Mass Transport

• What do cells need for metabolism?

  Oxygen and glucose
• How do single-celled organisms obtain oxygen and glucose?

  Directly from their surroundings
• Why can single-celled organisms diffuse molecules quickly?

  Due to short diffusion distances
• What happens to oxygen in larger organisms?

  It is rapidly used up before reaching cells
• Why is diffusion too slow in larger organisms?

  Because the diffusion distance is too big
• What is the role of mass transport systems in organisms?

  To supply substances and remove waste
• What is mass transport?

  Bulk movement of gases or liquids
• What connects exchange surfaces to mass transport systems?

  A system of vessels and tubes
• Name two examples of mass transport systems.

  Mammalian circulatory system and plant vascular system
• Why are mass transport systems important for waste removal?

  They ensure rapid excretion of waste substances
• How does metabolic rate affect mass transport demands?

  The greater the metabolic rate, the greater the demands
• What determines if diffusion alone can supply cells?

  Surface area: volume ratio
• What happens to the surface area: volume ratio as an organism grows?

  It becomes smaller
• What is the effect of a smaller surface area: volume ratio on diffusion?

  Diffusion takes much longer
• What is needed for metabolism?

  Oxygen and glucose
• What is the definition of metabolism?

  The chemical processes that occur within a living organism