Name: ______Date: ______Period: ____
Plasmolysis in Elodea Plant Cells
Introduction
Review the directions for the lab below. Then record your data and observations. Answer the questions on the last page of this handout.
Elodea Canadensis, also called American or Canadian Waterweed or Pondweed, is a perennial aquatic plant, or submergent macrophyte, native to most of North America. It was first recorded from the British Isles in about 1836. It is dioecious, with male and female flowers on different plants. The flowers have three small white petals; male flowers have 4.5-5 mm petals and nine stamens, female flowers have 2-3 mm petals and three fused carpels. The fruit is an ovoid capsule, about 6 mm long containing several seeds that ripen underwater. The seeds are 4-5 mm long, fusiform, glabrous (smooth), and narrowly cylindrical. It flowers from May to October. Young plants initially start with a seedling stem with roots growing in mud at the bottom of the water; further adventitious roots are produced at intervals along the stem, which may hang free in the water or anchor into the bottom. It grows indefinitely at the stem tips, and single specimens may reach lengths of 3 m or more. It is native to most of North America. It is widely naturalized in the British Isles (female plants only). Ireland: County Galway found at several sites along the Eglinton Canal, County Galway County Down, and from the Lagan Canal near Lisburn, Northern Ireland.
Investigative Methods
Elodea in Tap or Aquarium Water
1. Prepare a wet mount of an Elodea leaf with tap water. To do this, place a drop of water towards one end of the slide. Using forceps remove a small leaf from the tip of an Elodea plant and lay it flat in the drop of water. Cover with a cover slip.
2. Observe the leaf at 40X and record your observations.
3. Increase the magnification to 100X. Increase to 400X, observe, and record your observations.
Elodea in 10% Salt Solution
1. Remove the slide from the stage of the microscope.
2. Place 2 drops of the 10% salt solution on the slide at the left edge of the cover slip.
3. Tear off a small piece of paper towel and place the torn edge on the slide at the right edge of the cover slip. The piece of towel should begin to soak up water, drawing the salt solution under the cover slip as it does so. (See Figure)
4. Return the slide to the microscope stage and observe the cells at 100X and 400X.
5. Record your observations.
Flushing Out the Salt Solution
1. Remove the slide from the stage of the microscope.
2. Place 3-5 drops of tap water on the slide at the cover slip.
3. Draw the water through using a small piece of paper towel.
4. Observe the cells at 100x and 400x. Record your observations.
Remove the slide from the stage, clean it, and the cover slip, and put it away.
Observations
· Prepare sketches of a group of Elodea cells under each set of conditions (tap water, 10% salt solution, and restored).
· Label the magnification under which the plant cells are being observed (100x or 400x).
· Label the sketches to note the cell structures that you can identify.
· Be sure to note any changes in the color, size, and shape of the cells.
· Make your sketches as accurate as possible.
Conclusions
Answer the following questions in the space provided.
1. What is the shape of a typical Elodea cell? Draw it. Your drawing should include the cell wall, chloroplasts, and central vacuole. Identify the functions for each structure.
2. What happens to the cells as the salt water flows under the cover slip?
3. What happens to the cells when the salt water is flushed out with distilled water?
4. Why did the water in the vacuole pass out of the cell?
5. Why didn’t the outer boundary of the cell collapse?