environment, breaking them down, and eliminating wastes. The central idea is that life is sustained by a set of interconnected chemical and physical processes that repair, maintain, and grow the body. A student must understand that these processes are universal across organisms but are carried out by specialized organs in complex multicellular life.
Key Concepts (25)
Life processes
The maintenance functions of living organisms that must go on even when they are not doing anything particular, such as sitting in class or sleeping.
e.g. Even when you are asleep, your heart beats, you breathe, and your cells repair themselves — these are life processes.
Nutrition
The process of transferring a source of energy from outside the body of the organism, called food, to the inside.
e.g. Eating a meal provides energy and raw materials for growth and repair.
Autotrophic nutrition
A type of nutrition in which organisms use simple food material obtained from inorganic sources in the form of carbon dioxide and water.
e.g. Green plants make their own food using sunlight, CO₂, and water.
Heterotrophic nutrition
A type of nutrition in which organisms utilise complex substances that have to be broken down into simpler ones before they can be used for the upkeep and growth of the body.
e.g. Animals and fungi depend directly or indirectly on autotrophs for food.
Photosynthesis
The process by which autotrophs take in substances from the outside and convert them into stored forms of energy, using carbon dioxide and water in the presence of sunlight and chlorophyll to produce carbohydrates.
e.g. A plant leaf uses sunlight to convert CO₂ and water into glucose and oxygen.
Chlorophyll
The green pigment present in chloroplasts of plant cells that absorbs light energy for photosynthesis.
e.g. The green colour of leaves is due to chlorophyll.
Stomata
Tiny pores present on the surface of leaves through which massive amounts of gaseous exchange takes place for photosynthesis.
e.g. Stomata open during the day to let in CO₂ and release O₂.
Guard cells
Cells that control the opening and closing of stomatal pores; they swell when water flows into them, causing the pore to open, and shrink to close the pore.
e.g. When a plant is well-watered, guard cells swell and stomata open.
Enzymes
Bio-catalysts used by organisms to break down complex substances into simpler ones.
e.g. Salivary amylase is an enzyme that breaks down starch into sugar in the mouth.
Peristaltic movements
Rhythmic contractions of the muscles in the lining of the alimentary canal that push food forward along the digestive tube.
e.g. Food moves from the oesophagus to the stomach due to peristalsis.
Villi
Numerous finger-like projections on the inner lining of the small intestine that increase the surface area for absorption of digested food.
e.g. Villi are richly supplied with blood vessels to carry absorbed nutrients to all cells.
Respiration
The process of acquiring oxygen from outside the body and using it in the break-down of food sources for cellular needs.
e.g. When you breathe in, oxygen is used to break down glucose in your cells to release energy.
Aerobic respiration
The break-down of pyruvate using oxygen, taking place in the mitochondria, producing carbon dioxide and water, and releasing a large amount of energy.
e.g. In human cells, glucose is broken down with oxygen to produce CO₂, water, and ATP.
Anaerobic respiration
The break-down of pyruvate in the absence of oxygen, producing ethanol and carbon dioxide (in yeast) or lactic acid (in human muscle cells).
e.g. Yeast converts sugar into alcohol and CO₂ during fermentation.
ATP (Adenosine Triphosphate)
The energy currency for most cellular processes; energy released during respiration is used to make ATP from ADP and inorganic phosphate.
e.g. ATP provides energy for muscle contraction, protein synthesis, and nerve impulses.
Alveoli
Balloon-like structures at the end of the smallest tubes in the lungs where the exchange of gases takes place; they provide a large surface area.
e.g. Oxygen from inhaled air diffuses into blood through the walls of alveoli.
Haemoglobin
The respiratory pigment present in red blood corpuscles that has a very high affinity for oxygen and carries it to tissues.
e.g. Haemoglobin in your blood picks up oxygen from the lungs and delivers it to your toes.
Double circulation
The system in which blood goes through the heart twice during each cycle of passage through the body, keeping oxygenated and deoxygenated blood separate.
e.g. In humans, blood is pumped from heart to lungs, back to heart, then to the body.
Systolic pressure
The pressure of blood inside the artery during ventricular systole (contraction); normal value is about 120 mm of Hg.
e.g. When the doctor measures your blood pressure, the top number is systolic pressure.
Diastolic pressure
The pressure of blood inside the artery during ventricular diastole (relaxation); normal value is about 80 mm of Hg.
e.g. The bottom number in a blood pressure reading is diastolic pressure.
Transpiration
The loss of water in the form of vapour from the aerial parts of the plant, which helps in absorption and upward movement of water and minerals.
e.g. Water evaporates from leaves, creating a suction that pulls water up from the roots.
Translocation
The transport of soluble products of photosynthesis (and other substances like amino acids) from leaves to other parts of the plant through phloem.
e.g. Sugars made in leaves are moved to roots for storage or to fruits for growth.
Excretion
The biological process involved in the removal of harmful metabolic wastes from the body.
