Class 10 Science Notes Chapter 6 (Life processes) – Science Book

Okay, here are detailed notes for Chapter 6, 'Life Processes,' from the NCERT Class 10 Science textbook, structured for government exam preparation.

Chapter 6: Life Processes

Introduction

• Life Processes: The fundamental functions performed by living organisms to maintain their life and survive. These processes are essential for energy production, growth, repair, movement, and continuation of the species.
• Criteria for Life: While movement is often visible (like running), molecular movements within cells are invisible but essential for life. Growth, need for food (nutrition), respiration, transport, excretion are key characteristics. Viruses are an exception, showing characteristics of life only inside a host cell.
• Energy Requirement: All life processes require energy, which is obtained from food through nutrition and released through respiration.
• Maintenance: Living organisms need continuous repair and maintenance of their structures (cells, tissues).

1. Nutrition

• Definition: The process of taking in food (nutrients) by an organism and its utilization by the body for energy, growth, and repair.
• Modes of Nutrition:
  • Autotrophic Nutrition: Organisms synthesize their own food from simple inorganic raw materials (CO2, H2O). Example: Green plants, some bacteria (photosynthesis/chemosynthesis).
  • Heterotrophic Nutrition: Organisms obtain food directly or indirectly from autotrophs. They cannot synthesize their own food. Example: Animals, fungi, most bacteria.

A. Autotrophic Nutrition (Photosynthesis)

• Definition: The process by which green plants use sunlight, water, carbon dioxide, and chlorophyll to synthesize glucose (food). Oxygen is released as a byproduct.
• Site: Chloroplasts (containing chlorophyll) located mainly in the mesophyll cells of leaves.
• Equation:
  6CO₂ + 12H₂O --(Sunlight / Chlorophyll)--> C₆H₁₂O₆ + 6O₂ + 6H₂O
  (Carbon Dioxide + Water --(Sunlight / Chlorophyll)--> Glucose + Oxygen + Water)
• Raw Materials:
  • Carbon Dioxide (CO₂): Enters leaves through stomata.
  • Water (H₂O): Absorbed by roots from the soil and transported upwards through xylem.
  • Sunlight: Provides energy; absorbed by chlorophyll.
  • Chlorophyll: Green pigment that traps solar energy.
• Key Events of Photosynthesis:
  1. Absorption: Chlorophyll absorbs light energy.
  2. Conversion: Light energy is converted into chemical energy. Water molecules are split into hydrogen (H⁺) and oxygen (O₂). (Photolysis of water)
  3. Reduction: Carbon dioxide is reduced (using the chemical energy and H⁺) to form carbohydrates (glucose).
• Stomata: Tiny pores on the leaf surface, primarily for gaseous exchange (CO₂ intake, O₂ release). Also involved in transpiration (water loss). Each stoma is surrounded by two guard cells, which regulate its opening and closing based on turgor pressure (water content).

B. Heterotrophic Nutrition

• Types:

  1. Holozoic Nutrition: Organisms ingest complex solid food, digest it internally, absorb the nutrients, and egest undigested waste. (e.g., Amoeba, Humans, Animals). Involves Ingestion, Digestion, Absorption, Assimilation, Egestion.
  2. Saprophytic Nutrition: Organisms feed on dead and decaying organic matter. They secrete enzymes externally to break down complex matter into simpler forms, which are then absorbed. (e.g., Fungi like bread mould, yeast, mushrooms; some bacteria).
  3. Parasitic Nutrition: Organisms (parasites) derive nutrition from another living organism (host), usually harming the host. (e.g., Cuscuta (amarbel) plant, ticks, lice, leeches, tapeworms).

• Nutrition in Simple Organisms (Amoeba):

  • Holozoic.
  • Ingestion: Engulfs food particle using temporary finger-like extensions called pseudopodia, forming a food vacuole.
  • Digestion: Enzymes enter the food vacuole and break down complex food into simpler substances.
  • Absorption: Digested food diffuses into the cytoplasm.
  • Assimilation: Absorbed food is used for energy, growth, etc.
  • Egestion: Undigested waste is moved to the cell surface and thrown out.

