In studying more complex multicellular organisms like ourselves, there are 5 basic levels of organization we use.

The most basic level of organization is individual cells.

Groups of similar cells which work together are called tissues. Muscle and bone are examples of tissues.

Different types of tissues combine to form organs. Each organ performs a specific job in the body, such as pumping blood or filtering urine.

Groups of organs working together form organ systems. Each organ system performs a general function for the body, such as digestion or respiration.

And finally, the total combination of all the cells, tissues, organs and organ systems is the whole organism. We’ll take a closer look at all of these levels.

The cell is the basic biological unit for all living things. (click) One example of a cell is a neuron or nerve cell neuron

Another type of cell is a muscle cell. neuron muscle cell

Here’s a bone cell neuron muscle cell bone cell

And here’s a skin cell. neuron muscle cell skin cell bone cell

Tissues are made up of similar cells, all working together. (click) here is some nerve tissue nerve tissue

Here is some muscle tissue nerve tissue muscle tissue

Our bones are made up of skeletal tissue nerve tissue muscle tissue skeletal tissue

Epithelial tissue covers all the surfaces in our body, inside and out. nerve tissue muscle tissue epithelial tissue skeletal tissue

Organs are made up of groups of different tissues that work together to perform a specific activity or set of activities. (click) The brain is one organ. It has a lot of nerve tissue, but also contains other types of tissue. brain

The heart is another organ. It is made up largely of muscle tissue, but also has nerve tissue, connective tissue, and epithelial tissue, and others. brain heart

Another important organ is the liver. Like all organs, the liver is made up of a number of types of tissue. brain heart liver

An organ system is a group of two or more organs that work together to perform a general function in the body. (click) For example, the digestive system is a group of organs that break down our food and deliver its nutrients to all cells of the body. digestive system

And the respiratory system is a group of organs which extracts oxygen from the air and deliver it to all of the cells in our body. digestive system respiratory system

An organism is a complete individual animal or plant, including all of it’s cells, tissues, organs, and organ systems. (click) Here’s a cute organism

And here’s a pretty one!

Acknowledgements for Images Used License: CC0 Public Domain / FAQFree for commercial use / No attribution requiredFAQ Thank you Nemo License: CC0 Public Domain / FAQFree for commercial use / No attribution requiredFAQ Thank you Gerd Altmann

Acknowledgements for Images Used License: CC0 Public Domain / FAQFree for commercial use / No attribution required. Thank you Nemo.FAQ "Heart anterior exterior view" by Patrick J. Lynch, medical illustrator - Patrick J. Lynch, medical illustrator. Licensed under CC BY 2.5 via Wikimedia Commons - erior_view.jpg#mediaviewer/File:Heart_anterior_exterior_vi ew.jpg

Acknowledgements for Images Used License: CC0 Public Domain / FAQFree for commercial use / No attribution required. Thank you NemoFAQ

Acknowledgements for Images Used "Respiratory system complete en" by LadyofHats - The image i did myself as sources i used the books: Sobotta "atlas der anatomie des menschen" ISBN , Churchill livingstone "gray's anatomy" ISBN , Interamericana. McGraw-hill "atlas forografico de anatomia del cuerpo humano" ISBN Also used several online diagrams like ([1] and [2]) Image renamed from Image:Respiratory system complete.svg. Licensed under Public Domain via Wikimedia Commons - mplete_en.svg#mediaviewer/File:Respiratory_system_complete_ en.svg