Here’s a brief summary of each level in the organization of the human body:

### **Atom**  
- **Definition**: The smallest unit of matter that retains the properties of an element (e.g., oxygen, carbon).
- **Role**: Atoms form the building blocks of molecules that are essential for biological processes in the body.

### **Molecule**  
- **Definition**: A group of atoms bonded together (e.g., water, proteins, DNA).
- **Role**: Molecules form the structural components of cells and participate in chemical reactions that sustain life.

### **Organelles**  
- **Definition**: Specialized structures within cells (e.g., mitochondria, nucleus) that perform specific functions.
- **Role**: Organelles maintain the cell's functionality by handling processes like energy production, waste disposal, and genetic material management.

### **Cells**  
- **Definition**: The basic unit of life, capable of performing all necessary biological activities.
- **Role**: Cells carry out specific tasks such as metabolism, communication, and replication; examples include muscle cells and nerve cells.

### **Tissues**  
- **Definition**: Groups of similar cells working together to perform a specific function (e.g., muscle tissue, connective tissue).
- **Role**: Tissues create the structural framework of organs and support their functional roles in the body.

### **Organs**  
- **Definition**: Complex structures made up of different tissues that work together to perform a particular function (e.g., heart, lungs).
- **Role**: Organs carry out essential processes required for survival, such as pumping blood, filtering waste, or enabling respiration.  

Each level builds on the previous one, contributing to the complexity and functionality of the human body.