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Chapter 18: Body Fluids and Circulation – Part 1 📘 Class 11 Biology | NEET PYQs + Concept Series 🔗 Visit: Biologyatease | NEET PYQ All 🧠 Introduction to Body Fluids and Circulation The circulatory system is a critical component of human physiology. It helps in the transport of essential substances like oxygen, carbon dioxide, nutrients, hormones, and waste materials throughout the body. In this chapter, we begin with the body fluids — especially blood and lymph , and then dive into the types of circulatory systems and the structural and functional details of the human heart. 🩸 Types of Body Fluids 1. Blood Blood is the most vital transport fluid in the human body. It is a connective tissue composed of plasma and formed elements. Plasma : The liquid matrix of blood (~55%). It contains: 90-92% water 7-8% proteins (albumin, globulin, fibrinogen) Salts, hormones, enzymes, nutrients, and waste materials. Formed Elements (~45% of blood): Red Blood Cells...

✅ Chapter 17: Breathing and Exchange of Gases – Part 4 🔬 Respiratory Volumes, Capacities, and Transport of Gases 🧪 Respiratory Volumes: These are the measurements of air movement during different phases of breathing. Let’s understand each volume in detail: Volume Definition Average Value Tidal Volume (TV) Volume of air inspired or expired during normal breathing ~500 mL Inspiratory Reserve Volume (IRV) Additional air inspired with force after normal inspiration ~2500–3000 mL Expiratory Reserve Volume (ERV) Additional air expired forcefully after normal expiration ~1000–1100 mL Residual Volume (RV) Air remaining in lungs even after forced expiration ~1100–1200 mL ✅ Key point: Residual Volume prevents lung collapse . 🧪 Respiratory Capacities: These are combinations of two or more volumes. Capacity Formula Average Value Inspiratory Capacity (IC) TV + IRV 3000–3500 mL Expiratory Capacity (EC) TV + ERV 1500–1600 mL Functio...

  ✅ Chapter 17: Breathing and Exchange of Gases – Part 3 🔍 Regulation of Respiration and Disorders of the Respiratory System 🧠 How is Breathing Regulated? Breathing is an automatic, rhythmic process — but how does the body control it without conscious effort? The answer lies in the Respiratory Centers located in the brain. 🧬 Respiratory Centers in the Brain: Located primarily in the medulla oblongata and pons . Center Location Function Medullary Respiratory Center Medulla Controls rhythm of breathing Pneumotaxic Center Pons Regulates rate and pattern of breathing Chemosensitive Area Medulla Detects chemical changes in blood 🔵 Medullary Respiratory Center: Has two regions: Inspiratory center: Initiates inspiration Expiratory center: Active during forceful expiration ✅ Normal breathing (eupnea) is controlled by rhythmic impulses from the inspiratory center. 🔵 Pneumotaxic Center: Located in the upper part of the pons. ...

✅ Chapter 17: Breathing and Exchange of Gases – Part 2 🔍 Exchange of Gases and Transport of Respiratory Gases 📚 Gas Exchange at the Alveoli: The actual exchange of oxygen (O₂) and carbon dioxide (CO₂) between the lungs and blood occurs at the alveolar surface . Alveoli are tiny, balloon-like structures that provide: Large surface area Thin walls Rich capillary network ✅ Key point: Alveoli and capillaries together form the respiratory membrane , which is extremely thin (~0.5 micrometers). ⚙️ Mechanism of Gaseous Exchange: Passive Diffusion is the main mechanism based on differences in partial pressure . Gas Alveolar Air (mm Hg) Deoxygenated Blood (mm Hg) Oxygen (O₂) 104 40 Carbon dioxide (CO₂) 40 45 ✅ Direction of diffusion: O₂ diffuses from alveoli → blood (higher to lower partial pressure). CO₂ diffuses from blood → alveoli. Thus, gases move down their pressure gradients without requiring energy. 🌍 Partial Pressure: Par...

  ✅ Chapter 17: Breathing and Exchange of Gases – Part 1 🔍 Introduction and Mechanism of Breathing 📚 Introduction: Breathing is the physical process of exchanging gases — oxygen (O₂) intake and carbon dioxide (CO₂) release — between an organism and its environment. However, "respiration" is broader, involving cellular oxidation of food molecules to release energy. Thus, Breathing ≠ Respiration . Breathing is just the first step that supports internal respiration. ✅ Definition: "Breathing is a mechanical process involving inhalation (oxygen intake) and exhalation (carbon dioxide release) facilitated by respiratory structures." Organisms ranging from simple unicellular forms to complex multicellular animals have evolved different respiratory mechanisms suited to their size, environment, and metabolism. 🫁 Respiratory Organs in Animals: Animal Group Respiratory Organ Example Protozoans (e.g., Amoeba) General body surface Amoeba Pori...