e.g. The kidneys remove urea from the blood and excrete it as urine.
Nephron
The basic filtration unit in the kidney, consisting of a cluster of thin-walled blood capillaries (glomerulus) associated with a cup-shaped Bowman's capsule and a coiled tube.
e.g. Each kidney has millions of nephrons that filter blood to form urine.
Hemodialysis
A process using an artificial kidney to remove nitrogenous waste products from the blood through diffusion across a semi-permeable membrane into a dialysing fluid.
e.g. Patients with kidney failure undergo dialysis to clean their blood.
Formulas & Equations (6)
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (in the presence of sunlight and chlorophyll)
Reads as: Six molecules of carbon dioxide plus six molecules of water, in the presence of sunlight and chlorophyll, produce one molecule of glucose and six molecules of oxygen.
Variables: CO₂ = carbon dioxide, H₂O = water, C₆H₁₂O₆ = glucose, O₂ = oxygen
Use when: When writing the chemical equation for photosynthesis in a board exam question.
⚠ Students often forget to mention 'sunlight' and 'chlorophyll' as conditions above the arrow, or they write the equation backwards.
Glucose (6-carbon) → Pyruvate (3-carbon) [in cytoplasm]
Reads as: Glucose, a six-carbon molecule, is broken down into pyruvate, a three-carbon molecule, in the cytoplasm.
Variables: Glucose = C₆H₁₂O₆, Pyruvate = C₃H₄O₃
Use when: Describing the first step of respiration in any organism.
⚠ Students think this step produces ATP directly; it only produces a net gain of 2 ATP via glycolysis, but the main energy release is later.
Pyruvate (3-carbon) + O₂ → CO₂ + H₂O + Energy (aerobic respiration in mitochondria)
Reads as: Pyruvate, a three-carbon molecule, reacts with oxygen to produce carbon dioxide, water, and energy.
Variables: Pyruvate = C₃H₄O₃, O₂ = oxygen, CO₂ = carbon dioxide, H₂O = water
Use when: Explaining the complete oxidation of glucose in the presence of oxygen.
⚠ Students write 'glucose + oxygen → CO₂ + H₂O' directly, skipping the intermediate pyruvate step, which loses marks.
Pyruvate (3-carbon) → Ethanol (3-carbon) + CO₂ (anaerobic respiration in yeast)
Reads as: Pyruvate is converted into ethanol and carbon dioxide in the absence of oxygen.
Variables: Pyruvate = C₃H₄O₃, Ethanol = C₂H₅OH, CO₂ = carbon dioxide
Use when: Describing fermentation in yeast or anaerobic respiration in microorganisms.
⚠ Students confuse ethanol with lactic acid; ethanol is produced in yeast, lactic acid in human muscle cells.
Pyruvate (3-carbon) → Lactic acid (3-carbon) (anaerobic respiration in human muscle cells)
Reads as: Pyruvate is converted into lactic acid in the absence of oxygen in human muscle cells.
Variables: Pyruvate = C₃H₄O₃, Lactic acid = C₃H₆O₃
Use when: Explaining muscle cramps during sudden or strenuous activity.
⚠ Students think lactic acid is produced only in yeast; it is produced in human muscles during oxygen deficit.
ATP → ADP + Pi + Energy (30.5 kJ/mol released)
Reads as: Adenosine triphosphate is broken down into adenosine diphosphate and inorganic phosphate, releasing 30.5 kilojoules of energy per mole.
Variables: ATP = Adenosine triphosphate, ADP = Adenosine diphosphate, Pi = Inorganic phosphate
Use when: Explaining how energy is released from ATP to drive endothermic reactions in cells.
⚠ Students write 'ATP is energy' without specifying that energy is released when the terminal phosphate bond is broken using water.
How It Works
Photosynthesis
  1. Absorption of light energy by chlorophyll.
  2. Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen.
  3. Reduction of carbon dioxide to carbohydrates.
💡 Desert plants take up CO₂ at night and prepare an intermediate that is acted upon by energy absorbed during the day — this is a common exam point.
Nutrition in Amoeba
  1. Amoeba takes in food using temporary finger-like extensions of the cell surface called pseudopodia.
  2. The pseudopodia fuse over the food particle, forming a food-vacuole.
  3. Inside the food-vacuole, complex substances are broken down into simpler ones by enzymes.
  4. The digested food diffuses into the cytoplasm.
  5. The remaining undigested material is moved to the surface of the cell and thrown out.
💡 Amoeba uses pseudopodia for both locomotion and feeding — students often forget the fusion step to form the food-vacuole.
Digestion in Human Beings
  1. Food is crushed by teeth and mixed with saliva (containing salivary amylase) in the mouth; starch is broken down into sugar.
  2. Food is moved through the oesophagus by peristaltic movements to the stomach.
  3. In the stomach, gastric glands release HCl (creates acidic medium), pepsin (digests proteins), and mucus (protects stomach lining).
  4. Food exits the stomach via a sphincter muscle into the small intestine.
  5. In the small intestine, bile from the liver emulsifies fats, pancreatic juice (trypsin for proteins, lipase for fats) acts, and intestinal juice completes digestion of carbohydrates, proteins, and fats into glucose, amino acids, and fatty acids + glycerol.
  6. Digested food is absorbed through villi into the bloodstream.
  7. Unabsorbed food passes to the large intestine where water is absorbed; the remaining material is removed via the anus.
💡 The role of HCl is to create an acidic medium for pepsin — it does not digest food itself. Also, bile does not contain enzymes; it emulsifies fats.
Aerobic Respiration
  1. Glucose (6-carbon) is broken down into pyruvate (3-carbon) in the cytoplasm (glycolysis).
  2. Pyruvate is transported into mitochondria.
  3. In the presence of oxygen, pyruvate is completely broken down into carbon dioxide and water.
