Life processes are the basic functions that keep an organism alive — nutrition, respiration, transport and excretion. CBSE Class 10 dedicates its first biology chapter to this. The concepts are tested through direct questions and diagrams worth four to six marks.
Core Concepts
Nutrition
Autotrophic (photosynthesis) or heterotrophic. In humans, food is ingested, digested, absorbed, assimilated and egested. The alimentary canal has specialised regions for each step.
The human digestive system in detail:
| Organ | Function | Key Enzyme/Secretion |
|---|---|---|
| Mouth | Ingestion, mechanical digestion | Salivary amylase (starch → maltose) |
| Oesophagus | Peristalsis (food movement) | Mucus only |
| Stomach | Protein digestion, acid kills bacteria | HCl, pepsin (protein → peptides) |
| Small intestine | Main digestion and absorption site | Bile (fat emulsification), pancreatic enzymes, intestinal enzymes |
| Large intestine | Water absorption | No enzymes, bacterial action |
| Rectum | Storage and egestion | - |
The small intestine is the hero of digestion. It receives bile from the liver (emulsifies fats into tiny droplets), pancreatic juice from the pancreas (contains trypsin for proteins, lipase for fats, amylase for starch), and its own intestinal juice. The inner wall has millions of villi — finger-like projections that increase the surface area for absorption.
Villi are the key to absorption efficiency. Each villus has a rich blood supply and a lymph vessel (lacteal). Amino acids and sugars enter the blood capillaries; fatty acids enter the lacteals. The huge surface area (about 250 square metres in total) ensures maximum absorption.
Respiration
Glucose is oxidised to release energy. Aerobic respiration uses oxygen, produces CO2 and water, and yields 38 ATP per glucose. Anaerobic respiration (in muscles under low oxygen) produces lactate and only 2 ATP.
This happens in three stages: glycolysis (cytoplasm, 2 ATP), Krebs cycle (mitochondrial matrix), and electron transport chain (inner mitochondrial membrane, 34 ATP). The total of 38 ATP is theoretical; actual yield is about 36.
This happens during intense exercise when oxygen supply cannot keep up. The lactic acid accumulates and causes muscle cramps and fatigue. After exercise, the lactic acid is oxidised in the liver — this is the “oxygen debt.”
Yeast ferments glucose to ethanol and CO2. This is the basis of bread making (CO2 makes dough rise) and alcohol production.
Transport
In humans, blood carries gases, nutrients and wastes through a closed circulatory system. In plants, xylem carries water and minerals upward, phloem carries sugars in both directions.
Human circulatory system: Double circulation means blood passes through the heart twice in one complete circuit. Pulmonary circulation (heart → lungs → heart) oxygenates blood. Systemic circulation (heart → body → heart) delivers oxygen to tissues.
The heart has four chambers: two atria (receiving chambers) and two ventricles (pumping chambers). The left ventricle has the thickest wall because it pumps blood to the entire body. The septum prevents mixing of oxygenated and deoxygenated blood — this separation is crucial for efficient oxygen delivery.
Plant transport: Xylem carries water upward (from roots to leaves) by transpiration pull. Phloem carries sugars from source (leaves) to sink (roots, fruits, growing tissues) by the pressure flow mechanism.
Excretion
Removal of metabolic wastes. In humans, kidneys filter blood to form urine. In plants, waste is stored in leaves that fall, or in resin and gum.
How the kidney works:
Blood enters the kidney through the renal artery at high pressure. In the glomerulus (a ball of capillaries inside Bowman’s capsule), small molecules (water, urea, glucose, salts) are filtered out. Large molecules (proteins, blood cells) stay in the blood.
As the filtrate passes through the renal tubule, useful substances are reabsorbed: all glucose, most water, and needed salts go back into the blood. This is an active process requiring energy.
The remaining liquid (urine) — containing urea, excess water, and excess salts — passes into the collecting duct, then the ureter, then the bladder, and is expelled through the urethra.
Filtration (glomerulus) → Reabsorption (tubule) → Secretion (tubule) → Urine
About 180 litres of filtrate is produced per day, but only 1.5 litres of urine is excreted. The rest is reabsorbed — showing how efficient the kidneys are.
Worked Examples
Muscles use more oxygen and produce more CO2. Chemoreceptors detect high CO2 and low pH, signalling the breathing centre to speed up rate and depth. The result is more O2 in and more CO2 out.
Plants have a slow metabolism and no organs that need rapid nutrient delivery. Root pressure and transpiration pull are enough for their transport needs.
