Life Processes Class 10

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### 1. Introduction to Life Processes - **Definition:** Life processes are fundamental functions performed by living organisms to maintain their life. These include nutrition, respiration, transportation, and excretion. All these processes are essential for the survival of an organism. - **Why are they necessary?** - **Energy Requirement:** All living organisms require energy to perform various activities like growth, movement, repair, and maintenance. This energy is derived from food through the process of nutrition and then released through respiration. - **Cellular Maintenance:** Cells are constantly undergoing wear and tear. Life processes ensure continuous repair and replacement of damaged cells and tissues. - **Growth and Development:** Organisms grow and develop by adding new cells and tissues, which requires nutrients and energy supplied by these processes. - **Waste Removal:** Metabolic activities produce waste products that are toxic if accumulated. Excretion ensures their removal. - **Internal Environment Regulation:** Transportation helps in distributing substances and maintaining a stable internal environment (homeostasis). - **Unicellular vs. Multicellular Organisms:** - **Unicellular:** In single-celled organisms (e.g., Amoeba, Paramecium), all life processes occur within that one cell. Exchange of gases, intake of food, and removal of wastes happen directly across the cell surface. - **Multicellular:** In complex multicellular organisms (e.g., humans, trees), specialized organs and organ systems perform different life processes. This division of labor makes them highly efficient but also necessitates elaborate transportation systems. For example, humans have a digestive system for nutrition, a respiratory system for respiration, a circulatory system for transport, and an excretory system for waste removal. ### 2. Nutrition - **Definition:** The process by which an organism obtains nutrients from its surroundings and utilizes them to generate energy, for growth, repair, and maintenance of the body. Nutrients are substances that provide nourishment essential for the maintenance of life and for growth. - **Importance of Nutrients:** - **Energy Source:** Carbohydrates and fats are primary energy providers. - **Body Building:** Proteins are essential for growth and repair of tissues. - **Regulation:** Vitamins and minerals regulate various body functions and protect against diseases. - **Modes of Nutrition:** #### 2.1 Autotrophic Nutrition - **Meaning:** "Auto" (self) + "trophos" (nourishment). Organisms that can synthesize their own food from simple inorganic substances like carbon dioxide and water, using an external energy source. - **Types:** - **Photoautotrophs:** Use light energy (e.g., plants, algae, cyanobacteria). This is the most common form. - **Chemoautotrophs:** Use chemical energy from the oxidation of inorganic substances (e.g., some bacteria like nitrifying bacteria). - **Photosynthesis (in Photoautotrophs):** - **Equation:** $6CO_2 (Carbon Dioxide) + 6H_2O (Water) \xrightarrow{\text{Sunlight, Chlorophyll}} C_6H_{12}O_6 (Glucose) + 6O_2 (Oxygen)$ - **Raw Materials:** - **Carbon Dioxide ($CO_2$):** Taken from the atmosphere through stomata. - **Water ($H_2O$):** Absorbed from the soil by roots. - **Sunlight:** Energy source. - **Chlorophyll:** Green pigment present in chloroplasts, absorbs light energy. - **Site of Photosynthesis:** **Chloroplasts** within plant cells, primarily in the mesophyll cells of leaves. Chloroplasts contain stacks of thylakoids called grana, where light-dependent reactions occur, and a fluid-filled space called the stroma, where light-independent reactions (Calvin cycle) occur. - **Main Events of Photosynthesis:** 1. **Absorption of Light Energy:** Chlorophyll pigments in the thylakoid membranes absorb solar energy. 2. **Conversion of Light Energy to Chemical Energy and Splitting of Water Molecules (Photolysis):** The absorbed light energy is used to split water molecules into hydrogen ions ($H^+$), electrons ($e^-$), and oxygen ($O_2$). This process also generates ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate), which are energy carriers. 3. **Reduction of Carbon Dioxide to Carbohydrates:** The chemical energy (ATP and NADPH) produced in the light-dependent reactions is used in the stroma to fix carbon dioxide into glucose and other carbohydrates. This is often referred to as the Calvin cycle. - **Stomata:** - **Structure:** Tiny pores predominantly found on the surface of leaves. Each stoma is flanked by two kidney-shaped **guard cells**. - **Function:** - **Gaseous Exchange:** Allows $CO_2$ to enter the leaf for photosynthesis and $O_2$ to be released. - **Transpiration:** Evaporation of water vapor from the leaf surface. - **Opening and Closing:** Regulated by the guard cells. When guard cells absorb water, they swell, become turgid, and bend outwards, opening the stomatal pore. When they lose water, they shrink, become flaccid, and the pore closes. This mechanism helps to conserve water. #### 2.2 Heterotrophic Nutrition - **Meaning:** "Hetero" (other) + "trophos" (nourishment). Organisms that cannot synthesize their own food and depend on other organisms for their nutritional requirements. They consume complex organic substances. - **Types:** - **Holozoic Nutrition:** Involves the ingestion of solid or liquid organic food, which is then digested, absorbed, and assimilated. - **Examples:** Humans, animals, Amoeba. - **Steps:** Ingestion $\rightarrow$ Digestion $\rightarrow$ Absorption $\rightarrow$ Assimilation $\rightarrow$ Egestion. - **Saprophytic Nutrition (Saprophytism):** Organisms obtain nutrients from dead and decaying organic matter. They secrete digestive enzymes outside their body onto the substrate, and then absorb the digested simple molecules. - **Examples:** Fungi (mushrooms, bread mould), many bacteria. - **Parasitic Nutrition (Parasitism):** Organisms (parasites) live on or inside another living organism (host) and derive nutrition from it, often harming the host in the process, but usually not killing it immediately. - **Examples:** - **Plant Parasites:** Cuscuta (Amarbel) on other plants. - **Animal Parasites:** Ticks, lice, leeches (ectoparasites); tapeworms, roundworms, Plasmodium (endoparasites). #### 2.3 Nutrition in Humans (Holozoic) - **Human Digestive System:** A long, muscular tube called the **alimentary canal** (or digestive tract) and associated digestive glands. 1. **Mouth (Buccal Cavity):** - **Ingestion:** Taking food into the body. - **Mechanical Digestion:** Chewing (mastication) by teeth breaks food into smaller pieces, increasing surface area for enzyme action. - **Chemical Digestion:** Salivary glands secrete **saliva**, which contains: - **Salivary Amylase (Ptyalin):** Begins the digestion of complex carbohydrates (starch) into simpler sugars (maltose). - **Mucus:** Lubricates food for easy swallowing. - **Tongue:** Helps in mixing food with saliva and swallowing. 2. **Pharynx:** Common passage for food and air. 3. **Oesophagus (Food Pipe):** - Connects the pharynx to the stomach. - Food moves down by wave-like muscular contractions called **peristaltic movements**. This ensures food moves in one direction, regardless of body position. 4. **Stomach:** J-shaped muscular bag located in the upper abdomen. - **Mechanical Digestion:** Churning movements mix food thoroughly with digestive juices. - **Chemical Digestion:** Gastric glands in the stomach wall secrete **gastric juice**, containing: - **Hydrochloric Acid (HCl):** - Kills bacteria ingested with food. - Provides an acidic medium (pH 1.5-3.5) necessary for the activation and optimal action of pepsin. - **Pepsin:** An enzyme that begins the digestion of **proteins** into smaller peptides. It is secreted in an inactive form (pepsinogen) to protect the stomach lining. - **Mucus:** Protects the inner lining of the stomach from the corrosive action of HCl and pepsin. 5. **Small Intestine:** The longest part of the alimentary canal (about 6-7 meters in adults). It's the primary site for complete digestion and absorption of food. - **Structure:** Highly coiled and narrow tube. Its inner lining has millions of tiny, finger-like projections called **villi** (singular: villus). - **Role of Villi:** Villi significantly increase the surface area for efficient absorption of digested food. Each villus has a rich network of blood vessels to transport absorbed nutrients to the bloodstream. - **Receives Secretions from:** - **Liver:** Secretes **bile juice**, which is stored in the gallbladder. Bile does not contain enzymes but performs two crucial functions: - **Emulsification of Fats:** Breaks down large fat globules into smaller ones, increasing the surface area for lipase action. - **Alkaline Medium:** Makes the acidic food coming from the stomach alkaline, which is necessary for the action of pancreatic enzymes. - **Pancreas:** Secretes **pancreatic juice**, containing several digestive enzymes: - **Pancreatic Amylase:** Digestion of remaining starch. - **Trypsin:** Digestion of proteins (into smaller peptides). - **Lipase:** Digestion of emulsified fats (into fatty acids and glycerol). - **Intestinal Glands:** The wall of the small intestine itself secretes **intestinal juice (succus entericus)**, which contains enzymes that complete the digestion: - **Carbohydrates:** Complex carbohydrates are broken down into **glucose**. - **Proteins:** Peptides are broken down into **amino acids**. - **Fats:** Fatty acids and glycerol are already formed by pancreatic lipase. 6. **Large Intestine:** Wider and shorter than the small intestine (about 1.5 meters). - **Function:** Primarily absorbs excess water from the undigested food material. - **Faeces Formation:** The remaining undigested and unabsorbed food, now semi-solid, forms faeces. 7. **Rectum:** Stores faeces temporarily. 