Cells, Tissues & Organs
Understand that the body is organised in a hierarchy: tiny cells are the building blocks, groups of similar cells form tissues, tissues combine into organs (like the heart or stomach), and organs work together in organ systems (like the circulatory system)
What a learner can do afterwards
- State that cells are the body's smallest living units and that most individual body cells need a microscope to be seen clearly
- Describe the hierarchy: cells → tissues → organs → organ systems
- Give an example: muscle cells form muscle tissue; muscle tissue and other tissues form the heart; the heart works with blood vessels in the circulatory system
1 · Read
Your body contains trillions of cells. A cell is the body's smallest living unit. Most individual body cells are too small to see clearly with your eyes alone. A microscope makes them look larger so you can study them.
When many similar cells work together, they form a tissue. Different tissues work together in an organ, such as your heart, brain, lungs or stomach. Organs work together in an organ system. To place a part in this building order, check what it is made of and what it works with. Measuring its length does not tell you its level.
Muscle cells work together in muscle tissue. In your heart, muscle tissue works with other tissues. Together, these tissues form the heart, an organ that pumps blood. The heart works with blood vessels in the circulatory system.
Each box names a level. This chain does not show the route that blood follows.
An organ system is not one large organ. The heart is one organ. It works with blood vessels in the circulatory system. This system moves blood around the body.
Cells are tiny building blocks that group into tissues. Tissues build organs, and organs team up to form organ systems.
Original lesson, quiz and flashcard text written for this learning dataset.
Readings written for this learning dataset. Flashcards use the dataset's facts collection. Video: Making sense of how life fits together - Bobbi Seleski, TED-Ed.
More to read
Looking closely at cells
Most individual body cells are hard to see clearly with your eyes alone. A microscope makes them look larger. Looking through it does not make the cells grow.
A cell is the body's smallest living unit. There are smaller parts inside cells, but those parts are not living units on their own.
Cells with a shared job
Muscle cells can shorten and relax. Many muscle cells working together form muscle tissue. Their shared work helps the tissue produce movement.
The word tissue names a group of similar cells working together. It does not mean the paper tissue you might use for your nose.
What makes the heart an organ?
Muscle tissue helps the heart squeeze and pump blood. The heart also contains other tissues.
A body part made of different tissues working together is an organ. That is why the whole heart is an organ, while muscle tissue is one of its parts. The stomach is another organ made of different tissues.
A pump and its routes
The heart pushes blood. Blood vessels carry it through the body. These parts work together in the circulatory system.
The name organ system describes a team of organs doing a shared job. Calling the heart an organ and calling its team an organ system describe two levels of organization.
Different tissue jobs
Body tissues do different jobs. Some cover surfaces and line spaces inside you. Others support and join body parts. Muscle tissue shortens and relaxes to make movement. Nervous tissue carries messages.
An organ contains different tissues working together. The heart needs muscle tissue for pumping, along with other tissues that help it do its job.
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Where it sits
Learn first
Nothing; this is a starting point.
Optional connections
Where this leads
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