• Nutrition in Humans (Human Digestive System):

  • Alimentary Canal: A long tube extending from the mouth to the anus. Organs: Mouth, Pharynx, Oesophagus, Stomach, Small Intestine, Large Intestine, Rectum, Anus.
  • Associated Glands: Salivary glands, Liver, Pancreas.
  • Process:
    1. Mouth (Buccal Cavity):
       • Ingestion of food.
       • Teeth: Mastication (chewing).
       • Tongue: Mixing food with saliva, taste.
       • Salivary Glands: Secrete saliva containing salivary amylase (ptyalin), which starts digesting starch into simpler sugars (maltose).
    2. Oesophagus: Tube connecting mouth to stomach. Food moves down by rhythmic contractions called peristalsis. No digestion occurs here.
    3. Stomach: J-shaped muscular organ.
       • Gastric glands secrete gastric juice containing:
         • Hydrochloric Acid (HCl): Creates an acidic medium (pH 1.5-3.5) for pepsin action, kills germs.
         • Pepsin: Enzyme that digests proteins into smaller peptides.
         • Mucus: Protects the inner lining of the stomach from HCl.
       • Food is churned into a semi-solid paste called chyme.
    4. Small Intestine: Longest part of the alimentary canal (~6.5 m). Site of complete digestion and major absorption. Receives secretions from:
       • Liver: Secretes bile juice (stored in gall bladder). Bile emulsifies fats (breaks large fat globules into smaller ones, increasing surface area for enzyme action). Bile is alkaline, making the medium alkaline for pancreatic enzymes.
       • Pancreas: Secretes pancreatic juice containing:
         • Trypsin: Digests proteins/peptides.
         • Pancreatic Amylase: Digests remaining starch.
         • Lipase: Digests emulsified fats into fatty acids and glycerol.
       • Intestinal Glands: Secrete intestinal juice (succus entericus) containing enzymes that complete the digestion of carbohydrates (into glucose), proteins (into amino acids), and fats (into fatty acids and glycerol).
       • Absorption: Inner lining has numerous finger-like projections called villi, which increase the surface area for absorption. Villi are richly supplied with blood capillaries and lymph vessels (lacteals) to absorb digested food.
    5. Large Intestine: Shorter but wider (~1.5 m).
       • Absorbs excess water and some salts from undigested food.
       • Forms faeces.
    6. Rectum: Stores faeces temporarily.
    7. Anus: Opening through which faeces are egested (defecation). Regulated by anal sphincter.

2. Respiration

• Definition: The biochemical process of releasing energy from assimilated food (primarily glucose) for carrying out life processes. It occurs in all living cells.
  • Note: Often confused with Breathing, which is the physical process of inhaling oxygen and exhaling carbon dioxide (gaseous exchange). Respiration is cellular.
• Breakdown of Glucose (Common Pathways):
  • Step 1 (Glycolysis): Glucose (6-carbon molecule) is broken down into Pyruvate (3-carbon molecule) in the cytoplasm. This is common to both aerobic and anaerobic respiration.
• Types of Respiration:
  1. Aerobic Respiration: Occurs in the presence of oxygen.
     • Pyruvate enters the mitochondria.
     • Pyruvate is completely broken down into Carbon Dioxide (CO₂) and Water (H₂O).
     • Releases a large amount of energy (~38 ATP molecules per glucose molecule).
     • Equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (ATP)
  2. Anaerobic Respiration: Occurs in the absence of oxygen.
     • Occurs entirely in the cytoplasm.
     • In Yeast (Fermentation): Pyruvate is converted into Ethanol (C₂H₅OH) and Carbon Dioxide (CO₂). Used in brewing and baking industries.
       Pyruvate --(Absence of O₂)--> Ethanol + CO₂ + Energy (~2 ATP)
     • In Muscle Cells (During strenuous activity): When oxygen supply is limited, pyruvate is converted into Lactic Acid (C₃H₆O₃). Accumulation of lactic acid causes muscle cramps/fatigue.
       Pyruvate --(Lack of O₂)--> Lactic Acid + Energy (~2 ATP)
     • Releases much less energy than aerobic respiration.
• ATP (Adenosine Triphosphate): The energy currency of the cell. Energy released during respiration is stored in ATP molecules, which can be broken down later to release energy for cellular activities. (ADP + Pi + Energy → ATP)
• Gaseous Exchange in Organisms:
  • Plants: Exchange gases (O₂, CO₂) through stomata (leaves), lenticels (stems), and root surfaces via diffusion. Direction depends on environmental conditions and plant requirements (Photosynthesis vs. Respiration). Net exchange: O₂ out, CO₂ in during day; CO₂ out, O₂ in during night.
  • Aquatic Animals: Use oxygen dissolved in water. Rate of breathing is faster than terrestrial animals because dissolved oxygen concentration is low. Gills are the respiratory organs (e.g., fish).
  • Terrestrial Animals: Use atmospheric oxygen. Have specialized respiratory organs (e.g., lungs in humans, tracheal system in insects). Surface area for gas exchange is large and internal to reduce water loss.
• Human Respiratory System:
  • Organs: Nostrils → Nasal Cavity (air filtered, warmed, moistened) → Pharynx (common passage) → Larynx (voice box) → Trachea (windpipe, supported by rings of cartilage to prevent collapse) → Bronchi (singular: bronchus, trachea divides into two) → Bronchioles (finer branches) → Alveoli (singular: alveolus, tiny air sacs at the end of bronchioles).
  • Alveoli: The site of gaseous exchange. Have thin walls, a large surface area, and are richly supplied with blood capillaries. Oxygen diffuses from alveolar air into blood; Carbon Dioxide diffuses from blood into alveolar air.
  • Mechanism of Breathing:
    • Inhalation: Diaphragm contracts and flattens, rib muscles contract lifting ribs up and outwards → Thoracic cavity volume increases → Air pressure inside decreases → Air rushes into the lungs.
    • Exhalation: Diaphragm relaxes and moves up, rib muscles relax moving ribs down and inwards → Thoracic cavity volume decreases → Air pressure inside increases → Air is forced out of the lungs.
  • Respiratory Pigment: Haemoglobin in Red Blood Cells (RBCs) has a high affinity for oxygen and transports it from lungs to tissues. Carbon dioxide is transported mainly as bicarbonate ions dissolved in blood plasma, and also bound to haemoglobin.

