exchanging substances

• What are the three main factors that affect the movement of substances?

  Surface area to volume ratio, temperature, and concentration gradient
• How does surface area to volume ratio affect the rate of diffusion?

  A larger surface area to volume ratio increases the rate of diffusion
• Why do substances move faster in and out of cells when there is a large concentration gradient?

  Because there are more particles available to move across
• What happens to particles in a substance as the temperature increases?

  They gain more energy and move faster
• Calculate the surface area to volume ratio of a cube with a surface area of 24 cm² and a volume of 8 cm³.

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• Calculate the surface area to volume ratio of a cube with a surface area of 54 cm² and a volume of 27 cm³.


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• What are the challenges of exchanging substances in multicellular organisms?

  • Need to supply all cells with essential substances
  • Need to remove waste products
  • Longer distances for diffusion
  • Lower surface area to volume ratio
• Why can't proteins be stored in the body?

  Excess amino acids are converted into fats and carbohydrates
• What is produced as a waste product from reactions in the body?

  Urea
• Why is urea considered poisonous?

  It needs to be removed from the body
• How do single-celled organisms exchange substances?

  • Substances diffuse directly across the cell membrane
  • Short distance for diffusion
  • Large surface area to volume ratio
• Why is diffusion slower in multicellular organisms?

  • Longer distances to the outside environment
  • Some cells are deep inside the organism
  • Lower surface area to volume ratio
• What do multicellular organisms need for substance exchange?

  • Specialized exchange organs
  • Specialized exchange surfaces
  • Transport systems to carry materials
• What are the transport systems in plants called?

  Xylem and phloem vessels
• What is the purpose of specialized exchange organs in multicellular organisms?

  To facilitate the exchange of substances
• What is the transport system in animals called?

  The circulatory system