1. Cell Growth, Division, and Reproduction
Read the lesson title aloud to students.

2. Surface-Area-to-Volume Ratio
Surface area = the amount of “covering” of the object
Volume = the amount of space inside the object; the amount of space the object takes up
SAcube = l × w × 6
1 cm × 1 cm × 6 = 6 cm2
Explain to students that one of the main problems of a cell’s size (the “traffic problem”) is a matter of surface-area-to-volume ratio. Tell students that to look more closely at this problem, they can think of a cell as a cube like the one here and consider what happens as the cube, or cell, gets larger and larger.
Ask: How do you find the surface area of a cube like this one?
Answer: Calculate the area of one side and then multiply by 6 to account for the 6 sides of the cube. Find the area of each sided by multiplying length times width.
Click to reveal the formula for surface area.
Ask: How do you find the volume of a cube?
Answer: Multiply length times width times height.
Click to reveal the formula for volume.
Ask for volunteers to come up to the board to carry out the calculations, with class input as necessary, in the space below each equation.
Click to reveal the answers.
Vcube = l × w × h
1 cm × 1 cm × 1 cm = 1 cm3

3. Surface Area to Volume in Growing CellsSA SA
Tell students: Let’s look at what happens when the cube, or cell, grows. Here are two larger cubes.
Click once to reveal two sets of boxes for surface area and volume under the cube images.
Ask a volunteer to come to the board and calculate surface area and volume for the two cubes in the boxes. Elicit class input as necessary.
Click twice to reveal the correct answers.
Ask: What do you notice about these numbers? Are both surface area and volume growing at the same rate when the cell gets bigger?
Answer: No, both surface area and volume get bigger with a bigger cell, but volume grows relatively more than surface area does.
24 cm2
54 cm2 V V
8 cm3
27 cm3

4. Ratio of Surface Area to Volume in Cells
Use the table to confirm what students observed through the calculations on the previous slide.
Ask: Where is the ratio of surface area to volume greatest?
Answer: the smallest cube
Click to reveal the circle and label for the ratio for the smallest cube.
Ask: Where is the ratio of surface area to volume smallest?
Answer: the largest cube
Click to reveal the circle and label for the ratio for the largest cube.
Ask: How would an even larger cube with sides of 4 cm compare?
Answer: The ratio of surface area to volume would be even smaller.
Largest ratio
Smallest ratio

5. Cell Growth Limitations
Information crisis: too many demands placed on DNA
Traffic problems: volume grows too fast relative to surface area, material exchange is insufficient
Ask: Considering the problem of surface-area-to volume ratio, how could cell growth create a problem that is similar to the traffic jam in the growing town?
Answer: As a cell grows, it needs more materials to cross its membrane. Traffic is comparable to the movement of materials such as nutrients, water, oxygen, and wastes across a cell’s membrane. As a cell grows larger (increasing volume), the number of traffic lanes (amount of surface area to cross) does not keep up, and materials cannot enter or leave the cell as quickly as necessary.
Click to reveal the problems caused by a decreasing surface-area-to-volume ratio for growing cells.
Reiterate that if a cell grew too large, it would not have enough relative surface area to get sufficient amounts of oxygen and nutrients into the cell and waste products out.

6. Cell Division Produces two daughter cells
Cell must replicate DNA before cell division.
Dividing to make more, smaller cells keeps SA to V ratio high.
Explain that to solve the surface-area-to-volume ratio faced by a growing cell, an individual cell divides. The division of a cell produces two daughter cells.
Click to reveal the first bullet point.
Challenge students to think about what a cell would have to do before it divides. Guide their thinking as necessary by asking them what major components a cell needs (e.g., DNA, cytoplasm).
Point out that before it can divide to produce daughter cells, there has to be enough DNA for two cells. Before cell division, the cell must replicate, or make a copy of its DNA. This avoids the problem of information overload.
Click to reveal the second bullet point.
Tell students: Cell division solves the problem of increasing cell size by decreasing cell volume. Making more cells instead of larger cells keeps the surface-area-to-volume ratio high.
Click to reveal the third bullet point.
Misconception alert: Students may think that cells get smaller and smaller with each successive cell division. Tell students that cells go through a period of growth after they divide. Remind students that cell division helps a cell avoid the problems of growing too large.

