Life Processes - CBSE Class 10 Science

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1. Introduction to Life Processes (NCERT Page 93) Definition: Life processes are the fundamental biological activities that living organisms perform to maintain their existence, growth, and reproduction. These are essential for survival and to counteract the effects of entropy. Examples: Nutrition, Respiration, Transportation, Excretion, Control & Coordination, Growth, Movement, Reproduction. Why essential: Energy Production: All life activities require energy, obtained through nutrition and respiration. Maintenance & Repair: Constant wear and tear of body tissues necessitate repair mechanisms. Waste Removal: Metabolic activities produce toxic by-products that must be eliminated. Homeostasis: Maintaining a stable internal environment. 2. Nutrition - Obtaining and Utilizing Food 2.1 Modes of Nutrition (NCERT Page 93-94) Autotrophic Nutrition: Organisms (autotrophs) produce their own organic food from simple inorganic substances. Photoautotrophs: Use light energy (e.g., green plants, algae, cyanobacteria). Chemoautotrophs: Use chemical energy from oxidation of inorganic substances (e.g., sulfur bacteria, nitrifying bacteria). Photosynthesis (Detailed): Raw Materials: Carbon dioxide ($CO_2$), Water ($H_2O$). Energy Source: Sunlight. Pigment: Chlorophyll (present in chloroplasts). Products: Glucose ($C_6H_{12}O_6$), Oxygen ($O_2$). Overall Equation: $6CO_2 + 6H_2O \xrightarrow{\text{Sunlight, Chlorophyll}} C_6H_{12}O_6 + 6O_2$ Key Events: Light-dependent reactions: Light energy absorbed by chlorophyll, converted to chemical energy (ATP and NADPH). Water molecules split ($H_2O \to H^+ + O_2 + e^-$). Oxygen released. Light-independent reactions (Calvin Cycle): $CO_2$ is reduced to carbohydrates using ATP and NADPH. Occurs in the stroma of chloroplasts. Stomata: Small pores on the surface of leaves, primarily on the lower epidermis. Functions: Gaseous exchange ($CO_2$ intake, $O_2$ release) and Transpiration (loss of water vapour). Structure: Each stoma is guarded by two kidney-shaped guard cells containing chloroplasts. Mechanism: Guard cells swell (due to water absorption) and curve outwards, opening the stomata. They shrink and straighten, closing the stomata. This is regulated by water potential and $K^+$ ion movement. (NCERT Page 95, Fig 6.3) Heterotrophic Nutrition: Organisms (heterotrophs) cannot synthesize their own food and depend on other organisms for their organic food supply. Holozoic Nutrition: Involves ingestion, digestion, absorption, assimilation, and egestion of solid or liquid organic food. (e.g., humans, amoeba, animals). Saprophytic Nutrition: Organisms obtain nutrients from dead and decaying organic matter. They secrete digestive enzymes externally and absorb the digested nutrients. (e.g., fungi like bread mould, mushrooms, bacteria). Parasitic Nutrition: Organisms (parasites) live on or inside another living organism (host) and derive nutrition from it, often harming the host. (e.g., Cuscuta (dodder plant), ticks, lice, tapeworms, Plasmodium). 2.2 Nutrition in Amoeba (Holozoic) (NCERT Page 96, Fig 6.4) Process: Phagocytosis (cell eating). Steps: Ingestion: Amoeba extends temporary finger-like projections called pseudopodia to engulf the food particle, forming a food cup. Formation of Food Vacuole: The food particle, along with a small amount of water, is enclosed within a food vacuole. Digestion: Lysosomes containing digestive enzymes fuse with the food vacuole and break down complex food substances into simpler ones. Absorption: The digested food diffuses from the food vacuole into the cytoplasm. Assimilation: The absorbed food is used for energy, growth, and repair. Egestion: The undigested waste material is expelled out of the cell by rupturing the cell membrane at any point. 2.3 Nutrition in Humans (NCERT Page 97-100, Fig 6.6) Human Digestive System: Consists of the alimentary canal and associated digestive glands. Alimentary Canal (approx. 