Biology Chapter on Milieu Intérieur and Homeostasis
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Questions and Answers

What does Fick's Law of Diffusion relate to in terms of solute movement?

  • The rate of diffusion is directly proportional to the surface area of the membrane. (correct)
  • The rate of diffusion is inversely proportional to the concentration gradient.
  • The rate of diffusion is independent of the permeability coefficient.
  • The rate of diffusion is affected by the electrical charge of the solute.

    • Which factor does NOT influence the rate of diffusion across a cell membrane?

  • Color of the molecule (correct)
  • Lipid solubility
  • Concentration gradient
  • Mass of the molecule

    • In the context of diffusion, what is the relationship between time and distance according to Einstein's approximation?

  • Time for diffusion remains constant regardless of distance.
  • Time for diffusion increases in proportion to the square of the distance. (correct)
  • Time for diffusion increases linearly with distance.
  • Time for diffusion decreases with increasing distance.

    • What is meant by the term 'electrochemical gradient'?

    <p>The combined effect of electrical and concentration gradients for an ion.</p> Signup and view all the answers

    Which statement about ion channels is accurate?

    <p>Ion channels show ion selectivity and are transmembrane proteins.</p> Signup and view all the answers

    Which component comprises 40-50% of the plasma membrane by weight?

    <p>Phospholipids</p> Signup and view all the answers

    What is the primary function of cholesterol within the phospholipid bilayer of the cell membrane?

    <p>To buffer the membrane's fluidity</p> Signup and view all the answers

    Which fluid compartment has the largest volume in the human body?

    <p>Intracellular Fluid</p> Signup and view all the answers

    Which of the following is least permeable to the cell membrane?

    <p>Charged particles</p> Signup and view all the answers

    Which type of protein is most closely associated with the phospholipid bilayer and can cross the membrane?

    <p>Trans-membrane proteins</p> Signup and view all the answers

    What is the function of the Glycocalyx surrounding the cell membrane?

    <p>To provide a fuzzy coating with various biomolecules</p> Signup and view all the answers

    What structure is formed when pseudopodia engulf a particle?

    <p>Phagosome</p> Signup and view all the answers

    What is the primary function of phagosomes?

    <p>To degrade cellular debris</p> Signup and view all the answers

    Which type of cells primarily perform phagocytosis?

    <p>Macrophages, neutrophils and dendritic cells</p> Signup and view all the answers

    What is the main characteristic of receptor-mediated endocytosis?

    <p>It specifically targets molecules in the extracellular fluid</p> Signup and view all the answers

    What happens to the receptors after receptor-mediated endocytosis?

    <p>They are recycled back to the membrane</p> Signup and view all the answers

    Which of the following correctly describes clathrin's role in endocytosis?

    <p>It helps form clathrin-coated pits</p> Signup and view all the answers

    Which of these processes does NOT occur during phagocytosis?

    <p>Coating with clathrin</p> Signup and view all the answers

    What triggers receptor-mediated endocytosis?

    <p>Binding of ligands to receptors</p> Signup and view all the answers

    What primarily drives facilitated diffusion?

    <p>Carrier molecule assistance</p> Signup and view all the answers

    Which of the following is a characteristic of active transport?

    <p>Involves conformational change of the transporter</p> Signup and view all the answers

    Which transporter is primarily responsible for maintaining low intracellular sodium levels?

    <p>Na+/K+-ATPase</p> Signup and view all the answers

    What role do hormones play in facilitated diffusion?

    <p>They increase the number or affinity of transporters</p> Signup and view all the answers

    Which statement best describes secondary active transport?

    <p>It depends on the concentration gradient of another solute</p> Signup and view all the answers

    What is the outcome of phosphorylation of the Na+/K+-ATPase?

    <p>Alters the conformation of the transporter</p> Signup and view all the answers

    What is a key difference between facilitated diffusion and primary active transport?

    <p>Active transport can move solutes against their concentration gradient, while facilitated diffusion cannot</p> Signup and view all the answers

    Which component is crucial for the conformational change in primary active transporters?

    <p>Chemical energy from ATP</p> Signup and view all the answers

    What role does the glycocalyx play in cellular processes?

    <p>It contributes to cell-cell recognition and adhesion.</p> Signup and view all the answers

    Which of the following correctly describes passive transport mechanisms?

    <p>They occur independent of energy input.</p> Signup and view all the answers

    What characterizes active transport in cell membranes?

    <p>It always moves substances from low to high concentration.</p> Signup and view all the answers

    How does the fluid mosaic model describe the cell membrane?

    <p>It illustrates that proteins and lipids can freely move within the bilayer.</p> Signup and view all the answers

    Which type of transport requires specific protein interactions in the membrane?

