Biology Mitosis Lab

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AP BIOLOGY-
Mitosis and Meiosis Cell Division Lab

Part 1-MITOSIS

summary:
In this experiment first the stages of an onion cell undergoing mitosis are going to be observed and every stage is going to be detected and drawn on paper. A brief description to what is going on should be attached to the pictures. This is important to understand the basics of cell division which is necessary growth,repair and asexual reproduction. Second the number of cells undergoing each phase is going to be counted to figure out in which phase the cell remains the most. If interphase is the stage in which the cell grows and prepares for cell division then the number of cells undergoing interphase will be the most. After cells were counted it came out that indeed the number of cells in interphase is the most followed by prophase, metaphase=anaphase and telophase. This makes us come to the conclusion that the longest phase for a cell is interphase in which the cell grows and gets ready to divide. The second longest in prophase in which the chromatin fibers start to form chromosomes. The other phases which follow are very short and quick.

Introduction:

Mitosis is the division of the nucleus,providing equal amounts of nuclear material to the daughter cells,in eukaryotes. Equal amounts of chromosomes are provided for the forming daughter cells by replicating the DNA and chromosomes before the division. Mitosis occurs in somatic cells and produces 2 daughter cells. The whole process of mitosis consists of 5 stages.

1-Interphase:is the stage in which the cell rests and gets ready for division. Consists of 3 parts. -G1:number of organelles double,size increases. At the end of this phase is a G1 checkpoint which controls is the cell is ready for division or not. -S:chromosomes are duplicated.

-G2:special proteins and enzymes for cell division are synthesized.

2-Prophase:Centrioles move to opposite poles of the cell. Form spindle fibers which’ll become the microtubules holding the centromere. Chromosomes become visible as long threads and become shorter and thicker. Each chromosome joins another one forming sister chromatids attached in the middle by a centromere. Nuclear membrane dissolves.

3-Metaphase:spindle fibers from the centrioles attach to the chromosomes at the kinetochore lining the chromosomes in the center of the cell.

4-Anaphase: The centromeres divide and the sister chromatids separate. The spindle fibers full the chromosomes to different poles of the cell.

5-Telophase: When chromosomes have reached opposite poles a nuclear membrane forms around them. Chromosomes then untwist and stretch becoming invisible again. Spindle fibers break down.

At the end of mitosis cytokinesis takes place which is the formation of a cleaved membrane between the two new formed cells to separate them.

Materials:
-onion root tip cells
-microscope

Procedure:
1-Observe the onion root tips under the microscope first at 100X and then at 400X. 2-Draw each phase of mitosis you see.
3-Write a brief description of what you observe in each phase under the picture. 4-Under 400X count the number of cells undergoing different phases. Record data. 5-Calculate the total number of cells.

6-Calculate the percent amount of time the cells spend in each phase.

Analysis:
The data we collected shows that 52% of the cells were in stage interphase. This indicates that more than the half of the cells are recovering from their previous division and preparing to divide again. 40% of the cells were in the second phase prophase while the other phases had a cell percentage number of ~2%. This denotes that prophase is the second longest phase. This can be because it takes a longer time to duplicate the chromosomes than simply lining them up and pulling them apart.

Conclusion:
Our hypothesis that if interphase is the resting phase then it’ll be the...
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