9m long): Mouth: Ingestion: Food taken in. Mechanical Digestion: Chewing (mastication) by teeth. Chemical Digestion: Saliva (from salivary glands) contains salivary amylase (ptyalin) which breaks down complex starch into simpler sugars (maltose). Mucus lubricates food. Pharynx: Common passage for food and air. Oesophagus (Food Pipe): Connects pharynx to stomach. Food moves by peristalsis (rhythmic contraction and relaxation of muscular walls). Stomach: J-shaped muscular organ. Gastric Glands: Secrete gastric juice containing: Hydrochloric Acid (HCl): Kills bacteria, provides acidic medium ($pH \approx 1.5-3.5$) for pepsin, denatures proteins. Pepsin: Enzyme that begins protein digestion (breaks proteins into peptones and proteoses). Mucus: Protects the stomach lining from the corrosive action of HCl. Food churned for several hours, forming a semi-digested paste called chyme. Small Intestine: Longest part (approx. 6.5m), highly coiled. Site of complete digestion and absorption. Sphincter Muscles: Pyloric sphincter controls release of chyme into small intestine. Receives secretions from: Liver: Produces bile (stored in gallbladder). Bile emulsifies fats (breaks large fat globules into smaller ones), making them accessible for lipase. It also provides an alkaline medium. Pancreas: Produces pancreatic juice containing: Pancreatic Amylase: Continues starch digestion. Trypsin: Digests proteins. Lipase: Digests emulsified fats. Intestinal Glands: Secrete intestinal juice (succus entericus) containing enzymes that complete digestion: Maltase, Sucrase, Lactase: Break down disaccharides into monosaccharides (glucose). Peptidases: Break down peptides into amino acids. Intestinal Lipase: Digests remaining fats. Absorption: Inner lining has millions of finger-like projections called villi , which increase surface area for absorption. Villi have rich blood supply and lymphatic vessels (lacteals) for absorbing digested nutrients. Large Intestine: Shorter and wider than small intestine (approx. 1.5m). Functions: Absorbs excess water from undigested food and forms faeces. Houses beneficial bacteria. Rectum: Stores faeces temporarily. Anus: Egestion of faeces, controlled by the anal sphincter muscle. 3. Respiration - Energy Release Definition: The process by which organisms obtain energy from the food they eat. It involves the breakdown of glucose in the presence or absence of oxygen to release energy. Types: Feature Aerobic Respiration Anaerobic Respiration Oxygen Requirement Requires molecular oxygen ($O_2$). Does not require oxygen. Site of Occurrence Initial step (Glycolysis) in cytoplasm, subsequent steps (Krebs cycle, ETC) in mitochondria. Occurs entirely in the cytoplasm. Breakdown of Glucose Complete breakdown of glucose. Incomplete breakdown of glucose. Energy Yield High energy yield (38 ATP molecules per glucose). Low energy yield (2 ATP molecules per glucose). End Products Carbon dioxide ($CO_2$) and Water ($H_2O$). In Yeast/Bacteria: Ethanol ($C_2H_5OH$) and Carbon dioxide ($CO_2$). (Fermentation) In Muscle Cells: Lactic Acid ($C_3H_6O_3$). Equation (Glucose) $C_6H_{12}O_6 + 6O_2 \to 6CO_2 + 6H_2O + \text{Energy (38 ATP)}$ Yeast: $C_6H_{12}O_6 \to 2C_2H_5OH + 2CO_2 + \text{Energy (2 ATP)}$ Muscle: $C_6H_{12}O_6 \to 2C_3H_6O_3 + \text{Energy (2 ATP)}$ Common Pathway for Glucose Breakdown: (NCERT Page 101, Fig 6.8) $Glucose \text{ (6-carbon molecule)} \xrightarrow{\text{Cytoplasm (Glycolysis)}} Pyruvate \text{ (3-carbon molecule)} + \text{Energy}$ From pyruvate, the pathway diverges: Presence of Oxygen (Aerobic): Pyruvate $\xrightarrow{\text{Mitochondria}} CO_2 + H_2O + \text{Energy}$. Lack of Oxygen (Anaerobic in muscle): Pyruvate $\xrightarrow{\text{Cytoplasm}} Lactic Acid + \text{Energy}$. (Causes muscle cramps). Absence of Oxygen (Anaerobic in yeast): Pyruvate $\xrightarrow{\text{Cytoplasm}} Ethanol + CO_2 + \text{Energy}$. Respiration in Humans (NCERT Page 102, Fig 6.9): Respiratory System: Nostrils: Air enters, filtered by fine hairs and mucus, warmed and moistened. Pharynx: Common passage. Larynx (Voice box): Contains vocal cords. Trachea (Windpipe): Supported by C-shaped cartilaginous rings to prevent collapse. Divides into two bronchi. Bronchi: Enter lungs, branch into smaller bronchioles. Bronchioles: End in tiny air sacs called alveoli. Alveoli: (Singular: Alveolus) Thin-walled, balloon-like structures providing a vast surface area (approx. 