Cell Division SE - Summer AP Bio PDF

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Summer AP Bio...

Description

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Student Exploration: Cell Division Vocabulary: cell division, centriole, centromere, chromatid, chromatin, chromosome, cytokinesis, DNA, interphase, mitosis Prior Knowledge Questions (Do these BEFORE using the Gizmo.) •

Cells reproduce by splitting in half, a process called cell division. What do cells need to do between divisions to make sure that they don’t just get smaller and smaller?

The cell grows between its divisions •

The genetic information of a cell is carried in its DNA (short for deoxyribonucleic acid). What do cells need to do between divisions to make sure that a full set of DNA gets passed on to each daughter cell? They have to double their DNA.

Gizmo Warm-up On the SIMULATION pane of the Cell Division Gizmo, check that the Cycle Length is set to 12 hours. Click Play ( ), observe until the maximum number of cells is shown, and then click Pause ( ). •

Look at the cells. Do they all look the same? Yes

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Cells that are in the process of dividing are said to be in mitosis or cytokinesis. Cells that are not dividing are in interphase. Check the Magnify box and move the cursor over the cells. •

Of the 100 cells shown, how many are in the process of dividing? 12

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Select the BAR CHART tab, and turn on Show numerical values. How many cells are in the interphase stage of their life cycle? 84

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Based on these two observations, would you say that a cell spends most of its life cycle in interphase or in mitosis/cytokinesis? Interphase

Activity A: Phases of the cell cycle

Get the Gizmo ready: • Click Reset ( ). • Select the DESCRIPTION tab. • Click on the right arrow once so that Interphase is shown.

Question: What are the stages of the cell cycle? •

Observe: Click Play and hold the cursor over the cell. Observe the cell as it divides several times. (This happens quickly!) What do you notice happening during this process? The cell goes through several phases.

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Summarize: On the DESCRIPTION pane, read about each phase in the cell cycle. In the spaces below, sketch the cell in each phase and summarize what occurs in your own words. Phase

Sketch

Interphase

Prophase

Metaphase

Anaphase

Telophase

Cytokinesis

(Activity A continued on next page) Activity A (continued from previous page)

Summary The cell grows/matures in three stages, G1 is growth/development, S duplicates the DNA, and G2 is the synthesis of organelles. The nucleolus disappears and chromatin condenses to form chromosomes. Spindle fibers form between the centrioles, which go to the polar ends of the cell. The nuclear membrane dissolves near the end. The centromeres of chromosomes attach to spinde fibers which change in length, pulling the chromosomes into a line along the equator. Centromeres are split, sister chromatids are pulled to the opposite poles of the cell by spindle fibers. Phase ends when daughter chromosomes reach the end and stop moving Nuclear membrane forms around each set of daughter chromosomes and the nucleolus reappears, then the chromosomes unwind into chromatin. Two identical nuclei are formed, sides of the cell pinch inward, dividing the cytoplasm and forming two cells, each with a completely copy of the parent cell's DNA.

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Analyze: Use your summaries and the Gizmo to answer the following questions: •

What are the four phases of mitosis? Prophase, metaphase, anaphase, telophase

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During which phase is the DNA duplicated? Interphase What is the relationship between chromatin and chromosomes? Chromatin makes up chromosomes

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In which phase are chromatids pulled apart? Anaphase

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What is the role of the centrioles? Produce spindle fibers

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In which phase does a new nuclear membrane develop? Telophase

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A cell has a single line of chromosomes. What is the phase? Metaphase

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During which three phases are individual chromosomes no longer visible? Interphase, telophase, cytokinesis

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Think and discuss: Why is it important that the cell’s DNA is duplicated before cell division? So the daughter cells have a complete set of the parent cell's DNA.

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Challenge: Human cells have 46 chromosomes. Each chromosome consists of a pair of identical chromatids attached together by a structure called a centromere. Once the chromosome has split, each chromatid is called a daughter chromosome. At the end of cytokinesis, how many daughter chromosomes will be found in each cell? Explain. 46 chromosomes. Before mitosis, the cell duplicates its DNA so there are 46 chromosomes which means in total there are 92 sister chromatids. During mitosis, the sister chromatids first join in the middle of the cell and then separate towards the opposite sides of the cell. After they separate, there are 46 sister chromatids each side.

Activity B: Duration of phases

Get the Gizmo ready: • Click Reset. • Select the TABLE tab.

Question: What is the relative duration of each phase of the cell cycle? •

Collect data: Set the Cycle Length to 10 hours and click Play. Click Pause when the

maximum number of cells has been reached. On the TABLE tab, click Record data. Record the number of cells in each phase of the cell cycle in the table below. Then click Play, wait for a while, and click Record data again. Repeat this process until you have recorded four sets of results, and then find the average number of cells in each phase. Trial

Interphase

Prophase

Metaphase

Anaphase

Telophase

Cytokinesi s

1

80

11

3

2

3

1

2

77

10

4

3

3

3

3

78

10

3

3

3

1

4

81

10

3

2

3

1

Avg.

79

10.25

3.25

2.5

3

2

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Analyze: Which phase of the cell cycle is longest? Interphase Shortest? Cytokinesis Explain your answers: From the chart we can tell that interphase has the highest average number of cells while cytokinesis has the lowest, with anaphase being just . 5 above.

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Calculate: You can use your data to estimate the duration of each phase of the cell cycle. For example, if 8% of the cells were in prophase and the cell cycle was 10 hours long, then prophase would last 8% of 10 hours, or 0.8 hours (48 minutes). Use percentages to estimate the duration of each phase of the cell cycle. Show your work. Interphase: 79+10.25+3.25+2.5+3+2=100, 79% of 10hrs = 474min (7.9hrs) Prophase: 79+10.25+3.25+2.5+3+2=100, 10.25% of 10hrs = 61.5min (1.025hrs) Metaphase: 79+10.25+3.25+2.5+3+2=100, 3.25% of 10hrs = 19.5min (.325hrs) Anaphase: 79+10.25+3.25+2.5+3+2=100, 2.5% of 10hrs = 15min (.25hrs) Telophase: 79+10.25+3.25+2.5+3+2=100, 3% of 10hrs = 18min (.3hrs) Cytokinesis: 79+10.25+3.25+2.5+3+2=100, 2% of 10hrs = 12min (.2hrs)

Extension: Cell populations

Get the Gizmo ready: • Click Reset. • Select the GRAPH tab. • Set the Cycle Length to 5 hours.

Question: How quickly do cells multiply? •

Collect data: Click Play to start a new simulation. Click Pause when the maximum number of cells is reached. View the total number of cells on the GRAPH tab. (Click the “–” button until the whole graph is visible.) Draw a sketch of this graph here. What is the general shape of the graph? A positive exponential line graph

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Analyze: Look closely at the graph. •

About how long did it take to grow the first 20 cells? Around 23-24 hours

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About how long did it take to grow the last 20 cells? 1-2 hours

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Would you say the rate of cell growth is increasing or decreasing? Explain. Increasing. As you can see from the graph, the rate of cell growth is increasing exponentially.

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Extend your thinking: In living organisms, the cell cycle is closely regulated. What do you think will happen if cell division is not controlled? If gone unmonitored, cell growth can create a tumor and cause cancer, which causes cell divison to happen much faster than its usual pace....