  4. A large amount of energy is released and used to synthesise ATP.
💡 Aerobic respiration produces much more ATP than anaerobic respiration — this is why we need oxygen.
Anaerobic Respiration (Yeast)
  1. Glucose is broken down into pyruvate in the cytoplasm.
  2. In the absence of oxygen, pyruvate is converted into ethanol and carbon dioxide.
  3. This process is called fermentation and releases a small amount of energy.
💡 Yeast is used in baking and brewing because it produces CO₂ (makes dough rise) and ethanol.
Anaerobic Respiration (Human Muscle Cells)
  1. During sudden or strenuous activity, oxygen supply to muscles is insufficient.
  2. Pyruvate is converted into lactic acid (a three-carbon molecule).
  3. The build-up of lactic acid causes muscle cramps.
💡 Lactic acid is not produced in yeast; it is produced in human muscles. Cramps are due to lactic acid accumulation, not lack of oxygen directly.
Human Respiratory System (Breathing and Gas Exchange)
  1. Air enters through the nostrils, where it is filtered by fine hairs and mucus.
  2. Air passes through the throat and into the lungs; rings of cartilage prevent the air-passage from collapsing.
  3. Within the lungs, the passage divides into smaller tubes ending in alveoli.
  4. When we breathe in, the ribs lift and the diaphragm flattens, increasing chest cavity size and sucking air into the lungs.
  5. Oxygen from alveolar air diffuses into blood in the alveolar blood vessels; carbon dioxide from blood diffuses into alveoli.
  6. Haemoglobin in red blood cells carries oxygen to all body cells; carbon dioxide is transported mostly in dissolved form in plasma.
💡 Alveoli provide a huge surface area (about 80 m²) for gas exchange — this is why diffusion is efficient despite the distance.
Double Circulation in Humans
  1. Deoxygenated blood from the body enters the right atrium.
  2. Right atrium contracts, sending blood to the right ventricle.
  3. Right ventricle pumps blood to the lungs for oxygenation.
  4. Oxygenated blood from the lungs enters the left atrium.
  5. Left atrium contracts, sending blood to the left ventricle.
  6. Left ventricle pumps oxygenated blood to the rest of the body.
💡 The left ventricle has the thickest muscular wall because it has to pump blood to the entire body. Valves prevent backflow.
Transport of Water in Plants (Xylem)
  1. Root cells actively take up ions from the soil, creating a concentration difference.
  2. Water moves into the root from the soil by osmosis, creating root pressure.
  3. Water is pushed upwards into the xylem vessels.
  4. During the day, transpiration from leaves creates a suction (transpiration pull) that pulls water up the xylem.
  5. Water and minerals are transported to all parts of the plant.
💡 Root pressure is more important at night; transpiration pull is the major force during the day.
Transport of Food in Plants (Phloem)
  1. Sucrose and other products of photosynthesis are loaded into phloem sieve tubes using energy from ATP.
  2. This increases osmotic pressure in the phloem, causing water to move into it.
  3. The pressure difference moves the material in the phloem to tissues with lower pressure (e.g., roots, fruits, buds).
  4. Phloem can transport food both upward and downward depending on the plant's needs.
💡 Phloem transport requires energy (ATP), unlike xylem transport which is largely physical. This is a key difference.
Urine Formation in Human Kidneys
  1. Blood enters the kidney; each nephron has a cluster of thin-walled capillaries (glomerulus) that filters blood.
  2. The filtrate (containing water, glucose, amino acids, salts, and urea) collects in Bowman's capsule.
  3. As the filtrate flows through the coiled tubule, useful substances like glucose, amino acids, salts, and most water are selectively reabsorbed into the blood.
  4. The remaining fluid (urine) contains excess water, salts, and nitrogenous wastes like urea.
  5. Urine passes through the ureters to the urinary bladder, where it is stored until released via the urethra.
💡 The initial filtrate is about 180 L per day, but only 1-2 L of urine is excreted because most water is reabsorbed.
Exam Traps — Don't Make These Mistakes
⚠ Confusing autotrophs and heterotrophs
✗ Autotrophs get energy from other organisms.
→ Autotrophs (like green plants) make their own food from inorganic sources (CO₂ and water) using sunlight. They do not depend on other organisms for energy.
✓ Autotrophs obtain energy from inorganic sources (carbon dioxide and water) through photosynthesis, using sunlight and chlorophyll.
⚠ Mixing up the role of HCl in the stomach
✗ Hydrochloric acid digests food in the stomach.
→ HCl does not digest food; it creates an acidic medium that activates the enzyme pepsin, which digests proteins. HCl also kills bacteria.
✓ Hydrochloric acid creates an acidic medium in the stomach that facilitates the action of the enzyme pepsin, and it also kills harmful bacteria.
⚠ Thinking bile contains digestive enzymes
✗ Bile juice contains enzymes that digest fats.
→ Bile does not contain any digestive enzymes. It contains bile salts that emulsify fats (break them into smaller globules), increasing the surface area for lipase action.
✓ Bile juice from the liver does not contain enzymes; bile salts emulsify fats, breaking them into smaller globules to increase the efficiency of lipase.
⚠ Confusing the site of aerobic and anaerobic respiration
✗ Aerobic respiration takes place in the cytoplasm.
→ The first step (glycolysis) occurs in the cytoplasm, but the complete aerobic breakdown of pyruvate using oxygen takes place in the mitochondria.
