# INTRODUCTION :-
-> Life processes are the fundamental biological activities that are essential for the survival, growth, and reproduction of all living organisms.
-> All the activities that help an organism stay alive and keep its body working properly are called life processes.
-> These processes need energy because they prevent damage and keep the body functioning. This energy comes from food, so the body needs a process called nutrition to take in food from outside and use it inside.
-> The sources of food and energy in the environment can be very different. So, the body breaks down this food and converts it into a common form of energy that cells can use. This happens through many chemical reactions inside the body, especially oxidation-reduction reactions.
-> Many organisms use oxygen from the environment for this process. Taking in oxygen and using it to break down food to release energy is called respiration.
-> In single-celled organisms, there are no special organs for eating, breathing, or removing waste. This is because their entire surface is in direct contact with the environment, so everything happens through that surface.
-> But in multicellular organisms (like humans), different body parts do different jobs. Food and oxygen enter the body at specific places, but every cell needs them. So, the body needs a transport system (like blood circulation) to carry these substances everywhere.
-> When food is broken down using oxygen, it produces waste substances. These wastes can be harmful if they stay in the body, so they must be removed. The process of removing waste from the body is called excretion.
# TYPES :-
1) NUTRITION:
-> Nutrition is the process by which an organism obtains energy and raw materials from its environment for growth, repair, and maintenance.
-> The mode of nutrition varies greatly across the living world.
(A) AUTOTROPHIC NUTRITION -
->Autotrophs ('self-feeders') synthesise their own organic food from simple inorganic substances. This is the foundation of all food chains, as autotrophs are the primary producers.
- Sub-types:
• Photosynthesis (Photoautotrophs): Use light energy to convert CO2
and H2O into glucose.
Examples: Green plants, algae, cyanobacteria.
• Chemosynthesis (Chemoautotrophs): Use energy from chemical reactions (oxidation of inorganic compounds) to fix carbon.
Examples: Nitrifying bacteria (Nitrosomonas, Nitrobacter), sulphur bacteria.
(B) HETEROTROPHIC NUTRITION -
-> Heterotrophs ('other-feeders') cannot synthesise their own food and depend on other organisms for organic nutrients.
-> This category includes animals, fungi, and most bacteria.
- Sub-types:
• Holozoic- Ingestion of solid food, internal digestion, absorption, assimilation.
Ex: Humans, Amoeba, most animals.
• Saprotrophic- Secretes digestive enzymes onto dead organic matter; absorbs the products.
Ex: Mushrooms, Rhizopus (bread mould).
• Parasitic- Lives in/on a host organism, draws nutrition at the host's expense.
Ex: Tapeworm, Plasmodium, Cuscuta.
• Symbiotic- Both organisms benefit from the nutritional relationship.
Ex: Lichens (algae + fungi), legume–Rhizobium.
# PHOTOSYNTHESIS — The Master Anabolic Reaction
-> Photosynthesis is the biochemical process by which chlorophyll-containing organisms use light energy to convert carbon dioxide and water into glucose and oxygen.
-> It is the primary source of oxygen in Earth's atmosphere and the entry point of energy into virtually all food webs.
* Overall Equation:-
6CO2 + 6H2O → (light energy, chlorophyll) → C6H12O6 + 6O2 Carbon dioxide.+Water → Glucose + Oxygen.
-> Site of Photosynthesis: The Chloroplast
• Outer & inner membrane: Envelope enclosing the chloroplast.
• Thylakoids: Flattened membrane sacs stacked into grana; site of the light dependent reactions.
• Stroma: Fluid-filled matrix surrounding the thylakoids; site of the light-independent reactions (Calvin cycle).
• Pigments: Chlorophyll a (primary), Chlorophyll b, carotenoids (accessory) — absorb light at different .wavelengths.
Stage 1 — Light-Dependent Reactions (Thylakoid Membrane)
• Chlorophyll absorbs light (mainly red ~680 nm and blue ~450 nm).
• Water molecules are split by photolysis: 2H2O → 4H+ + 4e– + O2 (oxygen released as byproduct).
• Excited electrons pass through the electron transport chain (ETC).
• ATP is generated via photophosphorylation (chemiosmosis driven by proton gradient).
• NADP+ is reduced to NADPH — the key reducing agent for the next stage.
Stage 2 — Light-Independent Reactions / Calvin Cycle (Stroma)
• CO2 is fixed by RuBisCO onto RuBP (ribulose-1,5-bisphosphate) — the carbon fixation step.
• The 3-carbon product (3-phosphoglycerate, 3-PGA) is reduced using ATP and NADPH.
• Glyceraldehyde-3-phosphate (G3P) is produced — the building block for the glucose and other organic molecules.
