Life Processes Class 10: Notes and Important Questions

Life Processes is Class 10 Science chapter 5. Life processes are the jobs that keep a living body maintained and repaired: nutrition, respiration, transportation and excretion. This guide follows the chapter in order and ends with important questions, model answers and common mistakes.

The whole chapter is in the CBSE 2026-27 board syllabus (Unit II, World of Living). As in every Science chapter, information in the NCERT boxes is not assessed in the year-end exam. पढ़ें हिंदी में: जैव प्रक्रम कक्षा 10.

What are life processes?

A sleeping animal is still alive: its cells need energy, raw materials and a way to remove waste, even without visible movement.

• In a single-celled organism, the whole surface touches the surroundings, so diffusion is enough to exchange materials.
• In a large multicellular body, most cells are deep inside. Diffusion is too slow, so the body needs special surfaces and transport systems.

Autotrophic nutrition: photosynthesis

Autotrophs, such as green plants, make their own food. In photosynthesis, chlorophyll absorbs light energy and the plant builds carbohydrates from carbon dioxide and water, releasing oxygen. Extra carbohydrate is stored as starch.

6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O (sunlight and chlorophyll written over the arrow as conditions)

Photosynthesis involves three events:

1. Absorption of light energy by chlorophyll.
2. Conversion of light energy to chemical energy, and splitting of water into hydrogen and oxygen.
3. Reduction of carbon dioxide to carbohydrates.

These need not happen one after another: some desert plants take in CO₂ at night and use light energy captured by day.

Stomata are tiny pores on leaves, each controlled by two guard cells. When water enters the guard cells they swell and the pore opens; when they lose water the pore closes. Closing the pore saves water but limits gas exchange.

Heterotrophic nutrition

Heterotrophs use food made by other organisms.

• Saprophytes such as bread mould, yeast and mushrooms break down food outside the body and then absorb it.
• Parasites such as Cuscuta (amar-bel), ticks and leeches take nutrition from a living host.
• Amoeba surrounds a food particle with pseudopodia to form a food vacuole, where it is digested. Undigested remains are thrown out at the surface.
• Paramoecium has a fixed shape. Its cilia sweep food to a particular spot where it is taken in.

Human digestion

Final products: carbohydrates become glucose, proteins become amino acids, and fats become fatty acids and glycerol. Finger-like villi in the small intestine increase the surface area for absorption and are rich in blood vessels.

Respiration

The first step always happens in the cytoplasm: glucose (six carbons) breaks into two molecules of pyruvate (three carbons each). What happens next depends on the organism and the oxygen supply.

A build-up of lactic acid causes muscle cramps. The energy released is used to make ATP, the energy currency of the cell. Plants respire day and night.

Human respiratory system: nostrils (hairs and mucus filter the air) → pharynx and larynx → trachea (rings of cartilage stop it collapsing) → bronchi → bronchioles → alveoli. Alveoli have thin walls covered by blood capillaries and a very large surface (about 80 m² if spread out, a "Do You Know?" fact). When we breathe in, the diaphragm flattens and the ribs lift. Haemoglobin in red blood cells carries oxygen to the tissues.

Transportation in humans

The heart has four chambers: two atria above and two ventricles below. The right side handles deoxygenated blood, the left side oxygenated blood.

Body → right atrium → right ventricle → lungs → left atrium → left ventricle → body.

Blood passes through the heart twice in one cycle: double circulation. Ventricles have thicker walls because they pump blood to distant organs.

Platelets help blood clot at an injury. Lymph is a colourless fluid with less protein than plasma; it drains extra tissue fluid back into the blood and carries digested fat from the intestine. Blood pressure is measured with a sphygmomanometer. NCERT gives normal systolic pressure as about 120 mm of Hg and diastolic pressure as 80 mm of Hg, but this sits in a "More to Know!" box, so it is not assessed in the board exam.

Transportation in plants

• Xylem carries water and minerals up from the roots. Root pressure pushes water in at the roots; by day, evaporation from leaves (transpiration) creates a pull that lifts it even in tall trees.
• Phloem carries food such as sucrose and amino acids from leaves to other parts. This is translocation. It uses energy from ATP and can move food upwards or downwards, wherever it is needed.

Excretion in humans and plants

The human excretory system has two kidneys, two ureters, a urinary bladder and a urethra. Each kidney has a large number of filtering units called nephrons.

1. Filtration: blood is filtered in the glomerulus; the filtrate enters the cup-shaped Bowman's capsule.
2. Selective reabsorption: glucose, amino acids, salts and much of the water go back into the blood along the tubule.
3. Urine passes through the ureter to the bladder and leaves through the urethra.

A "More to Know!" box adds that a healthy adult makes about 180 litres of filtrate a day but passes only a litre or two of urine, and that an artificial kidney (haemodialysis) removes wastes by diffusion but, unlike a real kidney, does not reabsorb anything.

Plants release oxygen and water vapour through stomata, store wastes in vacuoles or in leaves that fall off, store resins and gums in old xylem, and release some wastes into the soil.

Remember this

• Four life processes: nutrition, respiration, transportation, excretion.
• Glucose → pyruvate happens in the cytoplasm; aerobic breakdown happens in mitochondria.
• Right side of the heart: deoxygenated blood. Left side: oxygenated blood.
• Xylem moves water up; phloem moves food both ways using energy.
• Nephron = glomerulus + Bowman's capsule + tubule.

Important questions with answers

1. Where does the first step of glucose breakdown take place? (1 mark) In the cytoplasm, where glucose is broken into pyruvate.

2. What is the role of HCl in the stomach? (1 mark) It makes the medium acidic, which pepsin needs to digest proteins.

3. Why is diffusion not enough in multicellular organisms? (2 marks) Most of their cells are not in contact with the surroundings, so diffusion is too slow to supply oxygen and food to all cells.

4. How do guard cells open and close a stoma? (3 marks) When water enters, the guard cells swell and the pore opens. When they lose water, they shrink and the pore closes. Closing reduces water loss when gas exchange is less needed.

5. Compare aerobic and anaerobic respiration. (3 marks) Aerobic respiration uses oxygen, takes place in mitochondria and gives carbon dioxide, water and much energy. Anaerobic respiration in yeast happens without oxygen and gives ethanol, carbon dioxide and much less energy.

6. Why is double circulation useful for mammals and birds? (3 marks) Oxygenated and deoxygenated blood stay separate, so the body gets a highly efficient oxygen supply. These animals need a lot of energy to keep their body temperature constant.

7. Describe how urine is formed in a nephron. (5 marks) Blood is filtered in the glomerulus and the filtrate collects in Bowman's capsule. It contains water, glucose, amino acids, salts and urea. As it flows through the tubule, useful substances and much of the water are reabsorbed into the surrounding capillaries. The remaining liquid is urine, which goes through the ureter to the bladder and leaves through the urethra.

Common mistakes to avoid

• Writing sunlight and chlorophyll as reactants in the photosynthesis equation. They are conditions.
• Calling HCl an enzyme, or saying bile digests fat. Bile only emulsifies fat; lipase digests it.
• Saying all respiration happens in mitochondria. The first step is in the cytoplasm.
• Mixing up egestion (removing undigested food) with excretion (removing metabolic waste such as urea).

To revise this chapter step by step and test yourself, study this chapter with Joy.