✓ Aerobic respiration occurs in the mitochondria, where pyruvate is broken down using oxygen to produce CO₂, water, and a large amount of energy.
⚠ Mixing up transpiration and translocation
✗ Translocation is the loss of water from leaves.
→ Translocation is the transport of soluble products of photosynthesis (food) through phloem. Transpiration is the loss of water vapour from aerial parts.
✓ Transpiration is the loss of water vapour from aerial parts of the plant; translocation is the transport of food (sucrose, amino acids) through phloem.
⚠ Thinking the right side of the heart carries oxygenated blood
✗ The right side of the heart carries oxygenated blood.
→ The right atrium and right ventricle receive deoxygenated blood from the body and pump it to the lungs. The left side carries oxygenated blood from the lungs to the body.
✓ The right side of the heart receives deoxygenated blood from the body and pumps it to the lungs; the left side receives oxygenated blood from the lungs and pumps it to the body.
Compare & Contrast
Source of food
Autotrophic nutrition
Heterotrophic nutrition
Autotrophs use simple inorganic substances (CO₂ and water) to make their own food; heterotrophs depend on complex organic substances obtained from other organisms.
Presence of oxygen
Aerobic respiration
Anaerobic respiration
Aerobic respiration uses oxygen to completely break down pyruvate into CO₂ and water, releasing a large amount of energy; anaerobic respiration occurs without oxygen, producing ethanol (in yeast) or lactic acid (in muscles) and releasing much less energy.
Direction of blood flow and wall thickness
Arteries
Veins
Arteries carry blood away from the heart under high pressure and have thick, elastic walls; veins carry blood towards the heart under low pressure and have thin walls with valves to prevent backflow.
Substance transported and direction
Xylem
Phloem
Xylem transports water and minerals from roots upwards; phloem transports food (sucrose, amino acids) from leaves to all parts of the plant in both upward and downward directions, using energy.
Exam Focus
Marks pattern: 2 MCQs (1 mark each), 1 Very Short Answer (1 mark), 1 Short Answer (3 marks), 1 Long Answer (5 marks) — typically 10-12 marks total in the board exam.
Most asked: Photosynthesis: equation, events, and experiments (variegated leaf, KOH experiment) · Human digestive system: organs, enzymes, and their functions · Respiration: aerobic vs anaerobic, ATP, and the breakdown of glucose · Human heart: double circulation, chambers, and blood flow · Excretion: nephron structure and urine formation · Transport in plants: xylem and phloem, transpiration and translocation
Don't skip: Explain the process of digestion in human beings with a labelled diagram (5 marks).; Describe the structure and functioning of the human heart (5 marks).; Compare and contrast aerobic and anaerobic respiration (3 marks).; Explain the mechanism of photosynthesis and the experiments to prove its requirements (3 or 5 marks).; Describe the excretory system of human beings and the process of urine formation (5 marks).
One-Line Revision (read aloud before the exam)
  1. Life processes are maintenance functions like nutrition, respiration, transport, and excretion that keep an organism alive.
  2. Autotrophic nutrition is the process by which plants make their own food using CO₂, water, sunlight, and chlorophyll.
  3. Photosynthesis occurs in chloroplasts and has three events: absorption of light, conversion to chemical energy with water splitting, and reduction of CO₂ to carbohydrates.
  4. Stomata are tiny pores on leaves that allow gas exchange; they are opened and closed by guard cells.
  5. Heterotrophic nutrition involves taking in complex food and breaking it down using enzymes.
  6. Salivary amylase in the mouth breaks down starch into sugar.
  7. The stomach secretes HCl (acidic medium for pepsin), pepsin (protein digestion), and mucus (protection).
  8. The small intestine is the site of complete digestion; bile emulsifies fats, pancreatic enzymes digest proteins and fats, and intestinal juice completes digestion.
  9. Villi in the small intestine increase surface area for absorption of digested food.
  10. Aerobic respiration uses oxygen and produces a large amount of ATP in mitochondria.
  11. Anaerobic respiration in yeast produces ethanol and CO₂; in human muscles it produces lactic acid causing cramps.
  12. ATP is the energy currency of the cell; it releases 30.5 kJ/mol when broken down.
  13. The human respiratory system includes nostrils, throat, trachea with cartilage rings, bronchi, and alveoli for gas exchange.
  14. Haemoglobin in red blood cells carries oxygen; carbon dioxide is mostly transported in dissolved form in plasma.
  15. Double circulation in humans keeps oxygenated and deoxygenated blood separate for efficient oxygen supply.
  16. The left ventricle has the thickest wall as it pumps blood to the entire body.
  17. Arteries have thick elastic walls; veins have valves to prevent backflow.
  18. Transpiration is the loss of water vapour from leaves, creating a pull that moves water up the xylem.
  19. Translocation is the transport of food through phloem using energy from ATP.
  20. The nephron is the filtration unit of the kidney; it filters blood, reabsorbs useful substances, and forms urine.
  21. The initial filtrate in kidneys is about 180 L daily, but only 1-2 L of urine is excreted due to reabsorption.
  22. Hemodialysis is an artificial process to remove nitrogenous wastes from blood when kidneys fail.

