MODULE #1: Biology: The Study of Life
Sensing and Responding to Change
Our third criterion for life is that it senses and responds to changes in its surroundings. It is important to realize that in order to meet this criterion, an organism's ability to sense changes is just as important as its ability to respond. After all, even a rock can respond to changes in its environment. If a boulder, for example, is perched on the very edge of a cliff, even a slight change in the wind patterns around the boulder might be enough for it to fall off of the cliff. In this case, the boulder is responding to the changes in its surroundings. The reason a boulder doesn't meet this criterion for life is that the boulder cannot sense the change.
Living organisms are all equipped with some method of receiving information about their surroundings. Typically, they accomplish this feat with receptors.
Receptors – Special structures that allow living organisms to sense the conditions of their internal or external environment
Your skin, for example, is full of receptors. Some allow you to distinguish between hard and soft substances when you touch them. Other receptors react to hot and cold temperatures. If you have your hand under a stream of water coming from a water faucet, for example, your receptors react to the temperature of the water. The receptors send information to your brain, and you can then react to the temperature. If the water is too hot or too cold, you can remove your hand from the stream to avoid the discomfort.
A living organism's ability to sense and respond to changes in its surrounding environment is a critical part of survival, because God's creation is always changing. Weather changes, seasons change, landscape changes, and the community of organisms in a given region changes. As a result, living organisms must be able to sense these changes and adapt, or they would not be able to survive.