1. Cell Growth and Division
Chapter 10
Cell Growth
and Division

2. 3. What is the advantage of cells being small?
Getting Through
Materials move through cells by diffusion. Oxygen and food move into cells, while waste products move out of cells. How does the size of a cell affect how efficiently materials get to all parts of a cell?
Work with a partner to complete this activity.
1. On a sheet of paper, make a drawing of a cell that has the following dimensions: 5 cm x 5 cm x 5 cm. Your partner should draw another cell about one half the size of your cell on a separate sheet of paper.
2. Compare your drawings. How much longer do you think it would take to get from the cell membrane to the center of the big cell than from the cell membrane to the center of the smaller cell?
3. What is the advantage of cells being small?

3. How big can a cell get?
• The largest human cell is an ovum (0.2mm)
• As a organism grows, can the cells get bigger?
– No, cells start to divide.
– Cells can’t keep growing indefinitely.
• There are Limits to Cell Size
– The amount of DNA
– The exchange of materials

4. DNA Overload = As cells increase in size, no extra DNA is made
• Analogy: books in a library =

5. Exchanging Materials
Food and oxygen need to enter, wastes need to exit.
• The larger the volume of the cell, the smaller the surface area gets.
– Surface Area = cell membrane

6. Surface Area to Volume Ratio
• Surface Area (SA) = Length x Width x # of sides
– 1 x 1 x 6 = 6
• Volume (V) = Length x Width x Height
– 1 x 1 x 1 = 1
• Ratio = SA / V
– 6 / 1 = 6:1

7. Surface Area to Volume Ratio
Cell Size
Surface Area (length x width x 6)
Volume
(length x width x height)
Ratio of Surface Area to Volume
• What happens to the V as SA goes up?
– It increases much more rapidly
• What happens to SA / V Ratio?
– It decreases
• This causes major problems for the cell
– Analogy: Town and Traffic

8. Division of the Cell
• Before a cell gets too large, it divides into two “daughter” cells.
• Before cell division takes place, the cell must replicate all of its DNA.
• The cell then divides and solves the problem of the cell becoming too large.

9. Chromosomes -Carriers of genetic information -made of DNA
-# in different organisms varies
-we have 46, squirrels have 40, dogs have 78, corn has 20

10. Events of The Cell Cycle
Interphase
G1 phase
G1: cells increase in size &
make new proteins
S: Chromosomes replicated
DNA synthesis takes place
G2: Organelles required for
division are produced
M phase
S phase
G2 phase
Mitosis
The process of cell division

11. Interphase Cell grows and replicates its DNA and centrioles Interphase
Nuclear envelope
Chromatin
Interphase
Cell grows and replicates its DNA and centrioles

12. Chromosomes (paired chromatids)
Prophase
Spindle forming
Centromere
Chromosomes (paired chromatids)
Prophase
Longest phase Spindle begins to form
Chromosomes become visible Nuclear envelope breaks Centrioles separate down

13. Metaphase Chromosomes line up across center of cell
Centriole
Metaphase
Centriole
Spindle
Chromosomes line up across center of cell
Microtubules connect centromeres to poles of cell

14. Individual chromosomes
Anaphase
Individual chromosomes
Anaphase
Sister chromatids separate into individual chromosomes
Chromosomes move apart
Spindle fibers shorten

15. Nuclear envelope reforming
Telophase
Telophase
Nuclear envelope reforming
Chromosomes gather at opposite ends of cell and lose shape
Nuclear envelopes form

16. Cytokinesis Cytoplasm pinches in half
Daughter cells has an identical duplicate set of chromosomes

17. Cytokinesis in plant cells

18. Control of Cell Division
Cells will continue to grow in a petri dish until they come into contact with other cells.
Controls can be turned on and off

19. Cell Cycle Regulators
The sample is injected into a second cell in G2 of interphase.
A sample of cytoplasm is removed from a cell in mitosis.
As a result, the second cell enters mitosis.
Cells in mitosis contain a protein that when injected into non-dividing cell causes spindle formation
Protein = cyclin. The amount of cyclin in a cell rises and falls in time w/cell cycle

20. Internal regulators External regulators
Proteins that respond to events inside the cell
Allow cycle to proceed only when certain events inside the cell have happened
-several make sure a cell doesn’t proceed with mitosis until all the chromosomes have been replicated
External regulators
Proteins that respond to events outside the cell
Direct cells to speed up or slow down division
-Ex: growth factors. Important in embryonic development and the wound healing

21. What happens when cell growth isn't controlled?