• RuBP is regenerated to continue the cycle (3 turns of the cycle fix 3 CO2 to produce 1 G3P net).
* Human Digestion (Holozoic Nutrition)
-> Digestion is the breakdown of complex insoluble food molecules into small, soluble molecules that can be absorbed into the bloodstream and used by cells.
->It involves both mechanical (physical) and chemical digestion.
| Organ | Mechanical Action | Enzymes/Secretions | Products |
| Mouth | Chewing (mastication), tongue mixing | Salivary amylase (ptyalin) — digests starch | Maltose, smaller polysaccharides |
| Oesophagus | Peristalsis moves bolus to stomach | No enzymes; mucus secreted | Bolus transported |
| Stomach | Churning, mixing (chyme formation) | Pepsin (from pepsinogen), HCl (pH ~2), gastric lipase, mucus | Polypeptides from proteins |
| Small Intestine (Duodenum) | Segmentation contractions | Pancreatic juice: trypsin, chymotrypsin, pancreatic amylase, lipase. Bile (from liver): emulsifies fats | Peptides, fatty acids, glycerol, maltose |
| Small Intestine (Ileum) | Peristalsis; villi increase surface area | Intestinal juice (succus entericus): maltase, lactase, sucrase, peptidases, enterokinase | Glucose, amino acids, fatty acids, glycerol |
| Large Intestine | Absorption of water, peristalsis | Gut bacteria; no major digestive enzymes | Water/electrolytes absorbed; faeces formed |
* Absorption:
-> Absorption occurs primarily in the small intestine. The inner surface is highly folded into villi and microvilli (brush border), massively increasing absorptive surface area. Glucose and amino acids are absorbed by inactive transport into capillaries; fatty acids and glycerol are reassembled into triglycerides and enter lacteals (lymph capillaries) as chylomicrons.
2) RESPIRATION:
-> Respiration is the metabolic process by which cells break down organic molecules (primarily glucose)to release energy in the form of ATP. Unlike breathing (ventilation), cellular respiration occurs in every living cell.
(A) AEROBIC RESPIRATION:-
-> Aerobic respiration requires oxygen and occurs in both the cytoplasm (glycolysis) and (Krebs cycle and electron transport chain), producing a high yield of about 30–32 ATP per glucose molecule, with carbon dioxide and water as end products .
| Pathway | Organism | Pyruvate → Product | Significance |
| Lactic acid fermentation | Animal muscle cells, Lactobacillus | Pyruvate + NADH $\rightarrow$ Lactate + NAD+ | Muscle fatigue; yogurt/cheese production |
| Alcoholic fermentation | Yeast, some plant cells | Pyruvate $\rightarrow$ Acetaldehyde + CO2 $\rightarrow$ Ethanol + NAD+ | Baking (CO2 leavening), brewing, biofuels |
# Stages of Aerobic Respiration:-
- Stage 1 — Glycolysis (Cytoplasm)
• Glycolysis ('sugar splitting') is the universal first stage of respiration occurring in the cytoplasm. It does not require oxygen and is the only pathway available to anaerobes.
• 1 glucose (6C) is phosphorylated and split into 2 molecules of pyruvate (3C).
• Net gain: 2 ATP and 2 NADH.
• Key enzymes: hexokinase, phosphofructokinase (the key regulatory enzyme), pyruvate kinase.
• Products: 2 pyruvate, 2 ATP (net), 2 NADH.
- Stage 2 — Pyruvate Oxidation / Link Reaction (Mitochondrial Matrix)
• Each pyruvate (3C) is decarboxylated and oxidised to Acetyl-CoA (2C) + CO2.
• NAD+ is reduced to NADH.
• Catalysed by the pyruvate dehydrogenase complex.
• Produces (per glucose): 2 Acetyl-CoA + 2 CO2 + 2 NADH.
- Stage 3 — Krebs Cycle / Citric Acid Cycle (Mitochondrial Matrix)
• The Krebs cycle is a series of 8 enzymatic reactions that completely oxidise Acetyl-CoA, transferring the extracted energy to electron carriers.
• Acetyl-CoA (2C) condenses with oxaloacetate (4C) to form citrate (6C).Through a series of reactions, 2 carbons are released as CO2 and oxaloacetate is regenerated.
• Per turn: 3 NADH, 1 FADH2, 1 GTP/ATP, 2 CO2
• Per glucose (2 turns): 6 NADH, 2 FADH2, 2 ATP, 4 CO2.
- Stage 4 — Oxidative Phosphorylation / Electron Transport Chain (Inner
Mitochondrial Membrane)
• NADH and FADH2 donate electrons to protein complexes (I, II, III, IV) in the inner mitochondrial membrane.
