1. Levels of Organization
How do unicellular and multicellular organisms differ?
How does cell differentiation lead to the organization within a multicellular organism?
Lesson 2 Reading Guide

2. Lesson 2 Reading Guide - Vocab
Levels of Organization
cell differentiation
stem cell
tissue
organ
organ system
Lesson 2 Reading Guide - Vocab

3. All living things are made up of cells….
The cell is the smallest unit of a living thing.
If an organism is unicellular, all functions of life happen within that one cell.
If an organism is multicellular, different cells have different jobs and they all work together.

4. 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

5. Multicellular Organisms
Multicellular organisms are made of many types of eukaryotic cells working together, each with a specialized function.
How do unicellular and multicellular organisms differ?
Lesson 2

6. 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
Advantages- can grow larger and have specialized cells for different functions
Link:

7. Multicellular Organisms (cont.)
All cells in a multicellular organism come from one cell: a fertilized egg.
The process by which cells become different types of cells is called cell differentiation.
Lesson 2

8. Multicellular Organisms (cont.)
Stem cells are unspecialized animal cells that are able to develop into many different cell types.
fiber
Science Use a long muscle cell
Common Use a thread
Lesson 2

9. Why do we hear so much about stem cells & what are they?
The human body is composed of many different types of cells
e.g. muscle cells, skin cells, liver cells, cardiovascular cells, etc.
Not all cells have the same potential
Some cells remain “immature”—these are stem cells
When stem cells “mature,” or differentiate they turn into the different cells of the body (or somatic cells)

10. Stem cells are multi-talented
Self-renew
a stem cell can reproduce itself
by cell division
Differentiate
a stem cell can specialize into a particular type of somatic cell

11. There are two main types of Stem Cells—Adult & Embryonic Stem Cells
Adult stem cells
found in adult tissue
can self-renew many times
are multipotent – they can differentiate to become only the types of cells in the tissue they come from.
hematopoietic stem cells – give rise to blood cells
mesenchymal stem cells – give rise to cells of connective tissues and bones
umbilical cord stem cells – a rich source of hematopoietic stem cells
stem cells found in amniotic fluid – might be more flexible than adult stem cells

12. There are two main types of Stem Cells—Adult & Embryonic Stem Cells
come from embryos
This stage embryo is called a Blastocyst
~5 days old, a hollow microscopic ball of cells
can self-renew forever; adult stem cells have a cell-division limit
are pluripotent – they can differentiate to become almost EVERY cell in the body
live in a Petri dish, not a woman's body

13. Multicellular Organisms (cont.)
Plants have unspecialized cells similar to animal stem cells.
These cells are grouped in areas of a plant called meristems.
Lesson 2

14. Level 1 : Cells Cells can be specialized (have a certain function)
The size and shape of a cell relates to its job or function.
Cells are made of different structures that perform different functions that keep a cell alive.

15. 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

16. 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

17. 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

18. Lesson 2

19. Levels of Organization
Cells
Tissues
Organs
Organ Systems
Organism
Cells  Tissues  Organs  Organ  Organism
Systems

20. Multicellular Organisms (cont.)
Multicellular organisms usually have many organ systems that work together to carry out all the jobs needed for the survival of the organism.
How does cell differentiation lead to the organization within a multicellular organism?
Lesson 2

21. A unicellular organism carries out all
A unicellular organism carries out all the activities necessary for survival within one cell.
Cells become specialized in structure and function during cell differentiation.
Lesson 2