What is the difference between an organ and an organelle?

Animals and plants are made up of tiny building blocks called cells. There are different types of cells that do different things, and cells that are similar to each other are grouped together in what's called a tissue. Each type of tissue then does something different; for example, muscle is a type of tissue that helps us to move, while nerve tissue helps different parts of our body to communicate with each other. An organ is when different types of tissue work together to achieve a particular outcome. An example of an organ is the heart. In the heart, muscle tissue contracts to pump blood around our body, while nervous tissue communicates important information between the heart, brain and body. Organs are then organised into groups called systems, whereby all organs in the system work together to perform a specific function. In our example, the heart is a part of the circulatory system with our lungs, and the two together help us to take in oxygen and pump it around the body to keep us alive. If an organ helps the body to perform a specific function, then an organelle helps the cell to perform a specific function. Organelles are tiny, specialised units - like mini organs - within cells that help them to do things. Therefore, the order of organisation in plant and animal bodies goes like this, starting from the smallest and least complex unit to the largest and most complex group: organelle -> cell -> tissue -> organ -> organ system.