    <p>Facilitated diffusion</p> Signup and view all the answers

    What is a characteristic feature of pinocytosis and phagocytosis?

    <p>They are both examples of active transport.</p> Signup and view all the answers

    What does the term osmotic pressure refer to in a biological system?

    <p>The pressure exerted by a solvent in equilibrium with solute concentration.</p> Signup and view all the answers

    What primarily drives secondary active transport?

    <p>The electrochemical gradient generated by primary active transport</p> Signup and view all the answers

    In symport systems, how is the transported solute related to Na+?

    <p>It is transported in the same direction as Na+</p> Signup and view all the answers

    Which of the following statements best describes regulated exocytosis?

    <p>It is triggered by specific extracellular signals and increased cytosolic Ca2+</p> Signup and view all the answers

    What is the main component that facilitates the extrusion of Na+ during secondary active transport?

    <p>Na+/K+-ATPase</p> Signup and view all the answers

    Which process involves the engulfment of extracellular fluid and solutes by a vesicle?

    <p>Pinocytosis</p> Signup and view all the answers

    What distinguishes antiport from symport transport mechanisms?

    <p>Antiport transports solutes in opposite directions to Na+, while symport transports them together</p> Signup and view all the answers

    Which of the following is a characteristic feature of endocytosis?

    <p>It involves the pinching off of the cell membrane to form vesicles</p> Signup and view all the answers

    Which type of transport mechanism utilizes the Na+/HCO3− cotransporter?

    <p>Symport</p> Signup and view all the answers

    Which factor does NOT influence the rate of mediated transport?

    <p>Temperature of the environment</p> Signup and view all the answers

    What characterizes primary active transport compared to facilitated diffusion?

    <p>It can transport substances uphill against their concentration gradient.</p> Signup and view all the answers

    What role does Na+/K+-ATPase play in cellular function?

    <p>It maintains a low intracellular concentration of Na+ and a high concentration of K+.</p> Signup and view all the answers

    Which statement about facilitated diffusion is accurate?

    <p>It utilizes transporters to enhance the rate of diffusion.</p> Signup and view all the answers

    What is a common characteristic of secondary active transport?

    <p>It couples the movement of one ion down its gradient to another against its gradient.</p> Signup and view all the answers

    What happens during the conformational change of the Na+/K+-ATPase?

    <p>The affinity of the transporter for Na+ or K+ changes due to phosphorylation.</p> Signup and view all the answers

    Which hormone is known to increase the uptake of glucose by affecting transporters?

    <p>Insulin</p> Signup and view all the answers

    Which statement best describes the term 'competitive inhibition' in the context of mediated transport?

    <p>Structurally similar substances vie for binding sites on the same transporter.</p> Signup and view all the answers

    What is the primary role of pseudopodia in phagocytosis?

    <p>To engulf and internalize particles</p> Signup and view all the answers

    Which type of cells are primarily involved in receptor-mediated endocytosis?

    <p>Macrophages and neutrophils</p> Signup and view all the answers

    What primarily happens to the ligands during receptor-mediated endocytosis?

    <p>They are internalized into the cell attached to receptors</p> Signup and view all the answers

    Which structure is formed when a phagocyte engulfs a bacterium?

    <p>Phagosome</p> Signup and view all the answers

    What is a key feature of the process of receptor-mediated endocytosis compared to other forms of endocytosis?

    <p>It is a highly specific process involving ligand-receptor interactions</p> Signup and view all the answers

    What occurs to the contents of a phagosome after it fuses with a lysosome?

    <p>They are broken down and degraded</p> Signup and view all the answers

    Which proteins are primarily involved in the formation of clathrin-coated pits during endocytosis?

    <p>Clathrin proteins</p> Signup and view all the answers

    During macrophage activity, what role do lysosomes play following phagocytosis?

    <p>They fuse with phagosomes to enable degradation of materials</p> Signup and view all the answers

    What initiates the formation of a clathrin-coated vesicle during receptor-mediated endocytosis?

    <p>Conformational change of the receptor</p> Signup and view all the answers

    Which of the following correctly describes the role of adaptor proteins in clathrin-dependent endocytosis?

    <p>They link the ligand-receptor complex to clathrin.</p> Signup and view all the answers

    What happens to clathrin after a vesicle is formed and has pinched off from the plasma membrane?

    <p>It is shed from the vesicle.</p> Signup and view all the answers

    In receptor-mediated endocytosis, how is the LDL receptor primarily characterized?

    <p>As a specific receptor for low-density lipoproteins</p> Signup and view all the answers

    Which process can occur when vesicles formed from clathrin-mediated endocytosis travel to different sides of the cell?