MCQs — 10 Questions with Answers

Q1. A student observes that when a plant is placed in a dark room for several days, it becomes pale and stops growing, but remains alive. Which life process explains why the plant is still alive despite the absence of visible growth?

  • A. Respiration, because molecular movements continue to maintain the plant's cellular structures even without photosynthesis ✓
  • B. Nutrition, because the plant still absorbs water from the soil
  • C. Growth, because the plant's cells are still dividing internally
  • D. Excretion, because the plant removes waste products from its leaves

Answer: A — Respiration maintains order in living structures through continuous molecular movements regardless of external visibility; students often mistakenly link visible growth (Option C) as the only indicator of life processes, or confuse nutrition with the overall maintenance function.

Q2. During a biology lab, a student seals a living mouse in a glass jar with calcium hydroxide solution (which absorbs CO₂). The mouse survives for some time but eventually shows distress. Based on your understanding of life processes, what best explains the mouse's distress?

  • A. Lack of nutrition, because food is not being replenished
  • B. Inability to excrete carbon dioxide produced during respiration, disrupting the balance needed for continued respiration ✓
  • C. Lack of oxygen, because the jar becomes airtight
  • D. Accumulation of water vapor, because respiration produces water

Answer: B — Respiration produces CO₂ as a waste product that must be removed; blocking CO₂ excretion disrupts the organism's chemical balance even with oxygen and food present, whereas students often incorrectly assume the jar's airtightness (Option C) or food depletion (Option A) as primary causes in a short timeframe.

Q3. A researcher studies single-celled organisms living in a petri dish and multi-cellular humans. She observes that single-celled organisms can exchange nutrients and gases directly across their cell membrane, but humans require specialized transport systems. What is the fundamental reason for this difference?

  • A. Single-celled organisms have larger surface area to volume ratios, allowing diffusion to meet all cellular needs, whereas human cells are too far from the external environment ✓
  • B. Single-celled organisms do not need respiration, so they do not require specialized gas exchange
  • C. Humans have a circulatory system, but single-celled organisms do not possess any structural complexity
  • D. Single-celled organisms are alive, but humans are not truly living organisms

Answer: A — The high surface-area-to-volume ratio in unicellular organisms enables simple diffusion to serve all cells, while multi-cellular organisms have internal cells distant from the environment requiring transport systems; students often incorrectly assume single-celled organisms do not respire (Option B) or deny the complexity of unicellular life.

