NCERT Science: Life Processes (Nutrition, Respiration, Transport, Excretion)

The one-line takeaway

Life processes are the basic functions that keep an organism alive: nutrition (obtaining and using food), respiration (releasing energy from food), transport (moving materials around the body) and excretion (removing wastes). Knowing how each works in plants and in humans, plus the key organs and a few definitions, covers the CAPF need.

Nutrition

• Nutrition is the process of taking in food and using it for energy, growth and repair.
• Autotrophic nutrition: making one's own food. Green plants are autotrophs; they perform photosynthesis, converting carbon dioxide and water into glucose and oxygen using sunlight captured by chlorophyll. It takes place mainly in the leaves; the tiny pores called stomata let gases in and out. Photosynthesis is the ultimate source of food and oxygen for almost all life.
• Heterotrophic nutrition: depending on others for food. It is holozoic (animals ingesting solid food), saprophytic (fungi and many bacteria feeding on dead matter), or parasitic (feeding on a living host).
• Human digestion: the alimentary canal runs from the mouth (saliva begins starch digestion) through the oesophagus to the stomach (gastric juice with hydrochloric acid and the enzyme pepsin), the small intestine (where bile from the liver and enzymes from the pancreas complete digestion and most absorption occurs through finger-like villi), and the large intestine (water absorption), ending at the anus.

Respiration

• Respiration is the breakdown of food (glucose) to release energy, stored as ATP. (Do not confuse it with breathing, which is only the exchange of gases.)
• Aerobic respiration uses oxygen, fully breaks glucose down into carbon dioxide and water, and releases a large amount of energy. This is the normal mode in most organisms.
• Anaerobic respiration occurs without oxygen and releases less energy: in yeast it produces ethanol and carbon dioxide (fermentation, the basis of bread and brewing); in human muscles during heavy exercise it produces lactic acid, which causes muscle cramps.
• In humans, gas exchange occurs in the lungs, in tiny air sacs called alveoli, where oxygen enters the blood and carbon dioxide leaves. The diaphragm and rib muscles drive breathing.

Transport (circulation)

• In humans, the heart is a four-chambered muscular pump (two atria, two ventricles). It drives double circulation: a pulmonary circuit (heart to lungs and back, to pick up oxygen) and a systemic circuit (heart to the body and back). Oxygenated and deoxygenated blood do not mix.
• Blood carries oxygen (on haemoglobin in red cells), carbon dioxide, nutrients, wastes and hormones; white cells fight infection; platelets clot blood. Arteries carry blood away from the heart (mostly oxygenated, at high pressure); veins carry it back (mostly deoxygenated); capillaries are the thin vessels where exchange happens. The lymphatic system carries lymph and supports immunity.
• In plants, transport uses two tissues: xylem carries water and dissolved minerals upward from the roots (driven by transpiration, the evaporation of water from leaves), and phloem carries the food made in the leaves to all parts (translocation), in both directions.

Excretion

• Excretion is the removal of metabolic wastes.
• In humans, the main excretory organ is the pair of kidneys, which filter the blood and produce urine; the functional unit of the kidney is the nephron. Urine passes through the ureters to the bladder and out via the urethra. The lungs (carbon dioxide), skin (sweat) and liver also help remove wastes.
• In plants, excretion is simpler: oxygen and carbon dioxide leave through stomata, excess water is lost by transpiration, and some wastes are stored in leaves, bark and as gums and resins.

Key terms to fix

• Photosynthesis: carbon dioxide plus water, using sunlight and chlorophyll, gives glucose and oxygen.
• Aerobic versus anaerobic respiration: with oxygen (more energy, gives carbon dioxide and water) versus without (less energy, gives lactic acid in muscle or ethanol in yeast).
• Double circulation: the four-chambered heart drives separate lung and body circuits.
• Xylem (water up) and phloem (food both ways); transpiration drives the upward pull.
• Nephron: the functional unit of the kidney.

CAPF angle

Human physiology underpins the demanding physical efficiency and medical standards of the forces. Understanding aerobic capacity, lactic-acid build-up and fatigue is directly relevant to endurance training and high-altitude operations (where oxygen is scarce, an ITBP concern on the Himalayan frontier). Knowledge of digestion, hydration and excretion matters for field nutrition and water discipline.

Authored practice