Life Processes — 50 Q&A

Life processes are the functions performed by living organisms to maintain life — mainly nutrition, respiration, transport and excretion.

Autotrophic (organisms make their own food — e.g., plants via photosynthesis) and heterotrophic (depend on others for food — e.g., animals, fungi).

Photosynthesis is the process by which green plants make food in presence of sunlight, chlorophyll & CO₂.
Equation: 6CO₂ + 6H₂O —(light/chlorophyll)—> C₆H₁₂O₆ + 6O₂. Occurs in chloroplasts (mesophyll cells of leaves).

Chlorophyll is a green pigment that absorbs light (mainly blue and red wavelengths) to provide energy for photosynthesis. Green light is reflected, making plants appear green.

Stomata are pores on leaf surfaces controlled by guard cells. They allow CO₂ entry for photosynthesis and permit transpiration (water vapour loss) and gas exchange.

• Holozoic: ingestion & digestion (animals).
• Parasitic: lives on/inside host (tapeworm).
• Saprophytic: decomposers (fungi on dead matter).
• Symbiotic: mutual benefit (lichens).

• Mouth: ingestion, chewing, salivary amylase starts starch digestion.
• Oesophagus: food transport by peristalsis.
• Stomach: protein digestion (pepsin), acidic environment.
• Small intestine: major digestion & absorption (duodenum + ileum).
• Large intestine: water absorption, formation of faeces.
• Liver/Pancreas: accessory glands — bile/emulsification; pancreatic enzymes, bicarbonate.

Saliva moistens food, helps form a bolus, and contains salivary amylase (ptyalin) which begins starch digestion to maltose.

Peristalsis is wave-like muscular contraction of the alimentary canal that propels food along (e.g., from oesophagus to stomach and through intestines).

Absorption occurs mainly in the small intestine — villi and microvilli increase surface area, allowing absorption of digested nutrients into blood and lymph (fat absorption via lacteals).

Mechanical: chewing, churning in stomach. Chemical: enzymatic breakdown (salivary amylase, pepsin, pancreatic enzymes, intestinal enzymes).

Bile (from liver) emulsifies fats — breaking them into small droplets — increasing surface area for lipase action; it does not contain digestive enzymes but aids fat digestion and absorption.

Light intensity, CO₂ concentration, temperature, and availability of water — the limiting factor among these controls the rate.

Respiration is the process of breaking down food to release energy (ATP). It can be aerobic (with O₂ — more ATP) or anaerobic (without O₂ — less ATP and by-products like lactic acid/ethanol).

Glucose + O₂ → CO₂ + H₂O + energy (ATP). Biochemical equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP. Occurs in mitochondria (cellular respiration).

In muscles (during strenuous exercise): glucose → lactic acid + small ATP. In yeast (fermentation): glucose → ethanol + CO₂ + small ATP.

Xylem transports water and minerals upwards (root → shoot) mainly by transpiration pull and cohesion-tension; Phloem transports solutes (sugars) bidirectionally from source to sink by translocation (pressure flow hypothesis).

Transpiration is loss of water vapour from aerial parts (mainly leaves). Rate increases with light, temperature, wind, and low humidity; decreases when stomata close.

System includes heart (pump), blood vessels (arteries carry blood away, veins bring blood back, capillaries enable exchange), and blood (transport oxygen, nutrients, wastes, hormones).

Double circulation: pulmonary (heart → lungs → heart) for oxygenation, and systemic (heart → body → heart) to supply oxygenated blood. Heart has four chambers: two atria (receive) and two ventricles (pump).

Valves prevent backflow of blood. Examples: atrioventricular valves — tricuspid (right) and mitral/bicuspid (left); semilunar valves — pulmonary and aortic valves.

• RBCs carry O₂ (hemoglobin).
• WBCs for immunity.
• Platelets help blood clotting.
• Plasma transports nutrients, hormones, wastes.

Exchange occurs by diffusion through thin, single-cell-thick capillary walls — oxygen and nutrients move out; CO₂ and metabolic wastes move in.

Lymph is a fluid collected from tissues by lymphatic vessels; it returns excess tissue fluid to blood and helps in immune responses (lymph nodes filter pathogens).

Excretion is removal of metabolic wastes (e.g., CO₂, urea) from the body to maintain internal balance (homeostasis).

