Function of plant, animal & human

Overview & Fundamental Concept

Complete preparation guide for Function of plant, animal & human under AISSEE Class VI General Knowledge (Syllabus Item 21). Master high-yield facts, exam matrices, solved models, and 10 interactive drill MCQs with detailed explanations.

• Plant Organ Hierarchy: Root System (anchorage and water absorption below soil) and Shoot System (stem, branches, leaves, flowers, and fruits above soil).
• Root Systems & Leaf Venation Correlation: • Taproot System: Single deep primary central root with smaller lateral branch roots; typical of Dicotyledonous plants (Carrot, Mustard, Gram, Pea, Mango); paired consistently with Reticulate (net-like) leaf venation. • Fibrous Root System: Dense cluster of thin, thread-like roots originating equally from the base of the stem; typical of Monocotyledonous plants (Wheat, Maize, Rice, Grass, Bamboo); paired consistently with Parallel leaf venation. • Modified Roots: Storage roots (radish, carrot, turnip), Prop roots (hanging support roots in Banyan tree), Stilt roots (support in maize and sugarcane), and Pneumatophores (breathing roots in mangrove trees like Rhizophora that grow vertically upward above waterlogged saline mud to take in air).
• Vascular Transport - Xylem vs Phloem: • Xylem: Complex vascular tissue composed of tracheids and vessels that conducts water and dissolved mineral ions absorbed by roots UNIDIRECTIONALLY upward to stems and leaves. • Phloem: Living vascular tissue composed of sieve tubes and companion cells that translocates organic nutrients (sucrose/glucose synthesized in leaves) BIDIRECTIONALLY to all growing shoot buds, fruits, storage organs, and roots.
• Photosynthesis Equation & Chloroplasts: Green plant cells synthesize glucose using atmospheric carbon dioxide ($CO_2$) and soil water ($H_2O$) in the presence of green chlorophyll pigment inside chloroplasts by absorbing solar photon energy: $6\text{CO}_2 + 6\text{H}_2\text{O} \xrightarrow[\text{Chlorophyll}]{\text{Sunlight}} \text{C}_6\text{H}_{12}\text{O}_6\text{ (Glucose)} + 6\text{O}_2\text{ (Oxygen)}$ Oxygen is discharged through microscopic leaf pores called Stomata (regulated by turgid/flaccid Guard Cells).
• Transpiration Mechanics: Evaporation of excess water vapor through open leaf stomata; creates a strong negative tension (Transpiration Suction Pull) that lifts continuous water columns up tall forest trees; cools plant foliage in hot sunlight.
• The Carnivorous Pitcher Plant (Nepenthes - NCERT Class 5 EVS Chapter 5): • Found natively in the state of Meghalaya in India (and in Australia and Indonesia). • Thrives in acidic, waterlogged soils severely deficient in bioavailable nitrogen compounds. • Anatomical Modification: The leaf lamina is modified into a hollow green pitcher jug with an overarching leaf lid; the pitcher mouth secretes an intoxicating sweet aromatic scent. • Trapping Mechanism: When flying or crawling prey (insects, spiders, small frogs, and even mice) land on the slippery rim, they slide down slick downward-pointing inner hairs into a pool of digestive enzymatic fluid at the bottom; the pitcher lid snaps shut, drowning and digesting the prey to absorb essential nitrogenous proteins!

• Comparative Animal Respiratory Adaptations: • Fish: Breathe via internal Gills (vascularized gill filaments that extract dissolved oxygen directly from water as water flows across them in a countercurrent gradient). • Amphibians (Frog): Exhibit Dual Respiration — breathe through moist, thin, permeable cutaneous skin when submerged in water or during winter hibernation; breathe via lungs and buccal cavity when active on terrestrial land. • Insects (Cockroach, Locust, Grasshopper): Possess a tracheal system consisting of lateral surface breathing pores called Spiracles that lead into an intricate network of branching internal air tubes (Tracheae) delivering oxygen directly to tissues without relying on blood hemoglobin. • Earthworm: Has no respiratory organs; absorbs atmospheric oxygen directly through its thin, moist, mucus-covered skin into cutaneous capillary loops. • Mammals, Birds & Reptiles: Possess paired internal sponge-like Lungs with branching airways for terrestrial gas exchange.
• Comparative Heart Chambers Across Vertebrates: • Fish: 2-Chambered Heart (1 Atrium + 1 Ventricle; Single circulation where deoxygenated blood is pumped to gills, oxygenated, and circulates directly to body tissues). • Amphibians & Most Reptiles: 3-Chambered Heart (2 Atria + 1 Ventricle; incomplete double circulation where oxygenated and deoxygenated blood partially mix in the single ventricle). • Crocodiles (Exception): The ONLY reptile possessing a fully divided 4-Chambered Heart! • Birds & Mammals: 4-Chambered Heart (2 Atria + 2 Ventricles; complete double circulation ensuring zero mixing of oxygenated and deoxygenated blood, enabling high metabolic rates and warm-blooded homeothermy).