7. Asexual Reproduction
A single parent produces genetically identical offspring.
Ex: mitosis, binary fission, budding
Remind students that reproduction is one of the most important characteristics of living things. Point out that for a single-celled organism like a bacterium, simple cell division makes the process of reproduction pretty straightforward, and it can allow a population to grow very quickly. This kind of cell division is a form of asexual reproduction, which is the production of genetically identical offspring from a single parent.
Click to reveal the bullet points.
Lead a discussion about how cell division relates to the process of asexual reproduction. To reinforce students’ knowledge, have them apply what they have learned to their everyday lives.
Ask: Why do bacterial infections spread so quickly through a school?
Answer: Bacteria can reproduce asexually, so they can reproduce quickly in the right environment, such as a crowded school.
Direct students to the photos of kalanchoe and hydra.
Ask: Both of these organisms are reproducing asexually. How are they different from the bacterium?
Answer: They are multicellular organisms.
Point out that tiny plantlets in the kalanchoe can break off and grow into full new plants. The bud on the hydra will eventually pinch off to become a separate individual.
Ask: What do the offspring off all three of these organisms have in common?
Answer: The offspring share the same genetic material as their parent.

8. Sexual Reproduction
Sexual reproduction involves the of two separate parent cells.
Offspring inherit some genetic information from each parent.
fusion
Remind students that at the start of the presentation you asked them about how asexual reproduction related to humans. Point out that humans, like other animals, grow and repair their bodies through cell division. But to reproduce themselves, humans use sexual reproduction.
Read the statement on the slide aloud.
Ask for a volunteer to identify verbally what term completes the statement.
Click to reveal the correct answer.
Tell students: Asexual reproduction involves separation of a cell. Sexual reproduction involves fusion, or joining, of cells.
Ask: How do offspring relate genetically to their parents?
Answer: They are not genetically identical to either parent. They inherit some genetic information from each parent.
Click to reveal the second bullet point.

9. Comparing Asexual and Sexual Reproduction
Produce many offspring in short period
Don’t need to find a mate
No genetic variation
Daughter cells are IDENTICAL to parent cell
Sexual
Relatively fewer offspring; growth takes more time
Need to find a mate
Daughter cells are NOT identical to the parent cell
Lots of genetic variation
Lead a short discussion in which students consider how one form of reproduction might be more advantageous than another. Remind students that characteristics that make an organism well adapted to its environment are critical for survival.
Ask: Under what kind of conditions would it be helpful to be able to create a very large number of offspring in a short period of time?
Answer: when resources such as food and space are unlimited
Ask: Under what kind of conditions would it be useful to have offspring that are genetically identical to the parent?
Answer: when environmental conditions are stable
Ask: Under what conditions would it be helpful to need only one parent to reproduce?
Answer: when finding a suitable mate might be difficult or impossible
Ask: Under what kind of conditions would it be useful to have offspring that are not identical to either parent?
Answer: when environmental conditions are changing and new combinations of traits may promote survival
Then, ask students to identify, based on the discussion, what the advantages and disadvantages of asexual and sexual reproduction are.
After students have shared their thoughts, click to reveal the advantages and disadvantages.
Discuss each bullet point as it is revealed to ensure students understand why it is an advantage or disadvantage.
Be sure to point out that most organisms they are familiar with can use only one strategy to reproduce themselves. However, some organisms, such as yeast, can use both strategies. Typically yeast undergo cell division to reproduce asexually, but under certain conditions can enter a sexual phase. Point out that the ability to use both reproductive strategies can be an excellent adaptation for some organisms!

11. Chromosomes
In prokaryotic cells, DNA is packaged into a single, circular chromosome.
Explain to students that all cells store genetic information in chromosomes and that most prokaryotes have a single, circular chromosome. This chromosome is found in the cytoplasm.

12. Prokaryotic Cell Cycle
Prokaryotes undergo binary fission.
Talk about the importance of each step shown in the diagram. Tell students that most prokaryotic cells begin to duplicate their DNA once they have grown to a certain size.
Ask: Why does the cell duplicate its DNA?
Answer: The cell duplicates its DNA so that each daughter cell will have a complete copy of the original cell’s DNA.
Tell students that once the DNA duplicates, the two molecules attach to different regions of the cell membrane and the cell begins to pinch inward.
Ask: What would happen if the cell membrane did not indent and pinch off?
Answer: The cell would not form two new cells. The original cell would maintain two complete copies of its DNA.
Point out that this is a simple cell cycle even though the diagram is not drawn as a cycle. Ask one or two volunteers to come to the board and redraw this diagram in the format of a cycle.
Ask: Is binary fission an example of sexual or asexual reproduction?
Answer: asexual
Ask a volunteer to explain.
Answer: The two daughter cells are genetically identical to the single parent cell.

