Life Processes
The basic functions performed by living organisms to maintain their life are called life processes. These include nutrition, respiration, transportation and excretion. Movement of molecules and structures (visible or molecular level) is a sign of life.
Nutrition
The process of taking in food and using it for energy, growth and repair is nutrition. Two modes:
- Autotrophic nutrition — organisms make their own food from simple inorganic materials (CO2, water) using sunlight. E.g. green plants, some bacteria.
- Heterotrophic nutrition — organisms depend on other organisms for food. Types: saprophytic (fungi, on dead matter), parasitic (cuscuta, ticks), holozoic (animals, ingest whole food).
Photosynthesis
The process by which green plants make food (glucose) using CO2 and water in the presence of sunlight and chlorophyll.
6CO2 + 6H2O —(sunlight, chlorophyll)→ C6H12O6 + 6O2
Steps: (1) absorption of light energy by chlorophyll, (2) conversion of light energy to chemical energy and splitting of water into hydrogen and oxygen, (3) reduction of CO2 to carbohydrate. Gaseous exchange occurs through stomata (guarded by guard cells). Raw materials: CO2 (from air via stomata), water (from soil via roots).
Human Digestive System (Nutrition in Humans)
The alimentary canal is a long tube from mouth to anus. Path of food:
- Mouth — teeth chew food; salivary glands secrete saliva containing salivary amylase (ptyalin) which digests starch into sugar.
- Oesophagus (food pipe) — moves food by peristaltic movements.
- Stomach — gastric glands release HCl (kills germs, provides acidic medium), pepsin (digests proteins), and mucus (protects stomach lining).
- Small intestine — site of complete digestion. Receives bile from liver (emulsifies fats, makes medium alkaline) and pancreatic juice (trypsin for proteins, lipase for fats, amylase for carbohydrates). Intestinal juice completes digestion. Absorption of digested food occurs through finger-like projections called villi (increase surface area, rich blood supply).
- Large intestine — absorbs water; undigested waste is removed through the anus (egestion).
Respiration
The process of breaking down food (glucose) to release energy in the form of ATP. Types:
Aerobic (in presence of O2, in mitochondria):
C6H12O6 → 2 pyruvate (in cytoplasm), then → 6CO2 + 6H2O + lots of energy
Anaerobic (absence of O2, in yeast):
C6H12O6 → 2C2H5OH (ethanol) + 2CO2 + less energy
In our muscles (lack of O2 during exercise):
Glucose → Lactic acid + less energy (causes cramps)
Aerobic respiration releases much more energy than anaerobic respiration.
Human Respiratory System
Air passes through nostrils → nasal cavity → pharynx → larynx → trachea → bronchi → bronchioles → alveoli. Rings of cartilage keep the trachea from collapsing. Alveoli are balloon-like structures where gaseous exchange occurs; they have thin walls and an extensive network of blood capillaries, giving a large surface area. Respiratory pigment haemoglobin (in red blood cells) carries oxygen. During breathing in, the diaphragm flattens and ribs lift (chest cavity expands).
Transportation
In Humans — Heart
The heart is a muscular organ with four chambers: two upper atria and two lower ventricles. It prevents mixing of oxygenated and deoxygenated blood. Right side handles deoxygenated blood, left side handles oxygenated blood. Ventricles have thicker walls (pump blood out). Valves prevent backflow of blood.
Double circulation: Blood passes through the heart twice in one complete cycle — pulmonary circulation (heart → lungs → heart) and systemic circulation (heart → body → heart). This ensures efficient oxygen supply for warm-blooded animals.
Blood Vessels
| Arteries | Veins |
|---|---|
| Carry blood away from the heart | Carry blood towards the heart |
| Carry oxygenated blood (except pulmonary artery) | Carry deoxygenated blood (except pulmonary vein) |
| Have thick, elastic muscular walls | Have thin walls |
| Blood flows under high pressure | Blood flows under low pressure |
| Valves absent | Valves present (prevent backflow) |
| Deep-seated | Superficial |
Capillaries are the smallest vessels (one-cell-thick walls) where exchange of materials between blood and cells occurs. Platelets help in clotting.
Lymph
Lymph is a colourless fluid formed from plasma that escapes capillaries; it carries digested and absorbed fats from the intestine and drains excess fluid back into blood. Flows in one direction.
Transport in Plants
- Xylem — conducts water and minerals from roots to leaves. Transport is upward; driven by transpiration pull (loss of water vapour from leaves creates suction). No energy needed.
- Phloem — translocation of food (sucrose) from leaves to other parts, in all directions. Requires energy (ATP); water enters increasing pressure that moves material.
- Transpiration — loss of water vapour through stomata; helps in absorption/upward movement of water and regulates temperature.
Excretion
The biological process of removing harmful metabolic wastes (like urea) from the body.
Human Excretory System
Consists of two kidneys, two ureters, a urinary bladder and a urethra. The basic filtration unit of the kidney is the nephron. Each nephron has a cluster of thin-walled capillaries called the glomerulus (inside Bowman's capsule) where blood is filtered. Useful substances (glucose, amino acids, salts, water) are reabsorbed as the filtrate flows through the tubule. The remaining fluid is urine, which passes to the bladder.
Dialysis
When kidneys fail, an artificial kidney (haemodialysis) is used to remove nitrogenous waste from the blood by passing it through a dialysing fluid separated by a semi-permeable membrane. Unlike the kidney, there is no reabsorption.
Excretion in Plants
Plants remove wastes by: releasing O2/CO2 through stomata, losing water by transpiration, storing wastes in leaves/bark that fall off, storing resins and gums in old xylem, and releasing some waste into the soil.
Exam tips: Balance the photosynthesis and respiration equations. Remember pulmonary artery/vein are the exceptions in the arteries vs veins table. Nephron = functional unit of kidney. Bile does NOT contain enzymes — it only emulsifies fats. Anaerobic respiration in muscles → lactic acid; in yeast → ethanol + CO2.
Note on rationalisation: No major sub-topic of this chapter was deleted in the latest NCERT rationalisation; content largely retained. Study all sections above.