1. Standard B-2.4
Cell Differentiation

2. The student will be able to:
Explain the process of cell differentiation as the basis for the hierarchical organization of organisms.

3. Key Concepts
Cell Organization
Cell Differentiation
Stem Cells

4. It is essential for you to know:
In the development of most multicellular organisms, a single cell (fertilized egg) gives rise to many different types of cells, each with a different structure and corresponding function.
Nearly all of the cells of a multicellular organism have exactly the same chromosomes and DNA.
Stem cells are unspecialized cells that continually reproduce themselves and have, under appropriate conditions, the ability to differentiate into one or more types of specialized cells.

5. TODAY’S OBJECTIVES: Explain the process of cell differentiation.
Recall that all of the cells of a particular
organism contain all of the genetic code.
Summarize the unique characteristics of
embryonic and adult stem cells.

6. How do we get from …..
ATOM to
ANTONIO? (a person)

7. Organization Levels of Life
Atom to Organism

8. Levels of Organization
Nonliving Levels:
ATOM (element)
MOLECULE (atoms joining together to create compounds like carbohydrates & proteins)
ORGANELLES (nucleus, ER, Golgi …)

9. Levels of Organization
Living Levels:
CELL (makes up ALL organisms)
TISSUE (cells working together)
ORGAN (heart, brain, stomach …)
ORGAN SYSTEMS (respiratory, circulatory, digestive…)
ORGANISM (you, frog, tree)

10. Levels of Organization
Living Levels continued:
POPULATION (one species in an area)
COMMUNITY (several populations in an area
ECOSYSTEM (forest, prairie …)
BIOME (Tundra, Tropical Rain forest…)
BIOSPHERE (all living and nonliving things on Earth)

11. Nonliving levels…..
Atom 
Molecule 

12. LIFE STARTS AT THE CELLULAR LEVEL!!
Organelles 
Cell 

13. Living levels
Tissue 
Organs ----

14. Living levels cont’d…
Organ Systems ----
Organism

15. Let’s go back to where life started…
LIFE STARTS AT THE CELLULAR LEVEL!

16. Now that we have learned how living things are organized, what’s next?
We will learn more about the lowest level or organization: cells
What is the first thing that we need to know about cells?
All cells fall into one of the 2 major classifications:
PROKARYOTIC or EUKARYOTIC

17. Prokaryotic vs. Eukaryotic

18. What’s the difference b/w prokaryotes and eukaryotes?
Prokaryotic cells were here 1st and for billions of years, they were the only form of life on Earth. All prokaryotic organisms are unicellular.
Eukaryotic cells appeared on Earth long after prokaryotic cells but they are much more advanced. Unlike prokaryotic organisms, eukaryotic organisms can be uni- or multicellular.

19. Characteristics of Prokaryotes
Simplest type of cell.
Oldest type of cell: appeared 4 billion yr ago.
Largest group of organisms. (more prokaryotes than eukaryotes)
Unicellular organisms that are found in all environments. (commonly called bacteria)

20. Characteristics of Prokaryotes
Prokaryotes DO NOT have a nuclear membrane: have a single, circular chromosome in a place called the nucleoid region. (middle of cell)
DO NOT have membrane bound organelles: have ribosomes to make proteins, but they don’t have a membrane.

21. Characteristics of Prokaryotes
Are much smaller in size than the eukaryotic cells.
Very simple internal structure.
So what do these simple cells look like?

22. Prokaryotic cell

23. Characteristics of Eukaryotes
Most complex type of cell.
Appeared about 1 billion yr ago.
Generally more advanced than prokaryotes.
Nuclear membrane surrounds linear genetic material (DNA).

24. Characteristics of Eukaryotes
Eukaryotic cells have several different parts which means they have a complex internal structure.
Larger in size than prokaryotic cells.
2 main types of Eukaryotic cells:
Plants
Animals

25. Eukaryotic Cell

26. How are they different? Organelles lack a membrane.
Ribosomes are the only organelles.
Genetic info floats around uncontained.
Organelles have a membrane.
Multiple organelles including ribosomes.
Genetic info is contained within the nucleus.
PROKARYOTIC CELLS
EUKARYOTIC CELLS

27. How are they different? Circular DNA Unicellular
Cells are small in size
Has large # of organisms
4 billion yr ago
Linear DNA
Uni- or multicellular
Cells are large in size
Has smaller # of organisms.
1 billion yr ago
PROKARYOTIC CELLS
EUKARYOTIC CELLS

28. How are they similar? Have cell membranes (outer covering of the cell)
Both:
Have cell membranes (outer covering of the cell)
Have ribosomes
Have DNA
Have a liquid environment within called the cytoplasm

29. Cells Differentiate…..

30. Life Begins…
All life begins with a single cell, a fertilized egg called a zygote.

32. Differentiation
The fertilized egg gives rise to many different types of cells in a multicellular organism.
Each cell has a special shape and job (structure/function)

33. As cells differentiate, they organize themselves into tissues, then organs, then organ systems.
Working together, the whole organism is complete.

34. Not so fast, though….
Even though cells are differentiated, they contain the same DNA in their nuclei.
During differentiation, only some parts of that DNA are activated (turned on)
Since all cells have the same DNA, they all have the potential to become any type of cell.
Once a cell specializes, it cannot be reversed.

35. Stem Cells A type of cell that is UNSPECIALIZED.
They have not yet differentiated into a certain cell type.
2 types of stem cells:
Embryonic stem cells
Adult stem cells

36. Embryonic stem cells Found in embryos
Can give rise to any type of cell
You kill the embryo when harvesting embryonic stem cells
Very controversial

37. Adult stem cells Found in human adults.
Bone marrow can give rise to blood or bone cells.
Not controversial b/c the human doesn’t die when adult stem cells are harvested.

38. HOMEWORK:
Make a Venn Diagram showing the SIMILARITIES and DIFFERENCES between Prokaryotic and Eukaryotic cells.