CBSE Class 10 · Science · board exam 2027
Chapter 5: Life Processes — notes
The chapter’s 10 parts in the book’s order — the first idea of each and the points Medha Ma’am writes on the board — and the summary at the end. The full lesson and a check question for each part are in the app.
1. What are life processes
First, a question.
- • Signs of life: movement, breathing, growth
- • Body structures break down with time
- • So they must be repaired all the time: maintenance
- • Life processes: all the processes which together perform the maintenance job
- • Nutrition: taking in food, the source of energy
- • Respiration: breaking down food to release energy
- • Transportation: carrying food and oxygen to every cell
- • Excretion: removing harmful wastes
- • Four life processes: nutrition, respiration, transportation, excretion
2. Nutrition and its types
Food gives us two things, energy and raw material to build the body.
- • Two modes of nutrition: autotrophic and heterotrophic
- • Autotrophs: make their own food from CO₂ and water, in sunlight
- • Examples: green plants, some bacteria
- • Heterotrophs: depend on other organisms for food
- • Complex food, broken by enzymes into simple substances
- • Examples: animals, fungi, human beings
- • (1) Saprophytic: break down food outside the body, then absorb it
- • Examples: bread mould, yeast, mushrooms
- • (2) Parasitic: feed on a host without killing it, e.g. Cuscuta, lice, tapeworm
- • (3) Holozoic: whole food taken in, digested inside, e.g. Amoeba, human beings
- • | Basis | Autotrophic | Heterotrophic |
- • | Food | made by itself | taken from others |
- • | Raw material | CO₂ and water (inorganic) | complex organic matter |
- • | Sunlight, chlorophyll | needed | not needed |
- • | Examples | green plants | animals, fungi |
3. Photosynthesis
The most important process of autotrophs.
- • Photosynthesis: green plants convert CO₂ and water into carbohydrates (glucose) in the presence of sunlight and chlorophyll
- • Word equation: carbon dioxide + water → glucose + oxygen
- • CO₂ + H₂O → C₆H₁₂O₆ + O₂ (unbalanced)
- • | Element | Left | Right |
- • | C | 6 | 6 |
- • | H | 12 | 12 |
- • | O | 12 + 6 = 18 | 6 + 12 = 18 |
- • 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
- • | Element | Left | Right |
- • | C | 6 | 6 |
- • | H | 24 | 12 + 12 = 24 |
- • | O | 12 + 12 = 24 | 6 + 12 + 6 = 24 |
- • 6CO₂(g) + 12H₂O(l) →[sunlight, chlorophyll] C₆H₁₂O₆(aq) + 6O₂(g) + 6H₂O(l)
- • (i) Absorption of light energy by chlorophyll
- • (ii) Light energy → chemical energy; water split into hydrogen and oxygen
- • (iii) Reduction of CO₂ to carbohydrates
- • Desert plants: take in CO₂ at night, store it, make food in the day
- • Unused carbohydrate → stored as starch (internal energy reserve)
- • Stomata: tiny pores on the surface of leaves
- • Functions: exchange of gases, transpiration
- • Water flows into guard cells → they swell → pore opens
- • Water flows out → they shrink → pore closes
- • Why close? To stop water loss when CO₂ is not needed
- • CO₂: from the air, through stomata
- • Water, minerals (N, P, Fe, Mg): from the soil, through roots
- • Nitrogen: for proteins, as nitrates or nitrites
- • Activity: CO₂ is essential for photosynthesis
- • Materials: two potted plants, two bell jars, glass plates, vaseline, KOH, iodine solution
- • 1. Keep both plants in the dark for three days (destarch)
- • 2. Bell jars on glass plates, sealed with vaseline (airtight)
- • 3. KOH in jar (a): it absorbs CO₂
- • 4. Keep both in sunlight for a few hours
- • 5. Boil the leaf, keep in alcohol, add iodine solution
- • Observation: leaf (b) blue-black (starch); leaf (a) not
- • Conclusion: CO₂ is essential for photosynthesis
4. Nutrition in Amoeba and Paramoecium
Single-celled organisms can take in food through the whole surface.
- • P: pseudopodia (temporary finger-like extensions) surround the food particle
- • Q: extensions fuse → food vacuole
- • R: complex → simple substances, diffuse into the cytoplasm
- • S: undigested material thrown out at the surface
- • Paramoecium: definite shape, food taken in at a specific spot
- • Movement of cilia brings food there
5. Nutrition in human beings
The human alimentary canal in the figure.
