Capture, Absorb, or Filter Gases
Oxygen, carbon dioxide, and nitrogen are all gases of particular importance to living systems. Living systems obtain these gases from water and air by trapping them, absorbing them across surfaces, or filtering them. Gases are low in density and viscosity, and when dissolved in liquids, are very low in concentration–so extracting them requires specialized strategies. As a result, living systems use the properties of gases, liquids, and solids to assist in capture, absorption, and filtering. For example, fish gills have many filaments to create a large surface area to maximize how many blood vessels come in close contact with oxygen dissolved in the water.
Distribute Gases
Gases of particular importance to living systems are oxygen, carbon dioxide, and nitrogen. Oxygen and carbon dioxide are involved in respiration, so distributing these gases efficiently and effectively is important for a living system’s survival. However, gases are difficult to contain because they disperse easily. To accommodate this, living systems have strategies for confining gases and using gases’ properties to their advantage. For example, prairie dogs and mound-building termites build systems of tunnels and mounds that take advantage of wind to ventilate their underground homes.
Modify Chemical Potential
Building a dam on a flowing river creates a difference in water level on either side of the dam. The difference in water level is called a potential because it takes advantage of the abiotic tendency of water to seek its own level. Once there is an opening in the dam, water will rush from the higher level to the lower level until they become equal. The flow of water can be used to do work, like turning a turbine to generate hydroelectric power. Similarly, a chemical potential can be set up to do work. For example, in photosynthesis, the energy of a solar photon striking a leaf forces an electron to flow along the electron transport chain. As the electron passes each point in the chain, a hydrogen ion is released within the plant cell’s thylakoid membrane. As the hydrogen ions build up on one side of the thylakoid membrane, it sets up a chemical potential due to the difference in hydrogen ion concentration on either side. Just as there is an abiotic tendency for water to seek its own level on either side of the dam, there is an abiotic tendency for chemical concentration of any particular ion or molecule to “seek its own concentration level” on either side of a membrane. In photosynthesis, hydrogen ions find their way to the other side of the thylakoid membrane through a pathway created by an embedded enzyme channel. The flow of hydrogen ions through the channel power the enzyme’s chemical synthesis machinery.
