Exchange of Substances with the environment

• What do all organisms need to exchange with their environment?

  Oxygen, nutrients, waste products, and heat
• Why do cells need to take in oxygen?

  For aerobic respiration
• What waste products do cells need to excrete?

  Carbon dioxide and urea
• What is the significance of surface area: volume ratio?

  It affects the rate of substance exchange
• How does the surface area: volume ratio change with size?

  Smaller organisms have higher ratios
• How can you mathematically represent a mouse's volume?

  1 cm³
• What is the surface area of a mouse represented as a cube?

  6 cm²
• What is the surface area: volume ratio of the mouse?


  1. 1
• What is the volume of a cube hippo measuring 2 cm x 4 cm x 4 cm?

  32 cm³
• What is the total surface area of the cube hippo?

  64 cm²
• What is the surface area: volume ratio of the hippo?


  1. 1
• How does the surface area: volume ratio of smaller animals compare to larger animals?

  Smaller animals have a bigger ratio
• Osmosis is the passive transport of water molecules across a selectively permeable membrane.
• The rate at which substances are exchanged between an organism and its surroundings is called permeability.
• The rate at which substances move across the cell membrane is determined by their concentration gradient.
• Diffusion is the movement of particles from an area of high concentration to low concentration until equilibrium is reached.