Organism

An organism is any living thing. It can be as large as a whale or as tiny as a single bacterium. All organisms share some basic features that show they are alive. They grow, take in energy, respond to their environment, and reproduce to make new organisms. Without organisms, our planet would have no life.

Organisms come in many shapes and sizes. Some are made of just one cell, called unicellular organisms, such as bacteria and some algae. Others, like humans, plants, and animals, are made of many cells, called multicellular organisms. Each cell in a multicellular organism has a special job. For example, human cells form tissues, which work together to make organs like the heart or lungs.

All organisms need energy to live. Plants make their own food through photosynthesis, using [[Sun|sunphotosynthesis, and carbon dioxide. Animals, on the other hand, eat plants or other animals to get energy. Even the smallest organisms, such as fungi or bacteria, must take in nutrients to survive. This flow of energy connects all living things in a web called an ecosystem.

Organisms also respond to their environment. They can sense changes and react to stay safe or comfortable. For example, plants grow toward sunlight, and animals move away from danger or seek food. This ability to respond helps organisms survive in different habitats, from deep oceans to icy mountains and hot deserts.

Over time, groups of organisms can change through a process called evolution. This happens when small differences build up over many generations, helping living things adapt to their surroundings. evolution explains how the great variety of life on earth came to be — from tiny insects to giant trees.

Scientists study organisms in a field called biology. They group organisms into categories such as plants, animals, fungi, and microorganisms. Understanding organisms helps humans learn about health, nature, and how to care for the planet. Every organism, no matter how small, plays an important role in keeping Earth’s systems in balance.