8. **Anus:** The exit point for faeces, controlled by the anal sphincter muscle. ### 3. Respiration - **Definition:** The biochemical process by which living organisms obtain energy by combining oxygen with food molecules (like glucose) to release energy, carbon dioxide, and water. It's distinct from breathing, which is the physical act of exchanging gases. - **Overall Goal:** To release energy (in the form of ATP) from digested food for various life activities. - **Types of Respiration:** #### 3.1 Aerobic Respiration - **Meaning:** "Aero" (air/oxygen). Occurs in the presence of molecular oxygen. It is the most efficient way to release energy from glucose. - **Equation:** $C_6H_{12}O_6 (Glucose) + 6O_2 (Oxygen) \rightarrow 6CO_2 (Carbon Dioxide) + 6H_2O (Water) + \text{Energy (38 ATP)}$ - **Steps:** 1. **Glycolysis:** - **Location:** Cytoplasm of the cell. - **Process:** One molecule of glucose (a 6-carbon compound) is partially broken down into two molecules of **pyruvate** (a 3-carbon compound). - **Energy Yield:** Produces a small amount of ATP (net 2 ATP) and NADH (electron carrier). - **Oxygen Requirement:** Does not require oxygen; it's common to both aerobic and anaerobic respiration. 2. **Krebs Cycle (Citric Acid Cycle) and Electron Transport Chain (ETC):** - **Location:** Mitochondria (specifically, the Krebs cycle in the mitochondrial matrix and ETC on the inner mitochondrial membrane). - **Process:** In the presence of oxygen, pyruvate is completely oxidized. - Pyruvate is converted to Acetyl-CoA, which enters the Krebs cycle. - The Krebs cycle generates $CO_2$, ATP (small amount), NADH, and $FADH_2$ (another electron carrier). - NADH and $FADH_2$ then deliver electrons to the Electron Transport Chain. As electrons pass down the chain, their energy is used to pump protons, creating a gradient. This proton gradient drives the synthesis of a large amount of ATP (oxidative phosphorylation). Oxygen acts as the final electron acceptor. - **Energy Yield:** The majority of ATP (approx. 36 ATP) is produced in these stages. - **Overall Energy:** Highly efficient, yielding a total of **38 ATP** molecules per glucose molecule. #### 3.2 Anaerobic Respiration - **Meaning:** "An" (without) + "aero" (air/oxygen). Occurs in the absence of molecular oxygen. It is less efficient in energy production compared to aerobic respiration. - **Common Pathway:** Glycolysis still occurs in the cytoplasm, producing pyruvate. However, without oxygen, pyruvate cannot enter the mitochondria for the Krebs cycle and ETC. Instead, it undergoes fermentation. - **Types of Anaerobic Respiration (Fermentation):** 1. **Lactic Acid Fermentation:** - **Occurs in:** Animal muscle cells during strenuous exercise when oxygen supply is insufficient. Also in some bacteria. - **Process:** Pyruvate is converted into **lactic acid**. - **Equation:** $C_6H_{12}O_6 \rightarrow 2 \text{ Lactic Acid} + \text{Energy (2 ATP)}$ - **Consequences:** Accumulation of lactic acid in muscle cells causes muscle cramps and fatigue. The lactic acid is eventually transported to the liver and converted back to pyruvate or glucose when oxygen becomes available. 2. **Alcoholic Fermentation:** - **Occurs in:** Yeast and some bacteria. - **Process:** Pyruvate is converted into **ethanol (alcohol)** and carbon dioxide. - **Equation:** $C_6H_{12}O_6 \rightarrow 2 \text{ Ethanol} + 2CO_2 + \text{Energy (2 ATP)}$ - **Applications:** Used in brewing (alcohol production) and baking (carbon dioxide causes dough to rise). - **Overall Energy:** Much less efficient, yielding only **2 ATP** molecules per glucose molecule. #### 3.3 Respiration in Humans - **Human Respiratory System:** Designed for efficient gaseous exchange. 1. **Nostrils:** The entry point for air. Air is filtered by fine hairs, moistened by mucus, and warmed by blood vessels. 2. **Nasal Passage:** Leads to the pharynx. 3. **Pharynx:** Common passage for food and air. 4. **Larynx (Voice Box):** Contains vocal cords. 5. **Trachea (Windpipe):** - A tube extending from the larynx into the chest cavity. - Supported by C-shaped rings of cartilage that prevent it from collapsing even when there is less air. 6. **Bronchi (singular: Bronchus):** The trachea divides into two bronchi, one entering each lung. These are also supported by cartilaginous rings. 7. **Bronchioles:** Within the lungs, each bronchus divides repeatedly into finer and finer tubes called bronchioles. These lack cartilaginous rings. 8. **Alveoli (Air Sacs):** - The bronchioles terminate in clusters of tiny, balloon-like structures called alveoli. - **Structure:** Each lung contains millions of alveoli, providing an enormous surface area (about 80 square meters) for gaseous exchange. Their walls are extremely thin (single-cell thick) and richly supplied with blood capillaries. - **Function:** The primary site of gaseous exchange. - **Oxygen ($O_2$) Diffusion:** Oxygen from the inhaled air diffuses across the thin alveolar and capillary walls into the blood, where it binds to hemoglobin in red blood cells. - **Carbon Dioxide ($CO_2$) Diffusion:** Carbon dioxide from the blood (a waste product from cellular respiration in tissues) diffuses into the alveoli to be exhaled. #### 3.4 Mechanism of Breathing (Ventilation) - **Breathing:** The mechanical process of taking in air (inhalation) and expelling it (exhalation). It involves changes in the volume of the thoracic (chest) cavity, which in turn changes the pressure within the lungs. 