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📑 In This Chapter Guide (Table of Contents)
1. Nutrition: Autotrophic vs Heterotrophic Mechanisms
Nutrition is the biochemical process of obtaining and utilizing nutrients for energy, growth, tissue repair, and biological maintenance.
A. Autotrophic Nutrition (Photosynthesis):
Green plants synthesize glucose from inorganic carbon dioxide and water in the presence of sunlight absorbed by chlorophyll:
6CO₂ + 12H₂O --[Chlorophyll + Sunlight]--> C₆H₁₂O₆ + 6O₂ + 6H₂O
Three Core Events in Photosynthesis:
- Absorption of light energy by photosynthetic chlorophyll pigments.
- Conversion of light energy into chemical energy and splitting (photolysis) of water molecules into Hydrogen and Oxygen.
- Reduction of Carbon Dioxide into carbohydrate sugars (glucose).
Stomatal Mechanism: Guard cells swell when water flows into them, opening the stomatal pore for gas exchange; they shrink when water exits, closing the pore to prevent transpiration water loss.
2. Respiration: Breakdown of Glucose Pathways
Respiration is the cellular release of metabolic energy through the biochemical breakdown of glucose molecules.
The 3 Pathways of Glucose Catabolism (Board Favourite):
- Glycolysis (in Cytoplasm): 1 Molecule of 6-carbon Glucose splits into two 3-carbon Pyruvate molecules. This step is common to all living organisms.
- Path 1: Absence of Oxygen (in Yeast - Fermentation): Pyruvate converts into Ethanol, CO₂, and 2 ATP molecules:
Pyruvate → Ethanol (C₂H₅OH) + CO₂ + Energy (2 ATP). - Path 2: Lack of Oxygen (in Human Muscle Cells during rigorous sprinting): Pyruvate converts into Lactic Acid:
Pyruvate → Lactic Acid + Energy. Accumulation of lactic acid in muscle tissue causes painful muscle cramps. - Path 3: Presence of Oxygen (in Mitochondria - Aerobic Respiration): Complete breakdown into Carbon Dioxide, Water, and 36–38 ATP molecules:
Pyruvate + O₂ → 6CO₂ + 6H₂O + Energy (38 ATP).
3. Transportation in Humans: The Heart & Double Circulation
The human heart is a four-chambered muscular pump designed to completely separate oxygen-rich arterial blood from deoxygenated venous blood.
Pathway of Blood Flow through Heart Chambers:
- Deoxygenated blood from body tissues enters the Right Atrium via the Superior and Inferior Vena Cava.
- Right Atrium contracts, pushing blood through the tricuspid valve into the Right Ventricle.
- Right Ventricle pumps deoxygenated blood to the lungs via the Pulmonary Artery for oxygenation.
- Oxygenated blood returns from lungs via four Pulmonary Veins into the Left Atrium.
- Left Atrium contracts, sending blood through the bicuspid (mitral) valve into the thick-walled Left Ventricle.
- Left Ventricle contracts forcefully, pumping oxygenated blood into the Aorta to supply the entire body.
Why Ventricles Have Thicker Walls: Ventricles must pump blood with high systolic pressure to distant organs (lungs and systemic capillary beds), whereas atria merely pump blood into adjacent ventricles.
4. Excretion in Humans: Structure & Function of Nephron
Excretion eliminates toxic nitrogenous metabolic wastes (primarily urea and uric acid) produced during protein metabolism. The basic functional filtration unit of the human kidney is the Nephron.
Three Stages of Urine Formation:
- 1. Ultrafiltration (Glomerulus & Bowman's Capsule): High hydrostatic capillary pressure forces water, glucose, amino acids, urea, and salts from blood into the Bowman's capsule, forming primary filtrate (~180 liters/day).
- 2. Selective Reabsorption (Tubular Portion of Nephron): Essential substances (all glucose, essential amino acids, major salts, and major water volume) are actively and passively reabsorbed back into peritubular capillaries.
- 3. Tubular Secretion: Excess ions (K⁺, H⁺, ammonia) are secreted directly from blood into urine to balance osmotic pressure and blood pH. Concentrated urine drains through collecting ducts into the urinary bladder.
💡 Frequently Asked Questions (FAQ)
❓ What is the function of digestive enzymes in the small intestine?
The small intestine receives bile juice from the liver (which neutralizes acid and emulsifies fats) and pancreatic juice containing Trypsin (digests proteins into amino acids) and Lipase (breaks down emulsified lipids into fatty acids and glycerol). Intestinal juice completes the digestion into soluble absorbable nutrients.
❓ Differentiate between Xylem and Phloem transport in plants.
Xylem transports water and dissolved mineral salts unidirectionally from roots upwards to leaves using physical suction pressure (transpiration pull); it consists mostly of dead cells (vessels, tracheids). Phloem translocates synthesized sugars and amino acids bidirectionally (translocation) using ATP cellular energy through living sieve tubes and companion cells.
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