Cells to Organ Systems
Describe the hierarchical organisation of multicellular organisms: cells → tissues → organs → organ systems → organism
What a learner can do afterwards
- Places cells, tissues, organs, and organ systems in the correct order of organisation
- Gives a specific example of each level (e.g. muscle cell → muscle tissue → heart → circulatory system → human)
- Explains why specialised cells are needed in a multicellular organism
The lesson
Your body is not one giant cell. It is built from trillions of tiny cells, and those cells are organised into levels, a bit like nesting boxes. Each level is a group of the level below it, doing a bigger job.
Take your heart. One muscle cell can squeeze, but it cannot pump blood alone. Many muscle cells join to form muscle tissue. That tissue, plus other tissues, builds your heart, an organ. Your heart and blood vessels together form the circulatory system. Every organ system in you makes up the whole organism: you.
Why not just use one plain, identical cell everywhere? Specialised cells are better at doing one job well. A nerve cell carries signals fast, a muscle cell contracts, a red blood cell carries oxygen. Grouping cells with the same job into tissue lets your body handle many jobs at once.
Cells group into tissues, tissues into organs, organs into organ systems, and organ systems into you.
Watch it
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.