80 $m^2$) for efficient gaseous exchange. Richly supplied with blood capillaries. Lungs: Primary respiratory organs, located in the thoracic cavity. Mechanism of Breathing: Inhalation (Active process): External intercostal muscles contract, pulling ribs up and outwards. Diaphragm contracts and flattens. Volume of thoracic cavity increases, reducing air pressure inside lungs. Air rushes into the lungs. Exhalation (Passive process at rest): External intercostal muscles relax, ribs move down and inwards. Diaphragm relaxes and domes upwards. Volume of thoracic cavity decreases, increasing air pressure inside lungs. Air is forced out of the lungs. Gaseous Exchange: Occurs in alveoli by diffusion. $O_2$ from high concentration in alveoli diffuses into blood (low $O_2$). $CO_2$ from high concentration in blood diffuses into alveoli (low $CO_2$). Transportation of Gases: Oxygen ($O_2$): Primarily transported by haemoglobin (a red pigment containing iron) in Red Blood Cells (RBCs) as oxyhaemoglobin. Carbon Dioxide ($CO_2$): More soluble in water. Mostly transported in dissolved form in plasma, some as carbamino-haemoglobin, and some as bicarbonate ions. 4. Transportation - Movement of Substances 4.1 Transportation in Humans (Circulatory System) Components: Heart, Blood, Blood Vessels. Heart (NCERT Page 104-105, Fig 6.10): A muscular pumping organ, size of a clenched fist, located between the lungs slightly to the left. Structure: Four chambers: two upper atria (receiving chambers) and two lower ventricles (pumping chambers). Septum: A muscular wall dividing the left and right sides of the heart, preventing the mixing of oxygenated and deoxygenated blood. This separation ensures an efficient supply of oxygen to the body. Valves: Present between atria and ventricles, and at the exits of ventricles into major arteries. They ensure unidirectional flow of blood and prevent backflow. Working (Cardiac Cycle): Deoxygenated blood from the body enters the right atrium (via vena cava). Oxygenated blood from the lungs enters the left atrium (via pulmonary veins). Atria contract, pushing blood into respective ventricles. Ventricles contract, pumping deoxygenated blood from the right ventricle to the lungs (via pulmonary artery) and oxygenated blood from the left ventricle to the rest of the body (via aorta). Double Circulation: The human circulatory system involves two separate circuits: Pulmonary Circulation: Blood flows from the heart to the lungs and back to the heart. Purpose: Oxygenation of blood ($O_2$ loading, $CO_2$ unloading). Systemic Circulation: Blood flows from the heart to the rest of the body (excluding lungs) and back to the heart. Purpose: Delivery of $O_2$ and nutrients, collection of $CO_2$ and wastes. This double circulation ensures efficient oxygen supply, crucial for warm-blooded animals like mammals and birds that have high energy demands to maintain constant body temperature. Blood: A fluid connective tissue. Plasma: Pale yellow fluid matrix (approx. 55% of blood volume). Composed of 90% water, remaining 10% includes proteins (albumin, globulins, fibrinogen), glucose, amino acids, salts, hormones, and waste products ($CO_2$, urea). Transports digested food, hormones, waste products. Formed Elements (Blood Cells): Red Blood Cells (Erythrocytes - RBCs): Biconcave, anucleated (in mammals). Contain haemoglobin, a red iron-containing pigment that binds with oxygen. Transport oxygen from lungs to tissues. White Blood Cells (Leukocytes - WBCs): Colourless, nucleated. Part of the immune system, fight infections and diseases. (Types: Neutrophils, Lymphocytes, Monocytes, Eosinophils, Basophils). Platelets (Thrombocytes): Small, irregular fragments of cells. Essential for blood clotting at sites of injury to prevent excessive blood loss. Blood Vessels (NCERT Page 106, Fig 6.11): Network of tubes that carry blood. Arteries: Carry oxygenated blood away from the heart to various body parts (except pulmonary artery, which carries deoxygenated blood to lungs). Have thick, elastic, muscular walls to withstand high pressure. No valves. Veins: Carry deoxygenated blood from body parts back to the heart (except pulmonary vein, which carries oxygenated blood from lungs to heart). Have thinner, less muscular walls. Contain valves to prevent backflow of blood due to lower pressure. Capillaries: Smallest blood vessels, one-cell thick walls. Form networks (capillary beds) within