AP Bio 2.2 Cell Size

the smallest, most basic unit of a living thing is a cell

key functions of living things

  • all living things must:

    • be made up of at least one cell

    • obtain nutrients

      • nutrients are received from the environment

    • eliminate waste

      • metabolism and reactions are not 100% efficient

        • there will be cellular byproducts

      • cell may need to be rid of

    • dissipate heat

      • because of the metabolic and chemical reactions that are constantly happening, excess heat is released, so it builds up heat

  • exchange of materials and energy with the environment is essential

    • there must be a constant exchange

cell size

  • the more surface area a cell has, the more it can interact with its environment

    • has more space to interact with its more environment because it is touching the environment more

  • the more volume a cell has, the greater the nutrient requirement and waste/heat elimination

    • needs more from its environment

    • less volume it has, the less nutrients, waste elimination, or heat dissipation it requires

  • the more surface area the cell has per unit of volume, the better

    • surface area makes it easier for it to exchange with its environment

  • cells that have a higher surface area to volume ratio have more efficient exchange with their environment

    • the larger a cell is, the lower its SA/V ratio is, which mean it’s less efficient at exchanging materials with its environment and requires more resources than a smaller cell

  • rate of heat exchange decreases in larger cells as well

    • smaller cells exchange proportionally more heat

  • smaller organisms have higher metabolic rate per unit of body mass than larger organisms

  • large cells exist, but they have specialized structures to increase surface area for material exchange

    • may have a very convoluted and folded membrane with many extensions coming off of it

    • membrane folds in some cells and cell structures increases surface area without increasing volume

      • inner membrane of the mitochondria is very folded and convoluted which increases surface area, which makes the inner part of the organelle more efficient at exchanging materials with its environment

        • folds in the mitochondria are called cristae

      • microvilli are structures that intestinal lining cells have in order to increase their surface area so that they can interact with their environment on at least one side

AP Bio requires you to be able to calculate the surface area to volume ratio of:

  • cubes

  • spheres

  • cylinder

  • rectangular prism

  • (formulas will be provided)