BACKGROUND INFORMATION ON ACTIVITY:
The most important aspect of a plants is the food-manufacturing process which occurs primarily in green leaves. Photosynthesis is the manufacture of food, mainly sugar from carbon dioxide and water in the presence of chlorophyll and light.
Photosynthesis occurs only in the chloroplast of plants cells. The rate of photosynthesis is dependent on light concentration, temperature, water, and organic and inorganic materials available. Three aspects of light are important for photosynthesis, intensity, quality, and duration. Intensity depends on the amount of sunlight falling on a given chloroplast per second. The rate of photosynthesis will increase if the light intensity is increased. The water available also influences the rate of photosynthesis.
The essentiality of various factors in photosynthesis can be determined by measuring photo synthetic activity in terms of the amount of sugar or oxygen produced. When a plant is actively undergoing photosynthesis much of the sugar produced in the leaves is converted into starch. Hence the presence of starch is indirect evidence for photosynthetic activity.
15 geranium plants, light shields (construction paper attached with paper clips), boiling water, hot alcohol, iodine with droppers, petri dishes.
Several days prior to lab place a number of geranium plants in a dark place. After 5 days in the dark, place light shields over some of the leaves on each plant. Illuminate the plants for a period of 3-4 days.
Remove 2 uncovered leaves and 2 covered leaves from a geranium plant per student group. Immerse them one by one in boiling water. Transfer them one by one into a dish filled with hot alcohol to remove the pigment and then drop iodine over the leaf in a petri dish to test for the presence of starch, which is the by product of photosynthesis. Have the students follow their lab sheets.
PLANTS - PHOTOSYNTHESIS
PROBLEM: Why is light necessary for a plant to grow?
MATERIALS: Geranium plants, boiling water, hot alcohol, iodine, droppers, petri dishes
Remove 2 uncovered leaves and 2 covered leaves from a geranium plant. Place each of the 4 leaves in separate dishes. Label the dish containing one uncovered leaf A-1 and the other A-2, then label one covered leaf B-1 and the other B-2. Immerse them one by one in boiling water. Transfer them one by one into a dish filled with hot alcohol to remove the pigment. Drop iodine over the leaf in the dish to test for the presence of starch. Black means there is starch.