tissues. Site of exchange of gases, nutrients, hormones, and waste products between blood and tissue cells. Lymphatic System (NCERT Page 107): Lymph (Tissue Fluid): A clear, yellowish fluid that leaks out of capillaries into the interstitial space. Similar to plasma but colourless (no RBCs) and contains less protein. Lymphatic Vessels: Collect lymph and eventually drain it back into major veins. Lymph Nodes: Small, bean-shaped organs that filter lymph and contain lymphocytes (WBCs), playing a role in immunity. Functions: Returns interstitial fluid and proteins to the blood. Transports digested fats from the small intestine (lacteals). Plays a crucial role in the immune system. 4.2 Transportation in Plants (NCERT Page 108-109) Plants have a well-developed transport system (vascular bundles) to move water, minerals, and food over long distances. Xylem: Transports water and dissolved minerals from the roots upwards to all aerial parts of the plant. Components: Tracheids, vessels, xylem parenchyma, xylem fibres. Mechanism: Root Pressure: Water enters root cells by osmosis, creating a pressure that pushes water up the xylem, though this is a minor force for tall trees. Transpiration Pull: The primary driving force. Water evaporates from the leaves (transpiration), creating a suction force (negative pressure) that pulls water column upwards through xylem vessels. Cohesion (water molecules sticking together) and adhesion (water molecules sticking to xylem walls) maintain the water column. (NCERT Page 108, Fig 6.12) Flow: Unidirectional (always upwards). Phloem: Transports synthesized food (sugars/sucrose) from the leaves (source) to other parts of the plant where it's needed for growth or storage (sinks like roots, fruits, growing tips). Components: Sieve tubes, companion cells, phloem parenchyma, phloem fibres. Translocation: The process of transporting food in phloem. Sugars are actively loaded into sieve tubes at the source (leaves), increasing osmotic pressure. Water from adjacent xylem moves into the sieve tubes by osmosis. The increased pressure drives the sap (water + sugars) towards areas of lower pressure (sinks). At the sink, sugars are unloaded (actively or passively), and water moves back into xylem. Flow: Bidirectional (upwards and downwards). Requires energy (ATP). 5. Excretion - Waste Removal Definition: The biological process of removal of harmful metabolic waste products (e.g., urea, uric acid, $CO_2$, excess water, salts) from the body of an organism. 5.1 Excretion in Humans (NCERT Page 110, Fig 6.13) Human Excretory System (Urinary System): Consists of: A pair of Kidneys: Bean-shaped organs located on either side of the backbone, behind the abdomen. Main function is to filter blood and produce urine. A pair of Ureters: Tubes that carry urine from each kidney to the urinary bladder. A Urinary Bladder: Muscular bag that stores urine temporarily. A Urethra: Tube that carries urine from the bladder out of the body. Nephron (NCERT Page 110, Fig 6.14): The structural and functional unit of the kidney. Each kidney contains over a million nephrons. Structure of a Nephron: Bowman's Capsule: Cup-shaped structure at the beginning of the nephron. Glomerulus: A tuft of capillaries located within Bowman's capsule. Renal Tubule: A long, convoluted tube extending from Bowman's capsule, consisting of: Proximal Convoluted Tubule (PCT) Loop of Henle Distal Convoluted Tubule (DCT) Collecting Duct: Several nephrons drain into a common collecting duct. Urine Formation Steps: Glomerular Filtration (Ultrafiltration): Blood flows through the glomerulus under high pressure. Water, salts, glucose, amino acids, urea, and other small solutes are filtered out of the blood and into Bowman's capsule, forming the glomerular filtrate. Blood cells and large proteins are retained. Tubular Reabsorption: As the filtrate flows through the renal tubule (PCT, Loop of Henle, DCT), useful substances like most of the water, glucose, amino acids, and essential salts are selectively reabsorbed back into the blood capillaries surrounding the tubule. This is an energy-dependent (active) process for some substances. Tubular Secretion: Certain waste products (e.g., excess $K^+$, $H^+$ ions, some drugs) that were not filtered initially, or are in