Life Processes
CBSE Class 10 · Science · Notes, formulas and practice questions
Life Processes is the Class 10 Science chapter covering nutrition, photosynthesis, respiration, transport of materials, and excretion in humans and plants.
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Every living organism needs energy to carry out its daily activities. The processes that together keep an organism alive are called life processes. These include nutrition, respiration, transportation, and excretion. The chapter describes each of these in detail, with special focus on the human body, while also covering the corresponding processes in plants. Understanding these processes helps explain how the body works and how different organs and systems are coordinated.
Nutrition is the first life process. Autotrophic organisms, such as green plants, make their own food through photosynthesis using carbon dioxide, water, and sunlight. Heterotrophic organisms obtain food from other sources. In humans, digestion breaks large food molecules into small soluble molecules that can be absorbed. The human digestive system consists of organs such as the mouth, stomach, small intestine, and large intestine, each with a specific role. The process also includes the role of enzymes in chemical digestion.
Respiration is the process of releasing energy from glucose. Aerobic respiration uses oxygen and releases a large amount of energy, whereas anaerobic respiration takes place without oxygen and produces less energy. In humans, the respiratory system brings in oxygen and removes carbon dioxide. The exchange of gases occurs in the alveoli of the lungs. Cellular respiration takes place inside mitochondria. The chapter also discusses the breakdown of glucose by different pathways, including the production of lactic acid in muscles during strenuous exercise.
Transportation carries vital substances to different parts of the body. In humans, blood, with its components like plasma, red blood cells, white blood cells, and platelets, transports oxygen, nutrients, and wastes. The heart pumps blood through arteries, veins, and capillaries. In plants, xylem transports water and minerals, while phloem transports food. Excretion removes metabolic wastes such as urea and carbon dioxide. The human excretory system includes kidneys, ureters, urinary bladder, and urethra. The nephron is the filtering unit of the kidney, and dialysis is an artificial replacement for kidney function.
Key terms
- Photosynthesis
- The process by which green plants manufacture glucose from carbon dioxide and water in the presence of sunlight and chlorophyll, releasing oxygen as a by product. The overall equation is 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. It supplies stored chemical energy for nearly all living organisms.
- Heterotrophic nutrition
- Nutrition in which an organism obtains organic food from other organisms. It includes holozoic nutrition (ingestion and digestion of food, as in humans), saprophytic nutrition (feeding on dead and decaying matter), and parasitic nutrition (feeding on a living host).
- Peristalsis
- The wave of rhythmic contractions and relaxations of the smooth muscles in the wall of the alimentary canal that pushes food forward from the oesophagus onwards. It is an involuntary action.
- Aerobic respiration
- The breakdown of glucose in the presence of oxygen to release energy, carbon dioxide, and water. It occurs in mitochondria and produces far more ATP than anaerobic respiration. The overall equation is C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy.
- Anaerobic respiration
- The breakdown of glucose without oxygen, yielding smaller amounts of energy. In our muscles it produces lactic acid, while in yeast it produces ethanol and carbon dioxide. The equation in yeast is C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + energy.
- Xylem
- Plant tissue consisting of tracheids, vessels, xylem parenchyma and xylem fibres. It transports water and dissolved minerals from roots to leaves, a movement that is generally unidirectional. The cohesive and adhesive properties of water help its ascent.
- Phloem
- Plant tissue composed of sieve tubes, companion cells, phloem parenchyma, and phloem fibres. It transports the food made in leaves to other parts of the plant such as roots and flowers, and the movement can be in both directions (translocation).
- Nephron
- The structural and functional unit of the kidney, numbering about a million per kidney. It consists of a Bowman’s capsule, glomerulus, proximal and distal tubules, and the loop of Henle. Its function is to filter blood and form urine through glomerular filtration, reabsorption and secretion.
