Why does elodea have chloroplasts

The cell membrane's main function is to regulate the movement of materials into and out of the cell. However, not everything can just pass through the cell membrane—only certain materials. Thus, scientists say that the cell membrane is selectively permeable, which means that only selective certain substances can permeate go through the membrane.

The cell wall is a structure that surrounds the cell membrane and provides strength and rigidity to cells. Unlike the cell membrane, the cell wall is not selectively permeable; things can easily pass through the wall.

Introduce the activity to students by saying: " As we have discussed, one of the functions of the cell membrane is to control the flow of materials into and out of the cell.

In this investigation, you will observe the effects of placing plant cells in solutions of various salt concentrations. Do not confirm right or wrong answers at this point. While the drawings and observations can be made directly on the sheet, it is recommended that students enter this information in lab notebooks. Review the directions for the lab, focusing on the techniques of slide preparation.

Demonstrate how to make a wet mount slide and review the use of the microscope. Lab Encourage students to make careful sketches of their observations using colored pencils and to attempt to label as many structures as they can identify. The students will likely need help in identifying suitable regions of the Elodea to observe.

You can prepare a typical slide and project it to help students do this. Post-lab The post-laboratory discussion should center on the students' explanations of the changes observed in the Elodea cells. Discuss what happens to the cell wall as the salt concentration increases.

Students should have been able to distinguish between the cell walls and the cell membrane more clearly as more water leaves the cell and the cytoplasm shrinks.

Ask students the following questions to guide the post-lab discussion. As students answer the questions, sketch an Elodea plant cell on the board, filling in the cell with the subcellular structures being discussed.

See the Elodea Plasmolysis website for pictures of Elodea cells in various salt solutions. You can review these with the class and ask students to compare these with what they saw in their observations. The following key concepts should be discussed with students:. Have students answer the Conclusions questions of the worksheet in their lab notebook.

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In this lab students observe Elodea leaves under magnification. They will see cell walls and chloroplasts. From the movement of chloroplasts they will infer that cyclosis, or protoplasmic streaming, is occurring. They also will observe that most chloroplasts are pressed tightly against the cell wall and should infer from this that much of the cell is occupied by a vacuole.

Elodea , , or In Elodea , cyclosis is easy to observe because chloroplasts move with the cytoplasm as it flows. Light and heat stimulate cyclosis in Elodea.

Tungsten or halogen substage microscope lamps produce both heat and light, so after 2—3 minutes, students should be able to observe the movement of chloroplasts.

If your microscopes have fluorescent or LED lamps, these produce very little heat and often will not stimulate cyclosis. To provide the needed heat, use a desk lamp equipped with a halogen bulb. Position the lamp so that it shines down on the lab bench. After a few minutes, the surface of the lab bench should become noticeably warm to the touch. Students can place their slides on this warm surface for 3 minutes and then look for signs of cyclosis. A somewhat better arrangement is to position the lamp so that it shines directly onto the stage of a microscope, thereby heating the slide while students view it.

Not all slides will show cyclosis, so have students share those that do, so that everyone has the opportunity see the movement. Ensure that students understand and adhere to safe laboratory practices when performing any activity in the classroom or lab. Demonstrate the protocol for correctly using the instruments and materials necessary to complete the activities, and emphasize the importance of proper usage. Use personal protective equipment such as safety glasses or goggles , gloves , and aprons when appropriate.

Model proper laboratory safety practices for your students and require them to adhere to all laboratory safety rules. Although you can receive Elodea and use it the same day, it is much better to condition the plants under lights for 2 days. On the day of the lab set up 2 or more small tanks or large beakers, each containing water and Elodea. Place forceps and droppers alongside each container. Also, set up stations for pickup of microscope slides, coverslips, and dissecting needles.

Optional: If students have studied osmosis, they can observe plasmolysis. Students are unlikely to observe nuclei in Elodea cells. However, nuclei are easily observed in stained cells of onion skin. Quarter an onion and separate the layers.

Use forceps to remove the skin from the inner concave surface of a layer. Cut or tear the onion skin into small pieces that will fit under a coverslip. Place the onion skin on a microscope slide and smooth out as many wrinkles as possible. Add a drop of stain to cover the onion skin. A number of stains can be used, including iodine solutions iodine-potassium iodide , Lugol solution , Gram iodine , crystal violet , toluidine blue , and methylene blue. After 1 minute, rinse away the stain with tap water, add a coverslip, and observe the cells.

Nuclei will be evident. The speed of movement during the avoidance response was dependent on the fluence rate, but the speed of the accumulation response towards the microbeam from cell periphery was constant irrespective of fluence rate. When a chloroplast was only partially irradiated with a strong microbeam, it moved away towards the non-irradiated region within a few minutes. During this avoidance response two additional microbeam irradiations were applied to different locus of the same chloroplast.

Under these conditions the chloroplast changed the moving direction after a lag time of a few minutes without rolling. Taken together, these findings indicate that chloroplasts can move in any direction and never have an intrinsic polarity.