Mitosis and Chromosome Number Lab Report PDF

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Lab Report includes Abstract, Introduction, Methods, Result and Discussion...

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Alexis Rodriguez

Mitosis and Chromosome Number ABSTRACT Mitosis is the process of one cell with a nucleus splitting into two cells. Mitosis can be broken down into 5 main stages: prophase, prometaphase, metaphase, anaphase and telophase. Plant and animal cells have a slight difference when undergoing mitosis. Looking through the microscope and comparing the onion cell to the whitefish cell helped us gain an understanding of the difference between them. Humans have 46 chromosomes in each of our cells while the onion cell has about 8 chromosomes.The mitotic cycle takes 90 minutes to complete. Prophase taking the longest, followed by telophase, metaphase and anaphase being the shortest. Two of my hypothesis were supported while one was refuted. INTRODUCTION: Mitotic cell division (mitosis) is the process of one cell with a nucleus splitting into two identical cells, for example plant and animal cells. This process is imperative for life to survive. Mitosis can be broken down into 5 main stages: prophase, prometaphase, metaphase, anaphase and telophase. Prophase is the first phase of mitosis, the chromosomes become visible in the center of cell and the nuclear membrane begins to dissolve. The centrioles separate and begin forming a spindle fiber apparatus. Next during prometaphase the formation of the spindle fibers is complete, the chromatids begin to move toward the center of the cell and the nuclear membrane disappears. Following metaphase is where the centrioles are on opposite poles, the replicated chromosomes line up at equator and the spindle fibers attach to centromeres that hold chromatids together. During anaphase, the chromatids split and each daughter chromosome is pulled toward opposite poles of the cell causing the cell to elongate. Finally, in telophase, the chromosomes reach opposite poles of the cell, chromosomes uncoil & decondense to become threadlike chromatin & a nuclear envelope forms around the chromosomes. The main difference between animal and plant cell mitosis is that animal cells undergo cell furrowing while a plant cell forms a cell plate during telophase. Also animal cells contain centrioles while plant cells do not. These are my hypotheses for this lab: 1.Plant and animal cell mitosis will be the same until the cell reaches telophase and cytokinesis. 2.The estimated duration of each stage (longest to shortest): Anaphase (sister chromatids have to separate to opposite poles) Metaphase (align in the middle of the cell and organize) Prophase (nuclear envelope dissolves) Telophase (uncoiling) and Prometaphase (substage- chromatids attach to microtubules.3. The number of chromosomes in an onion cell is less than a human cell because humans are more complex.

METHODS To test hypothesis one we looked at both the plant cell (onion cell) and animal cell (whitefish cell) under a microscope and sketched each phase of mitosis on a worksheet. (attached). To test our second hypothesis we looked at a longitudinal section of an onion root tip. We observed 20 defined root tip cells and tallied the frequency of occurrence of each mitotic phases. According to Lab Topic 9: Mitosis and Chromosome Number, “because frequency of occurrence is directly proportional to the length of a phase” we first divided the number of each phase occurring by 20 then multiplied that by 100 to get the percentage. Then, we multiplied the percentage of each phase by 90 minutes (time it takes to undergo mitosis) to get the exact duration of each stage. To test the third hypothesis, we counted the chromosomes of 10 cells during anaphase in the onion root tip. After we took the number of chromosomes and multiplied it to the number of cells it was seen in. To get the average, we divided the total chromosomes seen by the total cells seen. RESULTS The sketches for both the onion and white fish cells were fairly similar. The chromosome activity was the same during all phases except for telophase, the plant cell starts to form a cell plate while in animal cells a cleavage furrow is formed.(Look at worksheet) Looking at table 9.1 (attached), we found that prophase takes the longest time out of all the phases of mitosis. Out of the 20 cells looked at, we found 10 in prophase, 4 in metaphase, 2 in anaphase and 4 in telophase. Resulting in prophase taking the longest at 45 minutes, metaphase taking 18 minutes, anaphase taking 9 minutes and telophase taking 18 minutes to give us a total of 90 minutes. Referring to table 9.2 (also attached) we got the average of 7.8, rounding it up to 8 chromosomes because a cell cannot have a piece of a chromosome. DISCUSSION My first hypothesis, plant and animal cell mitosis will be the same until the cell reaches telophase and cytokinesis, was supported. Plant cells are unable to have a cleavage furrow due to the rigid cell wall therefore, forming a cell plate. My second hypothesis, the estimated duration of each stage (longest to shortest): Anaphase (sister chromatids have to separate to opposite poles) Metaphase (align in the middle of the cell and organize) Prophase (nuclear envelope dissolves) Telophase (uncoiling) and Prometaphase (substage- chromatids attach to microtubules), was refuted. Prophase takes longer than the other phases because the nuclear envelope fragments and the microtubules have to attach to the chromosomes. Metaphase and telophase take about the same duration of time. All that occurs is the lining up of the chromosomes at the center of the cell in metaphase and in telophase the chromosomes appear at the opposite ends of the cell and a new nuclear membrane begins to form around the

chromosomes in each half of the cell. The quickest duration of time is in anaphase where sister chromatids are pulled apart to opposite ends of the cell by the spindle fibers. My last hypothesis, the number of chromosomes in an onion cell is less than a human cell because humans are more complex, was supported. Human cells have a total number of 46 chromosomes while the onion cell only has 8 chromosomes. This makes sense because humans are more complex than an onion. Literature Cited Dolphin, Warren (2015) Determining the properties of an enzyme, Biological Investigations: Lab Topic 9 pp.105-113

Table 9.1 Determining Duration of Mitotic Phases Phases of Mitosis

Number seen

% of Total

Length in Minutes

Prophase

10

50%

45 min.

Metaphase

4

20%

18 min.

Anaphase

2

10%

9 min.

Telophase

4

20%

18 min.

20

100%

90 min.

Total Graph for table 9.1

Table 9.2 Number of Chromosomes Observed in 10 Onion Cells 1.

8 chromosomes

6.

6 chromosomes

2.

9 chromosomes

7.

9 chromosomes

3.

10 chromosomes

8.

8 chromosomes

4.

7 chromosomes

9.

7 chromosomes

5.

8 chromosomes

10.

6 chromosomes

*Total chromosomes seen 78 divided by total cells seen 10 = 7.8 → 8 average*...