• Electrons pass down an energy gradient, ultimately reducing O2 to H2O (Complex IV — cytochrome coxidase).
• The energy released pumps H+ ions from the matrix into the intermembrane space, creating a proton gradient.
• H+ions flow back through ATP synthase (Complex V) — this is chemiosmosis — driving ATP synthesis.
• Total ATP yield per glucose: ~30–32 ATP (NADH ≈ 2.5 ATP each; FADH2 ≈ 1.5 ATP each).
(B) ANAEROBIC RESPIRATION:-
-> anaerobic respiration does not require oxygen and takes place only in the cytoplasm, yielding just 2 ATP per glucose. Its end products vary: lactic acid in animals (such as muscle cells during intense exercise) or ethanol and carbon dioxide in organisms like yeast and some plants.
-> When oxygen is unavailable or insufficient, organisms resort to anaerobic pathways to regenerate NAD+ from NADH (essential to keep glycolysis running).
3) TRANSPORTATION:
-> Transportation is the process of moving substances — nutrients, gases, hormones, and waste products — to and from every cell in the body. It ensures that cells receive what they need and waste is efficiently removed.
* Human Circulatory System
-> Humans have a closed, double circulatory system: blood flows in enclosed vessels and passes through the heart twice per complete circuit — once through the lungs (pulmonary circuit) and once through the body (systemic circuit).
* The Heart
• 4 chambers: Right atrium, right ventricle (pumps deoxygenated blood to lungs); Left atrium, left ventricle (pumps oxygenated blood to body).
• Valves: Atrioventricular valves (tricuspid on right, bicuspid/mitral on left) prevent backflow into atria.
Semilunar valves guard exits to pulmonary artery and aorta.
• Cardiac conduction: Sinoatrial (SA) node generates the electrical impulse → AV node → Bundle of His → Purkinje fibres.
• Heartbeat: Diastole (relaxation/filling) + Systole (contraction/ejection).
• Normal rate: 60–100 bpm at rest.
* The Lymphatic System
-> The lymphatic system is a secondary transport network that collects excess interstitial fluid (from capillary filtration), transports fats absorbed from the gut, and serves as the highway for immune cells.
• Lymph capillaries drain interstitial fluid into lymph vessels → lymph ducts → subclavian veins (rejoins blood).
• Lymph nodes: Filter lymph; site of B and T lymphocyte activation.
• Thoracic duct: Largest lymph vessel; drains the majority of the body into the left subclavian vein.
• Lacteals: Specialised lymph capillaries in intestinal villi that absorb chylomicrons (dietary fats).
* Blood - composition and functions
1) Plasma (55%)- Straw-coloured liquid; ~92% water, dissolved proteins (albumin, globulins, fibrinogen), electrolytes, nutrients, hormones, CO2.
Key functions: Transport of substances; osmotic balance; clotting factors; immune proteins (antibodies).
2) Red Blood Cells(Erythrocytes)- Biconcave disc; anucleate; filled withhaemoglobin; ~4.5–5.5 million/µL.
Key functions: O2 transport (oxyhaemoglobin); CO2 transport (carbaminohaemoglobin); acid-base buffering.
3) White Blood Cells (Leucocytes)- Nucleated; 5 types: neutrophils, eosinophils, basophils, monocytes, lymphocytes; ~5,000–10,000/µL.
Key functions: Immune defence: phagocytosis(neutrophils/monocytes), antibody production (B lymphocytes), cell-mediated immunity (T lymphocytes).
4) Platelets (Thrombocytes)- Tiny cell fragments (anucleate); ~150,000–400,000/µL.
Key functions: Blood clotting (haemostasis); release clotting factors; form platelet plug at wound site.
* Blood vessels
| Vessel | Structure | Function | Blood Pressure |
| Arteries | Thick, elastic, muscular walls; narrow lumen | Carry blood AWAY from heart (mostly oxygenated) | High |
| Arterioles | Smaller branches of arteries; muscle layer regulates flow | Distribute blood to capillary beds; regulate blood pressure | Moderate–high |
| Capillaries | One cell thick (endothelium only); no muscle | Exchange of O2, CO2, nutrients, waste with tissues | Low |
| Venules | Small thin-walled vessels | Collect blood from capillaries | Low |
| Veins | Thin walls; large lumen; have valves | Return blood TO heart (mostly deoxygenated); valves prevent backflow | Very low |
* Transpiration:
-> Evaporation of water from stomata creates a negative pressure (tension) in xylem, pulling water up from roots.
-> Transpiration also cools the plant and drives mineral uptake.
