6.1 Energy and Energy Transformations
KEY CONCEPTS
By the end of this section, you will be able to do the following:
- Give cellular examples of kinetic and potential energy, and explain why those examples fall into the category of kinetic or potential energy.
- Describe examples of cellular processes that involve transformations of energy (first law of thermodynamics) and increases in entropy (second law of thermodynamics).
- Apply the concept of free energy to determine whether cellular processes (reactions) are endergonic or exergonic, and which of these processes can be used to do cellular work.
- Explain how activation energy limits chemical reaction rates
The challenge for all living organisms is to obtain energy from their surroundings in forms that they can transfer or transform into usable energy to do work. Examples of the types of work that cells need to do include building complex molecules, transporting materials, powering the beating motion of cilia or flagella, contracting muscle fibers to create movement, and reproducing. This chapter will explore the different types of energies, the laws of thermodynamics, and the fundamentals of energy during chemical reactions.
Thermodynamics
Thermodynamics refers to the study of energy and energy transfer involving physical matter. The matter and its environment relevant to a particular case of energy transfer are classified as a system, and everything outside that system is the surroundings. For instance, when heating a pot of water on the stove, the system includes the stove, the pot, and the water. Energy is transferred within the system (between the stove, pot, and water). There are two types of systems: open and closed. An open system is one in which energy and matter can transfer between the system and its surroundings. The stovetop system is open because it can lose heat (a form of energy) and water vapour (a form of matter) into the air. A closed system is one that can transfer energy but not matter to its surroundings. A boiling pot with a lid on would be an example of a closed system as heat can be lost but not matter (water vapour).
Biological organisms are open systems. Energy is exchanged between them and their surroundings, as they consume energy-storing molecules and release energy to the environment by doing work. Like all things in the physical world, energy is subject to the laws of physics. The laws of thermodynamics govern the transfer of energy in and among all systems in the universe. To begin our understanding of thermodynamics, first we need to establish what energy is, and how we can categorize that energy.
Energy Types
We define energy as the ability to do work. As you have likely learned, energy exists in different forms. For example, electrical, light and heat energy are all different energy types. In order to appreciate the way energy flows into and out of biological systems, it is important to understand more about the different energy types that exist in the phys