1. 10.1 & 10.2 Cell Growth, Division, and Reproduction
Lesson Overview
10.1 & 10.2 Cell Growth, Division, and Reproduction

2. Information “Overload”
Living cells store critical information in DNA.
As a cell grows, that information is used to build the molecules needed for cell growth.
As size increases, the demands on the information in DNA grow as well.
If a cell were to grow without limit, an “information crisis” would occur.

3. Information “Overload”
Compare a cell to a growing town. The town library has a limited number of books. As the town grows, these limited number of books are in greater demand, which limits access.
A growing cell makes greater demands on its genetic “library.” If the cell gets too big, the DNA would not be able to serve the needs of the growing cell.

4. Exchanging Materials
Food, oxygen, and water enter a cell through the cell membrane. Waste products leave in the same way.
The rate at which this exchange takes place depends on the surface area of a cell.
The rate at which food and oxygen are used up and waste products are produced depends on the cell’s volume.
The ratio of surface area to volume is key to understanding why cells must divide as they grow.

5. Ratio of Surface Area to Volume
Imagine a cell shaped like a cube.
As the length of the sides of a cube increases, its volume increases faster than its surface area, decreasing the ratio of surface area to volume.
If a cell gets too large, the surface area is not large enough to get enough oxygen and nutrients in and waste out.

6. Traffic Problems
To use the town analogy again, as the town grows, more and more traffic clogs the main street. It becomes difficult to get information across town and goods in and out.
Similarly, a cell that continues to grow would experience “traffic” problems. If the cell got too large, it would be more difficult to get oxygen and nutrients in and waste out.

7. Division of the Cell
Before a cell grows too large, it divides into two new “daughter” cells in a process called cell division.
Before cell division, the cell copies all of its DNA.
It then divides into two “daughter” cells. Each daughter cell receives a complete set of DNA.
Cell division reduces cell volume. It also results in an increased ratio of surface area to volume, for each daughter cell.

8. Asexual Reproduction
In multicellular organisms, cell division leads to growth. It also enables an organism to repair and maintain its body.
In single-celled organisms, cell division is a form of reproduction.

9. Asexual Reproduction
Asexual reproduction is reproduction that involves a single parent producing an offspring. The offspring produced are, in most cases, genetically identical to the single cell that produced them.
Asexual reproduction is a simple, efficient, and effective way for an organism to produce a large number of offspring.
Both prokaryotic and eukaryotic single-celled organisms and many multicellular organisms can reproduce asexually.

10. Sexual Reproduction
In sexual reproduction, offspring are produced by the fusion of two sex cells – one from each of two parents. These fuse into a single cell before the offspring can grow.
The offspring produced inherit some genetic information from both parents.
This creates genetic diversity ensuring better chances for a species to survive when it environment changes.
Most animals and plants, and many single-celled organisms, reproduce sexually.

11. Comparing Sexual and Asexual Reproduction

12. Chromosomes
The genetic information that is passed on from one generation of cells to the next is carried by chromosomes.
Every cell must copy its genetic information before cell division begins.
Each daughter cell gets its own copy or complete set of that genetic information.(ex. Parent cell has 4 chromosomes so each daughter cell receives 4 chromosomes

13. Important Cell Structures Involved in Mitosis
Chromatid – each strand of a duplicated chromosome
Centromere – the area where each pair of chromatids is joined
Centrioles – tiny structures located in the cytoplasm of animal cells that help connect the spindle fibers
Spindle fibers – a fanlike microtubule structure that helps separate the chromatids

14. Chromosomes
Cells of every organism have a specific number of chromosomes.

16. Prokaryotic Chromosomes
Prokaryotic cells lack nuclei. Instead, their DNA molecules are found in the cytoplasm.
Most prokaryotes contain a single, circular DNA molecule, or chromosome, that contains most of the cell’s genetic information.

17. Eukaryotic Chromosomes
In eukaryotic cells, chromosomes are located in the nucleus, and are made up of chromatin.

18. Chromatin is composed of DNA and histone proteins.

19. DNA coils around histone proteins to form nucleosomes.

20. The nucleosomes interact with one another to form coils and supercoils that make up chromosomes.

21. The Prokaryotic Cell Cycle
The cell cycle is a regular pattern of growth, DNA replication, and cell division.
Most prokaryotic cells begin to replicate, or copy, their DNA once they have grown to a certain size.
When DNA replication is complete, the cells divide through a process known as binary fission.(asexual)

22. The Eukaryotic Cell Cycle
The eukaryotic cell cycle consists of four phases: G1, S, G2, and M.
Interphase is the time between cell divisions. It is a period of growth that consists of the G1, S, and G2 phases. The M phase is the period of cell division.

23. Interphase…G1 Phase: Cell Growth
In the G1 phase, cells increase in size and synthesize new proteins and organelles.

24. Interphase…S Phase: DNA Replication
In the S (or synthesis) phase, new DNA is synthesized when the chromosomes are replicated.

25. Interphase…G2 Phase: Preparing for Cell Division
In the G2 phase, many of the organelles and molecules required for cell division are produced.

26. M Phase: Cell Division
In eukaryotes, cell division occurs in two stages: mitosis and cytokinesis.
Mitosis is the division of the cell nucleus.
Cytokinesis is the division of the cytoplasm.

28. Prophase (Prepare) I-PMAT
During prophase, the first phase of mitosis, the duplicated chromosome condenses and becomes visible.
The centrioles move to opposite sides of nucleus and connect the spindle fibers.
The spindle forms and DNA strands attach at a point called their centromere.
The nucleolus disappears and nuclear envelope breaks down.

29. Metaphase (Middle) I-PMAT
The centromeres of the duplicated chromosomes line up across the center of the cell.
The spindle fibers connect the centromere of each chromosome to the two poles of the spindle.

30. Anaphase (Apart) I-PMAT
The centromeres are pulled apart and the chromatids separate to become individual chromosomes.
The chromosomes separate into two groups near the poles of the spindle.

31. Telophase (Two) I-PMAT-C
The chromosomes spread out into a tangle of chromatin.
A nuclear envelope re-forms around each cluster of chromosomes.
The spindle breaks apart, and a nucleolus becomes visible in each daughter nucleus.

32. Cytokinesis Cytokinesis is the division of the cytoplasm.
The cell membrane is drawn in until the cytoplasm is pinched into two equal parts.
Each part contains its own nucleus and organelles.
The process of cytokinesis is different in animal
and plant cells.

33. Cytokinesis in Plant Cells
In plants, the cell membrane is not flexible enough to draw inward because of the rigid cell wall.
Instead, a cell plate forms between the divided nuclei that develops into cell membranes.
A cell wall then forms in between the two new membranes.

36. FUN FACT Skin cells, are constantly dividing.
We need to continuously make new skin cells to replace the skin cells we lose.
Did you know we lose 30,000 to 40,000 dead skin cells every minute? 
That means we lose around 50 million cells every day.

37. What is in house dust?
The composition varies from house to house, but in general, you might find
textile fibers
decomposing insect parts
pet dander
human and animal hair
food leftovers
pollen grains
mold spores
Bacteria
skin flakes
Sand
and the most likely offender, the dust mite and its fecal material.

40. The Stages of the Cell Cycle