Multicellular organisms develop through cell differentiation and organization into levels. The first level is cells, which can become specialized tissues that group into organs performing specific jobs. Organs systems integrate multiple organs to carry out functions, like the digestive system. This hierarchical organization allows multicellular organisms like humans to have diverse cell types organized as tissues, organs, and systems.

1. The Organization of
Living Things

2. Key Concept  As multicellular
organisms develop,
their cells differentiate
(change & separate)
and form levels of
organization
 Why it Matters: so
Humans (we are
multicellular) can have
different kinds of cells,
tissues, organs, and
organ systems

3. Unicellular Organisms
 “uni-”
= one
 Prokaryotes are unicellular organisms
 Some algae, some protists, and some
eukaryotes (yeasts), are unicellular
 Can still do everything they need to stay alive
 Benefits over multicellular organisms:
 Need fewer resources
 Can live in harsher conditions

4. Multicellular Organisms
 “multi-” = more than one
 Plants, animals, some protists, and most fungi
are multicellular
 Start as a single cell  many cells  cells
differentiate (change) into different types of
cells  cells group together

5. Multicellular Characteristics
 Larger size = have less predators and have more
options of things to eat
 Longer life – organism will continue to live even if
a single cell dies
 Specialization – each type of cell has a specific
job, making the organism more efficient

6. Levels of Organization
 1st Level: Cells
 2nd Level: Tissues
 3rd Level: Organs
 4th Level: Organ Systems
 Cells  Tissues  Organs  Organ Systems

7. Level 1 : Cells
 Cells can be specialized (have
a certain function)
 Function = job
 Function is related to the cell
structure
 Structure = how parts of the
cell are put together
 Shape
 Material it’s made from
 Structure of a brain cell is
different from muscle cell

8. Level 2: Tissues
 Tissue = group of cells that work together to do a
specific job
 Ex: Heart muscle tissue
is made of heart muscle
cells
 Animals have 4 types of
tissue: nerve, muscle,
connective, protective
 Plants have 3 types of
tissue : transport, protective, ground

9. Level 3: Organs
 Organ = structure that is made up of 2 or more
tissues working together to get a specific job done
 Ex: Stomach – muscle tissue moves food, special
tissues make chemicals to digest food, connective
tissue holds stomach together, nervous tissue
sends messages back and forth between the
stomach and brain

10. Level 4: Organ Systems
 Organ system = group of organs working
together to perform a specific function
 Each organ system has a specific job
 Ex: Digestive system is made of several
organs including the stomach and intestines

11. Structure of Animals
Cells
-basic unit of an animal’s structure
-become specialized
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Tissues
-made of cells that work together to perform a specific function
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Organs
-made of different types of tissues that work together to perform a specific function
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Organ Systems
-made of organs that work together to perform a specific function
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Organisms