Chapter 4.1 – The Nature of Life INB Pg40

The Nature of Life Theoretical physicist Stephen Hawking: “The laws of science do not distinguish between the past and the future. In order to survive, human beings have to consume food which is an ordered form of energy, and convert it into heat, which is a disordered form of energy… The progress of the human race in understanding the universe has established a small corner of order in an increasingly disordered universe.” The principle of physics called entropy, or randomness, appears to be the driving force of all life in our universe.

The Nature of Life Defining life appears simple if you compare a fish and a rock. From a scientific point of view, it’s not quite so cut-and-dried. Often life and nonlife share the same elements: matter, carbon atoms and energy reactions. Energy reactions found in living systems also exist outside of life. For example: fire results when a reaction releases chemical energy within substances. Living systems use energy similarly – by releasing chemical energy for life processes. All life uses energy. Therefore it is possible to define “life” based on the characteristics living systems have apart from nonliving systems with respect to energy use.

Elements Essential for Life Life requires matter and energy to exist. All living organisms are composed of about 13 of 118 known elements from the periodic table. Carbon, hydrogen, oxygen, and nitrogen account for 99% of the mass. Nine other elements account for the remaining 1%. These elements, in combinations, account for all biological chemicals.

Matter and Energy Scientists recognize more than 1.6 million different species, as many as 30 million may exist. Despite this huge number, all organisms organize matter into biological chemicals and into cells. A cell is the smallest whole structure that can be defined as a living system. Organisms can consist of a single cell or billions of codependent cells. All life organizes matter into cells.

Matter and Energy (continued) The first law of thermodynamics states that energy can be transferred from one system to another in many forms. However, it cannot be created nor destroyed. Energy is defined as the capacity to do work. Energy is necessary for life because living systems use it to accomplish the processes of life: reproduction, growth, movement, eating, etc..

Matter and Energy (continued) Organisms need energy to help break down complex molecules into simple molecules. They need more energy to build distinct complex molecules from simple molecules. Organisms cannot create energy – but can use it to perform useful work. Living systems must acquire energy from outside sources.

Entropy The second law of thermodynamics states that disorder increases with time and eventually all energy and matter will be distributed evenly. Entropy is the measure of how much unavailable energy exists in a system due to even distribution. High entropy = low organization and low energy potential.

Entropy Living systems use energy to create order and to gather and store potential energy. The increased order is local and temporary, and requires more energy to create than it retains. Here, matter exists in a low-entropy (organized) state. Example: About 85% of the energy required to organize protein into complex muscle tissue is ultimately lost as heat in creating the tissue.