The left ventricle pumps blood to the entire body through the systemic circuit — a much longer distance than the right ventricle’s pulmonary circuit (just to the lungs). Greater distance requires higher pressure, which requires a thicker muscular wall.
In kidney failure, urea and other wastes accumulate in the blood. Dialysis uses a semi-permeable membrane to filter wastes from the blood externally. Since the body continuously produces waste, dialysis must be repeated every 2-3 days until a transplant is available.
Common Mistakes
Writing that anaerobic respiration gives more ATP. Aerobic gives 19 times more.
Saying transport in plants requires a pump. It does not — physical forces drive it.
Confusing ingestion and digestion. Ingestion is taking food in; digestion is breaking it down.
Writing that oxygen is produced during respiration. Oxygen is consumed during respiration and produced during photosynthesis. Students often confuse the two.
Saying kidneys filter urea only. They filter everything small — glucose, amino acids, salts, water, urea. The useful stuff is then selectively reabsorbed. This distinction (filter everything, reabsorb what you need) is key.
Exam Weightage and Revision
Life Processes is the highest-weightage biology chapter in CBSE Class 10, carrying 6-8 marks. Questions include diagrams (digestive system, heart, nephron), differences (aerobic vs anaerobic, arteries vs veins), and process descriptions. NEET does not test this chapter directly but the concepts form the foundation for Class 11-12 physiology.
| Question Type | CBSE Frequency | Marks |
|---|---|---|
| Diagram: human digestive system | Most years | 3-5 |
| Difference: aerobic vs anaerobic respiration | Every year | 2-3 |
| Process: urine formation | Most years | 3 |
| Diagram: human heart with labels | Every 2 years | 3-5 |
| Short answer: role of villi | Most years | 2 |
For CBSE boards, practice drawing and labelling the digestive system, heart, and nephron. Diagram questions carry 3-5 marks and are the easiest to score if you have practised the labels. Always label at least 5-6 parts.
Practice Questions
Q1. What is the role of HCl in the stomach?
HCl serves three functions: (1) It creates an acidic environment (pH 1-2) which is optimal for pepsin to work. (2) It kills most bacteria that enter with food. (3) It denatures proteins, making them easier for pepsin to digest. Without HCl, pepsin would be inactive (pepsin is secreted as inactive pepsinogen and needs acid to become active).
Q2. Why do organisms need to remove waste from the body?
Metabolic wastes like urea, CO2, and excess salts are toxic if they accumulate. Urea in high concentrations damages cells. CO2 makes blood acidic (lowers pH), affecting enzyme function. Excess salts disrupt osmotic balance. Excretion removes these before they reach harmful levels.
Q3. Compare arteries and veins.
Arteries carry blood away from the heart (usually oxygenated, except pulmonary artery). They have thick, elastic walls to withstand high pressure. No valves (except at the heart). Veins carry blood towards the heart (usually deoxygenated, except pulmonary vein). They have thin walls, wider lumen, and valves to prevent backflow since blood pressure is low.
Q4. A plant is kept in a closed bell jar with KOH solution. What happens and why?
KOH absorbs CO2 from the air inside the jar. Without CO2, the plant cannot photosynthesise. It continues to respire, consuming O2 and producing CO2 (which is immediately absorbed by KOH). Eventually, O2 runs out and the plant dies. This experiment demonstrates that CO2 is essential for photosynthesis.
FAQs
Why is the small intestine so long?
The small intestine is about 6 metres long in humans because it is the main site of digestion and absorption. A long tube provides more surface area for enzymes to act and for nutrients to be absorbed. The villi and microvilli further increase this area.
What happens to food that is not digested?
Undigested food (mainly fibre/cellulose from plants) passes into the large intestine. Here, water is absorbed, and the remaining material is compacted into faeces. Bacteria in the large intestine also produce some vitamins (like vitamin K and B12) during this process.
Why do we feel tired after a heavy meal?
After eating, blood flow is redirected to the digestive organs to support digestion and absorption. This temporarily reduces blood flow to the brain and muscles, causing drowsiness. The parasympathetic nervous system (which promotes digestion) also suppresses alertness.
How do single-celled organisms manage life processes without specialised organs?
In organisms like Amoeba, the entire body surface serves for gas exchange and excretion (diffusion is sufficient for a small organism). Nutrition is by phagocytosis (engulfing food particles). No transport system is needed because diffusion is fast enough over the tiny distances involved.
Remember four verbs — eat, breathe, transport, waste. Each corresponds to one life process.
Life processes are the big-picture view. Every later chapter zooms into one of these four, so a strong base here pays off through the rest of biology.