Lesson 1: Inputs for Function

Key Idea

The human body is an open system, meaning it cannot operate in isolation. To function and survive, it must constantly take in materials from the external environment.

These necessary materials are known as inputs. The two most critical sources for these inputs are food and air. Without a steady intake of these external resources, the body cannot sustain its internal processes.

Key Idea

The body is composed of trillions of fundamental units called cells. Each cell performs a specific task, and the collective activity of these cells is what allows the human body to move, think, and breathe.

Therefore, the body's ability to function is entirely dependent on the health of its individual cells. If the cells stop working, the human body stops working. Medical conditions that affect the whole body often start with a problem at the cellular level.

Key Idea

Cells cannot simply "eat" food; they require specific chemical inputs to run. These inputs are molecules that are small enough to enter the cell and be used for biological processes.

The three most critical molecules are glucose (for energy), amino acids (for building and repair), and oxygen (to release energy). A cell must receive a continuous supply of all three specific molecules to remain healthy and functional.