Feedback Loops in Systems

Learning Objectives

Define a system in a scientific context.

Distinguish between negative and positive feedback loops.

Explain the role of negative feedback in maintaining homeostasis.

Provide real-world examples of both positive and negative feedback.

The Dynamics of Change: Feedback Loops

In science, a system is a group of interacting parts that form a complex whole. Systems are rarely static; they are dynamic and respond to change. This response is often controlled by feedback loops. A feedback loop is a process where the output of a system's action is used as an input to regulate the system's future actions.

Negative Feedback: The Stabilizer

A negative feedback loop is a regulatory mechanism in which the output of a system works to counteract or shut down the original stimulus, bringing the system back to a stable set point. Negative feedback promotes stability and homeostasis. Most biological systems are controlled by negative feedback.

Examples:

Thermostat: Your home's heating system is a classic example. If the temperature drops below the set point (stimulus), the thermostat turns the furnace on (response). The furnace produces heat (output), which raises the temperature. Once the temperature reaches the set point, the thermostat turns the furnace off. The output (heat) counteracts the original stimulus (cold).

Body Temperature Regulation: If your body temperature rises, you sweat. The evaporation of sweat cools your body, bringing your temperature back down. If you get too cold, you shiver, which is a rapid muscle contraction that generates heat, warming you up.

Positive Feedback: The Amplifier

A positive feedback loop is a mechanism in which the output of a system works to amplify or reinforce the original stimulus, pushing the system further and further away from its starting point. Positive feedback leads to rapid change and is often a 'runaway' process.

Examples:

Fruit Ripening: A ripening apple releases a small amount of ethylene gas. This gas acts as a hormone that causes nearby apples to ripen faster. These ripening apples then release more ethylene, which accelerates the ripening of other apples, and so on. This creates a cascade of ripening.

Blood Clotting: When a blood vessel is cut, platelets begin to stick to the site. As they stick, they release chemicals that attract more platelets. This quickly creates a large clot to seal the wound.

Microphone Feedback: If a microphone is too close to its speaker, it picks up its own amplified sound. This sound is then amplified again, creating a loud, high-pitched screech that grows in volume until the system is stopped.

Key Terms