1. Cell Growth and Cell Division Central High School Biology
Unit 4 Lesson 5
Cell Growth and Cell Division
Central High School Biology

2. Questions to Ponder From Lesson 4 Part 2
What is passive transport into cells?
What is active transport in cells?
What are osmosis and diffusion?
What are endocytosis and exocytosis?
What is mitosis?
What is the cell cycle?
What is meiosis?
What is the cell membrane and how is it formed?
What are the three conditions that a cell can find itself in?
What happens to the cell in each of these conditions?
Why do animal cells burst easily but plant cells do not?

3. Cell Growth and Cell Size
Cell size is restricted due to three factors :
- Diffusion
- DNA
- The change in surface area to volume ratio as cell enlarges.

4. Cell size is limited due to diffusion
Diffusion and osmosis only work well in small places.
Cells depend upon the diffusion of oxygen, glucose, and other nutrients into the cell across the plasma membrane.
The cell also relies on diffusion to remove wastes.
Cell size is limited due to diffusion.
If cells get too large, then they can no longer get enough oxygen to survive; moreover, they become poisoned by their own wastes. Therefore, cells must be small.

5. Cell size is limited to DNA
DNA is a coded blueprint for when, where, and how proteins are made.
DNA controls enzyme production.
What are enzymes?
Enzymes are a type of protein that control chemical reactions in living things.
There is a limit to how fast the information about protein production can be copied from the DNA and brought to the cytoplasm where proteins are made.
Therefore, if the cell gets too large, the information cannot be copied fast enough to meet the needs of the cell thus cells must be small.

6. Cell size is limited to the change in surface area to volume ratio as cell enlarges.
As a cell grows its volume increases faster than its surface area. 
How does surface area to volume ratio affect cell functions?
If the cell size doubles the cell will require eight times more nutrients and produce eight times as much waste.
The surface area, if the cell doubled its size, would only have four times more plasma membrane to bring in nutrients and let out the waste.
The cell would starve and be poisoned by its own wastes.
So cells must be small.

7. Cell theory 3 points of cell theory :
1) All organisms are made up of cells which continually divide and multiply.
2) All cells come from preexisting cells.
3) Cell is the basic unit of life.

8. Cell Division There are two main types of cell division – Mitosis
– Meiosis
Mitosis is duplication of the cell and all of its parts.
- The cell goes through one cell division process resulting in two daughter cells.
- Creates somatic cells, any cell other than gametes.
Meiosis is cell division in sexually reproducing organisms that results in sex cells.
- The cell carries out two cell division known as Meiosis I and Meiosis II.
- Creates gametes as known as sex cells.
- a process in which the genes are shuffled.
- End product results in four haploid gametes.

9. Cells Come from Preexisting Cells
One of the key points of cell theory.
How does that happen?
Cell cycle – A growth cycle for the cell by which the cells enlarge and divide.
There are two important periods in the cell cycle :
Interphase – Resting stage of the cell cycle. Cells spends most of its time during this phase.
Mitosis – The process of cell division.
Interphase has 3 subphases :
G1 phase – proteins are made and the cells grow rapidly.
S phase – DNA replication and a second copy of DNA is produced.
G2 phase – Cell prepares for cell division
Mitosis is cell division and there are 4 phases: Prophase
Metaphase
Anaphase
Telophase

10. The Cell Cycle http://www.youtube.com/watch?v=evH0I7Coc54
Consist of two major periods: Interphase
Mitosis
What are the three subphases in interphase?
G1 phase (first gap) – Cells grow rapidly and makes more proteins
S phase – The phase in which DNA are synthesized. Chromatin doubled and the sister chromatid are held together by a centromere.
G2 phase (second gap) – Continue to grow and preparation for mitosis is completed. Chromatin shorten and coil into chromosomes.

11. Cont. The Cell Cycle 2nd major period is mitosis.
What are the 4 phases in mitosis?
Prophase, Metaphase, Anaphase, and Telophase
Prophase - Chromatin coiled and visible into chromosomes. Sister chromatids are held together at centromere. Nuclear envelope and nucleolus disintegrates.
In animal cells, Centrioles move to opposite ends of the nucleus.Spindles of microtubules begin to form.
Metaphase - The doubled chromosomes become attached to the spindle fibers by their centromeres.
Each sister chromosome is attached to its own spindle fiber.
They are lined up in the middle of the nucleus.
The fiber attach to opposite side of the nucleus
The chromosomes are pulled by the spindle fibers.

12. Cont. The Cell Cycle
Anaphase - Anaphase starts when the sister chromosomes separate. The microtubules shorten, pulling the chromosomes to the cell’s poles.
Telophase - Telophase begins when the chromosomes reach the poles.
The chromosomes begin to uncoil.
The spindles break down.
The nuclear envelope and nucleolus reform on opposite sides of the dividing cell.
A phospholipid bilayer begins to grown between the
two developing cells, making a new cell membrane.
Cytokenesis:
  The actual separation of the new daughter cells is called cytokenesis.

13. Results of Mitosis Mitosis allows genetic continuity.
Daughter cells have same DNA as parent cells.
Daughter cells carry out the same function as parent cells.
Single cell organisms remain unicellular.
Now there are two instead of one.
Multicellular organisms cells diversify.
Cells that work together to perform specific functions are tissues.
Tissues organize in various combinations to form complex roles.
Organs working together form organ systems.
Organ systems working together form complex organisms.

14. Meiosis
Meiosis is a form of cell division in which one diploid (2n) cell produces four haploid (n) cells or gametes.
Meiosis provides a way for offspring to have the same number of chromosomes as their parents.
There are two consecutive cell division that takes place during the process of meiosis.
The cell divisions are known as meiosis I and meiosis II.
Meiosis I contains 4 phases which are similar to mitosis
Prophase I
Metaphase I
Anaphase I
Telophase I
Meiosis II contains 4 phases
Prophase II
Metaphase II
Anaphase II
Telophase II

15. Cont. Meiosis Meiosis I occurs after Interphase.
What are the 4 phases of meiosis I?
Prophase I , Metaphase I , Anaphase I , and Telophase I.
Prophase I – Prophase I lasts longer than prophase in mitosis. The duplicated chromosomes condense. Each chromosome contain two sister chromatids. Crossing over occurs at the latter stage of this phase. Crossing over combines genes from both of the parents.
Metaphase I - The chromosomes become attached to the spindle fibers by their centromeres.
Each sister chromatid is attached to its own spindle fiber.
They are lined up in the middle of the nucleus.
The fiber attach to opposite side of the nucleus
The chromosomes are pulled by the spindle fibers.

16. Cont. Meiosis Meiosis II
Anaphase I – The microtubules shortens and pulls the chromosomes towards the pole with the sister chromatids remain attached.
Telophase I – Telophase begins when the chromosomes reach the poles.
Each pole has one chromosome from the homologous 1 pair.
Cytokenesis – occurs right after telophase to form two daughter cells.
Meiosis II
Prophase II – DNA does not replicate! The microtubules form and the chromosome moves towards the center.
Metaphase II – The chromosomes are aligned in the center of the nucleus. The fiber attach to opposite side of the nucleus
The chromosomes are pulled by the spindle fibers.

17. Questions to Ponder
What are the three factors that limits the size of the cell?
How does surface area to volume ratio affect cell functions?
How do cells remove their waste products?
What are the two main types of cell division?
What is the cell cycle?
What is mitosis?
What is meiosis?
What are the subphases in interphase?
What are the phases in mitosis?
What are the phases of meiosis?
Explain the differences between mitosis and meiosis

18. Credits http://centralscience.net/
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