2. Tutorial 2 Worksheet


Plasma Membrane Structural Arrangement

  • Structures of the Plasma Membrane
    a) Double layer arrangement of phospholipids

    • Phospholipid bilayer
      b) Integral Membrane Proteins

    • Proteins that deeply penetrate the lipid bilayer, usually extending from one side to the other.

    • Many are transmembrane proteins.
      c) Peripheral Membrane Proteins

    • Proteins that loosely attach to the surface of the plasma membrane.
      d) Hydrophobic Region of the Phospholipid Molecule

    • Fatty acid tails.
      e) Hydrophilic Region of the Phospholipid Molecule

    • Phosphate (polar) head.

  • Description of Structural Arrangement

    • The plasma membrane is a phospholipid bilayer with the hydrophilic phosphate heads facing the inside and outside watery environments and the hydrophobic fatty acid tails facing each other in the middle. Embedded within this bilayer are integral proteins, while peripheral proteins are attached to the inner or outer surfaces. Together these components form a flexible "fluid mosaic" that controls what enters and leaves the cell.

Cellular Respiration

  • Equation:
    extglucose+extoxygen<br>ightarrowextATP+extcarbondioxide+extwaterext{glucose} + ext{oxygen} <br>ightarrow ext{ATP} + ext{carbon dioxide} + ext{water}

  • Sources of Glucose

    • Obtained from the digestion of carbohydrates in food, absorbed from the small intestine into the blood, and delivered to cells.

  • Sources of Oxygen

    • Obtained from the air we breathe, taken up by the lungs, transported in the blood (bound to hemoglobin), and delivered to tissues.

  • Purpose of ATP

    • ATP is the main energy currency of the cell; it provides usable energy for processes such as muscle contraction, active transport, and synthesis of molecules.

  • Fate of Carbon Dioxide and Water

    • Carbon dioxide diffuses out of cells into the blood, is carried to the lungs, and exhaled.

    • Water remains in body fluids or is excreted via kidneys, skin, or lungs.

  • Location of Aerobic Cellular Respiration

    • Occurs mainly in the mitochondria (with glycolysis starting in the cytoplasm and later stages in the mitochondrion).

Transport Across the Plasma Membrane

  • Passive vs. Active Transport
    a) Passive Transport:

    • Movement of substances down their concentration gradient (from higher to lower concentration) without using cellular energy (no ATP).

    • Includes:

      • Simple diffusion

      • Facilitated diffusion

      • Osmosis

    b) Active Transport:

    • Movement of substances against their concentration gradient (from lower to higher concentration) using energy from ATP, often via carrier proteins or pumps.

  • Matching Transport Method to Description

    • Movement of solutes directly through the plasma membrane from an area of higher concentration to an area of lower concentration → Simple diffusion.

    • Movement of a solute from higher to lower concentration by attaching to a protein that changes shape to transport the substance → Carrier-mediated facilitated diffusion.

    • Movement of a solute from higher to lower concentration by passing through a protein channel → Channel-mediated facilitated diffusion.

    • Movement of water from higher water concentration to lower water concentration → Osmosis.

    • Movement of solute from lower solute concentration to higher solute concentration → Active transport.

    • Movement of substances into a cell by vesicles → Endocytosis.

    • Movement of substances out of a cell by vesicles → Exocytosis.

  • Label the Illustration (assumed to refer to an accompanying figure):

    • Simple diffusion – small non-polar molecules moving directly through the phospholipid bilayer down their concentration gradient.

    • Channel-mediated diffusion – ions or small polar molecules moving through an open protein channel from high to low concentration.

    • Carrier-mediated diffusion – solute binding to a carrier protein that changes shape while moving down its gradient.

    • Osmosis – water moving through the membrane (often via aquaporins) from high to low water concentration.

    • Active transport – solute moving through a pump protein from low to high concentration using ATP.

  • Substances, Transport Process, and ATP Use:

    • Oxygen:

    • Movement through plasma membrane: Simple diffusion through lipid bilayer down its gradient.

    • Is ATP used?: No.

    • Carbon dioxide:

    • Movement through plasma membrane: Simple diffusion through lipid bilayer down its gradient.

    • Is ATP used?: No.

    • Glucose:

    • Movement through plasma membrane: Carrier-mediated facilitated diffusion (e.g. GLUT transporters).

    • Is ATP used?: No (for basic uptake; some tissues can use secondary active).

