Life Processes — RBSE Class 10 (Science)
Look at a moving bus and a sleeping cat. Both are still on the inside? No — the cat's heart is beating, its cells are burning glucose, its kidneys are filtering blood, even in deep sleep. Those invisible, ceaseless maintenance jobs are life processes: the work an organism must do just to stay alive. This chapter is the engineering manual of the living body.
1. What is a "life process"?
The basic functions an organism performs to maintain life are life processes. The four you study in depth:
- Nutrition — taking in and using food for energy and growth.
- Respiration — breaking down food to release energy.
- Transportation — carrying materials around the body.
- Excretion — removing harmful wastes.
Even when an organism appears motionless, molecular movements (repair, energy supply) continue — which is why we say life needs a constant energy input.
2. Nutrition
Autotrophic nutrition — making your own food
Green plants and some bacteria are autotrophs: they make food by photosynthesis.
Three raw materials — carbon dioxide (through stomata), water (from soil via roots), and sunlight captured by chlorophyll. Events: absorption of light → conversion to chemical energy + splitting of water into H and O → reduction of CO₂ to carbohydrate. Stomata open and close by the swelling/shrinking of guard cells.
Heterotrophic nutrition — eating others
Heterotrophs depend on others for food:
- Saprophytic (fungi, bread mould) — feed on dead/decaying matter by external digestion.
- Parasitic (cuscuta, ticks, leeches) — feed on a living host.
- Holozoic (Amoeba, humans) — take in whole food and digest it inside the body.
Amoeba engulfs food with pseudopodia into a food vacuole where it is digested — a one-cell model of holozoic nutrition.
Nutrition in human beings — the alimentary canal
Food travels: mouth → oesophagus → stomach → small intestine → large intestine → anus.
- Mouth: teeth chew; saliva's salivary amylase (ptyalin) starts digesting starch.
- Stomach: gastric glands release HCl (kills germs, makes the medium acidic), pepsin (digests protein) and mucus (protects the stomach lining).
- Small intestine: the main site of digestion and absorption. Bile (from liver) emulsifies fats; pancreatic juice has trypsin (protein) and lipase (fat); intestinal juice completes digestion. Finger-like villi hugely increase surface area for absorption into blood.
- Large intestine: absorbs water; the rest is egested.
3. Respiration — releasing the energy in food
Glucose is broken down to release energy stored as ATP (the cell's energy currency). Glucose first splits into pyruvate in the cytoplasm; what happens next depends on oxygen:
| Pathway | Products | Energy | |
|---|---|---|---|
| Aerobic (in mitochondria, with O₂) | pyruvate → | CO₂ + H₂O | most |
| Anaerobic in yeast (no O₂) | pyruvate → | ethanol + CO₂ | less |
| Anaerobic in our muscles (lack of O₂) | pyruvate → | lactic acid | least |
The build-up of lactic acid during hard exercise causes muscle cramps — relieved by rest and a hot bath that improves blood flow.
Breathing in humans: air enters through nostrils → trachea → bronchi → lungs → alveoli (balloon-like sacs with a huge surface area and rich blood supply where gas exchange occurs). The diaphragm and rib muscles change the chest volume to move air in and out. Haemoglobin in red blood cells carries oxygen.
Respiration is not the same as breathing. Breathing is the physical exchange of air; respiration is the chemical breakdown of glucose in cells.
4. Transportation
In human beings — the circulatory system
The heart has four chambers — two atria (upper) and two ventricles (lower). Why four? To keep oxygenated and deoxygenated blood from mixing, so the body always gets fully oxygen-rich blood. The path:
Body → right atrium → right ventricle → lungs (pick up O₂) → left atrium → left ventricle → body.
Because blood passes through the heart twice in one full circuit, this is double circulation. Valves prevent backflow. The ventricles have thicker walls because they pump blood out under pressure; the left ventricle is thickest as it pumps to the whole body.
Blood vessels:
- Arteries — carry blood away from the heart, thick elastic walls, no valves, high pressure.
- Veins — carry blood to the heart, thinner walls, valves to stop backflow.
- Capillaries — one-cell-thick walls where exchange of materials with tissues happens.
Blood = plasma + RBCs (carry O₂) + WBCs (fight infection) + platelets (clotting). Lymph is a related fluid that drains tissue spaces and helps absorb fats.
In plants
- Xylem carries water and minerals upward from roots to leaves. The pull is created by transpiration (evaporation of water from leaves) — the transpiration pull.
- Phloem carries food (sucrose) made in leaves to all parts — a process called translocation, which uses energy (ATP).
5. Excretion — getting rid of waste
In human beings
The excretory system = two kidneys, two ureters, a urinary bladder and the urethra. The kidney's filtering unit is the nephron:
- Blood is filtered under pressure in the glomerulus (a tuft of capillaries) into Bowman's capsule.
- As the filtrate flows down the tubule, useful substances — glucose, amino acids, salts and most water — are reabsorbed into the blood.
- The remaining liquid is urine, collected and sent to the bladder.
When kidneys fail, dialysis (an artificial kidney) cleans the blood.
In plants
Plants have no special excretory organs. They lose O₂/CO₂ through stomata, store waste as gums/resins (in old xylem) or in leaves that fall off, and release some waste into the soil.
6. Closing thought
Strip away the diagrams and this chapter is one idea repeated four times: a living body is a flow system. Food flows in and is broken down (nutrition, respiration); materials flow around (transportation); waste flows out (excretion). Each system has the same design logic — maximise surface area (villi, alveoli, capillaries, root hairs) and keep the right things separated (four-chambered heart, xylem vs phloem).
For the RBSE board this is a diagram-heavy, high-yield chapter. Master the labelled diagrams of the human digestive system, the heart, the nephron and the alveoli — they alone can carry the long-answer marks.