* Transport of plants
| Tissue | Cells | What it Transports | Direction | Mechanism |
| Xylem | Vessel elements, tracheids (dead, thick-walled) | Water and dissolved minerals | Unidirectional: roots -> stem -> leaves | Transpiration pull (cohesion-tension); root pressure |
| Phloem | Sieve tube elements (living) + companion cells | Organic solutes (sucrose, amino acids) — 'sap' | Bidirectional: source -> sink | Pressure-flow hypothesis (mass flow) |
4) EXCRETION:
-> Excretion is the process of removing metabolic waste products from the body. These wastes primarily nitrogenous compounds, CO2, excess water, and salts are toxic if allowed to accumulate and must be expelled to maintain homeostasis.
* The Kidney
-> The kidneys are the primary excretory organs in humans. Each kidney contains approximately 1 million nephrons — the functional units of the kidney.
- Gross Structure of the Kidney:
• Cortex: Outer region; contains glomeruli and Bowman's capsules; site of filtration.
• Medulla: Inner region; contains renal pyramids made up of loops of Henle and collecting ducts.
• Renal pelvis: Funnel-shaped cavity that collects urine; leads to the ureter.
• Renal artery & vein: Supply and drain blood from the kidney.
• Ureter: Carries urine from kidney to urinary bladder
* Excretory organs and it's roles
| Organ | Waste Excreted | Mechanism |
| Kidneys (primary) | Urea, uric acid, creatinine, excess salts, water | Filtration, reabsorption, secretion and urine formation |
| Lungs | CO2, water vapour | Diffusion across alveolar-capillary membrane during expiration |
| Skin (sweat glands) | Water, NaCl, small amounts of urea | Sweating; primarily thermoregulation, not excretion |
| Liver | Bile pigments (bilirubin from haemoglobin breakdown), cholesterol | Bile secreted into intestine and excreted in faeces |
| Large intestine | Bile pigments, intestinal bacteria, dead cells | Eliminated in faeces (defaecation) |
* Nephron
-> The nephron is the structural and functional unit of the kidney. Each kidney has about 1–1.5 million nephrons. Its structure is specially designed for filtration, reabsorption, and secretion to form urine.
1. Renal Corpuscle (Malpighian Body)
-> This is the starting part of the nephron and is located in the cortex.
a) Glomerulus
- A network of tiny capillaries.
- Receives blood from the afferent arteriole and drains into the efferent arteriole.
- Function: Ultrafiltration of blood (filters water, glucose, salts, urea, etc.).
b) Bowman’s Capsule
- Cup-shaped structure surrounding the glomerulus.
- Has two layers: inner (visceral) and outer (parietal).
- Collects the filtrate formed in the glomerulus.
2. Renal Tubule
-> A long, coiled tube where reabsorption and secretion occur.
a) Proximal Convoluted Tubule (PCT)
- Located in the cortex.
- Highly coiled and lined with microvilli (for absorption).
- Function: Reabsorbs glucose, amino acids, salts, and most water.
- Very important for selective reabsorption.
b) Loop of Henle
- U-shaped structure extending into the medulla.
- Has two limbs:
i) Descending Limb
-> Permeable to water.
-> Water moves out → filtrate becomes concentrated.
ii) Ascending Limb
-> Impermeable to water.
-> Actively transports salts (Na⁺, Cl⁻) out.
-> Filtrate becomes dilute.
c) Distal Convoluted Tubule (DCT)
- Located in the cortex.
- Less coiled than PCT.
- Function: Selective reabsorption of salts and water.
- Secretion of ions like K⁺ and H⁺.
- Regulated by hormones (like aldosterone).
3. Collecting Duct
- Receives filtrate from multiple nephrons.
- Passes through medulla to renal pelvis.
- Function: Final concentration of urine.
- Water reabsorption controlled by ADH (Antidiuretic Hormone).
4. Blood Supply of Nephron
- Afferent arteriole → brings blood to glomerulus.
- Efferent arteriole → carries blood away.
- Forms peritubular capillaries (around tubules) and vasa recta (around loop of Henle).
- Helps in exchange of substances during reabsorption.
* Urine formation
-> Urine formation in the nephron occurs through three main processes: glomerular filtration, selective reabsorption, and tubular secretion. First, in glomerular filtration, blood is filtered under high pressure in the glomerulus, allowing small substances like water, glucose, salts, and urea to pass into Bowman’s capsule, while large molecules such as proteins and blood cells remain in the blood. Next, during selective reabsorption, useful substances like glucose, amino acids, most of the water, and essential salts are reabsorbed from the filtrate back into the blood, mainly in the proximal convoluted tubule. Finally, in tubular secretion, additional wastes and excess ions such as hydrogen ions, potassium ions, and ammonia are actively secreted from the blood into the filtrate in the distal convoluted tubule. Together, these processes help in forming urine and maintaining the body’s internal balance.
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