A Comparison of Plant and Animal Cells

Objective: Student will compare the stages of mitosis in plant and animal cells

Engagement: Review the stages of mitosis from the previous lesson. Ask in what part of the cell did this process take place. What did we observe breaking up inside of the cell and why was this happening?

Divide students into pairs giving each pair two strands of yarn approximately one meter long. Instruct students to twist the two pieces of yarn together as tightly as possible and observe what happens. (Students should observe that the yarn begins to coil as it is twisted.) Tell students that objects that coil can be refereed to as a helix and since we have two strands this could be refereed to as a _________ ________? (double helix) Ask students if this double helix could now be contained in a smaller area? (yes) This is a model of what happens inside of our cells. Each cell contains deoxyribonucleic acid better know as DNA. As the DNA molecules coil and fold chromosomes are formed. During cell division these chromosomes become visible.

Exploration: Have students work in pairs to complete the following lab activity. All information will be recorded in student's lab journals.

For this activity students can grow onions in advance and use the squash method to make slides or you can purchase prepared slides. The time allowed for this activity will depend on the method that you choose.

Title: Cell Mitosis Part 2

Question: How do the phases of mitosis in plant cells (onion root tips) compare to the phases of mitosis in animal cells(white fish cells)?

Materials:

Procedure: 1. Prepare a wet mount slide of the onion root tip. (Best results will be achieved by using the end farthest from the bulb of the onion) 2. Place paper towel over the slide. 3. With your thumb, press firmly above the cover slip. 4. Remove paper towel and add aceto-orcein stain. Blot area if necessary. 5.Observe, draw and label the stages observed.

Explanation: As students complete their observations have them answer the following questions:

1. How many phases of mitosis were you able to observe?

2. Were any of the phases different from the phases you observed in the white fish cells and if so how were they different?

3. How did the activity in the plant cell compare to that of the animal cell? (Were more, less or about the same number of cells actively involved in mitosis)

4. Was any one phase visible more often than others within a field of view? If so which one ?

Once students have returned to their seats discuss their answers. Next, display the images of onion cell mitosis below:

 

PROPHASE

METAPHASE

ANAPHASE

TELOPHASE & CYTOKINESIS

INTERPHASE

 

During prophase changes occur in the nucleus and the cytoplasm. Each of the chromosomes that formed during the coiling process have duplicated and are now joined together at a point known as the centromere. Miotic spindles begin to form in the cytoplasm. At this stage chromosomes are visible under our microscopes.

As the cell moves into metaphase the nuclear envelope breaks up. The centromeres of each chromsome line up with each other. Chromosomes line up on an imaginary plate known as the metaphase plate. At this point the spindle is clearly visible.

In anaphase the paired centromeres of each chromosome separate and move to opposite poles of the cell. As this occurs the poles of the cell also move further apart. At the end of this phase each pole has an exact copy of each set of chromosomes.

During telophase in animal cells, a cleavage furrow forms giving the cell a snowman like appearence. Nuclear envelopes form and two genetically identical nuclei are formed. Chromosomes become less tightly coiled and so they become less visible. The division of cytoplasm is nearly complete so two new cells will be shortly visible.

In plant cells there are no cleavage furrows. A cell plate forms across the middle of the original cell well the imaginary metaphase plate had been. Two membranes form inside of the existing cell dividing the original cell into two new cells. A cell wall then forms between the two membranes.

These phases are known as mitosis but they are not the only changes that take place in cell division. Cells spend a much greater time period growing and reproducing chromosomes. This period is known as Interphase

Elaboration: Encourage students to further research the stages of mitosis and complete their lab write up.

Evaluation: Use pictures from this activity to play Mitosis Jeopardy. Divide students into teams. Display images of various stages of cell division and use information above as verbal clues.

Homework / Project:

1. Have students design and complete two dimentional models of cell division.

2. Have students test family members (siblings, parents and grandparents at least if possible) for frequency of phenotypes such as widow's peak / continuous hairline, cleft in chin / no cleft, unattached / attached earlobes, freckles / no freckles, eye color, tongue rolling / non rolling, etc. This activity will be needed for the next lesson

3. Have students draw and label stages of cell division on a piece of cardboard. Then have them cut the drawing into pieces to form a puzzle. Have students exchange puzzles with classmates to try them out. ( If students have access to wood and a jigsaw this would be even better.)

4. If students made circuit game boards earlier in the year they could insert the information and have this to use as a study tool.

(If you have Tech Ed. in your building perhaps you can work with that teacher as an interdisciplinary activity.)

Test:

Have students identify stages of mitosis from actual stored images.

Have students to explain what is happening in each of these phases.

Show a sample section of plant or animal cells and have students identify the phase that is most often visible

 

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