- • Alimentary canal: mouth → oesophagus → stomach → small intestine → large intestine → anus
- • Glands: salivary glands, liver, pancreas
- • Mouth: teeth crush food, tongue mixes it with saliva
- • Starch →[salivary amylase] simple sugar
- • Peristalsis: rhythmic contraction of muscles of the gut pushes food forward
- • Muscular walls: mix food with digestive juices
- • Gastric glands → HCl + pepsin + mucus
- • HCl: acidic medium for pepsin
- • Pepsin: digests proteins
- • Mucus: protects the inner lining from the acid
- • No mucus → acid damages the inner lining
- • Sphincter: releases food into the small intestine in small amounts
- • Small intestine: longest part, site of complete digestion
- • Herbivores: longer (to digest cellulose)
- • Carnivores: shorter (meat is easier to digest)
- • Bile (from the liver): makes the acidic food alkaline
- • Bile salts: emulsify fats (large globules → small)
- • Bile has no enzyme
- • Pancreatic juice: trypsin (proteins), lipase (emulsified fats)
- • Intestinal juice: completes digestion
- • | Food | Finally converted to |
- • | Proteins | amino acids |
- • | Complex carbohydrates | glucose |
- • | Fats | fatty acids + glycerol |
- • Villi: finger-like projections of the inner lining
- • Function: increase the surface area for absorption
- • Blood vessels carry absorbed food to every cell
- • Large intestine: absorbs water from unabsorbed food
- • Anal sphincter: regulates the exit of waste
- • Dental caries: acids from bacteria soften the enamel
6. Respiration
The glucose from nutrition will now give energy.
- • Respiration: breaking down food (glucose) to release energy
- • Step 1 (in cytoplasm): glucose (6-carbon) → pyruvate (3-carbon) + energy
- • (1) In yeast, no oxygen: pyruvate → ethanol + CO₂ + energy (fermentation, anaerobic)
- • (2) In muscle cells, lack of oxygen: pyruvate → lactic acid + energy
- • Build-up of lactic acid → cramps
- • (3) In mitochondria, with oxygen: pyruvate → CO₂ + H₂O + energy (aerobic)
- • Aerobic gives the most energy: complete breakdown of glucose
- • glucose + oxygen → carbon dioxide + water + energy
- • C₆H₁₂O₆ + O₂ → CO₂ + H₂O (unbalanced)
- • | Element | Left | Right |
- • | C | 6 | 6 |
- • | H | 12 | 12 |
- • | O | 6 + 12 = 18 | 12 + 6 = 18 |
- • C₆H₁₂O₆(aq) + 6O₂(g) → 6CO₂(g) + 6H₂O(l) + energy
- • Respiration: exothermic (energy released), oxidation
- • C₆H₁₂O₆(aq) →[yeast, no oxygen] 2C₂H₅OH(aq) + 2CO₂(g) + energy
- • | Element | Left | Right |
- • | C | 6 | 4 + 2 = 6 |
- • | H | 12 | 12 |
- • | O | 6 | 2 + 4 = 6 |
- • ADP + phosphate + energy → ATP
- • ATP → ADP + phosphate + energy (for the cell's work)
- • ATP: the energy currency of the cell
- • (I) Atmospheric air: turns milky late
- • (II) Exhaled air: turns milky soon (more CO₂)
- • Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l)
- • CaCO₃ is insoluble, so the lime water turns milky
- • Plants: diffusion through stomata (leaves) and lenticels (stems)
- • Night: CO₂ given out
- • Day: CO₂ taken in, O₂ given out (photosynthesis is fast)
- • Fish: gills, oxygen dissolved in water
- • Dissolved oxygen is low → aquatic organisms breathe much faster
- • Terrestrial animals: oxygen of the atmosphere, lungs
7. The human respiratory system
The human respiratory system.
- • Path: nostrils → nasal cavity → pharynx → larynx → trachea
- • Hairs and mucus: filter the air
- • Rings of cartilage: the air passage does not collapse
- • Trachea → two bronchi → bronchioles → alveoli
- • Alveoli: surface for exchange of gases
- • Network of blood vessels: O₂ into blood, CO₂ out
- • Area about 80 m²
- • Breathing in: ribs lifted, diaphragm flattens → chest cavity larger → air in
- • Breathing out: ribs come down, diaphragm dome-shaped → air out
- • Residual volume: time for O₂ to be absorbed and CO₂ released
- • Respiratory pigment: haemoglobin (in red blood cells)
- • High affinity for O₂ → carries O₂ from lungs to tissues
- • CO₂: mostly dissolved in blood
8. Transportation in human beings
Blood carries food, oxygen and waste materials in the body.