Q4. A gardener notices that a potted plant on a sunny windowsill grows faster than an identical plant in a dimly lit corner, even though both are watered equally. Considering the concept of life processes, which explains the difference in growth rate?

  • A. The sunny plant absorbs more water through its roots due to increased light
  • B. The sunny plant produces more glucose through photosynthesis, providing greater energy and raw materials for growth and maintenance ✓
  • C. The sunny plant requires less respiration, so it conserves more energy for growth
  • D. The dim plant loses water faster through transpiration, limiting nutrient availability

Answer: B — Photosynthesis in light produces glucose for energy and carbon-based structures needed for growth; students often incorrectly believe respiration decreases in sunlight (Option C) or confuse water absorption with light-dependent processes (Option A).

Q5. A student reads that viruses do not show molecular movement until they infect a cell. Based on the chapter's explanation of why molecular movement is necessary for life, why is the alive/not-alive status of viruses controversial?

  • A. Viruses lack the molecular movements needed to maintain order in their structures, so they may not qualify as truly alive until they infect and use a host cell's machinery ✓
  • B. Viruses are definitely not alive because they cannot move on their own
  • C. Viruses are definitely alive because they can reproduce inside cells
  • D. Viruses lack cells, so they cannot be considered living organisms

Answer: A — The chapter explicitly states molecular movements are necessary to maintain organized structures and prevent breakdown, and viruses lack this until infection; students often oversimplify by denying viruses life status based on visible movement (Option B) or automatically granting it based solely on reproduction (Option C).

Q6. Assertion (A): In multi-cellular organisms, a transportation system is necessary to carry oxygen and food from the site of uptake to all body cells. Reason (R): All cells in multi-cellular organisms are in direct contact with the external environment. Choose the correct option:

  • A. Both A and R are true and R is the correct explanation of A
  • B. Both A and R are true but R is not the correct explanation of A
  • C. A is true but R is false ✓
  • D. A is false but R is true

Answer: C — Assertion is correct because multi-cellular organisms need transport systems for distributed nutrient delivery, but the Reason is false because NOT all cells are in direct contact with the environment (this is precisely why transport is needed); students often accept both statements without critical evaluation.

Q7. Assertion (A): Respiration is needed to break down food molecules and provide energy for maintaining the ordered structure of living organisms. Reason (R): Without respiration, molecules in the cell would stop moving and the organism would immediately die. Choose the correct option:

  • A. Both A and R are true and R is the correct explanation of A
  • B. Both A and R are true but R is not the correct explanation of A ✓
  • C. A is true but R is false
  • D. A is false but R is true

Answer: B — Assertion is correct (respiration does provide energy for maintenance), and Reason is partially true (without respiration organisms die), but R is oversimplified and does not properly explain *why* respiration is necessary (the mechanism of maintaining order through molecular movement), making it not the correct explanation of A.

Q8. Assertion (A): Autotrophic organisms obtain their energy and raw materials from inorganic sources such as CO₂ and water. Reason (R): All autotrophic organisms use photosynthesis to convert inorganic molecules into organic food. Choose the correct option:

  • A. Both A and R are true and R is the correct explanation of A
  • B. Both A and R are true but R is not the correct explanation of A
  • C. A is true but R is false ✓
  • D. A is false but R is true

Answer: C — Assertion is true (the chapter defines autotrophs using inorganic sources), but Reason is false because some autotrophic bacteria use chemosynthesis rather than photosynthesis; students often assume all autotrophs use photosynthesis, confusing the definition of autotrophy with the specific mechanism.

Q9. A scientist compares the respiration rates of a sleeping human and an active human by measuring oxygen consumption over one hour. The active human consumes 20 liters of oxygen while the sleeping human consumes 4 liters. What does this observation best demonstrate?

  • A. The sleeping human is not alive because respiration continues at a lower rate
  • B. Life processes require different amounts of energy depending on the organism's activity level, even though maintenance processes occur continuously in both states ✓
  • C. The sleeping human does not need to maintain cellular structures because respiration is minimal
  • D. Oxygen is only needed during physical activity, not during rest

Answer: B — The data shows respiration continues in both states but at different rates, reflecting both basal maintenance and activity-level demands; students often incorrectly conclude that low respiration means reduced life processes (Option C) or that rest eliminates maintenance needs (Option D).

Q10. A student conducts an experiment by placing a green plant and a small animal in a sealed transparent container exposed to sunlight for 48 hours. After 48 hours, both organisms are still alive and healthy. Which combination of life processes best explains how both organisms survived together in this closed system?

