What is energy and how do living cells obtain and use it?

Living organisms require energy to perform all tasks, from heavy labor to even thinking and sleeping. Cells constantly use energy to import, metabolize, synthesize, and transport molecules. Energy is transferred and transformed through stepwise chemical reactions that make up the cell's metabolism. Biological organisms are open systems that exchange energy with their surroundings, and energy is subject to physical laws, specifically the laws of thermodynamics. The first law states that the total amount of energy in the universe is constant and conserved, while the second law explains why energy transfers and transformations are never completely efficient. The challenge for living organisms is to obtain energy from their surroundings and transform it into usable energy to do work. The more energy that is lost to surroundings, the less ordered and more random the system becomes, and entropy increases as molecules diffuse and spread out.

• Living organisms require energy for all tasks, including thinking and sleeping.
• Bioenergetics describes energy flow in living systems.
• Cells use chemical reactions to build and break down molecules and transport them.
• Cells must constantly produce energy to replenish that used by chemical reactions.
• Thermodynamics is the study of energy transfer involving physical matter.
• Energy is the ability to do work or create change, and exists in many forms.
• The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or transformed.
• The second law of thermodynamics explains that all energy transfers and transformations are inefficient and result in some energy being lost as heat energy, increasing entropy (disorder) within a system.
• Living cells are open systems that exchange energy with their surroundings, and must obtain energy from their surroundings in forms that they can transform into usable energy to do work.
• Chemical energy stored within organic molecules is transferred and transformed into energy within molecules of ATP, which is easily accessible for cells to do work.
• Examples of work that cells do include building complex molecules, transporting materials, powering motion, and contracting muscles.