1. **Inhalation (Inspiration):** - **Diaphragm:** Contracts and flattens, moving downwards. - **Rib Muscles (External Intercostals):** Contract, causing the rib cage to lift upwards and outwards. - **Chest Cavity Volume:** Increases significantly. - **Pressure in Lungs:** Decreases below atmospheric pressure. - **Air Movement:** Air rushes into the lungs to equalize the pressure. 2. **Exhalation (Expiration):** - **Diaphragm:** Relaxes and domes upwards. - **Rib Muscles:** Relax, causing the rib cage to move downwards and inwards. - **Chest Cavity Volume:** Decreases. - **Pressure in Lungs:** Increases above atmospheric pressure. - **Air Movement:** Air is forced out of the lungs. #### 3.5 Transportation of Gases - **Oxygen Transport:** - Primarily transported by **hemoglobin**, a red pigment present in red blood cells (RBCs). - Hemoglobin has a high affinity for oxygen and forms unstable oxyhemoglobin ($HbO_2$). - At the tissues, where oxygen concentration is low and $CO_2$ concentration is high (and pH is lower), oxyhemoglobin releases oxygen. - **Carbon Dioxide Transport:** - More soluble in water than oxygen. - Transported in three ways: 1. **Dissolved in Plasma:** About 7% of $CO_2$ is transported as dissolved gas in blood plasma. 2. **Bicarbonate Ions:** About 70% of $CO_2$ diffuses into RBCs and reacts with water to form carbonic acid, which then dissociates into bicarbonate ions ($HCO_3^-$). These ions are transported in the plasma. This is the most significant form of transport. 3. **Carbaminohemoglobin:** About 23% of $CO_2$ binds to hemoglobin (at a different site than oxygen) to form carbaminohemoglobin. - At the lungs, where $CO_2$ concentration is low, these processes reverse, and $CO_2$ is released into the alveoli for exhalation. ### 4. Transportation - **Definition:** The process by which substances absorbed or synthesized in one part of the body are carried to other parts of the body. This includes the movement of nutrients, oxygen, hormones, and waste products. #### 4.1 Transportation in Plants - Plants have specialized vascular tissues for long-distance transport. - **1. Xylem:** - **Function:** Transports water and dissolved minerals from the roots upwards to the leaves and other aerial parts of the plant. - **Components:** Consists of tracheids, vessels (xylem vessels), xylem parenchyma, and xylem fibres. Tracheids and vessels are the main conducting elements. - **Mechanism of Water Transport:** - **Root Pressure:** Roots actively absorb mineral ions from the soil. This creates an osmotic gradient, causing water to move into the root xylem by osmosis. This builds up a positive pressure (root pressure) that pushes water up a short distance. This is more significant at night when transpiration is low. - **Transpiration Pull (Cohesion-Tension Theory):** This is the most important mechanism for water transport in tall plants. - **Transpiration:** Evaporation of water from the stomata of leaves creates a "suction" or "pull" on the water column in the xylem. - **Cohesion:** Water molecules are cohesive (stick to each other) due to hydrogen bonding. - **Adhesion:** Water molecules adhere (stick) to the hydrophilic walls of the xylem vessels. - **Continuous Column:** Due to cohesion and adhesion, water forms an unbroken, continuous column in the xylem vessels, extending from the roots to the leaves. As water evaporates from leaves, the entire column is pulled upwards, like drinking through a straw. - **2. Phloem:** - **Function:** Transports synthesized food (mainly sugars like sucrose) from the leaves (site of photosynthesis) to other parts of the plant, including storage organs (roots, fruits) and growing regions (buds, young leaves). This process is called **translocation**. - **Components:** Consists of sieve tubes, companion cells, phloem parenchyma, and phloem fibres. Sieve tubes are the main conducting elements. - **Mechanism of Translocation (Pressure Flow Hypothesis):** 1. **Loading at Source:** At the source (e.g., leaves), glucose is synthesized and converted to sucrose. Sucrose is then actively transported (requires ATP) into the sieve tubes of the phloem. 2. **Osmosis:** The increase in solute concentration (sucrose) in the sieve tubes causes water from the adjacent xylem to move into the phloem by osmosis. 3. **Pressure Gradient:** This influx of water increases the turgor pressure within the sieve tubes. This high pressure at the source pushes the phloem sap towards regions of lower pressure (sinks). 4. **Unloading at Sink:** At the sink (e.g., roots, fruits, growing points), sucrose is actively transported out of the phloem and utilized or stored. 