✅ Chapter 16: Excretory Products and Their Elimination – Part 4 🔍 NEET PYQs (Q26 to Q50) with Detailed Solutions Q26. The excretory product in birds is: A) Urea B) Ammonia C) Creatinine D) Uric acid ✅ Answer: D) Uric acid 🧠 Explanation: Birds are uricotelic — they conserve water by excreting nitrogen in the form of uric acid , which is excreted as a paste or solid. Q27. Which part of the nephron absorbs maximum water? A) Loop of Henle B) Collecting duct C) Distal convoluted tubule D) Proximal convoluted tubule ✅ Answer: D) Proximal convoluted tubule 🧠 Explanation: Nearly 70% of water is reabsorbed in the PCT through passive reabsorption along with solutes. Q28. Which hormone controls reabsorption of water in the kidneys? A) Thyroxine B) Aldosterone C) ADH D) Insulin ✅ Answer: C) ADH 🧠 Explanation: ADH (vasopressin) increases permeability of the collecting duct , helping in reabsorption of water , thus reducing urine volume. Q29. The condition w...

🐾 Chapter 16: Excretory Products and Their Elimination – Part 3 🌍 Excretion in Other Organisms + Human Accessory Organs 🐸 Excretion in Different Animals Various organisms have evolved different excretory structures based on their body type, habitat, and physiology. Organism Excretory Structure Type of Waste Protozoa (Amoeba) Contractile vacuole Ammonia Platyhelminthes Flame cells (protonephridia) Ammonia Annelids (Earthworm) Nephridia Urea Insects (Cockroach) Malpighian tubules Uric acid Crustaceans Green glands Ammonia Reptiles, Birds Cloaca + uricotelic nature Uric acid Mammals (Humans) Kidneys Urea 🔍 Many aquatic animals are ammonotelic (dilutes easily in water) Land animals prefer ureotelism or uricotelism to conserve water 🌬️ Role of Other Human Organs in Excretion Even though kidneys are the main excretory organs, other organs assist in waste elimination. 🫁 Lungs Excrete CO₂ and water vapour Important in ...

🚽 Chapter 16: Excretory Products and Their Elimination – Part 2 💧 Urine Formation & Water Balance in the Body 🧬 Overview of Urine Formation Urine formation in humans involves three key steps : Glomerular Filtration Tubular Reabsorption Tubular Secretion All these processes occur within the nephron . 1️⃣ Glomerular Filtration (Ultrafiltration) Occurs in Bowman’s capsule Blood enters via afferent arteriole into the glomerulus High pressure filters small molecules: Water, glucose, urea, amino acids, salts Large molecules (RBCs, proteins) do not filter Filtrate is called: Glomerular filtrate 🧠 GFR (Glomerular Filtration Rate) = ~125 mL/min = 180 L/day 2️⃣ Tubular Reabsorption Reabsorption of essential substances from filtrate back into blood Occurs mainly in PCT (Proximal Convoluted Tubule) What gets reabsorbed? Glucose, amino acids, water, Na⁺, Cl⁻, HCO₃⁻ Segment Reabsorbed Substances PCT 70% of water, gluc...

🚽 Chapter 16: Excretory Products and Their Elimination – Part 1 💧 Waste Management in Living Organisms 🧬 Why Excretion? Metabolic reactions produce nitrogenous wastes , mainly from the breakdown of amino acids and nucleic acids. These wastes are toxic and must be removed to maintain homeostasis . 🧪 Types of Nitrogenous Wastes Waste Product Description Examples Ammonia (NH₃) Highly toxic, requires lots of water Fish, amphibians Urea Less toxic, moderate water required Mammals, amphibians Uric Acid Least toxic, excreted as paste/crystals Birds, reptiles, insects 🧠 This gives rise to: Ammonotelic organisms – e.g., Bony fishes Ureotelic organisms – e.g., Humans Uricotelic organisms – e.g., Birds 🧍 Human Excretory System The human excretory system primarily removes urea and involves: ✅ Main Excretory Organs: Organ Function Kidneys Filter blood, form urine Ureters Transport urine to bladder Urinary Bladder Stor...

🌬️ Chapter 15: Breathing and Exchange of Gases – Part 4 ❌ Respiratory Disorders & Final Recap 🚨 Common Respiratory Disorders 1️⃣ Asthma Chronic inflammation of bronchi and bronchioles . Causes: Allergens (dust, pollen) Cold air, pollution, exercise Symptoms: Wheezing Shortness of breath Chest tightness Coughing Treated with bronchodilators and anti-inflammatory drugs . 2️⃣ Emphysema Alveolar walls are damaged , reducing surface area for gas exchange. Main cause: Smoking . Results in: Poor O₂ exchange Breathlessness Reduced lung elasticity 🧠 Alveolar walls fuse → less surface → poor oxygenation 3️⃣ Bronchitis Inflammation of bronchial tubes . Can be acute or chronic. Leads to: Cough Excess mucus Breathing difficulty 4️⃣ Occupational Lung Diseases Due to long-term exposure to industrial dust and chemicals: Disease Cause Affected People Silicosis Silica dust Miners, quarry...

