Transport and Excretion

  • Transportation: Movement of substances within an organism.
    • Transportation in Plants:
      • Xylem: Transports water and minerals from roots to aerial parts.
        • Components: Tracheids, vessels, xylem parenchyma, xylem fibres.
        • Mechanism:
          1. Root Pressure: Osmotic pressure in root cells pushes water up (minor role).
          2. Transpiration Pull: Main driving force. Evaporation of water from stomata creates a suction force (pulls water column up). Cohesion (water molecules stick to each other) and adhesion (water molecules stick to xylem walls) maintain continuous column.
      • Phloem: Transports food (sugars, amino acids) from leaves (source) to other parts (sink).
        • Components: Sieve tubes, companion cells, phloem parenchyma, phloem fibres.
        • Mechanism (Translocation): Active transport of sugars into sieve tubes at source creates high osmotic pressure, causing water to move in by osmosis. This pressure drives the sap to the sink where sugars are actively transported out.
    • Transportation in Humans (Circulatory System):
      • Components: Heart, blood vessels, blood.
      • Blood:
        • Plasma: Fluid matrix (water, proteins, salts, hormones, waste).
        • Red Blood Cells (RBCs/Erythrocytes): Biconcave, no nucleus, contain hemoglobin (oxygen transport).
        • White Blood Cells (WBCs/Leukocytes): Immune response (various types: neutrophils, lymphocytes, monocytes, etc.).
        • Platelets (Thrombocytes): Blood clotting.
      • Lymph: Tissue fluid that enters lymphatic capillaries. Contains plasma proteins, WBCs, fats. Returns fluid to blood, part of immune system.
      • Blood Vessels:
        • Arteries: Thick, elastic, muscular walls; carry oxygenated blood away from heart (pulmonary artery carries deoxygenated blood). High pressure.
        • Veins: Thin, less muscular walls; carry deoxygenated blood towards heart (pulmonary vein carries oxygenated blood). Contain valves to prevent backflow. Low pressure.
        • Capillaries: Single-celled thick walls; site of exchange of gases, nutrients, wastes between blood and tissues.
      • Heart: Muscular, four-chambered pump.
        • Chambers: Right atrium, right ventricle, left atrium, left ventricle.
        • Valves: Prevent backflow (tricuspid, bicuspid/mitral, aortic, pulmonary).
        • Double Circulation:
          1. Pulmonary Circulation: Heart → Lungs → Heart (deoxygenated to oxygenated).
          2. Systemic Circulation: Heart → Body → Heart (oxygenated to deoxygenated).
        • Advantages of Double Circulation: Efficient separation of oxygenated and deoxygenated blood, high pressure supply to body tissues, allowing for higher metabolic rates.
        • Blood Pressure: Systolic (contraction), Diastolic (relaxation). Measured by sphygmomanometer.
  • Excretion: Removal of metabolic waste products.
    • Excretion in Plants:
      • Gaseous wastes \((\text{O}_2, \text{CO}_2)\) via stomata/lenticels.
      • Excess water via transpiration.
      • Solid/liquid wastes stored in vacuoles, leaves (fall off), bark, gums, resins.
    • Excretion in Humans:
      • Kidneys (Urinary System): Main excretory organs.
        • Structure: Pair of kidneys → Ureters → Urinary Bladder → Urethra.
        • Nephron: Functional unit of kidney.
          1. Glomerulus: Tuft of capillaries, site of ultrafiltration (blood filtered under pressure).
          2. Bowman’s Capsule: Cup-shaped structure enclosing glomerulus.
          3. Renal Tubule: Loop of Henle, PCT (proximal convoluted tubule), DCT (distal convoluted tubule), collecting duct.
        • Urine Formation:
          1. Ultrafiltration: Blood plasma minus large proteins and blood cells filters into Bowman’s capsule.
          2. Selective Reabsorption: Useful substances (glucose, amino acids, salts, water) reabsorbed back into blood in renal tubule.
          3. Tubular Secretion: Additional waste products (e.g., some ions, drugs) secreted from blood into renal tubule.
        • Osmoregulation: Kidneys maintain water and salt balance.
      • Other Excretory Organs:
        • Lungs: Excrete \(CO_2\)​ and water vapor.
        • Skin: Excretes sweat (water, salts, urea) via sweat glands.
        • Liver: Processes wastes, converts ammonia to urea.
  • Artificial Kidney (Dialysis): Used in kidney failure. Blood is passed through a dialyzing unit where wastes diffuse into dialyzing fluid.

