1. Why are Cells Small?
A eukaryote cell is very small with an average size of 10 microns across.
1 micron = 1/1,000,000 of a meter or 1 x 10-6m
1 micron = 1/1000 of a millimeter or
1 x 10-3mm

2. Why are Cells Small? A human is made of about 10 trillion cells.
But the number of prokaryote cells both on and in one human is more than that!!!
Prokaryote cells are much smaller than eukaryote cells.

3. Comparison of Prokaryote and Eukaryote Cells

4. Most Plants and Animals begin life as a fertilized cell

5. Egg Fertilization

6. But Rather than Growing Bigger
Each fertilized cell (=zygote) DIVIDES and Divides and DIVIDES and DIVIDES .

7. Development of a Sea Urchin Embryo*
Early development in a sea urchin (Lytechinus pictus) embryo illustrates how a single egg develops into a hollow blastula.
Elapsed time about 18 hours.

8. Modeling With your group: Fold your boxes Measure the volume
Complete worksheet

9. Conclusions Cells are small to maximize their surface area
A high surface area is critical to the rapid diffusion of material into and out of the cell.

10. Conclusions
Rapid diffusion of glucose, oxygen, carbon dioxide and other molecules is necessary for the maintenance of cell function.

11. Conclusion
A cell grows to its optimal size and then it divides in half.
Each half will form a new cell that grows until it reaches its optimal size, and then it too will divide in half.

12. Exceptions! Large cells
With your table design a cell that has a volume of 36 cm3 AND the largest possible surface area.
Use whole number for each dimension!
Consider: How do you maximize surface area?

13. Exceptions Another type of large cell is an egg.
A bird’s egg is one large cell. The yolk is a food source for the growing embryo.
How is it possible for a bird’s egg to function when it is so large?
Food is already present—diffusion isn’t needed to
meet the nutritional needs of cell

14. Why are cells small?
Small cells optimize the movement of material in and out of the cell
DNA in the nucleus of the cell controls the activity of the cell. If a cell increased in size, its activity would increase.
The quantity of DNA in the cell would not be able to control all the activities of the larger cell.

15. How do Cells Divide?
1 parent cell divides into 2 daughter cells. This decreases volume and increases surface area of each cell.
When the cell divides in half, the material must be divided evenly except for the…

16. Prokaryote – cell division
Cell division occurs through binary fission= reproduction (in prokaryotes)
All genetic material (DNA) in the cell is found on one chromosome floating in the cytoplasm.

17. Prokaryote – cell division
Cell division begins with replication (doubling) of the chromosome.
The two chromosomes move to opposite ends of the cell.
Cell splits apart into two daughter cells--each containing one chromosome and half of the cytoplasm
Each daughter cell is genetically identical*

18. Cell Division in Prokaryotes AND Eukaryotes
Histones
DNA
Cell Division in Prokaryotes AND Eukaryotes
Chromosome = a structure in eukaryotes and prokaryotes made of a long strand of a DNA molecule bonded to histones.
Histones are proteins that provide structure for the chromosome

19. Eukaryotic – Cell Division
Each eukaryotic cell contains a nucleus with chromosomes.
Each species has a characteristic number of chromosomes. Humans have 46 chromosomes in the nucleus of each of their cells (23 chromosomes from each parent)

20. Eukaryotic Cell Division
Eukaryote cells are much more complex than prokaryote cells and the cell cycle is much more complex.
Four phases of cell cycle. The cell cycle represents the entire lifetime of a single cell
M phase (mitotic phase)
G1 phase (gap 1)
S phase (synthesis)
G2 phase (gap 2)
INTERPHASE

21. Interphase
Longest part of cell cycle (90%). This is when the cell is “doing its job”.
Divided into 3 phases
G1 phase - (gap 1) - Period of cell growth, development and repair. Cell increases in size; proteins and organelles are produced.

22. This is what the nucleus of the cell looks like during interphase
Interphase continued
This is what the nucleus of the cell looks like during interphase
This is what the nucleus of the cell looks like at the start of cell division
S phase - (synthesis) – Preparation for cell division.
Occurs in nucleus: All genetic material is doubled.
The genetic material before mitosis begins is called chromatin. Chromatin is made of long strands of DNA wrapped around histones.
Chromatin is not yet “condensed” into chromosomes and  fills up the entire nucleus.

23. Interphase Continued
G2 phase - (gap 2) --Organelles (example: centrioles) and molecules specifically required for cell division are produced.

24. Cell Cycle
Interphase

25. Mitotic Phase* Mitotic Phase – The division of the cell Includes
Mitosis (4 phases) = division of the nucleus AND
Cytokinesis = division of the cytoplasm

26. Mitosis – Prophase What happens?
Cell in Prophase
What happens?
Chromatin in the nucleus condenses and forms chromosomes
Each chromosome is made up of two identical copies (sister chromatids), which are attached together in the middle (centromere).

27. During Prophase… Centrioles Spindles The nucleolus disappears.
Sister
Chromatids
During Prophase…
Centrioles
Four found in the cytoplasm of each animal cell
Move to opposite ends of the cell (2 on each side)
Spindles
Fan-like structures made of microtubules grow out from the centrioles towards the center of the cell
The nucleolus disappears.
The nuclear envelope breaks down*.

28. Vocabulary Worksheet Quick vocabulary check!
Centromere vs. sister chromatids
Cytokinesis vs. Mitosis
DNA vs. histone.
Macromolecules
Interphase
Gap1 and Gap2 and Synthesis
Mitotic Phase vs. Mitosis
Chromosomes vs. chromatin

29. Metaphase Chromatids line up at the center of the cell.
Each chromatid is attached to a spindle fiber at the centromere*

30. Anaphase Anaphase Centromeres separate.
Each sister chromatid becomes a separate chromosome.
Spindles contract --causing chromosomes to move towards opposite ends of the cell near the poles of the spindles*.

31. Telophase
Telophase
Chromosome gathers at either end of the cell and begin to lose their shape. They turn back into ________________
A nuclear envelope forms around each group of chromosomes.
Nucleolus forms in each nucleus.
Spindle fibers break apart.  
chromatin

32. Cytokinesis Division of cytoplasm Occurs at same time as telophase
Division of cytoplasm
Occurs at same time as telophase
Cell membrane pinched into two parts with one nucleus and an equal number of organelles in each part.
New cell membrane forms around each cell*.

33. Cell Division*

34. Differences Between Plant and Animal Cell Division
In plants--Spindle fibers form during prophase BUT there are no centrioles.
In plants - Cytoplasm
Does NOT pinch together
Instead, a cell plate forms which divides the cell in half.
Each half contains a nucleus and equal amounts of organelles and cytoplasm.
New cell wall forms in cell plate

35. Cell Division in Eukaryotes
Unicellular organisms = reproduction (one organism divides into two organisms)
Multicellular organisms = growth, development and repair

36. Cell Division
Complete packet!