1. Cell Growth and Division

2. Cell Growth When living things grow what happens to its cells?
Living things grow by producing more cells.
On average, the cell size of an adult animal = the cell size of a young animal. There are just more!
Does an animal get larger because each cell increases in size or because it produces more of them?

3. Limits to Cell Growth
2 main reasons why cells divide rather than continue to grow indefinitely
The larger the cell becomes, the more demands the cell places on its DNA
The cell has more trouble moving enough nutrients and wastes across the cell membrane

4. Limit to Cell Growth: DNA overload
As cell increases in size, it does not make extra copies of DNA…causes information crisis
A larger cell would have to make greater demands on its available genetic library = DNA
Analogy: if a small town’s library had only a few thousand books, and the population grew, there would be more people borrowing books and greater demand on the popular books.

5. Limits to Cell Growth: Exchange
Cell size is limited because the rate at which food and oxygen are used up and waste products produced depends on the cell’s volume
If a cell got too large, it would be more difficult to get sufficient amounts of oxygen and nutrients in and waste products out.

6. Cell Size Small cells function more efficiently
Small cells can exchange substances more readily than larger cells because small objects have a higher surface area-to-volume ratio than larger objects
As a result, substances do not need to travel as far to reach the center of a smaller cell
Analogy: a main street in the town. As the population grew, more and more people would walk on the street. The size of the street is not getting bigger, so people would encounter more and more traffic.

7. Higher SA:V, the more efficient
Relative Cell Size

8. Higher SA:V, the more efficient

9. Division of the Cell
Before it becomes too large, a growing cell divides to form two daughter cells
Each daughter cell gets one complete set of genetic information
By dividing the cell, surface area to volume ratio will be high and allow for efficient exchange

10. Cell Division

11. Cell Division
Cell division is at the heart of the reproduction of cells and organisms
Organisms can reproduce sexually or asexually

12. Asexual Reproduction:
Some organisms make exact copies of themselves
Review Cell Theory

13. Cells arise only from pre-existing cells
All cells come from other cells
Cellular reproduction is called cell division
Allows an embryo to develop into an adult
It also ensures the continuity of life from one generation to the next

14. Prokaryotes reproduce by binary fission
Prokaryotic cells divide asexually
These cells contain a single chromosome, containing genes
The chromosome is replicated
The cell then divides into two cells, a process called binary fission

15. Binary Fission of Prokaryote
Plasma membrane
Prokaryotic chromosome
Cell wall
Duplication of chromosome and separation of copies
Continued growth of the cell and movement of copies
Division into two cells

16. Multicellular Organisms Grow and Develop by Mitosis

17. Cell Division : Mitosis
In multicellular organisms, mitosis is the source of new cells during growth and development
Mitosis occurs in humans shortly after the egg is fertilized- produces the vast number of cells needed for the embryo to take form

18. Cells divide at different rates.
The rate of cell division varies with the need for those types of cells.
Liver cells go through mitosis about once a year.
Skin and intestinal cells go through mitosis every few hours.

19. Large, complex chromosomes of eukaryotes duplicate with each cell division
A eukaryotic cell has many more genes than a prokaryotic cell.
The genes are grouped into multiple chromosomes

20. Chromosomes Humans have 46 chromosomes
Chromatin condense to form chromosomes only during cell division
23 pairs

21. Chromosomes Before cell division, each chromosome is replicated.
Same genetic information
Before cell division, each chromosome is replicated.
One half of a duplicated chromosome is a chromatid

22. Chromosome distribution to daughter cells
When the cell divides, the sister chromatids separate
Chromosome duplication
Sister chromatids
Centromere
Two daughter cells are produced
Each has a complete and identical set of chromosomes
Chromosome distribution to daughter cells
Figure 8.4C

23. The cell cycle multiplies cells
The cell cycle consists of two major phases:
Interphase, where DNA duplicates and cell parts are made
The mitotic phase, when
cell division occurs
Figure 8.5

24. The Cell Cycle
a cell grows, prepares for division, and divides to form 2 daughter cells, each of which begin the cycle again.
2 phases
Interphase
G1 phase (gap)
S phase (DNA replication or synthesis)
G2 phase (gap)
M phase
mitosis and cytokinesis

25. The Cell Cycle

26. Interphase Made up of G1, S, G2 phase
Gap 1 (G1): cells increase in size
Synthesis (S) phase: DNA is replicated

27. Interphase S-Phase DNA must be duplicated… cell nucleus cell nucleus
chromosomes in cell
4 single-stranded chromosomes
nucleus
cell
DNA in chromosomes
nucleus
cell
duplicated chromosomes
duplicated
chromosomes
4 double-stranded chromosomes

28. Interphase Made up of G1, S, G2 phase
Gap1 (G1): cells increase in size, organelles duplicate
Synthesis phase: DNA is replicated
Gap2 (G2): shortest phase, cells check for mistakes, make needed repairs