Movement into and out of cells

• Diffusion


  The net movement of particles from a region of their higher concentration to a region of their lower concentration, down a concentration gradient, as a result of their random movement
• Diffusion


  • How molecules move in and out of cells through the cell membrane
  • Molecules that cells need move into the cell for use in metabolic reactions and storage
  • Waste products that need to be disposed of move out of the cell into the blood to be excreted
• Diffusion occurs


  Until the number of nutrients inside and outside the cell are balanced
• Factors influencing diffusion


  • Surface area
  • Temperature
  • Concentration gradient
  • Distance
• Osmosis


  The net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution) through a partially permeable membrane
• Role of water


  • Acts as a solvent in organisms
  • Allows transport of dissolved substances
  • Needed for digestion
  • Needed for excretion
• Water potential


  A measure of the tendency of water to move from one area to another by osmosis
• Osmosis experiment using dialysis tubing

  1. Dialysis tubing filled with concentrated sucrose solution suspended in distilled water

  2. Water moves from higher water potential (distilled water) to lower water potential (sucrose solution) through partially permeable membrane

  3. Water level outside tubing decreases as water moves into tubing
• Effects of different solutions on plant cells


  • In pure water or dilute solution, water moves into cell, making it turgid
  • In concentrated solution, water moves out of cell, making it flaccid(shrinks) and potentially plasmolysed(when cytoplasm shrinks due to the loss of water but the cell wall fails to shrink because of its tuff structure, eventually tearing away from the cell wall)
• Turgor pressure


  The pressure on the cell wall from the cell membrane pushing upon it
• Importance of osmosis in plants

  • Plants obtain water by osmosis through roots
  • Water transports minerals and nitrate ions
  • Water maintains cell turgidity, providing support and strength
• Active transport


  The movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration, against a concentration gradient, using energy from respiration
• Active transport


  • Used when diffusion or osmosis cannot be relied upon
  • Protein carriers in cell membranes capture molecules on one side and transport them to the other side, using energy from respiration
• Active transport requires energy input and involves the use of ATP.
• Passive transport does not require energy input and occurs by diffusion or osmosis.
• The cell membrane is selectively permeable, allowing certain substances to pass through while preventing others from doing so.
• Surface Area: The amount of surface available for molecules to diffuse through.
• Note: The greater the surface area the faster the rate of diffusion.
• Active transport is used to move substances across the plasma membrane against their concentration gradients.
• Diffusion is the net movement of particles down their concentration gradient without requiring any energy input.
• Examples of active transport include moving sodium (Na+) ions out of animal cells and moving glucose (C6H12O6) into bacterial cells.
• Substances that can easily cross the cell membrane are called lipid-soluble, while those that cannot are referred to as hydrophilic.
• Osmosis is the net movement of solvent (water) across a partially permeable membrane from an area of low solute concentration to high solute concentration until equilibrium is reached.
• Concentration Gradient: The difference in concentration between two areas that drives diffusion.
• Concentration gradient: The difference between the concentration of a substance inside and outside the cell.
• Osmosis is the passive movement of water molecules across a semi-permeable membrane from an area of low solute concentration to high solute concentration until equilibrium is reached.