excess, are actively secreted from the blood into the filtrate in the tubule. The fluid remaining in the collecting duct is urine. Micturition: The process of expelling urine from the bladder. The bladder has stretch receptors that signal the brain when full, leading to an urge to urinate. It is controlled by a nervous reflex and voluntary control. Role of Lungs, Liver, Skin in Excretion: Lungs: Excrete $CO_2$ and water vapour during respiration. Liver: Detoxifies harmful substances and breaks down proteins, producing urea (which kidneys excrete). Skin: Excretes excess salts and water through sweat glands. Artificial Kidney (Dialysis): A procedure used for kidney failure patients. Blood is drawn from an artery, passed through a dialyzing unit (containing a semi-permeable membrane and dialyzing fluid). Waste products diffuse from the blood into the dialyzing fluid, while useful substances are retained in the blood, which is then returned to the patient's vein. 5.2 Excretion in Plants (NCERT Page 111) Plants have simpler excretory mechanisms as their metabolic activities are generally less intense, and they produce fewer waste products. Gaseous Wastes: Oxygen (during photosynthesis) and carbon dioxide (during respiration) are excreted through stomata in leaves and lenticels in stems. Excess Water: Removed by transpiration (evaporation from leaves) and guttation (loss of liquid water from leaf margins). Solid/Liquid Wastes: Many waste products are stored in cellular vacuoles. Some wastes are stored in leaves that eventually fall off (e.g., decaying leaves). Other wastes are stored as resins, gums (especially in old xylem), and latex. Some waste substances are excreted into the soil around the plant roots. 6. Important NCERT In-text & End-of-chapter Questions (with answers/hints) 6.1 In-text Questions (NCERT Page 95) Q1: What are outside raw materials used for by an organism? A: Food (organic matter for energy and body-building), Water (for metabolic reactions, transport, solvent), Oxygen (for aerobic respiration). Minerals (for various physiological functions). Q2: What processes would you consider essential for maintaining life? A: Nutrition (intake of food), Respiration (energy release), Transportation (distribution of substances), Excretion (waste removal), Control & Coordination (response to stimuli), Growth, Reproduction. 6.2 In-text Questions (NCERT Page 101) Q1: What are the differences between autotrophic nutrition and heterotrophic nutrition? A: Feature Autotrophic Nutrition Heterotrophic Nutrition Food Source Synthesize own food from inorganic sources. Depend on other organisms for food. Energy Source Sunlight (photoautotrophs) or chemical reactions (chemoautotrophs). Chemical energy stored in organic food consumed. Organisms Green plants, algae, cyanobacteria, some bacteria. Animals, fungi, most bacteria. Q2: Where do plants get each of the raw materials for photosynthesis? A: Carbon dioxide ($CO_2$): From the atmosphere, enters through stomata on leaves. Water ($H_2O$): From the soil, absorbed by roots and transported to leaves via xylem. Sunlight: From the sun, absorbed by chlorophyll. Chlorophyll: Present in the chloroplasts of plant cells, especially in leaves. Q3: What is the role of the acid in our stomach? A: Hydrochloric acid (HCl) in the stomach: Creates an acidic medium (pH 1.5-3.5) necessary for the activation and optimal functioning of the enzyme pepsin. Kills harmful bacteria that may enter with food, sterilizing it to some extent. Helps in the partial digestion of proteins by denaturing them. Q4: What is the function of digestive enzymes? A: Digestive enzymes are biological catalysts that speed up the breakdown of complex, large, insoluble food molecules (like carbohydrates, proteins, fats) into simpler, smaller, soluble, and absorbable forms (like glucose, amino acids, fatty acids, glycerol) that can be absorbed into the bloodstream. Q5: How is the small intestine designed to absorb digested food? A: The small intestine is highly adapted for efficient absorption due to: Length: It is very long (approx. 