This MCQ module is based on: Transport and Excretion

This assessment will be based on: Transport and Excretion

Hypothetical Experiment: Optimizing Ultrafiltration and Selective Reabsorption in a Bio-Mimetic Kidney Model

  • Objective: To design and test a simplified artificial kidney model to understand the principles of ultrafiltration, selective reabsorption, and the factors affecting their efficiency.
  • Materials:
    • High-pressure pump (simulating heart).
    • Pressure gauge.
    • Semi-permeable membranes of varying pore sizes (simulating glomerulus and tubule walls).
    • Containers for “blood” (simulated plasma with dissolved glucose, urea, salts, large proteins), “filtrate,” and “urine.”
    • Peristaltic pump for active transport simulation.
    • Glucose test strips, urea test kits, conductivity meter (for salts).
    • Thermostatic bath to maintain physiological temperature.
  • Procedure:
    • Ultrafiltration Setup: Connect the high-pressure pump to a chamber containing the “glomerular membrane” (smallest pore size). Pump “blood” through it, collecting the “filtrate” that passes through the membrane.
    • Selective Reabsorption Setup: Pass the collected “filtrate” through a second chamber containing “tubular membranes” (larger pore size than glomerular, representing different segments of the tubule).
    • Active Transport Simulation: Use a peristaltic pump to actively transport specific substances (e.g., glucose, essential salts) from the “filtrate” back into a separate “blood” reservoir, simulating reabsorption.
    • Waste Collection: The remaining fluid after reabsorption is collected as “urine.”
    • Analysis: Measure concentrations of glucose, urea, and salts in the initial “blood,” “filtrate,” and final “urine” at different flow rates and pressures.
  • Expected Observations:
    • Ultrafiltration: Initial filtrate will contain glucose, urea, salts, but no large proteins or blood cells.
    • Selective Reabsorption: Glucose will significantly decrease in the “filtrate” after passing through the reabsorption unit. Urea concentration will increase in the “urine” relative to the filtrate as water is reabsorbed. Salt concentrations will be finely tuned.
    • Increasing blood pressure (pump speed) will increase filtration rate but might lead to less efficient reabsorption if flow is too fast.
    • Membrane integrity (pore size) will critically determine what is filtered.
  • Theoretical Outcomes & Advanced Concepts:
    • Starling Forces: Quantify how hydrostatic pressure (from pump) and oncotic pressure (due to proteins) govern ultrafiltration across the glomerular membrane.
    • Active Transport Kinetics: Explore how the rate of reabsorption for specific solutes (e.g., glucose) can be saturated if the concentration in the filtrate exceeds the transport maximum (Tm​). This explains why glucose appears in urine in diabetes.
    • Countercurrent Multiplier System (Loop of Henle): While complex to model perfectly, discuss how the design of the loop of Henle (descending limb permeable to water, ascending limb permeable to salts) creates an osmotic gradient in the medulla, crucial for concentrating urine.
    • Hormonal Regulation: Extend the model conceptually to include ADH (Antidiuretic Hormone) affecting water reabsorption in the collecting duct and aldosterone affecting salt reabsorption in the DCT.
    • Dialysis Principles: Directly relate the experiment to the mechanism of hemodialysis, where waste products diffuse across a semi-permeable membrane into a dialyzing fluid.
  • Real-Life Connections:
    • Kidney Diseases: How damage to glomeruli (e.g., glomerulonephritis) or tubules (e.g., acute tubular necrosis) impacts filtration and reabsorption, leading to accumulation of wastes or loss of essential substances.
    • Diabetes Mellitus: Explanation of glucose in urine when blood glucose levels exceed the renal threshold due to saturated reabsorption transporters.
    • Hypertension (High Blood Pressure): Its long-term damaging effects on the kidney’s delicate filtration units.
    • Dehydration and Overhydration: How the body’s osmoregulation via the kidneys maintains fluid balance.
    • Drug Excretion: Understanding how drugs are filtered and secreted by the kidneys, influencing dosage and frequency.
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