Multicellular organisms like humans are made of cells that differentiate and organize into different levels. Individual cells specialize and combine to form tissues. Tissues work together to form organs, and organs systems are groups of organs that perform major functions. This allows multicellular organisms to be larger, live longer through cell specialization, and continue living even if individual cells die.

1. Cells and Systems
How do individual cells function
together in a multicellular organism?

2. Key Concept
 As multicellular organisms develop, their
cells differentiate (change & separate) to
form different levels of organization

3. Key Concept
 Why it Matters: so
organisms like humans
(we are multicellular) can
have different kinds of
cells, tissues, organs, and
organ systems

4. Unicellular Organisms
 “uni-” = one
 Prokaryotes are unicellular organisms
 Some algae, some protists, and some
eukaryotes (yeasts), are unicellular
 Can individually do everything they need to
stay alive

6.  Benefits over multicellular organisms:
 Need fewer resources
 Can live in harsher conditions

7. Multicellular Organisms
 “multi-” = more than one
 Plants, animals, some protists, and most fungi
are multicellular

8. Multicellular Organisms
 Start as a single cell  many cells  cells
differentiate (change) into different types of
cells  cells group together to form tissues

9. Multicellular Benefits
 Larger size = have less predators and have more
options of things to eat

10. Multicellular Benefits
 Longer life – organism will continue to live even if
a single cell dies

11. Multicellular Benefits
 Specialization – each type of cell has a specific
job, making the organism more efficient

12. Levels of Organization
 1st Level: Cells

13. Levels of Organization
 1st Level: Cells
 2nd Level: Tissues
example
muscle tissue

14. Levels of Organization
 1st Level: Cells
 2nd Level: Tissues
 3rd Level: Organs

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

16. 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

17. 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

18. Level 3: Organs
 Organ = structure that is made up of 2 or more
tissues working together to get a specific job done

19. Level 3: Organs
 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

20. 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

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