- Dialysis
- A medical procedure that removes nitrogenous wastes such as urea from the blood when the kidneys fail. The patient’s blood is passed through a machine with a semipermeable membrane that allows wastes to diffuse out, and the cleaned blood is returned to the body.
Formula sheet
| What | Formula | Notes |
|---|---|---|
| Photosynthesis | 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ | Takes place in chloroplasts in the presence of sunlight and chlorophyll. Carbon dioxide and water are converted to glucose, and oxygen is released. |
| Aerobic respiration | C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy | Glucose is broken down completely in the presence of oxygen, in the mitochondria. It releases much more energy than the anaerobic route. |
| Anaerobic respiration in yeast | C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + energy | Glucose is broken down without oxygen, giving ethanol and carbon dioxide. In our muscle cells the anaerobic product is lactic acid instead. |
Practice questions with answers
1. What are the major life processes mentioned in the chapter?
The major life processes are nutrition (obtaining food), respiration (releasing energy from food), transportation (moving substances within the body), and excretion (removing metabolic wastes). These processes are essential for maintaining life.
2. Write the chemical equation for photosynthesis.
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. This shows that six molecules of carbon dioxide combine with six molecules of water in the presence of sunlight and chlorophyll to produce one molecule of glucose and six molecules of oxygen.
3. Why does the small intestine play a central role in digestion and absorption?
The small intestine receives bile from the liver and pancreatic juice from the pancreas, which digest fats, proteins and carbohydrates. Its inner surface has finger-like projections called villi, which greatly increase the surface area for absorption of digested food into the blood and lymph.
4. Distinguish between aerobic and anaerobic respiration.
Aerobic respiration occurs in the presence of oxygen and completely oxidises glucose into CO₂ and water, releasing a large amount of energy. Anaerobic respiration occurs without oxygen, partially breaks down glucose, releases much less energy, and produces lactic acid (in muscles) or ethanol and CO₂ (in yeast).
5. Why do our muscles cramp after strenuous exercise?
During intense activity, oxygen supply to muscles may become insufficient, so they switch to anaerobic respiration. This converts glucose into lactic acid instead of completely oxidising it. Accumulation of lactic acid along with muscle fatigue causes cramps.
6. Describe double circulation in the human heart.
Double circulation means blood passes through the heart twice in one complete circuit. In pulmonary circulation, deoxygenated blood is pumped from the right ventricle to the lungs for oxygenation and returns to the left atrium. In systemic circulation, oxygenated blood from the left ventricle is carried by aorta to all body parts and returns to the right atrium through veins.
7. What is the importance of valves in the heart?
Valves are flaps that prevent backflow of blood. The atrioventricular valves (mitral and tricuspid) guard the openings between the atria and ventricles, while the semilunar valves at the bases of the pulmonary artery and aorta prevent blood from flowing back from these arteries into the heart. This ensures one-way circulation.
8. Where does selective reabsorption occur in the nephron, and why is it important?
Selective reabsorption occurs mainly in the proximal convoluted tubule (and also in other parts of the tubule). During urine formation, useful substances such as glucose, amino acids and some water are reabsorbed from the filtrate back into the blood, while harmful nitrogenous wastes remain in the tubule, a process essential for maintaining homeostasis.
9. A patient has a pulse rate of 72 beats per minute. Calculate the number of heartbeats in one day.
Number of beats in one hour = 72 × 60 = 4320 beats. Number of beats in one day = 4320 × 24 = 103,680 beats. Therefore the heart beats 103,680 times in a day.
10. How do plants excrete metabolic wastes?
Plants have no specialised excretory organs, and they deal with wastes by several simple routes instead. Oxygen and carbon dioxide leave by diffusion through stomata and lenticels, excess water is lost by transpiration, and organic wastes such as resins, tannins and gums are stored in vacuoles, in old xylem, in the bark and in leaves that are later shed. Some waste is also released into the soil around the roots. Plants can manage without an excretory organ because they produce relatively little nitrogenous waste.
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