    <p>Transcytosis</p> Signup and view all the answers

    What is the role of low-density lipoproteins (LDL) within the bloodstream?

    <p>Transport cholesterol and other lipids</p> Signup and view all the answers

    What structure forms around the ligand-receptor complex during the initial stages of clathrin-mediated endocytosis?

    <p>Clathrin-coated pit</p> Signup and view all the answers

    What is the primary fate of receptors after they have been involved in receptor-mediated endocytosis?

    <p>They are recycled back to the cell membrane.</p> Signup and view all the answers

    What is the primary relationship between osmotic pressure and osmolarity in a solution?

    <p>Osmotic pressure is directly proportional to osmolarity.</p> Signup and view all the answers

    How many osmol of solute particles are present in 1 mol of MgCl2?

    <p>3 osmol</p> Signup and view all the answers

    Which solution would be classified as hyperosmotic compared to an extracellular osmolarity of 300 mOsm?

    <p>350 mOsm MgCl2 solution</p> Signup and view all the answers

    In a scenario where a cell is placed in a 0.15 M NaCl solution, what is likely to occur regarding water movement?

    <p>Water will leave the cell, causing it to shrink.</p> Signup and view all the answers

    Which of the following statements best describes an isotonic solution?

    <p>Has a concentration of 300 mOsm of nonpenetrating solute particles.</p> Signup and view all the answers

    Which solute behaves as a nonpenetrating solute in physiological conditions?

    <p>Na+ ions under certain conditions</p> Signup and view all the answers

    How is osmolarity measured in a solution?

    <p>By calculating the molarity of solute particles.</p> Signup and view all the answers

    Study Notes

    Milieu Intérieur and Homeostasis

    • Claude Bernard coined the term Milieu Intérieur in 1854 to describe the body's ability to maintain a stable internal environment despite external fluctuations.
    • Walter Cannon coined the term Homeostasis in 1930, referring to the process living organisms use to maintain stable conditions necessary for survival.
    • Maintaining Milieu Intérieur and homeostasis requires exchanging nutrients, salts, gases, and waste products in and out of the body.

    Body Fluid Compartments

    • Total body water accounts for 60% of body weight.
    • Intracellular fluid (ICF): 28 liters
    • Interstitial fluid (ISF): 11 liters
    • Plasma: 3 liters

    Cell Membrane Structure

    • Plasma membrane: 6-10 nanometers thick, composed of a phospholipid bilayer.
    • Phospholipids: Amphipathic molecules with polar (hydrophilic) heads and nonpolar (hydrophobic) tails.
    • Cholesterol: Embedded in the phospholipid bilayer, providing fluidity and preventing extreme changes in membrane fluidity due to temperature fluctuations.
    • Proteins: Integral proteins are embedded in the lipid bilayer, while peripheral proteins are loosely associated with the membrane.
    • Glycocalyx: A fuzzy coating surrounding the cell membrane, composed of glycans, glycoproteins, and glycolipids. It contributes to cell recognition, communication, adhesion, and protection.

    Cell Membrane Transport Mechanisms

    • Passive Transport: Does not require energy.
      • Diffusion: Random movement of molecules from high to low concentration.
      • Facilitated diffusion: Movement of molecules across the membrane with the help of transporter proteins.
      • Osmosis: Movement of water across a semipermeable membrane from high to low water concentration.
    • Active Transport: Requires energy.
      • Primary active transport: Directly uses ATP to move molecules against their concentration gradient.
      • Secondary active transport: Uses the energy stored in the concentration gradient of one molecule (usually Na+) to move another molecule against its concentration gradient.

    Diffusion

    • Fick's Law of Diffusion: Describes the rate of diffusion, influenced by the concentration gradient, permeability coefficient, and surface area of the membrane.
    • Diffusion time: Increases proportionally to the square of the distance traveled.
    • Factors Affecting Diffusion: Mass of molecule, concentration gradient, lipid solubility, electrical charge, presence of ion channels and membrane carriers.

    Mediated Transport Systems

    • Facilitated Diffusion: Involves transporter proteins.
      • Passive process: Does not require energy.
      • Net flux: Moves molecules from high to low concentration.
    • Active Transport: Requires energy.
      • Primary active transport: Uses ATP to move molecules against their concentration gradient.
      • Secondary active transport: Uses the energy stored in the concentration gradient of one molecule to move another against its concentration gradient.

    Endocytosis

    • Phagocytosis: Engulfment of large particles (e.g., bacteria) by forming phagosomes.
    • Fluid Endocytosis: Nonspecific uptake of extracellular fluid and solutes.
    • Receptor-mediated Endocytosis: Specific uptake of molecules bound to receptors on the cell membrane.

    Competition

    • Structurally similar substances can compete for the same binding site on a membrane carrier.

