Cell transport

• What is diffusion?

  Net movement of particles from an area of high concentration to an area of low concentration along a concentration gradient
• Name three factors that affect the rate of diffusion

  concentration gradient, temperature, membrane surface area
• How are villi adapted for exchanging substances?

  Long and thin - increases surface area

  One cell thick membrane - short diffusion pathway

  Good blood supply - maintains a steep concentration gradient
• How are the lungs adapted for efficient gas exchange?

  Alveoli - large surface area

  Moist Membranes - increases rate of diffusion

  One cell thick membranes - short diffusion pathway

  Good blood supply - maintains a steep concentration gradient
• How are gills adapted for efficient gas exchange?

  Large surface area for gases to dilute across

  Thin layer of cells - short diffusion pathway

  Good blood supply - maintains a steep concentration gradient
• What is osmosis?


  Diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane
• Give one example of osmosis in a plant

  Water moves from the soil into the root hair cell
• What is active transport?

  Movement of particles against a concentration gradient - from a dilute solution to a more concentrated solution - using energy from respiration
• Why is active transport needed in plant roots?

  Concentration of mineral ions in the soil is lower than inside the root hair cells - the mineral ions must move against the concentration gradient to enter the root hair cells
• What is the purpose of active transport in the small intestine?

  Sugars can be absorbed when the concentration of sugar in the small intestine is lower than the concentration of sugar in the blood