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Question 1
A researcher counts cells in a section of human skin tissue under a microscope. Of the 250 cells observed, 200 are in interphase and 50 are in various stages of mitosis. What is the mitotic index of this tissue sample?
No clue? Show me the answer
Correct answerCorrect!Incorrect
A0.20
Step-by-step walkthrough
Choose a solution method
Method #1Approach 1
Step 1: Identify the formula
The mitotic index is calculated as: $Mitotic Index = \frac{Number of cells in mitosis}{Total number of cells}$
Step 2: Extract the values
The number of cells in mitosis = 50. The total number of cells = 250.
Step 3: Calculate
$Mitotic Index = \frac{50}{250} = 0.20$
Step 4: State the answer
The mitotic index is 0.20, meaning 20% of cells are actively dividing.
Method #2Approach 2
Step 1: Identify what is being asked
We need to find the mitotic index using cells in mitosis divided by total cells: $\frac{50}{250}$ .
Step 2: Eliminate 0.80
0.80 would result from $\frac{200}{250}$ , which is the fraction of cells in interphase, not mitosis. This is the wrong numerator.
Step 3: Eliminate 0.25
0.25 would result from $\frac{50}{200}$ — dividing by the number of interphase cells rather than the total. This is an incorrect denominator.
Step 4: Eliminate 4.00
4.00 would result from $\frac{200}{50}$ , which inverts the correct ratio and uses the wrong values. A mitotic index greater than 1 is impossible.
Step 5: Select the correct answer
0.20 is correct: $\frac{50}{250} = 0.20$ , representing 20% of cells in active division.
Question 2
A student observes a cell under a microscope and notes the following: the nuclear envelope is absent, chromosomes are clearly visible and thickening, and a spindle is beginning to assemble. Which phase of mitosis is this cell in?
No clue? Show me the answer
Correct answerCorrect!Incorrect
BProphase
Step-by-step walkthrough
Choose a solution method
Method #1Approach 1
Step 1: List the observable features
The cell shows: (1) nuclear envelope absent, (2) chromosomes condensing and becoming visible, (3) spindle beginning to form.
Step 2: Match features to a phase
Prophase is defined by chromosome condensation (chromatin → visible chromosomes), breakdown of the nuclear envelope, and assembly of the mitotic spindle.
Step 3: Confirm the identification
All three features match prophase perfectly. The chromosomes are still thickening (not yet maximally condensed for metaphase), and the spindle is only beginning to form, consistent with early-to-mid prophase.
Step 4: State the answer
The cell is in Prophase.
Method #2Approach 2
Step 1: Identify what is being asked
We need to identify the mitotic phase from three key observations: no nuclear envelope, condensing chromosomes, and a forming spindle.
Step 2: Eliminate Metaphase
In Metaphase, chromosomes are fully condensed and aligned at the metaphase plate, and the spindle is complete — not 'beginning to assemble.' This does not match.
Step 3: Eliminate Telophase
In Telophase, the nuclear envelope is reforming (not absent) and chromosomes are decondensing. Both features are the opposite of what is described.
Step 4: Eliminate Anaphase
In Anaphase, sister chromatids are being pulled to opposite poles — they would appear as two separating groups. No chromosome movement is described here.
Step 5: Select the correct answer
Prophase matches all observations: nuclear envelope breakdown, chromosome condensation, and spindle assembly beginning.

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13 more questions in this topic

