Transport Across Membranes

• What is the difference between passive and active transport?

  Passive doesn't require ATP, whereas active does require the use of ATP.
• How can the movement of particles be described?

  Particles are constantly in random motion due to kinetic energy. They bounce off each other and their surroundings.
• What is the definition of diffusion?


  The net movement of particles from a higher concentration to a lower concentration down a diffusion gradient. It is passive and does not need ATP.
• What kind of molecules can diffuse through the cell-surface membrane?

  Small, non-polar molecules.
• What does polar mean?

  The molecule has a charge.
• Define the term facilitated diffusion.


  The movement of molecules from a higher concentration to a lower concentration, across a partially permeable membrane, via specific channel or carrier proteins. It is passive, and does not require ATP.
• What is a channel protein?

  A protein which creates a water-filled hydrophilic channel through the cell membrane through which ions can pass.
• What is a carrier protein?

  A protein which changes shape to allow larger molecules to pass through the membrane.
• What is the definition of osmosis?

  The net movement of water from a region of higher water potential to a region of lower water potential, down a water potential gradient, through a selectively permeable membrane.
• What is meant by water potential?


  The pressure applied by water molecules.
• What is the protoplast?

  The cell surface membrane, nucleus, cytoplasm, and vacuole membrane.
• What does turgid mean?

  This is when the protoplast pushes against the cell wall.
• What does plasmolysed mean?


  This is when water has left the cell and the protoplast no longer pushes against the cellulose cell wall.
• What does incipient plasmolysis mean?

  Any further loss of water would lead to plasmolysis.
• What is the definition of active transport?

  The movement of particles into or out of a cell from a region of lower concentration to a region of higher concentration, against a concentration gradient, using ATP and carrier proteins.
• What is the ileum?


  The small intestine.
• What is the purpose of the microvilli in the ileum?

  To increase surface area to aid absorption.
• What is the process by which amino acids and glucose are absorbed from the ileum?

  Co-transport.
• What is the basic principle of co-transport of glucose or amino acids from the ileum?

  The molecules are taken into the cells along with sodium ions which have been actively transported out by the sodium potassium pump. The sodium can then diffuse back into the epithelial cell bringing glucose in with it by facilitated diffusion.