What this chapter is about
Life processes are the essential functions that all living organisms perform to stay alive. These include nutrition, respiration, transportation, and excretion. Understanding these processes helps us see how organisms obtain energy, use it for growth and repair, move substances within their bodies, and remove waste products.
A Class 10 student studies this chapter to understand how living beings, from single-celled amoeba to complex humans, carry out these vital activities. The chapter connects biology to chemistry by showing how food molecules are broken down, how oxygen reacts with glucose, and how waste products form. Students learn the structures involved—digestive organs, lungs, heart, kidneys—and how each structure suits its function.
After studying this chapter, you should be able to explain how plants and animals obtain nutrients, describe the breathing and cellular respiration processes, trace the path of blood through the heart, and explain how waste removal occurs in humans and plants.
Key ideas
- Nutrition is the process of taking in food and converting it into energy and body-building materials. Autotrophs (like green plants) make their own food through photosynthesis; heterotrophs (like animals) depend on others for food.
- Photosynthesis occurs in chloroplasts where carbon dioxide and water, using sunlight energy, produce glucose and oxygen: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.
- Digestion in humans involves mechanical breakdown (chewing) and chemical breakdown by enzymes. Saliva contains amylase; stomach secretes pepsin and hydrochloric acid; small intestine completes digestion with bile, pancreatic juice, and intestinal enzymes.
- Respiration has two meanings: breathing (exchange of gases) and cellular respiration (breakdown of glucose in cells to release energy). Aerobic respiration uses oxygen; anaerobic respiration occurs without oxygen.
- Transportation in humans is done by blood through arteries, veins, and capillaries. The heart acts as a double pump with four chambers. In plants, xylem carries water upward; phloem transports food.
- Excretion removes metabolic waste. In humans, kidneys filter blood to form urine. In plants, waste products are stored in leaves that fall off, or in vacuoles, or released as oxygen during photosynthesis.
- Double circulation means blood passes through the heart twice in one complete cycle—once for lungs (pulmonary) and once for the body (systemic).
Formulas and facts to remember
- Photosynthesis equation: 6CO₂ + 6H₂O + sunlight energy → C₆H₁₂O₆ + 6O₂ (carbon dioxide and water form glucose and oxygen in presence of chlorophyll).
- Aerobic respiration equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (glucose breaks down with oxygen to release energy, stored as ATP).
- Anaerobic respiration in yeast: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + energy (glucose forms ethanol and carbon dioxide).
- Anaerobic respiration in muscles: C₆H₁₂O₆ → 2C₃H₆O₃ + energy (glucose forms lactic acid, causing muscle cramps).
- Blood flow path: Right atrium → Right ventricle → Lungs → Left atrium → Left ventricle → Body organs → Right atrium.
- Nephron is the functional unit of the kidney; each human kidney contains about one million nephrons.
- Stomata are tiny pores on leaf surfaces that allow gas exchange and transpiration; guard cells control their opening and closing.
- Villi are finger-like projections in the small intestine that increase surface area for absorption of digested food.
Worked examples
Example 1: Calculating oxygen released in photosynthesis
Problem: A plant produces 90 grams of glucose during photosynthesis. How much oxygen is released?
Solution: From the balanced equation: C₆H₁₂O₆ + 6O₂ Molecular mass of glucose (C₆H₁₂O₆) = 6(12) + 12(1) + 6(16) = 72 + 12 + 96 = 180 grams Molecular mass of 6O₂ = 6 × 32 = 192 grams
For every 180 g of glucose produced, 192 g of oxygen is released. For 90 g of glucose: oxygen released = (192/180) × 90 = 96 grams
Answer: 96 grams of oxygen is released.
Example 2: Understanding blood circulation
Problem: Deoxygenated blood enters the heart from the body. Trace its path until it returns to the body tissues as oxygenated blood.
Solution: Step 1: Deoxygenated blood from body enters the right atrium through vena cava. Step 2: Right atrium contracts, pushing blood into right ventricle. Step 3: Right ventricle pumps blood to lungs through pulmonary artery. Step 4: In lungs, blood releases CO₂ and picks up O₂, becoming oxygenated. Step 5: Oxygenated blood returns to left atrium through pulmonary vein. Step 6: Left atrium contracts, pushing blood into left ventricle. Step 7: Left ventricle (thickest wall, most muscular) pumps blood to body through aorta.
Answer: The blood completes two circuits—pulmonary and systemic—which is called double circulation.
Example 3: Calculating energy from anaerobic respiration
Problem: During intense exercise, Meera's muscle cells respire anaerobically. If 360 grams of glucose undergoes anaerobic respiration, how much lactic acid forms?
Solution: Equation: C₆H₁₂O₆ → 2C₃H₆O₃ Molecular mass of glucose = 180 grams Molecular mass of 2 lactic acid molecules = 2 × 90 = 180 grams
180 g glucose produces 180 g lactic acid. 360 g glucose produces 360 g lactic acid.
Answer: 360 grams of lactic acid is produced, which causes muscle fatigue and cramps.
Common mistakes
- Confusing breathing with respiration → Breathing is physical gas exchange; respiration is chemical breakdown of glucose in cells.
- Thinking arteries always carry oxygenated blood → Pulmonary artery carries deoxygenated blood from heart to lungs.
- Believing photosynthesis occurs only in leaves → It occurs in all green parts containing chlorophyll, including green stems.
- Assuming plants respire only at night → Plants respire continuously day and night; photosynthesis occurs only in light.
- Mixing up xylem and phloem functions → Xylem transports water upward; phloem transports food in both directions.
Quick revision
- Autotrophs make food; heterotrophs consume food made by others.
- Photosynthesis needs CO₂, water, chlorophyll, and sunlight to produce glucose and oxygen.
- Aerobic respiration releases more energy than anaerobic respiration.
- Human heart has four chambers; double circulation keeps oxygenated and deoxygenated blood separate.
- Kidneys filter blood; nephrons are their functional units; urine contains urea, excess water, and salts.
- In plants, xylem moves water up by transpiration pull; phloem moves food by translocation.