Essential Knowledge 2.A.3

Organisms must exchange matter with the environment to grow, reproduce and maintain organization

Molecules and atoms from the environment are necessary to build new molecules. Carbon moves from the environment to organisms where it is used to build carbohydrate, proteins, lipids or nucleic acids. Carbon is used in storage compounds and cell formation in all organsisms.

Nitrogen moves from the environment to organisms where it is used in building proteins and nucleic acids. Phosphorus moves from the environment to organisms where it is used in nucleic acids and certain lipids.

Living systems depend on properties of water that result from its polarity and hydrogen bonding. The following illustrate the properties of water:

• cohesion
• adhesion
• high specific heat capacity
• universal solvent supports reactions
• heat of vaporization
• heat of fusion
• water's thermal conductivity

Surface area-to-volume ratios affect a biological system's ability to obtain necessary resources or eliminate waste products. As cells increase in volume, the relative surface area decreases and demand for material resources increases; more cellular structures are necessary to adequately exchange materials and energy with the environment. These limitations restrict cell size. Structures that increase surface area for the exchange of materials include:

• root hairs
• cell of the alveoli
• cells of the villi
• microvilli

The surface area of the plasma membrane must be large enough to adequately exchange materials; smaller cells have a more favorable surface area-to-volume ratio for exchange of materials with the environment.

Students should be able to:

LO 2.6 Use calculated surface area-to-volume ratios to predict which cell(s) might eliminate wastes or procure nutrients faster by diffusion.

LO 2.7 Explain how cell size and shape affect the overall rate of nutrient intake and the rate of waste elimination.

LO 2.8 Justify the selection of data regarding the types of molecules that an animal, plant or bacterium will take up as necessary building blocks and excrete as waste products.

LO 2.9 Represent graphically or model quantitatively the exchange of molecules between an organism and its environment, and the subsequent use of these molecules to build new molecules that facilitate dynamic homeostasis, growth and reproduction.