Cell Transport

• Diffusion is the net movement of particles from an area of high concentration to an area of low concentration along a concentration gradient - this is a passive process (does not require energy from respiration).
• Factors that affect the rate of diffusion:

  Concentration gradient.

  Temperature.

  Membrane surface area.
• Villi adaptations for exchanging substances:

  Long and thin - increases surface area.

  One-cell thick membrane - short diffusion pathway.

  Good blood supply - maintains a steep concentration gradient.
• Lung adaptations for efficient gas exchange:

  Alveoli - large surface area.

  Moist membranes - increased rate of diffusion.

  One-cell-thick membranes - short diffusion pathway.

  Good blood supply - maintains a steep concentration gradient.
• Fish gill adaptations for efficient gas exchange:

  Large surface area for gases to diffuse across.

  Thin layer of cells - short diffusion pathway.

  Good blood supply - maintains a steep concentration gradient.
• Osmosis is diffusion of water from a dilute solution to a concentrated solution through a partially permeated membrane.
• In a plant, osmosis takes place when water moves from the soil into the root hair cell.
• Active transport is movement of particles against a concentration gradient - from a dilute solution to a more concentrated solution - using energy from respiration.
• Active transport are needed in plant roots because concentration of mineral ions in the soil is lower than in the root hair cells - the mineral ions must move against the concentration gradient to enter the root hair cells.
• In the small intestine, active transport is used to absorb sugars when the concentration of sugar in the small intestine is lower than the concentration of sugar in the blood.
• If the concentration of solutes in the solution outside the cell is the same as the internal concentration, the solution is isotonic to the cell and will not affect the cell.
• If the concentration of solutes in the solution outside the cell is higher than the internal concentration, the solution is hypertonic to the cell and water will leave the cell through osmosis.
• If the concentration of solutes in the solution outside the cell is lower than the internal concentration, the solution is hypotonic to the cell and water will enter the cell through osmosis.