6.5 meters), providing ample time and surface area for digestion and absorption. Villi: Its inner lining has millions of tiny, finger-like projections called villi, which dramatically increase the surface area for absorption. Microvilli: The epithelial cells lining the villi also have microscopic projections called microvilli, further increasing the surface area. Rich Blood Supply: Each villus has a rich network of blood capillaries and a lacteal (lymphatic vessel), ensuring rapid transport of absorbed nutrients away from the intestine, maintaining a steep concentration gradient. Thin Walls: The walls of the villi are very thin (one-cell thick), allowing for quick diffusion of nutrients. 6.3 In-text Questions (NCERT Page 105) Q1: What advantage does a terrestrial organism have over an aquatic organism with regard to obtaining oxygen for respiration? A: Terrestrial organisms breathe atmospheric oxygen, which is abundant ($~21\%$) and diffuses rapidly. Aquatic organisms rely on dissolved oxygen in water, which is much less concentrated (typically $ Q2: What are the different ways in which glucose is oxidised to provide energy in various organisms? A: (Refer to detailed table and breakdown pathway in section 3). Q3: How is oxygen and carbon dioxide transported in human beings? A: Oxygen ($O_2$): Primarily transported by haemoglobin (a red pigment in RBCs) as oxyhaemoglobin. A small amount is dissolved in plasma. Carbon Dioxide ($CO_2$): More soluble in water. About 7% is dissolved in plasma, 20-25% binds to haemoglobin (forming carbamino-haemoglobin), and the majority (70%) is transported as bicarbonate ions ($HCO_3^-$) in plasma. Q4: How are the lungs designed in human beings to maximise the area for exchange of gases? A: (Same as Q7 in Exercises section below, detailed answer in section 3, Alveoli). 6.4 In-text Questions (NCERT Page 109) Q1: What are the components of the transport system in human beings? What are the functions of these components? A: (Refer to section 4.1). Heart: Muscular pump, circulates blood throughout the body. Blood: Fluid connective tissue; transports $O_2$, $CO_2$, nutrients, hormones, waste products, and protects against disease. Blood Vessels (Arteries, Veins, Capillaries): Form a network of tubes to carry blood to and from all parts of the body, facilitating exchange. Q2: Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds? A: Mammals and birds are warm-blooded animals, meaning they need to maintain a constant body temperature regardless of the external environment. This requires a large amount of energy. Separating oxygenated and deoxygenated blood ensures a highly efficient supply of oxygen to the body cells, which is crucial for generating the high amount of energy needed for their metabolic demands and thermoregulation. Q3: What are the components of the transport system in highly organised plants? A: Xylem and Phloem, which together form the vascular bundles. Q4: How are water and minerals transported in plants? A: Water and minerals are transported by the xylem tissue. The primary mechanism is the transpiration pull (cohesion-tension theory), where water loss from leaves creates a suction force that pulls water up from the roots. Root pressure also plays a minor role. Q5: How is food transported in plants? A: Food (mainly sugars like sucrose) is transported by the phloem tissue through a process called translocation. This process is driven by osmotic pressure gradients created by the active loading of sugars into sieve tubes at the source (leaves) and unloading at the sink (growing parts, storage organs). 6.5 In-text Questions (NCERT Page 111) Q1: Describe the structure and functioning of nephrons. A: (Refer to detailed structure and urine formation steps in section 5.1). Q2: What are the methods used by plants to get rid of excretory products? A: (Refer to section 5.2). Plants use various methods: Gaseous wastes ($O_2, CO_2$) via stomata/lenticels. Excess water via transpiration. Storing wastes in old leaves that eventually fall off. Storing wastes in cellular vacuoles. Storing wastes as gums, resins, or latex, especially in old xylem. Excreting some wastes into the surrounding soil. Q3: How is the amount of urine produced regulated? A: The amount of urine produced is regulated by: Amount of excess water in the body: If there's plenty of water, less water is reabsorbed, leading to more urine. Amount of dissolved waste: Higher waste load requires more water for dilution and excretion. Hormones: Antidiuretic hormone (ADH) or vasopressin, secreted by the pituitary gland, regulates water reabsorption in the kidneys. When ADH is released, more water is reabsorbed, and less urine is produced. Alcohol and caffeine inhibit ADH, leading to increased urine production. 