3. Transportation

• Definition: The process by which substances synthesized or absorbed in one part of the body are carried to other parts. Essential for supplying nutrients, oxygen and removing wastes.

A. Transportation in Humans

• Circulatory System: Consists of Blood, Blood Vessels, and Heart.
• Blood: Fluid connective tissue.
  • Plasma: Liquid matrix (mostly water). Transports food, CO₂, hormones, waste products. Contains proteins, salts etc.
  • Red Blood Cells (RBCs / Erythrocytes): Biconcave discs, no nucleus (mature). Contain haemoglobin for O₂ transport.
  • White Blood Cells (WBCs / Leukocytes): Irregular shape, have nucleus. Provide immunity, fight infections (soldiers of the body).
  • Platelets (Thrombocytes): Cell fragments. Help in blood clotting at the site of injury, preventing excessive blood loss.
• Blood Vessels: Tubes carrying blood.
  • Arteries: Carry oxygenated blood away from the heart (except pulmonary artery). Have thick, elastic walls to withstand high pressure. No valves (except at start of aorta/pulmonary artery).
  • Veins: Carry deoxygenated blood towards the heart (except pulmonary vein). Have thinner walls, lower pressure. Have valves to prevent backflow of blood.
  • Capillaries: Extremely narrow tubes connecting arteries and veins. Walls are one-cell thick, allowing exchange of materials (O₂, CO₂, food, waste) between blood and tissues.
• Heart: Muscular pumping organ. Located in the thoracic cavity, slightly tilted to the left.
  • Chambers: Four chambers:
    • Two upper chambers: Atria (singular: Atrium) - receive blood. Right Atrium receives deoxygenated blood from body; Left Atrium receives oxygenated blood from lungs.
    • Two lower chambers: Ventricles - pump blood out. Right Ventricle pumps deoxygenated blood to lungs; Left Ventricle pumps oxygenated blood to the entire body (has thicker walls).
  • Septum: Muscular wall separating the right and left sides, preventing mixing of oxygenated and deoxygenated blood.
  • Valves: Ensure unidirectional blood flow, prevent backflow between atria and ventricles, and between ventricles and major arteries.
  • Double Circulation: Blood flows through the heart twice in one complete circuit.
    • Pulmonary Circulation: Blood flows from Heart (Right Ventricle) → Lungs (for oxygenation) → Heart (Left Atrium).
    • Systemic Circulation: Blood flows from Heart (Left Ventricle) → Body Tissues → Heart (Right Atrium).
    • Advantage: Efficient separation of oxygenated and deoxygenated blood, allowing efficient oxygen supply needed for warm-blooded animals with high energy demands.
• Blood Pressure: The pressure exerted by blood on the walls of blood vessels.
  • Systolic Pressure: Pressure in arteries during ventricular contraction (systole) (~120 mm Hg).
  • Diastolic Pressure: Pressure in arteries during ventricular relaxation (diastole) (~80 mm Hg).
  • Measured using a Sphygmomanometer. High blood pressure is called Hypertension.
• Lymphatic System: Another transport system.
  • Lymph: Tissue fluid that leaks out of blood capillaries into intercellular spaces. Similar to plasma but colorless, fewer proteins, contains lymphocytes (WBCs).
  • Drains into lymphatic capillaries → lymph vessels → large veins.
  • Functions: Carries digested fats (absorbed in lacteals of villi), drains excess fluid back to blood, helps in immunity (lymph nodes filter lymph and trap pathogens).