🌬️ Chapter 15: Breathing and Exchange of Gases – Part 3 💨 Transport of CO₂ & Regulation of Respiration 🫀 Transport of Carbon Dioxide Carbon dioxide (CO₂) is produced continuously in tissues as a waste product of cellular respiration. It needs to be transported to the lungs for exhalation. Here's how that happens: 🧪 Modes of Transport of CO₂: Mode of Transport Percentage As Bicarbonate (HCO₃⁻) ~70% Carbaminohaemoglobin (HbCO₂) ~20-23% Dissolved in Plasma ~7% 1️⃣ As Bicarbonate Ions (HCO₃⁻) – Most Important CO₂ enters RBCs and reacts with H₂O to form carbonic acid (H₂CO₃) . Enzyme carbonic anhydrase speeds this up. H₂CO₃ quickly dissociates into H⁺ and HCO₃⁻ ions. HCO₃⁻ diffuses into plasma for transport. Reaction inside RBC: CO₂ + H₂O ⟶ H₂CO₃ ⟶ H⁺ + HCO₃⁻ At lungs, this process reverses : HCO₃⁻ converts back to CO₂ and is exhaled. 2️⃣ As Carbaminohaemoglobin (HbCO₂) CO₂ combines with free amino groups of Hb (n...

🌬️ Chapter 15: Breathing and Exchange of Gases – Part 2 🔄 Exchange of Gases and Transport of Oxygen 🔁 Gaseous Exchange: External and Internal Respiration 🫁 1. External Respiration (Pulmonary Gas Exchange) Takes place between the alveoli and blood capillaries . Oxygen from alveolar air diffuses into the blood. Carbon dioxide from blood diffuses into alveolar air. Both gases move by simple diffusion due to partial pressure gradients (ΔpO₂ and ΔpCO₂). Fun fact: Alveolar surface area is ~70 m² — almost like a tennis court! 🧬 2. Internal Respiration (Tissue Respiration) Occurs between blood capillaries and tissue cells . Oxygen moves from blood to tissues. Carbon dioxide moves from tissues to blood. Driven by differences in partial pressures: Tissue cells : Low pO₂, High pCO₂ Arterial blood : High pO₂, Low pCO₂ 📊 Partial Pressure (pO₂ and pCO₂) Location pO₂ (mm Hg) pCO₂ (mm Hg) Alveolar air 104 40 Oxygenated blood ...

🌬️ Chapter 15: Breathing and Exchange of Gases – Part 1 🫁 Introduction Every cell in our body needs oxygen to carry out cellular respiration , and it produces carbon dioxide as a waste. The process by which oxygen is taken in and carbon dioxide is expelled out is called breathing , and the overall exchange and transport of gases in the body is termed respiration . 🔍 Types of Respiration Aerobic respiration – Uses oxygen to release energy from glucose. Anaerobic respiration – Does not require oxygen (e.g., in some microorganisms and muscle cells temporarily). In humans, we perform aerobic respiration , and our respiratory system supports this vital function. 🏗️ Human Respiratory System – Structure Let’s go step-by-step through the parts of the human respiratory system: 📌 1. External Nares (Nostrils) Openings through which air enters the body. 📌 2. Nasal Passage Warms, moistens, and filters air. Lined with mucus and cilia. 📌 3. Pharynx Com...

🔬 Human Physiology – The Digestive System (Part 4) 😷 Common Disorders of the Digestive System Despite its efficiency, the digestive system can suffer from various disorders. These can range from minor issues like indigestion to more severe conditions that impact nutrient absorption and overall health. ⚠️ 1. Indigestion (Dyspepsia) Cause : Improper secretion of digestive enzymes or acid, overeating, spicy food, or stress. Symptoms : Bloating, nausea, discomfort, and gas. Management : Eating light meals, avoiding irritants, antacids. ⚠️ 2. Constipation Cause : Poor dietary fiber, low water intake, sedentary lifestyle. Symptoms : Hard, dry stools and difficulty in defecation. Management : Fiber-rich diet, adequate hydration, physical activity. ⚠️ 3. Diarrhoea Cause : Infection (bacteria/virus), food intolerance, or medication. Symptoms : Frequent loose stools, dehydration. Management : Oral rehydration therapy (ORS), rest, sometimes antibiotics....