    Factors Affecting Mediated Transport

    • Solute concentration, transporter affinity for the solute, transporter quantity, and transporter conformational change rate all influence mediated transport.

    Mediated Transport Systems

    • Facilitated diffusion
      • Uses transporter molecules to increase solute permeability compared to simple diffusion.
      • Involves solute binding to the transporter, transporter configuration change, solute delivery to the other side of the membrane, and transporter return to its original configuration.
    • Active transport
      • Requires energy, usually from ATP hydrolysis.
      • Susceptible to metabolic inhibitors.
      • Allows transport against the concentration gradient.

    Primary Active Transport

    • Involves ATP hydrolysis by a transporter.
    • Transporter phosphorylation alters conformation and solute binding affinity.
    • Examples include the Na+/K+-ATPase, Ca2+-ATPase, H+-ATPase, and H+/K+-ATPase.

    Na+/K+-ATPase

    • Phosphorylation and dephosphorylation alter binding site affinity for transported solutes.

    Secondary Active Transport

    • Sodium ion movement down its concentration gradient drives the uphill transport of another solute.
    • Relies on the electrochemical gradient established by primary active transport.
    • Examples include symport and antiport mechanisms.

    Symport vs Antiport

    • Symport: Solute X is transported in the same direction as sodium ions.
    • Antiport: Solute X is transported in the opposite direction to sodium ions.
    • Examples of each include:
      • Symport: Na+/HCO3− cotransporter, Na+/amino acid cotransporter, Na+/glucose cotransporter
      • Antiport: Na+/H+ exchanger, Na+/Ca2+ exchanger

    Endocytosis & Exocytosis

    • Both are active transport mechanisms involving the cell membrane itself.
    • Endocytosis: The cell membrane invaginates and pinches off to create a vesicle.
    • Exocytosis: An intracellular vesicle fuses with the cell membrane, releasing its contents into the extracellular fluid.

    Types of Exocytosis

    • Constitutive: Non-regulated, replaces plasma membrane, delivers proteins to the cell membrane, and removes substances from the cell.
    • Regulated: Triggered by extracellular signals and increased cytosolic calcium. Responsible for secretion of hormones, digestive enzymes, and neurotransmitters.

    Types of Endocytosis

    • Pinocytosis: Nonspecific, constituitive, engulfs extracellular fluid with solutes.
    • Phagocytosis: Specific, triggered, engulfs particulate matter (e.g., dust, debris, microorganisms). Involves pseudopodia, phagosomes, and lysosomes.
    • Receptor-mediated: Ligands bind specific protein receptors on the plasma membrane, initiating the endocytosis process. Involves clathrin coated pits, vesicle formation, and potential fusion with other organelles.

    Osmotic Pressure

    • Pressure required to prevent the inward flow of water across a semipermeable membrane.
    • Proportional to the number of solute particles per unit volume (osmolarity).
    • Not impacted by solute size, configuration, or charge.

    Osmolarity

    • Total solute concentration of a solution.
    • Measured in osmoles per liter (Osm).

    Osmotic Pressure of Physiological Saline

    • 0.9% saline solution is approximately 0.30 Osm (300 mOsm), corresponding to an osmotic pressure of 5092 mmHg.

    Osmolarity Classifications

    • Isosmotic: Solution with the same osmolarity as normal extracellular or intracellular fluid (300 mOsm).
    • Hypoosmotic: Solution with osmolarity lower than 300 mOsm.
    • Hyperosmotic: Solution with osmolarity greater than 300 mOsm.

    Tonicity

    • Describes the effect of a solution on cell volume.
    • Dependent on the concentration of nonpenetrating solutes.
    • Isotonic: No net water movement, cell volume remains stable.
    • Hypotonic: Water enters the cell, cell swells.
    • Hypertonic: Water exits the cell, cell shrinks.

    Nonpenetrating Solutes

    • Solutes that cannot readily cross cell membranes.
    • Contribute to osmotic pressure without equalizing solute concentration across the membrane.
    • Example: Extracellular sodium ions.

    LDL Receptor-Mediated Endocytosis

    • Low-density lipoproteins (LDL) bind to specific receptors on the cell membrane.
    • The receptor-ligand complex triggers clathrin-dependent endocytosis.
    • The clathrin-coated vesicle delivers the LDL to endosomes and lysosomes, where they are broken down.
    • The receptors are recycled back to the cell membrane.

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    Description

    Explore the essential concepts of Milieu Intérieur and homeostasis, as introduced by Claude Bernard and Walter Cannon. This quiz covers body fluid compartments and the structure of cell membranes, highlighting the importance of maintaining internal stability for survival. Test your knowledge on these fundamental biological principles!

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