The Cell Cycle

The Cell Cycle

By David Fink

Open Ended

Discussion Question: Cells reproduce by mitosis (by dividing into two cells identical to the original). What are some things that would have to happen for a cell to copy itself?

​Living things must grow and develop. At times they suffer injuries or damage, or cells simply wear out. New cells must be formed for the organism to survive, though in multicellular organisms, the rate at which these are produced in different organs can vary. There are even some cells in the human body that cannot be regenerated! Consider what processes must occur to make a new, properly functioning cell.

Multiple Choice

How many phases are in the cell cycle as shown in the diagram in Model 1?

• 2

• 3

• 4

• 5

Open Ended

Starting at the starred cell, what is the order of the stages of a cell’s life?

Multiple Choice

During which phase does the size of the cell increase?

• M

• G₁

• s

• G₂

Multiple Choice

During which phase does the number of cells increase?

• M

• G₁

• s

• G₂

Open Ended

Consider your answer to Questions 3 & 4, identify two ways that the growth of an organism can be accomplished through the events of the cell cycle.

Match

Match the Label from Model 1 with the phase from Model 2.

• G₁

• M

• G₂

• s

Gap₁

Mitosis

Gap₂

Synthesis

• Gap₁

• Mitosis

• Gap₂

• Synthesis

Open Ended

Looking at the third column of Model 2, compare the time spent in mitosis with the time spent in Gap 1 in humans cells and describe any difference.

Open Ended

Imagine 100 cells were chosen randomly from a tissue sample and examined under a microscope. In which phase of the cell cycle would you expect to find the largest number of cells? Explain.

Open Ended

Look again at Model 2. Compare the amount of DNA at the beginning and end of synthesis. Why did the amount of DNA change?

Open Ended

Write below the text that should go in the “Key Process” column for the synthesis phase in Model 2.

Open Ended

Look carefully at information given to you in Model 1 and Model 2. Fill in the key process column in the table for gap 1.

Multiple Choice

According to the data in Model 2, if a culture in the lab starts with one human cell, how many cells will there be after 24 hours?

• 1

• 2

• 3

• 4

Multiple Choice

How many human cells will be in the culture after another 24 hours? Explain.

• 1

• 2

• 3

• 4

Open Ended

If a starfish sustains damage to a limb, it often grows a new one. If a gecko loses its tail, it may grow a new one. On the other hand, if a human adult sustains damage to their spinal cord, mobility is often impaired and never regained. Which type of cell is less likely to go through the cell cycle after being damaged – starfish limb, human spinal cord, or gecko tail? Support your answer.

Open Ended

Occasionally cells stop dividing and enter another phase, G₀. If you damage your liver, new liver cells can be produced to replace up to 75% of the liver. However, if you sustain brain damage, your body does not produce new brain cells. Which is more likely to be found in the G₀ phase, brain cells, or liver cells, and what is happening during the G₀ phase?

Open Ended

Which phase of the cell cycle would you expect G₀ to take place during? Explain your answer.