Investigating the Structures of a Leaf

Investigating the Structures of a Leaf

Photosynthesis is the process by which green plants make their own food using water, carbon dioxide, and energy from the sun. Photosynthesis takes place in the leaves. The green colour, which is caused by the presence of chlorophyll, absorbs the sunlight and uses that energy to convert CO2 and H2O into glucose.

A leaf consists of a broad, at part called the lamina that is joined to the rest of the plant by a leaf stock or petiole. Running through the petiole are vascular bundles which then form the veins in the leaf. These contain tubes that carry substances to and from the leaf. Each vein contains large, thick walled xylem vessels for carrying water and smaller, thin walled phloem tubes for carrying away food that the leaf has made.

Learning Objectives

To describe the different structures in a leaf and their roles in photo-synthesis.

Materials

Variety of leaves, razor blades, GV stain*, water drop microscope*, plastic slides*, plastic cover slips*, and water.

Hazards and Safety

Use caution when cutting with razor blades. Make sure to cut away from your ngers. Have available soap and water for cleaning cuts. Do not use dull razor blades where you have to apply more pressure, increasing the risk of cuts.

Preparation Procedure

1. Put collected leaves into a beaker with water and a few drops of GV.

Activity Procedure

1.           Collect Materials.

2.           Cut a leaf in half, vertically. Next, cut a very thin transverse section from the centre of the leaf, so that the mid rib is included. The result will be in a thin diamond-like cross section of the leaf.

3.           Mount the cross section on a slide with a drop of water and cover it with a cover slip.

4.           Observe the specimen under the water drop microscope. You should be able to see the vascular bundles in the mid rib and differentiate between the upper and lower surface.

5.           Draw what you see in the microscope.

Results and Conclusions

The upper and lower epidermis will be seen in the water drop microscope. You should also be able to view the palisade cells.

Clean Up Procedure

1.           Collect all the used materials, cleaning and storing items that will be used later.

2.           Dispose of waste containing GV in a pit latrine.

Notes

The water drop microscope can only show the outlines of cells. The stom-ata and conducting tissues cannot be seen clearly. The best result can be obtained through the use of succulent leaves like a comelina plant.