Pair Share
8-March
Brainstorm
What do you know about stem cells?
What are they?
What do they do?
Essential Question: How do you start with one cell and wind
up with ~200 different types of cells?
Answer = Cell
Differentiation
(aka cell
specialization)
CELL SPECIALIZATION
200 different types of human cells
- differ in size, shape, and function
Let’s start from the beginning…
sperm and egg are considered GAMETES i.e. sex cells
sperm + egg form a zygote…in a process called fertilization
ZYGOTE
1st cell division
3rd cell division
4th cell division (morula)
2nd cell division
5th cell division
CELL DIFFERENTIATION = the specialization of cells
least specialized cells are stem cells
(i.e. have the ability to “turn into” other cell types)
Stem
Cell
zygote
blastocyst
8-9 days (hundreds of cells)
a blastocyst is composed of hundreds of stem cells which
begin to specialize
single cell
zygote
8 cells
morula
16 cells
blastocyst
>100 cells
Human embryos developing in vitro. The photos show a fertilized egg, 8-cell
stage, cell adhesion, a compacted morula, a blastocyst and zona hatching.
potency = potential to become other cell types
Cells of the embryo differentiate based on a number of
chemical and physical signals that are produced within
the embryo including;
Signals/Cues
Internal
(transcription
factors)
External
(transcription
factors)
Environmental
Factors