5. **Water Recycles:** The removal of sucrose from the phloem at the sink reduces the osmotic potential, causing water to move out of the phloem and back into the xylem. #### 4.2 Transportation in Humans (Circulatory System) - The human circulatory system (or cardiovascular system) is a closed, double circulatory system. - **Components:** 1. **Blood:** The fluid connective tissue that circulates throughout the body. - **Plasma:** The liquid matrix (about 55% of blood volume). It transports water, dissolved proteins, digested food (glucose, amino acids, fats), salts, hormones, and waste products ($CO_2$, urea). - **Red Blood Cells (RBCs) / Erythrocytes:** - Biconcave, anucleated cells (in mammals). - Contain **hemoglobin**, an iron-containing red pigment that binds reversibly with oxygen. - Primary function: Transport oxygen from the lungs to the body tissues. - **White Blood Cells (WBCs) / Leukocytes:** - Larger than RBCs, nucleated. - Part of the immune system; fight infections by phagocytosis (engulfing pathogens) or producing antibodies. - **Platelets / Thrombocytes:** - Small, irregular, anucleated cell fragments. - Essential for **blood clotting (coagulation)** to prevent excessive blood loss from injuries. 2. **Blood Vessels:** A network of tubes that carry blood. - **Arteries:** - Carry oxygenated blood **away from the heart** to various organs (except the pulmonary artery, which carries deoxygenated blood to the lungs). - Have thick, muscular, and elastic walls to withstand the high pressure generated by the heart's pumping action. - Branch into smaller arterioles. - **Veins:** - Carry deoxygenated blood **towards the heart** from various organs (except the pulmonary vein, which carries oxygenated blood from the lungs to the heart). - Have thinner walls and larger lumens than arteries. - Contain **valves** to prevent the backflow of blood, as blood pressure is lower in veins. - Small venules merge to form veins. - **Capillaries:** - The smallest and most numerous blood vessels. - Form a vast network within tissues, connecting arterioles and venules. - Have extremely thin walls (single-cell thick endothelium) to facilitate the exchange of gases, nutrients, hormones, and waste products between blood and tissue cells. 3. **Heart:** A muscular, four-chambered pumping organ located in the chest cavity, slightly to the left. - **Structure:** - **Four Chambers:** Two upper chambers called **atria** (singular: atrium) and two lower, thicker-walled chambers called **ventricles**. - Right atrium receives deoxygenated blood from the body. - Right ventricle pumps deoxygenated blood to the lungs. - Left atrium receives oxygenated blood from the lungs. - Left ventricle pumps oxygenated blood to the rest of the body. - **Septum:** A muscular wall that completely divides the left and right sides of the heart. This prevents the mixing of oxygenated and deoxygenated blood, which is crucial for maintaining a high oxygen supply in warm-blooded animals (mammals and birds). - **Valves:** Located between atria and ventricles (tricuspid on right, bicuspid/mitral on left) and at the exit of ventricles into arteries (semilunar valves). They ensure unidirectional flow of blood and prevent backflow. - **Cardiac Cycle:** The sequence of events that occurs during one complete heartbeat. It involves the rhythmic contraction (systole) and relaxation (diastole) of the heart chambers. - **Double Circulation:** In humans, blood passes through the heart twice during one complete cycle. This ensures efficient delivery of oxygen to the body. - **Pulmonary Circulation:** Deoxygenated blood from the right ventricle is pumped to the lungs via the pulmonary artery. In the lungs, blood gets oxygenated and returns to the left atrium via the pulmonary veins. - **Systemic Circulation:** Oxygenated blood from the left ventricle is pumped to all parts of the body (except lungs) via the aorta and its branches. Deoxygenated blood from the body returns to the right atrium via the vena cava. - **Blood Pressure:** - The force that blood exerts against the wall of a vessel. - **Systolic Pressure:** Pressure during ventricular contraction (pumping). (Normal: ~120 mm Hg) - **Diastolic Pressure:** Pressure during ventricular relaxation (filling). (Normal: ~80 mm Hg) - **Hypertension (High Blood Pressure):** A chronic condition where blood pressure remains consistently high (e.g., 140/90 mm Hg or higher). It can lead to heart disease, stroke, and kidney damage. #### 4.3 Lymphatic System - **Lymph:** A colorless fluid that is formed when some plasma, proteins, and blood cells escape from the capillaries into the intercellular spaces. It is similar to blood plasma but contains less protein. - **Lymphatic Vessels:** A network of vessels that collect lymph from the intercellular spaces and eventually drain it back into the major veins. - **Lymph Nodes:** Small, bean-shaped organs located along lymphatic vessels. They filter lymph, trapping bacteria and other harmful substances, and contain lymphocytes (a type of WBC) that fight infection. - **Functions:** 1. **Drainage:** Returns excess tissue fluid (interstitial fluid) and leaked proteins from the intercellular spaces back into the bloodstream, maintaining blood volume. 2. **Fat Absorption:** Carries digested and absorbed fats from the small intestine (via lacteals) to the bloodstream. 