1. LEQ:
Why do cells divide at different rates?
Key terms: cell cycle, cell division, differentiation
Journal entry – Identify some large organisms, why is it advantageous to be large? Are there any drawbacks to building big bodies?
think about trophic pyramids

2. Cells multiply at different rates:
why would the rates of cell division for muscle cells and skin cells differ from neurons?

3. A regulated cell cycle is shared among eukaryotes.
The cell cycle is a regular pattern of growth and division.
Gap 1 (G1) varies the most.
DNA synthesis (S)
Gap 2 (G2)
Mitosis (M)
G0:
normal biological functions
Non-dividing

4. Cell differentiation - cells mature & specialize
Specialized cells express combinations of genes to perform specific functions.
Cell differentiation - cells mature & specialize
Signaling shapes cell memory
location is related to function
Outer: skin cells
Middle: bone cells
Inner: intestines

5. Different sets of genes are expressed in different types of cells.
cells respond to signals from their environment
gene expression
Example:
Liver cells; albumin
Lens fiber cells; crystallin
gene
switches
Enhancer
Albumin gene
Crystallin gene
Promoter

6. Different sets of genes are expressed in different types of cells.
Fig
Different sets of genes are expressed in different types of cells.
Signals can specify gene expression  changes in cell
Available
signals
(b) Lens cell
Crystallin gene
expressed
LENS CELL
NUCLEUS
LIVER CELL
(a) Liver cell
not expressed
Albumin gene
Figure Cell type–specific transcription

7. Stem cells add news cells to a body when they divide
divide and renew as a population (below)
self-renewing, top
Asymmetric replication, bottom
Can become specialized cell types (below, right)
Signals, transcription factors

9. Summary:
How does communication between cells help maintain homeostasis?
Explain why cell differentiation is an important part of the development of a multicellular organism.
What are the defining characteristics of stem cells?
Describe how tissues, organs, and organ systems are similar

10. Answers:
Different cells are needed for different functions, and their activities need to be coordinated to maintain the body’s internal environment
It is needed for different functions because one kind of cell cannot perform all the activities required for life
Stem cells divide continually, while remaining undifferentiated for long periods of time; yet they can develop into specialized cell types
Tissues are groups of specialized cells that make up organs, and organs work together in organ systems