B. Transportation in Plants

• Plants need to transport water, minerals, and food. They have two main transport tissues: Xylem and Phloem.
• Transport of Water and Minerals:
  • Tissue: Xylem (composed of tracheids, vessels, xylem parenchyma, xylem fibres). Vessels and tracheids are non-living, form continuous channels.
  • Mechanism: Water and minerals are absorbed by root hairs from soil (osmosis/active transport). Water moves upwards through xylem due to:
    • Root Pressure: Active absorption of ions creates a water potential gradient, pushing water up to small heights.
    • Transpiration Pull: The major driving force. Transpiration is the loss of water vapour from aerial parts (mainly stomata). This evaporation creates a suction force (tension) that pulls the water column upwards through the xylem from roots to leaves.
  • Direction: Unidirectional (roots to leaves).
• Transport of Food (Translocation):
  • Tissue: Phloem (composed of sieve tubes, companion cells, phloem parenchyma, phloem fibres). Sieve tubes are living cells, transport food. Companion cells help regulate sieve tube function.
  • Substance: Food (mainly sucrose) synthesized during photosynthesis in leaves.
  • Mechanism: Food is loaded into phloem (source, e.g., leaves) using energy (ATP). This increases osmotic pressure, causing water to enter phloem from xylem. High pressure pushes the food towards regions of low pressure (sink, e.g., roots, fruits, growing points) where it is unloaded, again using energy.
  • Direction: Bidirectional (can move up or down, depending on source and sink).

4. Excretion

• Definition: The biological process of removal of harmful metabolic wastes from the body.
• Metabolic Wastes: Byproducts of metabolic activities, e.g., Urea (in humans), Carbon Dioxide, excess water, salts.

A. Excretion in Humans

• Excretory System: Consists of: A pair of Kidneys, a pair of Ureters, a Urinary Bladder, and a Urethra.
• Kidneys: Bean-shaped organs located in the abdomen. Filter blood and produce urine.
  • Nephron: The structural and functional unit of the kidney (~1 million per kidney). Responsible for filtering blood and forming urine.
  • Structure of Nephron:
    • Bowman's Capsule: Cup-shaped structure containing a bundle of blood capillaries called the Glomerulus.
    • Tubular Part: Long coiled tube consisting of Proximal Convoluted Tubule (PCT), Loop of Henle, and Distal Convoluted Tubule (DCT). DCT opens into a Collecting Duct.
• Urine Formation (Steps):
  1. Glomerular Filtration (Ultrafiltration): Blood enters the glomerulus under high pressure. Water, glucose, amino acids, salts, urea, etc., are filtered out from blood into Bowman's capsule, forming the glomerular filtrate. Large molecules like proteins and blood cells remain in the blood.
  2. Tubular Reabsorption: As the filtrate passes through the tubular part, useful substances like glucose, amino acids, most salts, and a major amount of water are selectively reabsorbed back into the blood capillaries surrounding the tubule. The amount of water reabsorbed depends on body's need and ADH hormone.
  3. Tubular Secretion: Some waste products (like urea, potassium ions, hydrogen ions, certain drugs) that remained in the blood are actively secreted from the blood capillaries into the filtrate in the tubule.
• The fluid remaining after these steps is Urine. Urine contains water, urea, uric acid, salts, etc.
• Pathway of Urine: Collecting Ducts → Renal Pelvis → Ureters → Urinary Bladder (stores urine temporarily) → Urethra (tube through which urine is expelled).
• Artificial Kidney (Haemodialysis): A procedure used when kidneys fail.
  • Blood from the patient's artery is passed through a dialyzer machine.
  • The dialyzer contains tubes made of a selectively permeable membrane, suspended in a dialyzing fluid.
  • Dialyzing fluid has the same composition as normal plasma, but lacks urea and excess salts.
  • Waste products (urea, excess salts) diffuse from the blood into the dialyzing fluid across the membrane. Useful substances remain in the blood.
  • Purified blood is returned to the patient's vein.

B. Excretion in Plants

• Plants lack a specialized excretory system. They use various strategies:
  • Gaseous Wastes: Oxygen (byproduct of photosynthesis) and Carbon Dioxide (byproduct of respiration) are removed through stomata and lenticels.
  • Water Waste: Excess water is removed by transpiration.
  • Solid/Liquid Wastes:
    • Stored in cell vacuoles.
    • Stored in leaves or bark, which are then shed.
    • Excreted as gums and resins, especially in old xylem.
    • Some waste substances are excreted into the soil around them.

Conclusion

All life processes – Nutrition, Respiration, Transportation, and Excretion – are interconnected and essential for the survival and maintenance of living organisms. They ensure the supply of energy and materials, removal of waste, and overall functioning of the organism. Understanding these processes is fundamental to biology.