3. **Immunity:** Part of the immune system, producing lymphocytes and filtering pathogens. ### 5. Excretion - **Definition:** The biological process of removing harmful metabolic waste products (by-products of cellular reactions) from the body. These waste products, if allowed to accumulate, can become toxic and disrupt normal physiological functions. #### 5.1 Excretion in Plants - Plants have simpler excretory mechanisms than animals because their metabolic rates are generally lower, and they produce fewer waste products. - **Gaseous Wastes:** - **Oxygen ($O_2$):** A by-product of photosynthesis, removed through **stomata** (on leaves) and **lenticels** (on stems). - **Carbon Dioxide ($CO_2$):** A by-product of respiration, also removed through stomata and lenticels. - **Excess Water:** - Removed primarily through **transpiration** (evaporation from stomata). - Also by **guttation** (loss of water droplets from leaf margins) in some plants. - **Solid and Liquid Wastes:** - **Storage in Vacuoles:** Many waste products are stored in the large central vacuoles of plant cells, where they are isolated from the rest of the cytoplasm. When leaves fall, these wastes are removed. - **Gums and Resins:** Old xylem often stores waste products in the form of gums, resins, and latex. These are eventually secreted or become part of the non-living heartwood. - **Crystals:** Some plants store waste as insoluble crystals (e.g., calcium oxalate). - **Excretion into Soil:** Some waste substances are secreted into the surrounding soil through the roots. - **Shedding Parts:** Plants can shed waste-laden leaves, bark, or fruits. #### 5.2 Excretion in Humans (Excretory System) - The human excretory system (or urinary system) is primarily responsible for filtering blood and forming urine. - **Main Organs:** 1. **Kidneys (Pair):** - **Location:** Two bean-shaped organs located on either side of the backbone, in the abdomen. - **Function:** The primary organs of excretion. They filter the blood to remove nitrogenous waste products (urea, uric acid, creatinine), excess salts, and excess water, forming urine. They also play a crucial role in maintaining fluid balance, electrolyte balance, and blood pH. - **Nephrons:** Each kidney contains millions of microscopic functional units called **nephrons**. A nephron is the structural and functional unit of the kidney. Each nephron consists of two main parts: - **A. Renal Corpuscle (Malpighian Body):** - **Bowman's Capsule:** A cup-shaped structure that encloses a tuft of capillaries. - **Glomerulus:** A network of tiny blood capillaries within the Bowman's capsule. - **Ultrafiltration/Glomerular Filtration:** Blood enters the glomerulus under high pressure. The thin walls of the glomerular capillaries act as a filter, allowing water, salts, glucose, amino acids, urea, and other small molecules to pass from the blood into the Bowman's capsule, forming the **glomerular filtrate**. Larger molecules like proteins and blood cells do not pass. - **B. Renal Tubule:** A long, coiled tube extending from the Bowman's capsule. It has different segments: Proximal Convoluted Tubule (PCT), Loop of Henle, Distal Convoluted Tubule (DCT), and Collecting Duct. - **Selective Reabsorption:** As the filtrate flows through the renal tubule, useful substances like all glucose, amino acids, most of the water, and necessary salts are reabsorbed back into the blood capillaries surrounding the tubule. This process is selective and can be active or passive. - **Tubular Secretion:** Additional waste products (e.g., excess ions like $K^+$, some drugs) are actively secreted from the blood in the capillaries directly into the filtrate within the renal tubule. This helps in fine-tuning the composition of urine and maintaining blood pH. - **Urine Formation:** The fluid remaining in the collecting duct after filtration, reabsorption, and secretion is **urine**. Its composition is mainly water, urea, uric acid, creatinine, and excess salts. 2. **Ureters (Pair):** - Two muscular tubes that carry urine from each kidney to the urinary bladder. Peristaltic movements help propel urine. 3. **Urinary Bladder:** - A muscular, elastic sac that temporarily stores urine until it is voluntarily released from the body. - Its walls are stretchable, allowing it to hold a significant volume of urine. 4. **Urethra:** - A tube that carries urine from the urinary bladder to the outside of the body. - Its opening is controlled by a sphincter muscle. - **Other Excretory Organs:** - **Lungs:** Excrete carbon dioxide ($CO_2$) and water vapor during respiration. - **Skin:** Excretes sweat through sweat glands. Sweat contains water, salts (NaCl), and a small amount of urea and lactic acid. It also helps in thermoregulation (cooling the body). - **Liver:** Processes many waste products and toxic substances, converting them into less harmful forms that can be excreted by the kidneys or in bile (e.g., breakdown of hemoglobin, detoxification of drugs). - **Dialysis (Artificial Kidney):** - A life-saving procedure used for patients whose kidneys have failed (kidney failure). - The patient's blood is drawn from an artery, passed through a dialyzing unit (artificial kidney). - The dialyzing unit contains a semi-permeable membrane that separates the blood from a dialyzing fluid (dialysate). - The dialyzing fluid has the same composition as blood plasma, except it lacks nitrogenous wastes. - Waste products (urea, excess salts) from the patient's blood diffuse across the membrane into the