Free preview 2/15

Question 1
A researcher counts cells in a section of human skin tissue under a microscope. Of the 250 cells observed, 200 are in interphase and 50 are in various stages of mitosis. What is the mitotic index of this tissue sample?
No clue? Show me the answer
Correct answerCorrect!Incorrect
A0.20
Step-by-step walkthrough
Choose a solution method
Method #1Approach 1
Step 1: Identify the formula
The mitotic index is calculated as: $Mitotic Index = \frac{Number of cells in mitosis}{Total number of cells}$
Step 2: Extract the values
The number of cells in mitosis = 50. The total number of cells = 250.
Step 3: Calculate
$Mitotic Index = \frac{50}{250} = 0.20$
Step 4: State the answer
The mitotic index is 0.20, meaning 20% of cells are actively dividing.
Method #2Approach 2
Step 1: Identify what is being asked
We need to find the mitotic index using cells in mitosis divided by total cells: $\frac{50}{250}$ .
Step 2: Eliminate 0.80
0.80 would result from $\frac{200}{250}$ , which is the fraction of cells in interphase, not mitosis. This is the wrong numerator.
Step 3: Eliminate 0.25
0.25 would result from $\frac{50}{200}$ — dividing by the number of interphase cells rather than the total. This is an incorrect denominator.
Step 4: Eliminate 4.00
4.00 would result from $\frac{200}{50}$ , which inverts the correct ratio and uses the wrong values. A mitotic index greater than 1 is impossible.
Step 5: Select the correct answer
0.20 is correct: $\frac{50}{250} = 0.20$ , representing 20% of cells in active division.
Question 2
A student observes a cell under a microscope and notes the following: the nuclear envelope is absent, chromosomes are clearly visible and thickening, and a spindle is beginning to assemble. Which phase of mitosis is this cell in?
No clue? Show me the answer
Correct answerCorrect!Incorrect
BProphase
Step-by-step walkthrough
Choose a solution method
Method #1Approach 1
Step 1: List the observable features
The cell shows: (1) nuclear envelope absent, (2) chromosomes condensing and becoming visible, (3) spindle beginning to form.
Step 2: Match features to a phase
Prophase is defined by chromosome condensation (chromatin → visible chromosomes), breakdown of the nuclear envelope, and assembly of the mitotic spindle.
Step 3: Confirm the identification
All three features match prophase perfectly. The chromosomes are still thickening (not yet maximally condensed for metaphase), and the spindle is only beginning to form, consistent with early-to-mid prophase.
Step 4: State the answer
The cell is in Prophase.
Method #2Approach 2
Step 1: Identify what is being asked
We need to identify the mitotic phase from three key observations: no nuclear envelope, condensing chromosomes, and a forming spindle.
Step 2: Eliminate Metaphase
In Metaphase, chromosomes are fully condensed and aligned at the metaphase plate, and the spindle is complete — not 'beginning to assemble.' This does not match.
Step 3: Eliminate Telophase
In Telophase, the nuclear envelope is reforming (not absent) and chromosomes are decondensing. Both features are the opposite of what is described.
Step 4: Eliminate Anaphase
In Anaphase, sister chromatids are being pulled to opposite poles — they would appear as two separating groups. No chromosome movement is described here.
Step 5: Select the correct answer
Prophase matches all observations: nuclear envelope breakdown, chromosome condensation, and spindle assembly beginning.

Free preview

Step-by-step walkthrough

Step 1: Identify the formula

Step 2: Extract the values

Step 3: Calculate

Step 4: State the answer

Step 1: Identify what is being asked

Step 2: Eliminate 0.80

Step 3: Eliminate 0.25

Step 4: Eliminate 4.00

Step 5: Select the correct answer

Step-by-step walkthrough

Step 1: List the observable features

Step 2: Match features to a phase

Step 3: Confirm the identification

Step 4: State the answer

Step 1: Identify what is being asked

Step 2: Eliminate Metaphase

Step 3: Eliminate Telophase

Step 4: Eliminate Anaphase

Step 5: Select the correct answer

13 more questions in this topic

Step-by-step walkthrough

Step 1: Identify the formula

Step 2: Extract the values

Step 3: Calculate

Step 4: State the answer

Step 1: Identify what is being asked

Step 2: Eliminate 0.80

Step 3: Eliminate 0.25

Step 4: Eliminate 4.00

Step 5: Select the correct answer

Step-by-step walkthrough

Step 1: List the observable features

Step 2: Match features to a phase

Step 3: Confirm the identification

Step 4: State the answer

Step 1: Identify what is being asked

Step 2: Eliminate Metaphase

Step 3: Eliminate Telophase

Step 4: Eliminate Anaphase

Step 5: Select the correct answer

13 more questions in this topic