  • A. The plant's photosynthesis produced oxygen and glucose, which the animal used for respiration, and the animal's respiration produced CO₂, which the plant used for photosynthesis ✓
  • B. The plant absorbed all waste from the animal through its roots, and the animal consumed the plant's leaves for nutrition
  • C. Both organisms entered a dormant state and did not require respiration or nutrition
  • D. The plant transported oxygen directly to the animal through atmospheric diffusion

Answer: A — This describes a closed-loop exchange where photosynthesis and respiration are complementary processes; students often incorrectly assume dormancy (Option C), direct transport mechanisms (Option D), or predator-prey relationships (Option B) rather than recognizing the gas and nutrient cycling between the two processes.

Flashcards

What is the main defining characteristic of all living organisms?

Continuous molecular movement and chemical reactions needed to maintain organised structures against environmental breakdown.

Define life processes.

Maintenance functions that continuously occur in living organisms to prevent damage and breakdown of structures, even during rest.

Why is nutrition essential for all organisms?

Nutrition provides energy from outside sources and raw materials needed for growth, development, and maintaining the ordered state of living structures.

Distinguish between autotrophs and heterotrophs.

Autotrophs (green plants and bacteria) make their own food using inorganic sources; heterotrophs (animals and fungi) obtain energy from complex substances.

What is photosynthesis and what does it produce?

Process where autotrophs convert carbon dioxide and water into carbohydrates using sunlight and chlorophyll; excess carbohydrates stored as starch.

Why do multi-cellular organisms need specialised transport systems?

All body cells cannot be in direct contact with the environment, so food and oxygen must be transported from specialised tissues to all cells.

What is respiration and why is it necessary?

Process of acquiring oxygen from outside and using it to break down food through oxidation-reduction reactions, converting food energy into usable cellular energy.

Why is excretion necessary in living organisms?

Chemical reactions during respiration produce harmful waste by-products that cannot be used by cells and must be removed from the body.

Why is diffusion insufficient in large multi-cellular organisms like humans?

Diffusion alone cannot deliver oxygen and food to all cells deep within the body that are not in direct contact with the environment.

Why are viruses considered controversial regarding whether they are alive?

Viruses lack molecular movement until they infect a cell, and since molecular movement is necessary for life, their living status is debated.

Important Board Questions

Why is molecular movement considered a better criterion for determining whether something is alive compared to visible movement? [2 marks]

Explain that visible movement is not always present (e.g., sleeping organisms, non-growing plants) but molecular movement in chemical reactions continues in all living things. Molecular movement is necessary to prevent ordered structures from breaking down due to environmental effects.

Explain why diffusion alone is insufficient to meet the oxygen and food requirements of multi-cellular organisms like humans. What alternative mechanism do these organisms use? [3 marks]

State that not all cells in multi-cellular organisms are in direct contact with the environment, so simple diffusion cannot reach internal cells. Multi-cellular organisms possess specialised tissues and a transport system (circulatory system) to carry oxygen and food from absorption sites to all body cells and to carry waste away.

Describe the relationship between nutrition and respiration in living organisms. Explain how both processes together maintain life and energy flow in the body. Use examples to support your answer. [5 marks]

Explain that nutrition provides food (carbon-based molecules) and raw materials from outside, while respiration breaks down this food using oxygen through oxidation-reduction reactions to release energy in usable forms. Show how the energy released powers all maintenance processes needed to prevent breakdown of organised structures. Use example: plants absorb CO₂ and water via photosynthesis; animals eat plants and break down the carbohydrates via respiration to fuel cellular work and growth. The waste products from respiration (CO₂) are excreted and eventually used by plants again, completing the cycle.

Assertion-Reason Questions for Life Processes

Q1. Assertion (A):

Life processes must continue even when an organism is sleeping or inactive.

Reason (R):

Living organisms need continuous molecular movements to maintain their ordered structures against environmental breakdown.

Answer: A — Both A and R are true, and R is the correct explanation of A — Both the assertion and reason are true, and the reason correctly explains why life processes are continuous. Even during sleep, maintenance functions like respiration and circulation continue because the body must constantly repair and maintain its organized structure.

Q2. Assertion (A):

Autotrophic organisms do not require external sources of organic food.

Reason (R):

Autotrophs can synthesize their own food from inorganic sources like carbon dioxide and water through photosynthesis.

Answer: A — Both A and R are true, and R is the correct explanation of A — Both statements are true and the reason correctly explains the assertion. Autotrophs like green plants produce their own organic compounds from inorganic materials, so they are self-sufficient regarding food.

Q3. Assertion (A):

Multi-cellular organisms require specialized transportation systems for nutrients and gases.

Reason (R):

All cells in multi-cellular organisms are in direct contact with the external environment.

Answer: C — A is true but R is false — The assertion is true—multi-cellular organisms do need transport systems. However, the reason is false because interior cells in multi-cellular organisms are NOT in direct contact with the environment, which is precisely why transportation systems are needed.