dialyzing fluid, following the concentration gradient. Useful substances are retained in the blood. - The cleaned blood is then returned to the patient's body through a vein. ### 6. Control and Coordination (Brief Overview) - **Definition:** The process by which various body functions are regulated and integrated to maintain a stable internal environment (homeostasis) and respond appropriately to changes in the external environment. It involves two main systems: the nervous system and the endocrine system. - **Need for Control and Coordination:** - To respond to stimuli (e.g., touch, light, pain). - To maintain body balance and posture. - To regulate internal processes like digestion, respiration, and circulation. - To ensure coordinated actions of different organs for complex tasks. #### 6.1 Control and Coordination in Animals ##### 6.1.1 Nervous System - **Function:** Provides rapid, short-term, and precise control through electrical impulses. - **Basic Unit: Neuron (Nerve Cell):** The structural and functional unit of the nervous system. - **Structure:** - **Dendrite:** Short, branched extensions that receive nerve impulses (information) from other neurons or sensory receptors. - **Cell Body (Soma):** Contains the nucleus and cytoplasm; processes the incoming information. - **Axon:** A long, slender projection that transmits nerve impulses away from the cell body to other neurons, muscles, or glands. It can be covered by a myelin sheath, which insulates the axon and speeds up impulse transmission. - **Nerve Endings/Axon Terminals:** The branched ends of the axon that release neurotransmitters. - **Transmission of Nerve Impulse:** 1. Information is acquired by the dendrite. 2. It travels as an electrical impulse (action potential) from the dendrite to the cell body and then along the axon to its end. 3. At the axon terminal, the electrical impulse triggers the release of chemical substances called **neurotransmitters**. 4. These neurotransmitters cross a tiny gap called the **synapse** (or synaptic cleft) and bind to receptors on the dendrite of the next neuron, generating a new electrical impulse in that neuron. - **Types of Nerves/Neurons:** - **Sensory Neurons (Afferent):** Carry information from sensory receptors (e.g., skin, eyes) to the Central Nervous System (CNS). - **Motor Neurons (Efferent):** Carry commands from the CNS to effectors (muscles or glands). - **Relay Neurons (Interneurons):** Connect sensory and motor neurons, primarily within the CNS. - **Divisions of the Nervous System:** 1. **Central Nervous System (CNS):** - **Brain:** The main coordinating center. Receives and interprets information, controls thoughts, emotions, memory, voluntary movements, and maintains homeostasis. Protected by the skull and meninges (membranes), and cushioned by cerebrospinal fluid. - **Forebrain:** Cerebrum (thinking, memory, voluntary actions, sensory perception), Thalamus (relay station), Hypothalamus (controls pituitary gland, regulates hunger, thirst, body temperature). - **Midbrain:** Connects forebrain and hindbrain, involved in visual and auditory reflexes. - **Hindbrain:** Cerebellum (coordination of voluntary movements, balance, posture), Pons (relays signals between cerebrum and cerebellum, regulates respiration), Medulla Oblongata (controls involuntary actions like heartbeat, breathing, blood pressure, swallowing, vomiting). - **Spinal Cord:** A long, cylindrical bundle of nerves extending from the medulla oblongata down the back. It carries signals between the brain and the rest of the body and mediates reflex actions. Protected by the vertebral column. 2. **Peripheral Nervous System (PNS):** - Consists of all the nerves that branch out from the brain and spinal cord to all other parts of the body, including muscles and organs. - **Somatic Nervous System:** Controls voluntary movements of skeletal muscles. - **Autonomic Nervous System:** Controls involuntary actions of internal organs and glands (e.g., heartbeat, digestion, breathing). - **Sympathetic Nervous System:** Prepares the body for "fight or flight" response (e.g., increases heart rate, dilates pupils). - **Parasympathetic Nervous System:** Promotes "rest and digest" functions (e.g., slows heart rate, stimulates digestion). - **Reflex Arc:** - A rapid, involuntary, and automatic response to a stimulus that does not involve conscious thought from the brain. It is the functional unit of the nervous system. - **Pathway:** 1. **Receptor:** Detects the stimulus (e.g., pain receptors in the skin). 2. **Sensory Neuron:** Transmits the impulse from the receptor to the spinal cord. 3. **Relay Neuron (Interneuron):** In the spinal cord, it processes the information and transmits it to a motor neuron. 4. **Motor Neuron:** Carries the impulse from the spinal cord to the effector organ. 