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Circulation and Gas Exchange in General Biology

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  • Function of circulatory systems
    Facilitate exchange of resources and wastes between cells and the environment, especially in larger multicellular organisms.
  • Difference between open and closed circulatory systems
    Open systems have hemolymph in direct contact with organs; closed systems have blood confined to vessels, allowing faster oxygen delivery.
  • Three basic components of specialized circulatory systems
    Circulatory fluid, interconnecting vessels, and a muscular pump (heart).
  • Role of hemoglobin in blood
    A respiratory pigment in red blood cells that reversibly binds oxygen, increasing oxygen transport efficiency.
  • Single vs. double circulation in vertebrates
    Single circulation passes blood through two capillary beds with a 2-chambered heart; double circulation has separate pulmonary and systemic circuits with 3- or 4-chambered hearts.
  • Function of capillaries
    Sites of exchange between blood and tissues where oxygen, nutrients, and wastes diffuse.
  • How blood flow is regulated in capillaries
    By muscle constriction of arterioles and precapillary sphincters controlled by nervous system and hormones.
  • Mechanism of water movement in capillaries
    Blood pressure forces water out at arterial end; osmotic pressure draws water back at venous end.
  • Role of lymphatic system
    Drains excess interstitial fluid not recovered by capillaries and returns it to the circulatory system.
  • Heart's pacemaker function
    Autorhythmic cells in the sinoatrial (SA) node generate electrical impulses causing heart contractions.
  • Path of electrical signal in heart contraction
    SA node → AV node (delay) → bundle branches → heart apex → Purkinje fibers → ventricles contract.
  • Composition of blood
    Cells and cell fragments (~45%) including erythrocytes, leukocytes, platelets, suspended in plasma (liquid matrix).
  • Main function of erythrocytes
    Transport oxygen using hemoglobin; lack nuclei and mitochondria.
  • Function of leukocytes
    White blood cells involved in immune defense.
  • Role of platelets
    Cell fragments that participate in blood clotting.
  • Gas exchange principle
    Gases diffuse from higher to lower partial pressure across thin, moist respiratory surfaces.
  • Why aquatic organisms have efficient gas exchange surfaces
    Gills provide large surface area and use countercurrent exchange to maximize oxygen uptake.
  • Terrestrial adaptations for breathing air
    Insects use tracheal systems; vertebrates use lungs with branching bronchioles and alveoli.
  • Difference between positive and negative pressure breathing
    Amphibians push air in by shrinking oral cavity (positive); mammals pull air in by expanding thoracic cavity (negative).
  • Why hemoglobin is necessary
    Oxygen has low solubility in water; hemoglobin binds oxygen to reduce required cardiac output.