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Case-Based Questions (CBQ) for Life Processes

Case Study:

A biologist conducted an experiment to study how different organisms obtain energy. She observed a potted green plant in sunlight producing glucose and storing starch. She also observed a rabbit eating clover from the same plant and converting the plant material into energy for movement and growth. Additionally, she noted a fungus breaking down dead plant matter in the soil. The biologist recorded that all three organisms required continuous energy input to maintain their body functions, even during periods of inactivity.

Q1. Which organism in the experiment is classified as an autotroph?

  • A. The rabbit
  • B. The green plant ✓
  • C. The fungus
  • D. All three organisms

Answer: B

Q2. Why does the rabbit depend on the plant for survival?

  • A. The plant produces oxygen only
  • B. The plant converts inorganic materials into organic compounds that the rabbit cannot produce itself ✓
  • C. The plant moves faster than the rabbit
  • D. The plant absorbs water for the rabbit

Answer: B

Q3. What do all three organisms have in common according to the observation?

  • A. They all photosynthesize
  • B. They all eat the same food
  • C. They all require continuous energy to maintain their life processes ✓
  • D. They all move at the same speed

Answer: C

Q4. The fungus in this experiment can be classified as a heterotroph because:

  • A. It synthesizes its own food from sunlight
  • B. It moves faster than the plant
  • C. It breaks down complex organic matter from other organisms to obtain energy ✓
  • D. It stores energy as starch

Answer: C

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Previous Year Questions (PYQ) for Life Processes

Real CBSE board exam questions from past papers — free to attempt.

CBSE 2026 · Set 31/4/1 · 1 mark

Observe the given figure and select the statement that correctly states how these fungi obtain nutrition.

  • By eating the bread on which it is growing.
  • By using nutrients from the bread to prepare their own food.
  • By breaking down the nutrients of bread outside the body and then absorbing them.
  • By allowing other organisms to grow on the bread and then consuming them.

CBSE 2026 · Set 31/4/1 · 1 mark

In human beings the oxygen rich blood is pumped out to the body by:

  • contraction of right atrium
  • relaxation of left ventricle
  • contraction of right ventricle
  • contraction of left ventricle

CBSE 2026 · Set 31/4/1 · 2 marks

"Transpiration in plants is a necessary evil." Comment on the statement giving two reasons.

CBSE 2026 · Set 31/4/1 · 5 marks

(A) (a) Draw a labelled diagram showing open and closed stomatal pore. (b) List the main events that occur during the process of photo-synthesis. (c) Write a balanced chemical equation showing photo-synthesis in plants.

CBSE 2026 · Set 31/4/2 · 1 mark

Opening of stomata is regulated by:

  • Entry of water into guard cells
  • Exit of water from guard cells
  • Entry of air into the stomatal pore
  • Entry of water into the stomatal pore

CBSE 2026 · Set 31/4/2 · 2 marks

(A) Varun is diabetic. His latest ultrasound reports showed a blockage in his pancreatic duct. How will this affect the dual functioning of the pancreas?

CBSE 2026 · Set 31/4/2 · 2 marks

Give reasons for the following: (a) Plants do not have an excretory system so how they excrete their wastes? (b) Why do mammals and birds have double circulation?

CBSE 2026 · Set 31/4/3 · 1 mark

Four chambered heart is a characteristic of:

  • Fishes
  • Amphibians
  • Reptiles
  • Mammals

CBSE 2026 · Set 31/4/3 · 1 mark

Translocation is the process in which plants deliver:

  • Minerals from leaves to other parts of the plant.
  • Plant growth hormones from leaves to other parts of the plant.
  • Water and inorganic substances from leaves to other parts of the plant.
  • Organic substances from leaves to the other parts of the plant.

CBSE 2026 · Set 31/4/3 · 2 marks

The leaves of a plant first prepares food 'P' by photo-synthesis. Food 'P' is then converted to food 'Q', which is stored in the leaves if not used immediately. What are 'P' and 'Q'? What are the raw materials and conditions required for synthesis of 'P'?

CBSE 2026 · Set 31/4/3 · 2 marks

Varun is diabetic. His latest ultrasound reports showed a blockage in his pancreatic duct. How will this affect the dual functioning of the pancreas?

CBSE 2026 · Set 31/4/3 · 5 marks

(a) Draw a labelled diagram showing open and closed stomatal pore. (b) List the main events that occur during the process of photo-synthesis. (c) Write a balanced chemical equation showing photo-synthesis in plants.

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Class 10 Science Formula Sheet

Every formula and chemical equation from the 10 chapters on one page, checked against the NCERT textbook and the CBSE 2026-27 syllabus. Free PDF download.

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Class 10 Science Previous Year Questions, Chapter-wise

All 875 CBSE board questions from 2022–2026, sorted by chapter and question type. Free PDF download.

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