• The Human Heart: Muscular organ roughly the size of a clenched fist; positioned in the mediastinum between the lungs, tilted slightly to the left; beats rhythmically ~72 times per minute in a resting adult (pumping ~5 liters of blood per minute).
• Four Heart Chambers: • Right Atrium: Receives deoxygenated blood returning from the upper and lower body via the Superior and Inferior Vena Cava. • Right Ventricle: Pumps deoxygenated blood through the Pulmonary Artery to the lungs for oxygenation. • Left Atrium: Receives freshly oxygenated blood from the lungs via four Pulmonary Veins. • Left Ventricle: The thickest, most muscular chamber; pumps oxygenated blood under high pressure into the Aorta to supply the entire body.
• Arteries vs Veins: • Arteries: Carry oxygenated blood AWAY from the heart to tissues under high hydrostatic pressure; possess thick, muscular, elastic walls and have NO internal valves (Exception: Pulmonary Artery carries deoxygenated blood to lungs). • Veins: Carry deoxygenated blood BACK toward the heart under low pressure; possess thin muscular walls and feature internal one-way Valves to prevent retrograde backflow of blood (Exception: Pulmonary Vein carries oxygenated blood from lungs to left atrium).
• Blood Components: • Plasma: Pale yellow liquid matrix constituting ~55% of total blood volume; composed of 90-92% water, plasma proteins (albumin, globulin, fibrinogen), glucose, and electrolytes. • Red Blood Cells (RBCs / Erythrocytes): Biconcave enucleated discs loaded with Hemoglobin; transport oxygen; average lifespan of ~120 days (broken down in spleen - 'graveyard of RBCs'). • White Blood Cells (WBCs / Leukocytes): Nucleated immune defense cells ('soldiers of the body'); phagocytose invading pathogens and produce protective antibodies. • Blood Platelets (Thrombocytes): Cell fragments essential for blood clotting (hemostasis) via fibrin mesh generation.
• The Human Respiratory Tract: Nostrils → Nasal Cavity (lined with mucus and cilia to filter dust) → Pharynx → Larynx (Voice box) → Trachea (Windpipe braced with C-shaped hyaline cartilage rings to prevent collapse) → Left & Right Primary Bronchi → Bronchioles → Alveoli.
• Alveoli (The Functional Unit): Millions of microscopic, thin-walled, balloon-like air sacs enveloped in dense capillary networks; provide an immense surface area (~80 m²) where Oxygen diffuses into blood and Carbon Dioxide diffuses out.
• Inhalation vs Exhalation: Inhalation is an active process where the Diaphragm contracts and flattens downward while external intercostal muscles lift ribs upward and outward, expanding thoracic chest volume and sucking air inward; Exhalation is passive relaxation where the diaphragm springs back into its dome shape, compressing thoracic volume and pushing air out.

• The Human Skeleton: Framework of bones providing structural support, organ protection, mineral storage (calcium/phosphorus), and hematopoiesis (blood cell production in red bone marrow); adult skeleton comprises 206 distinct bones (infants are born with ~300 softer cartilaginous bones that fuse together during growth).
• Skeletal Superlatives: • Longest, Heaviest & Strongest Bone: FEMUR (Thigh bone) — supports up to 30 times an adult's weight. • Smallest & Lightest Bone: STAPES (Stirrup) — situated inside the middle ear, measuring just ~3 millimeters in length and weighing ~3 milligrams. • Tendon vs Ligament: - Tendon: Tough fibrous connective cord that attaches MUSCLE TO BONE (transmits contractile pulling force). - Ligament: Elastic fibrous band that connects BONE TO BONE across a movable joint (stabilizes joint alignment).
• The Human Brain & Nervous System: The central processing unit of the body, weighing ~1.3 to 1.4 kg: • Cerebrum: The largest, uppermost part of the brain; divided into left and right hemispheres; center of intelligence, logical reasoning, conscious thought, learning, sensory perception, and voluntary motor actions. • Cerebellum ('Little Brain'): Positioned beneath the back of the cerebrum; coordinates voluntary muscle movements, fine motor skills, body posture, and physical balance (walking in a straight line, riding a bicycle; affected severely by alcohol intake). • Medulla Oblongata: Brainstem base connecting to spinal cord; controls vital involuntary autonomic reflex functions: rhythmic breathing, heartbeat rate, blood pressure, swallowing, coughing, and sneezing. • Spinal Cord: Cylindrical bundle of nerve fibers running through the vertebral spinal column; acts as information superhighway and coordinates rapid protective Reflex Actions (e.g., instantly pulling hand away from a burning flame).
• The Human Excretory System: Pair of bean-shaped Kidneys located against the posterior abdominal wall; functional microscopic filtration units are NEPHRONS (~1 million per kidney); nephrons filter urea, excess mineral salts, and metabolic wastes from blood to produce Urine; urine flows via Ureters to be stored in the muscular Urinary Bladder before discharge through the Urethra.