1. How do you grow? Give examples and be specific.

2. Cell Division (Mitosis)

3. What if there was no more Mitosis?
Start the explore by saying we used wound healing to introduce mitosis.
Ask the students what Mitosis is? (Process of cellular division/replication)
In order to have them think about why mitosis is important and all of its functions, ask – what if there was no more mitosis? What would be the consequences?
(Allow for student response)
Expected responses:
-Wounds would not heal
-Growth could not happen
-Zygote division would not occur
-Cell replacement and repair would not happen

4. Reasons for Mitosis: Generate new cells for: Growth Repair Maintenance
Emphasize these three main functions of mitosis. Relate these to the previous slide and why organisms could not complete these tasks without mitosis.

5. DNA Deoxyribonucleic acid
During mitosis, DNA gets reorganized from messy, spaghetti-like CHROMATIN into organized, neat CHROMOSOMES!
Humans have 46 chromosomes (23 from your mom, 23 from your dad)

6. Neat & tidy chromosome
Relaxed chromatin

7. Chromosome

8. What initiates cell division?
A cell or cells that need to undergo cell division receive a signal to begin division
QUESTION: What do you think are examples of division signals?
Students need to understand that cells do not undergo cell division at all times, only when a division signal is received.
Ask students what they think are examples of division signals/when they occur?
Expected answers:
Inflammation from wound or cut
Puberty
General growth signals
Fertilization of an egg
Development of an embryo
Hair growth
Etc..

9. Preparation - Interphase.
Interphase: the preparation stage for a cell going through division
During interphase, 3 main preparations occur:
Growth
DNA replication (4692 Chromosomes)*IN HUMANS
New organelles and cellular materials are made (proteins made in ribosomes!)
There is a preparation stage before mitosis that ensures a cell is properly prepared to undergo mitosis. Students need to understand why all of these preparations are necessary and must happen before mitosis can be completed. Emphasize the 3 main preparations that occur during interphase – growth, DNA replication, and new organelles and cellular materials. The steps of interphase are outline in the next slide.

10. Interphase G1 S G1: Growth 1 S: Synthesis G2: Growth 2
As demonstrated in the pie chart, cells spend much more time in interphase preparing for mitosis rather than actually undergoing mitosis. Explain that this is because the preparation is so important for a cell to divide and it needs to be done efficiently and accurately.
Explain what happens during G1 (growth and production of new organelles and material), S (DNA synthesis or replication) and G2 (additional growth and production of organelles and material)
*emphasize that new organelles, plasma membrane, cytoplasm, etc. all needs to be made S

11. Why is interphase so important?
A cell must prepare accurately in order to divide into two identical cells
DNA must be replicated properly so that both cells have the same genetic material (46  92  46) *IN HUMANS
The cell must grow and make new organelles/cellular material in order to give half to the new cell

12. Preparation complete!
The cell is now ready to undergo mitosis!

13. Steps of Mitosis Prophase 2. Metaphase
-Microtubules start to form
-Nuclear envelope starts to disappear
2. Metaphase
-Chromosomes align at the center of the cell (metaphase plate)
-Spindles attach to the chromosomes (each chromatid)

14. Steps of Mitosis 3. Anaphase 4. Telophase
-Spindle fibers shorten to pull sister chromatids apart
4. Telophase
-Nuclear envelope starts to reform
-Cell elongates

15. Prophase

16. Late Metaphase

17. Anaphase

18. Telophase

19. What happens during mitosis? Chromosome alignment.
The replicated chromosomes (DNA) move towards the middle
This alignment allows the chromosomes to be separated equally between the two cells
Proteins move and align the chromosomes
Explain that as the cell goes through mitosis, it is sorting or aligning the chromosomes that allows the DNA to divide and be sorted evenly between the two cells.
Also emphasize that it is the proteins that move and align the chromosomes.
The new curriculum does not place an emphasis on the names of the mitosis phase, therefore try to get the students to see and understand more of what is actually going on in the cell rather than the specific phases.

20. What is the point of alignment?B.
Have students draw in their notes the different products for A and B.
Then draw the results on the board and discuss why chromosome alignment is so important.
What would be the result of these two cells dividing?

21. Mitosis

22. What happens during mitosis? Physical division (Cytokinesis).
Not only is the DNA divided equally, but the new organelles and cellular material must be divided equally as well
Cytokinesis: The cell pinches or furrows in the middle then physically separates into two identical cells. (cleavage)
Discuss briefly how cytokinesis occurs, pinching then physically separating into two identical cells.

23. What is the result of mitosis?
Two identical cells (the original and a new cell)
Think of a photocopier machine:
(Interphase, mitosis, cytokinesis)
Use the analogy of a photocopier machine. The original is copied but still exists. Therefore, it is not two new cells rather the original cell and a copy of that cell. Students often get confused by the term “daughter cells” which is why it has been omitted. Focus on the original cell still existing but producing a new cell as well.
Original
(46 chromosomes)
Copy
(46 chromosomes)

24. Plant Cell Division
Plant cells divide just like animal cells EXCEPT they do not have centrioles and their cell wall causes cytokinesis to occur differently
A new cell wall forms in between the two new cells in plant cells rather than furrowing/cleavage
This could be a good time to review the stages since they are not labeled.

25. UNDERLYING BLOOD VESSEL
Mitosis in action! Cross section of a wound
BLOOD (BLOOD CELLS)
UNWOUNDED SKIN CELLS
SCAB
The purpose of this slide is to show how cell division aids in the healing of wounds. Ask the students to imagine that this is a cross section of the finger wound they saw earlier in the YouTube.
The site starts off with a gaping hole in the layer of skin cells. The underlying vessel is broken and blood fills the gap. As the blood clots/dries, certain fibers within it attempt to contract the wound site. Cells at the perimeter of the cut “realize” they no longer have a neighbor and are chemically signaled (yellow explosion clip art) to divide. The goal is for the cells to continually divide in the direction of the green arrows in order to close the gap/heal! (It’s only the cells on the basal layer that are actually dividing and sending new cells up. For the sake a simplicity this will suffice, I think.) The developing scab acts as a mechanical barrier to protect the healing process occurring just beneath it. When this process is complete the scab usually falls off to reveal the newly created skin tissue. If the scab is pulled off too early then the healing process may be stunted and therefore take longer.
*the newly created cells are a shade lighter for two reasons: 1) so students can visualize the newly created cells and 2) represents the tendency of scars to have a slightly different appearance from the uninjured tissue around it.
**see if students can guess which cells will be signaled to divide by, at least, the last round of mitosis. From this you can see if they understand that only cells without their neighbor will be signaled to undergo mitosis, in this scenario.
UNDERLYING BLOOD VESSEL

26. Alert! Zooming in on one cell in the cross section… -Growth
-DNA Replication
-More Organelles Made
As the preview slide shows, there is an exterior signal for the cells to divide due to the wound. ALERT! Skin is wounded and needs to be repaired! More cells are needed!The first thing that occurs is Interphase, where the cell grows and increases its supply of organelles, and most importantly, copies its DNA.
Mitosis will begin, and the replicated chromosomes will align on the metaphase plate
Cell receiving division signal
Cell undergoing mitosis

27. Once aligned, the cell continues to go through Mitosis then Cytokinesis, and separate to create two identical cells. This increases the population of cells, filling the gap in the skin to heal the wound.