Levels of Organisation within Organisms

Cells: These are the basic building blocks of all organisms. They can carry out all necessary functions to sustain life, such as producing energy and removing waste.
Unicellular and multicellular organisms: Single-celled organisms, like bacteria, carry out all their life processes within one cell. On the other hand, multicellular organisms, like humans, have many cells that work together to carry out life processes.
Specialised cells: In multicellular organisms, cells often specialise to perform specific functions. For example, nerve cells carry signals around the body, while red blood cells transport oxygen.
Tissues: A tissue is a group of similar cells that work together to perform a common function. For example, muscle tissue is made of muscle cells which contract to enable movement.
Organs: An organ is a structure made of different types of tissues that work together to carry out a specific job. For example, the heart is an organ that pumps blood around the body.
Organ systems: An organ system is a group of organs that work together to perform a complex function. For example, the digestive system, which includes the stomach and intestines, breaks down food so nutrients can be absorbed into the bloodstream.
Organisms: An organism is a complex individual that consists of organ systems. For example, human beings are organisms that have several organ systems including the nervous system, circulatory system, and digestive system.
Movement across membranes: Organisms need ways to move materials in and out of cells. This happens across cell membranes through processes such as diffusion, osmosis, and active transport.