13. Chromosomes
In eukaryotic cells, DNA is packaged into multiple chromosomes.
DNA double helix
duplicated chromosome
coils
sister chromatids
centromere
nucleosome
Use the figure to start a discussion on the structure of eukaryotic chromosomes. Discuss the levels of organization within the chromosome structure.
Click to reveal each level of organization: DNA double helix; histone proteins and nucleosome; coils and supercoils; and centromere, sister chromatids, and duplicated chromosome.
Ask: What are nucleosomes composed of?
Answer: DNA wrapped around histone molecules
Ask: Tightly packed nucleosomes form what structure?
Answer: coils
supercoils
histone proteins

14. Cell Cycle Lingo
Gene – section of DNA that codes for one polypeptide (protein)
Chromatin – DNA bound to proteins; not as condensed as chromosomes
Chromosome – one double stranded DNA helix containing many genes and wrapped around histones (proteins); tightly condensed
Chromatid – one half of a doubled chromosome (DNA molecule that has copied itself). produced after DNA replication
2 identical chromatids called sister chromatids

15. Chromosome Structure
Doubled Chromosome

16. Key Mitosis Terms Centrioles: t-shaped structures in animal cells
* Spindle fibers: threadlike fibers that attach to chromosomes and separates them during Mitosis.
* Animal cells: centrioles produce these fibers.
* Plant cells: spindle fibers are formed by cell wall.

17. Cell Cycle Interphase Mitosis Cytokinesis
Repeated pattern of growth and division that occurs in eukaryotic cells
Three phases:
Interphase
Mitosis
Cytokinesis

18. Eukaryotic Cell Cycle
Eukaryotic cells have a more complex cell cycle than prokaryotic cells.
Focus on each phase of the cell cycle individually.
Click to highlight each phase.
Tell students that cells spend most of their life in interphase, which is divided into three phases: G1, S, and G2. Cells do most of their growing during G1 phase. It begins when mitosis is complete and ends when DNA replication begins. In S phase, DNA is synthesized as chromosomes are replicated. In G2 phase, many of the molecules and cell structures required for cell division are produced; usually this is the shortest phase of the cell cycle.
Misconception alert: Students may think that cells get smaller with each successive cell division. Point out that the cells grow during interphase and that cell division helps a cell avoid the problems of growing too large.

19. Which Cell Cycle? bacteria plants
Ask students: Which cell cycle do the cells of a plant undergo? Which does a bacterium undergo?
Ask volunteers to answer each question verbally or by writing the correct answer on the board.
Once the volunteers have shared their answers, click to reveal the correct answers.
bacteria
plants

20. Cell Cycle: Interphase and Mitosis
Takes 1 hr- 48 hrs
depending on
Organism.

21. M Phase Cell division occurs during M phase.
Tell students that M phase is usually much shorter than interphase. Explain that M phase results in two daughter cells.
Tell students that the first step of M phase is mitosis. Explain that the cell’s nucleus divides during mitosis. Mitosis can be divided into four phases that lead up to cytokinesis. The cytoplasm divides and two cells are formed during cytokinesis.
Ask students to describe the importance of the cell cycle to the growth of organisms.
Answer: Multicellular organisms grow by adding more cells rather than by allowing individual cells to grow infinitely larger. Cell division helps the cell avoid problems associated with cells that are too large.

22. Interphase
Divided into 3 phases:
G1 (gap 1) – carries out normal functions; cell grows in size, makes proteins, organelles duplicate, must pass checkpoint
S (synthesis) – chromosomes replicate to form identical sister chromatids held together by centromere
G2 (gap 2) – cell grows and carries out normal functions, prepares for cell division, must pass another checkpoint
Doubled
Chromosome.
“X” shape
Single
chromosome

23. Mitosis Process of cell division 4 stages: (in order):
Prophase, Metaphase, Anaphase, Telophase, (PMAT)
Creates 2 daughter cells with
IDENTICAL chromosome numbers.

24. Prophase
1. Chromosomes condense and become visible 2. Nuclear membrane disappears 3. Centrioles migrate to opposite poles 4. Spindle fibers appear

25. Metaphase Spindle fibers attach to centromeres of chromosomes.
Sister chromatids (doubled chromosome) line up in the middle of the cell
Shortest phase

26. Anaphase Sister chromatids split apart
Each chromosome moves to the opposite side of the cell.

27. Telophase Chromosomes uncoil into chromatin. Nuclear membrane reforms.
Spindle fibers break down.

28. Cytokinesis Division of cytoplasm into 2 cells
Different in animal and plant cells:
In animal cells, cell membrane forms a cleavage furrow which pinches cell into 2
In plant cells, cell plate forms nuclei, develops as separating membrane. Cell plate forms the cell wall.

29. Cytokinesis
Animal Cell
Plant Cell

30. Somatic/Body/Diploid cells
Cell Cycle Results
2 daughter cells identical to the parent cell
These are referred to as:
Somatic/Body/Diploid cells