Biology Lab Report on the Effects of Photosynthesis

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For this lab the rate of photosynthesis was analyzed upon plant leaves. A sample of a light exposed and a not-light exposed leave were used to clearly identify the role of sunlight in the process of producing and storing energy.


We are trying to find proof, to demonstrate the necessity of light and chlorophyll in the process of photosynthesis.


Photosynthesis occurs in organisms which contain chlorophyll. It's a process that involves the chloroplasts to synthesize glucose molecules from carbon dioxide and water. Energy (ATP), initially in the form of glucose (monosaccharide) is later formed by condensation reaction into starch (polysaccharide). These alpha-glucose units are attached together by glycosidic bonds. Starch is formed after the Calvin Cycle in the Stroma. Carbon dioxide is present in the air and the water is gained from precipitation or morning dew. The water is broken down in photosystem I (sourcing invisible light of 700nm) by photolysis. This process sets free electrons and helps close the cycle of the light dependent stage. But before this process can be set off, a gradient in energy must be achieved. The most energy is gained in the first part of the light dependent stage (which creates the gradient) of photosystem II, sourcing in visible light of 680nm.

There are 5 major requirements for photosynthesis to take place: 1) A temperature in the environment between 5 - 35 degree Celsius, 2) Chlorophyll available in chloroplasts, 3) Water, 4) Carbon dioxide and 5) Light of favorable intensity. If any of these factors are absent, photosynthesis cannot occur.

Materials required

Materials list

Geranium, begonia, or impatiens plants (entirely green leaves), coleus with variegated leaves (green and white colored), hot plates and hot-water bath, Lugol's iodine solution in dropper bottles, 250-mL beakers, 100-mL beakers, tongs, foreceps, Petri dishes, glass-marking pencil, 70% alcohol


PART I - Effects Of Light And Dark On Starch Formation

The leaves used for Part I are completely green. A few of these leaves have been entirely and partially covered with black paper two days before the lab. Then the plant was exposed to good light during the day.

1. With a glass-marking pencil, label one 250-mL beaker light, and label another 250-mL beaker dark. Half-fill the two beakers with water. Place a uncovered leaf to light, and both a entirely covered and a semi-covered leaf in the dark, in the appropriately marked beakers. Place the beakers on the hot plate, bring the water to boiling, and boil the leaves 5 minutes.

2. While the leaves are boiling, use another hot plate to prepare a hot-water bath. Label one 100-mL beaker light, and one dark. Half-fill each with 70% alcohol. With forceps or tongs, remove the boiled leaves from the water and transfer each to the appropriately marked smaller beaker. Place both 100-mL beakers in the boiling water bath. Bring the alcohol to boiling, and boil gently until all the chlorophyll in the leaves has dissolved in the alcohol.

3. While the leaves are boiling, label one Petri dish lightand another one dark. When the leaves have lost their chlorophyll, use the forceps to transfer each to the correctly marked Petri dish.

4. Gently spread out the leaves in the Petri dishes. Add drops of Lugol's iodine solution to each leaf until iodine has come into contact with the entire leaf.

5. Wash all glassware thoroughly. Dry the table top with a paper towel

PART II - Effect Of Chlorophyll On Starch Formation

The plants used in Part II have been exposed to bright light. You will test their leaves for starch, as you did in Part I. One leaf will be all green, and the other will be partly green and partly white (variegated).

1. Repeat Steps 1 through 4 of Part I using one all-green leaf, and one green-and-white leaf. Label the beakers and Petri dishes G for the green leaf and G W for the green and white leaf.

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