5. **Effector:** A muscle or gland that responds to the stimulus (e.g., muscle contracts to withdraw hand). - **Example:** Withdrawing your hand immediately after touching a hot object. ##### 6.1.2 Endocrine System - **Function:** Provides slower, long-term, and widespread control through chemical messengers called hormones. - **Hormones:** Chemical substances secreted by specialized glands (endocrine glands) directly into the bloodstream, which then transport them to target cells or organs to exert their specific effects. - **Endocrine Glands (Ductless Glands):** - **Pituitary Gland (Master Gland):** Located at the base of the brain. Secretes **Growth Hormone** (GH, regulates growth and development) and several stimulating hormones that control other endocrine glands (e.g., TSH, ACTH, FSH, LH). - **Thyroid Gland:** Located in the neck. Secretes **Thyroxine**, which regulates metabolism (carbohydrate, fat, and protein metabolism) and is essential for normal growth and development. Requires iodine for synthesis. Deficiency causes goiter. - **Pancreas:** Located behind the stomach. Acts as both an exocrine and endocrine gland. Its endocrine part (Islets of Langerhans) secretes: - **Insulin:** Lowers blood glucose levels by promoting glucose uptake by cells and its conversion to glycogen in the liver and muscles. - **Glucagon:** Raises blood glucose levels by stimulating the breakdown of glycogen into glucose. - **Diabetes Mellitus:** Caused by insufficient insulin secretion or resistance to insulin, leading to high blood glucose levels. - **Adrenal Glands:** Located on top of each kidney. - **Adrenaline (Epinephrine):** Secreted by the adrenal medulla. Known as the "fight or flight" hormone. Prepares the body for stress by increasing heart rate, blood pressure, breathing rate, and blood glucose levels. - **Corticosteroids:** Secreted by the adrenal cortex. Involved in metabolism, immune response, and stress response. - **Gonads:** - **Testes (in males):** Secrete **Testosterone**, responsible for male secondary sexual characteristics and sperm production. - **Ovaries (in females):** Secrete **Estrogen** (responsible for female secondary sexual characteristics and uterine lining development) and **Progesterone** (maintains pregnancy). - **Feedback Mechanism:** The regulation of hormone secretion is often achieved through feedback loops. For example, high blood sugar stimulates insulin release, which lowers blood sugar. When blood sugar drops, insulin release is inhibited. #### 6.2 Control and Coordination in Plants - Plants do not have a nervous system or muscles. Their control and coordination are achieved through chemical substances called **phytohormones** (plant hormones) and various types of movements. ##### 6.2.1 Phytohormones (Plant Hormones) - **Functions:** Regulate growth, development, and responses to environmental stimuli. 1. **Auxins:** - **Location:** Primarily produced at the tips of shoots and roots. - **Functions:** Promote cell elongation (especially in shoots), root growth, phototropism (growth towards light), gravitropism (growth towards gravity), and apical dominance (inhibition of lateral bud growth by the apical bud). 2. **Gibberellins:** - **Functions:** Promote stem elongation, seed germination, and flowering. 3. **Cytokinins:** - **Location:** Primarily synthesized in regions of rapid cell division (e.g., roots, developing fruits). - **Functions:** Promote cell division, delay leaf senescence (aging), and help break dormancy in seeds and buds. 4. **Abscisic Acid (ABA):** - **Functions:** Often called a "stress hormone." Inhibits growth, promotes dormancy in seeds and buds, causes stomatal closure during water stress (to conserve water), and promotes abscission (shedding of leaves and fruits). 5. **Ethylene:** - **Functions:** A gaseous hormone that promotes fruit ripening and senescence (aging) of leaves and flowers. ##### 6.2.2 Plant Movements - **1. Tropic Movements (Tropisms):** - **Definition:** Growth movements of a plant part in a particular direction in response to an external stimulus. These are typically slow and irreversible. - **Types:** - **Phototropism:** Growth towards or away from light. Shoots are positively phototropic (grow towards light), while roots are negatively phototropic (grow away from light or are indifferent). - **Geotropism (Gravitropism):** Growth towards or away from gravity. Roots are positively geotropic (grow downwards), while shoots are negatively geotropic (grow upwards). - **Hydrotropism:** Growth towards water. Roots are positively hydrotropic. - **Chemotropism:** Growth in response to chemical stimuli. Example: Pollen tube grows towards the ovule due to chemical signals. - **Thigmotropism:** Growth in response to touch. Example: Tendrils of climbing plants coil around a support. - **2. Nastic Movements:** - **Definition:** Non-directional movements of a plant part in response to a stimulus. The direction of the response is independent of the direction of the stimulus. These are often faster and reversible. - **Types:** - **Thigmonasty (Seismonasty):** Movement in response to touch or mechanical shock. Example: The leaves of the "touch-me-not" plant (Mimosa pudica) fold up rapidly when touched due to changes in turgor pressure in specialized cells (pulvini) at the base of the petioles. - **Photonasty:** Movement in response to light intensity (e.g., opening and closing of certain flowers). - **Thermonasty:** Movement in response to temperature changes.