    • Sodium (Na⁺):

    • Movement through plasma membrane: Channel-mediated diffusion (leak channels) and active transport via Na⁺/K⁺ pump.

    • Is ATP used?: Pump uses ATP.

    • Potassium (K⁺):

    • Movement through plasma membrane: Channel-mediated diffusion (leak channels) and active transport via Na⁺/K⁺ pump.

    • Is ATP used?: Pump uses ATP.

    • Amino Acids:

    • Movement through plasma membrane: Carrier-mediated transport, often secondary active transport coupled to Na⁺.

    • Is ATP used?: Yes (indirectly via Na⁺ gradient from ATP-dependent pump).

    • Water:

    • Movement through plasma membrane: Osmosis, often via aquaporin channels.

    • Is ATP used?: No.

    • Hormones (lipid-soluble, e.g., steroids):

    • Movement through plasma membrane: Simple diffusion through lipid bilayer.

    • Is ATP used?: No.

Sodium-Potassium Pump

  • Greater Na⁺ Concentration:

    • There is a greater concentration of sodium ions outside the cell (extracellular fluid) than inside.

  • Greater K⁺ Concentration:

    • There is a greater concentration of potassium ions inside the cell (intracellular fluid) than outside.

  • Direction of Diffusion through Ion Channels:

    • Na⁺ diffuses into the cell (from high outside to lower inside) through sodium channels.

    • K⁺ diffuses out of the cell (from high inside to lower outside) through potassium channels.

  • Role of Na⁺/K⁺ Pump in Resting Membrane Potential:

    • The Na⁺/K⁺ pump actively transports 3 Na⁺ out of the cell and 2 K⁺ in for each ATP used.

    • This maintains high extracellular Na⁺ and high intracellular K⁺.

    • This unequal movement of positive charges helps keep the inside of the cell more negative than the outside and maintains the ion gradients needed for the resting membrane potential.

Osmosis

  • Definitions
    a) Isotonic Solution

    • Same solute concentration as the cell; no net movement of water and cell size stays the same.
      b) Hypotonic Solution

    • Lower solute concentration (higher water concentration) than the cell; water moves into the cell and it swells (may lyse).
      c) Hypertonic Solution

    • Higher solute concentration (lower water concentration) than the cell; water moves out of the cell and it shrinks (crenates).

  • NaCl Concentration in Normal Saline

    • Normal saline contains 0.9% NaCl.

  • Normal NaCl Concentration Inside a Body Cell

    • Intracellular fluid is roughly 0.9% NaCl equivalent in tonicity (about the same osmolarity as 0.9% saline), so 0.9% NaCl is isotonic to body cells.

  • Effect on Red Blood Cells
    a) 0.2% NaCl Solution

    • Hypotonic to red blood cells, so water moves into the cells and they swell and may burst (haemolysis).
      b) 5% NaCl Solution

    • Hypertonic, so water moves out of red blood cells and they shrink and crenate.
      c) 0.9% NaCl Solution

    • Isotonic, so there is no net water movement and red blood cells keep their normal shape.

Connective Tissue

  • Roles of Fibres and Cells
    a) Collagen

    • Provides great tensile strength and resists stretching; helps tissues withstand pulling forces.
      b) Elastic Fibres

    • Allow tissues to stretch and then recoil to their original shape (elasticity).
      c) Fibroblasts

    • Main connective tissue cells that produce fibres (collagen, elastic) and ground substance.
      d) Macrophages

    • Phagocytic cells that engulf debris and pathogens; important in defense and cleaning up tissue.
      e) Mast Cells

    • Release histamine and other chemicals during inflammation and allergic responses; help in defense.

  • Matching Connective Tissue Type to Description

    • Dense Regular Connective Tissue

    • Tightly packaged bundles of parallel collagen fibres oriented in the same direction to withstand high tension when pulled in one direction; examples: tendons and ligaments.

    • Dense Irregular Connective Tissue

    • Irregularly arranged bundles of collagen and elastic fibres; withstands tension in many directions; example: dermis of skin.

    • Areolar Connective Tissue

    • Loose arrangement of random fibres in a large amount of ground substance; most widely distributed; example: subcutaneous layer under skin.

    • Adipose Tissue

    • Areolar connective tissue with abundant fat cells.

    • Elastic Connective Tissue

    • Densely arranged connective tissue with many elastic fibres allowing recoil; examples: walls of large arteries.