6.6 Exercises (NCERT Page 112-113) - Selected PYQ/Important Q1: The kidneys in human beings are a part of the system for (a) nutrition. (b) respiration. (c) excretion. (d) transportation. A: (c) excretion. Q2: The xylem in plants are responsible for (a) transport of water. (b) transport of food. (c) transport of amino acids. (d) transport of oxygen. A: (a) transport of water. Q3: The autotrophic mode of nutrition requires (a) carbon dioxide and water. (b) chlorophyll. (c) sunlight. (d) all of the above. A: (d) all of the above. Q4: The breakdown of pyruvate to give carbon dioxide, water and energy takes place in (a) cytoplasm. (b) mitochondrion. (c) chloroplast. (d) nucleus. A: (b) mitochondrion (specifically for aerobic respiration). Q5: How is fat digested in our bodies? Where does this process take place? A: Fat digestion primarily occurs in the small intestine. Bile (from liver) emulsifies large fat globules into smaller ones. Pancreatic lipase (from pancreas) and intestinal lipase (from intestinal wall) then break down these emulsified fats into fatty acids and glycerol. Q6: What are the differences between aerobic and anaerobic respiration? Name some organisms that use the anaerobic mode of respiration. A: (Refer to detailed table in section 3). Organisms: Yeast, certain bacteria (e.g., Clostridium), parasitic worms (e.g., Ascaris), and human muscle cells during strenuous exercise. Q7: How are the alveoli designed to maximise the exchange of gases? A: The design of alveoli maximizes gas exchange efficiency due to: Large Surface Area: Millions of alveoli provide an enormous surface area (about 80 $m^2$) for gas exchange. Thin Walls: The alveolar walls are extremely thin (one-cell thick), facilitating rapid diffusion of gases. Rich Blood Supply: Alveoli are surrounded by an extensive network of blood capillaries, ensuring that a large volume of blood is always available for gas exchange. Moist Surface: The inner surface of alveoli is moist, which helps in the dissolution of gases before diffusion. Q8: What would be the consequences of a deficiency of haemoglobin in our bodies? A: A deficiency of haemoglobin (a condition called anaemia) would lead to: Reduced oxygen-carrying capacity of the blood. Cells receiving insufficient oxygen for respiration. Symptoms like fatigue, weakness, pale skin, shortness of breath, dizziness, and reduced stamina. In severe cases, it can impair organ function due to lack of energy. Q9: Describe double circulation in human beings. Why is it necessary? A: (Refer to detailed explanation in section 4.1, Heart - Double Circulation). Q10: What are the differences between the transport of materials in xylem and phloem? A: Feature Xylem Transport Phloem Transport Materials Transported Water and minerals. Food (sugars, amino acids). Direction of Flow Unidirectional (mostly upwards from roots). Bidirectional (from source to sink). Driving Force Transpiration pull (mainly), root pressure. Osmotic pressure gradient, active loading/unloading. Energy (ATP) Mostly passive, little metabolic energy. Requires ATP for active loading/unloading. Q11: Compare the functioning of alveoli in the lungs and nephrons in the kidneys with respect to their structure and functioning. A: Feature Alveoli (Lungs) Nephrons (Kidneys) Primary Function Gaseous exchange ($O_2$ in, $CO_2$ out). Blood filtration, urine formation, waste removal. Location Lungs (respiratory system). Kidneys (excretory system). Structural Units Tiny air sacs. Tubular structures (Bowman's capsule, tubules). Surface Area Large surface area (millions of alveoli). Large surface area (many nephrons, convoluted tubules). Blood Supply Rich capillary network surrounding each alveolus. Glomerulus (capillary tuft) and peritubular capillaries. Exchange/Filtration Diffusion of gases across thin walls. Ultrafiltration in glomerulus, selective reabsorption and secretion in tubules. Substances Involved $O_2$, $CO_2$. Water, salts, glucose, amino acids, urea, other wastes.