Nephron includes Bowman's capsule (glomerulus), proximal tubule, loop of Henle, distal tubule and collecting duct. Urine formation: ultrafiltration at glomerulus, reabsorption of useful substances, and secretion of excess ions — final urine excreted.

Dialysis is an artificial method to remove waste products and excess water from the blood when kidneys fail — using a dialysis machine that filters blood externally.

Liver deaminates excess amino acids producing ammonia which is converted to urea (less toxic) — urea is transported to kidneys for excretion. The liver also detoxifies many harmful substances.

Urea, uric acid, creatinine, excess salts (Na⁺, K⁺), excess water, and metabolic by-products are excreted in urine.

Human circulation is closed (blood circulates within vessels) and double (pulmonary & systemic circuits), pumped by the heart.

Majority of O₂ is carried by RBCs bound to hemoglobin as oxyhemoglobin (Hb–O₂). In tissues, O₂ is released for respiration (aided by lower pO₂ and higher CO₂).

CO₂ is transported dissolved in plasma, as bicarbonate ions (major route), and as carbaminohaemoglobin (bound to hemoglobin). Conversion to bicarbonate occurs in RBCs (chloride shift maintains ionic balance).

Inspiration: diaphragm contracts & moves down, rib muscles lift ribs → thoracic cavity volume increases → pressure falls → air flows in. Expiration: diaphragm relaxes, volume decreases, pressure rises → air flows out.

Alveoli have very thin walls (one cell thick), large surface area, rich blood supply (capillaries), and surfactant to reduce surface tension — all aiding efficient gas exchange.

Diffusion is slow and insufficient over large distances. Transport systems (blood, xylem/phloem) rapidly move gases, nutrients, hormones and wastes to maintain homeostasis.

At source (leaf), sugars are loaded into phloem, water follows osmotically raising pressure; at sink (root/fruit), sugars are removed, water exits, creating a pressure gradient that moves sap from source to sink.

Haemodialysis (blood filtered through a dialyser) and peritoneal dialysis (uses peritoneal membrane in abdomen as the filter).

Normal urine is mostly water with urea, uric acid, creatinine, salts; pale yellow color (due to urochrome); pH can vary (typically 4.5–8); abnormalities indicate disease/dehydration.

Skin (sweat — salts, small amount of urea), lungs (excrete CO₂ and water vapour), and liver (detoxification, bile excretion) also contribute to excretion.

Plants excrete wastes by storing in leaves (later shed), exudation (resins, gums), guttation, volatilization, or storage in vacuoles; xylem may transport some waste to leaves.

Kidneys adjust reabsorption of water and ions in response to hormones (ADH, aldosterone) to maintain blood osmolarity and blood pressure, producing concentrated or dilute urine as needed.

Exercise increases breathing rate and heart rate to deliver more O₂ and remove CO₂. If O₂ demand exceeds supply, muscles respire anaerobically producing lactic acid → cramps/fatigue.

A balanced diet provides carbohydrates, proteins, fats, vitamins, minerals and water for energy, growth, repair and regulation. Deficiencies cause diseases (e.g., scurvy — vitamin C; beriberi — vitamin B₁ deficiency).

Breathing = physical process of inhalation & exhalation. Respiration = biochemical process of releasing energy from food.

Ingestion (mouth) → mechanical & chemical digestion (stomach, small intestine) → absorption (small intestine) → transport (blood) → assimilation/utilisation → egestion (large intestine & rectum).

Yes — plants respire continuously (day & night) to release energy for cellular activities. Photosynthesis occurs in light, but respiration occurs both in light and darkness in mitochondria.

Decomposers break down dead organic matter, releasing nutrients back into the soil (nitrogen, carbon) which are reused by plants — crucial for nutrient cycling.

Vitamin D is synthesized in skin under sunlight (UV) and is essential for calcium absorption and bone health.

Transport across membranes: diffusion (down concentration gradient), osmosis (water diffusion), facilitated diffusion (carrier proteins), and active transport (energy-dependent movement against gradient).

• Nutrition: autotrophic (photosynthesis) & heterotrophic.
• Respiration: aerobic (high ATP) vs anaerobic (low ATP).
• Transport: xylem/phloem in plants; blood/lymph in animals.
• Excretion: kidneys (nephrons), lungs, skin, liver roles.
• Homeostasis maintained via coordinated transport & excretion.