- • Blood: a fluid connective tissue
- • Plasma: carries food, CO₂, nitrogenous wastes in dissolved form
- • Red blood cells: oxygen; white blood cells: defence; platelets: clotting
- • Heart: muscular organ, four chambers
- • Above: right atrium, left atrium
- • Below: right ventricle, left ventricle
- • Right and left sides separate: oxygenated and deoxygenated blood do not mix
- • Gain: efficient O₂ supply (birds, mammals)
- • Lungs → pulmonary vein → left atrium → left ventricle → aorta → body
- • Body → vena cava → right atrium → right ventricle → pulmonary artery → lungs
- • Double circulation: blood goes through the heart twice in each cycle
- • Ventricles: thicker walls (pump blood to the body)
- • Valves: no backward flow
- • | Animal | Chambers |
- • | Fish | 2 (once in a cycle) |
- • | Frog, reptiles | 3 |
- • | Birds, mammals | 4 (double) |
- • | Basis | Artery | Vein |
- • | Direction | heart to organs | organs to heart |
- • | Wall | thick, elastic (high pressure) | thin (low pressure) |
- • | Valves | absent | present |
- • Capillaries: walls one cell thick, exchange of materials
- • Systolic ≈ 120 mm of Hg; diastolic ≈ 80 mm of Hg
- • Measured with a sphygmomanometer
- • High blood pressure: hypertension
- • Platelets: clot the blood at the injury
- • Gain: less blood loss, pressure and pumping efficiency kept
- • Lymph (tissue fluid): colourless, less protein
- • Formed: plasma, proteins, blood cells escape through pores of capillaries
- • Function: carries digested fat; drains excess fluid back into blood
9. Transportation in plants
Plants need less energy, because they do not move, and many of their tissues are made of dead cells.
- • Plant transport is slower: low energy needs, many dead cells
- • Xylem: water and minerals (roots upwards)
- • Phloem: food (from leaves to other parts)
- • Root pressure: root takes up ions → concentration difference → water enters root → column pushed up
- • Transpiration: loss of water as vapour from the aerial parts of a plant
- • Transpiration pull (suction): water pulled from roots to leaves
- • Day: transpiration pull; night: root pressure
- • Uses: upward movement of water and minerals; temperature regulation
- • Loss: water is lost
- • So: a necessary evil
- • Translocation: transport of soluble products of photosynthesis through phloem
- • Sieve tubes + companion cells; upward and downward
- • Sucrose + energy from ATP → into phloem
- • Osmotic pressure rises → water enters → food moves to lower pressure
- • | Basis | Xylem | Phloem |
- • | Carries | water, minerals | food |
- • | Direction | upwards | up and down |
- • | Energy | not used (physical forces) | ATP used |
10. Excretion
Metabolic activities in the body produce harmful nitrogenous wastes, like urea and uric acid.
- • Excretion: removal of harmful metabolic wastes from the body
- • Nitrogenous wastes: urea, uric acid
- • Excretory system: a pair of kidneys, a pair of ureters, urinary bladder, urethra
- • Path of urine: kidney → ureter → urinary bladder → urethra → outside
- • Nephron: the basic filtration unit of the kidney
- • Bowman's capsule: cup-shaped end of the tube
- • Glomerulus: cluster of thin-walled capillaries
- • (1) Filtration: blood filtered in the glomerulus, collected by Bowman's capsule
- • (2) Selective reabsorption (in the tubule): glucose, amino acids, salts, water back into blood
- • Water reabsorbed depends on: how much excess water there is, how much dissolved waste is to be removed
- • Urinary bladder: muscular, under nervous control
- • Daily ≈ 180 L filtrate, only 1 to 2 L urine
- • Artificial kidney: removes nitrogenous wastes by dialysis
- • Semi-permeable tubes + dialysing fluid (same osmotic pressure, no wastes)
- • Wastes diffuse out; purified blood back; no reabsorption
- • Excretion in plants:
- • O₂: through stomata; excess water: transpiration
- • Stored in vacuoles; lost with falling leaves
- • Resins, gums: in old xylem; some into the soil
Summary
Very good! You learnt a lot today, so let us revise it once together. The processes that maintain the body are life processes: nutrition, respiration, transportation and excretion. Nutrition is autotrophic or heterotrophic. In photosynthesis six CO₂ and twelve H₂O give glucose, and the stomata exchange gases. In human beings, food is digested in the mouth, stomach and small intestine, and the villi absorb it. In respiration glucose breaks into pyruvate, and then three paths. Energy is stored in ATP. Blood flows by double circulation. In plants xylem carries water and phloem carries food. And the nephrons filter the blood to make urine. Draw today's diagrams once in your notebook yourself: the alimentary canal, the respiratory system, the heart, the nephron and the stomata, all with labels. Write the equations of photosynthesis and respiration, balanced. If anything was not clear, press the Ask button and ask me. Done, you worked very well today!
AskMedha · Medha Ma’am — CBSE Class 10 Science, Chapter 5. Written from the textbook, checked twice.
Questions parents and students ask
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