![]() Many factors affect how quickly plants are able to conduct photosynthesis. Thus, it is not only crucial for plants, but also for all organisms that rely on oxygen for their survival. Photosynthesis is responsible for replenishing Earth's atmosphere with oxygen that we breathe. These sugars can be stored for later use by the plant as an energy source to fuel its metabolism and growth. In the Calvin cycle, the plants take carbon dioxide (CO 2) from the air and use it to ultimately make sugars such as glucose or sucrose. In this step, the two energy-carrier molecules, NADPH and ATP, are utilized in a series of chemical reactions called the Calvin cycle. The next stage is light-independent and is often referred to as the dark reaction. At the same time, water is split into oxygen (O 2) and protons (H +). During the first part of photosynthesis-the light-dependent reaction-chlorophyll and other pigments harness the light energy to produce NADPH and ATP, which are two types of energy-carrier molecules. This is why leaves with chlorophyll usually appear green. Chlorophyll does not absorb light in the green spectrum of light but reflects it instead. Chlorophyll is one of the pigments that can absorb light in the blue and red spectrum from the visible light spectrum. The chloroplasts contain special pigments that react to light. Photosynthesis takes place in the chloroplasts within the plant's cells. During photosynthesis, plants convert water (H 2O), carbon dioxide (CO 2), and light into oxygen (O 2) and glucose (C 6H 12O 6). Leaves that have more chloroplasts and more green chlorophyll pigments should also be able to photosynthesize better than other leaves.įigure 1. If you did some of the experiments suggested in the Explore More section, you should have noticed that more light, higher temperatures, and more carbon dioxide all increased the rate of photosynthesis. How long it takes for all the leaf disks to float up depends on many different factors. Without carbon dioxide, photosynthesis is not possible. This is because the baking soda, which is sodium bicarbonate, provides the plant leaf with the carbon dioxide that it needs for photosynthesis. ![]() However, in the cup without the baking soda, no leaf disks should have floated during the whole experiment. The first leaf disks in the cup with the baking soda should have come up within a couple of minutes. As the leaf disks accumulate more oxygen gas, they will eventually float to the top. More air in the vest makes the diver float to the top, and less air makes the diver sink to the bottom. This is similar to a diver who can change his buoyancy by putting air into his vest (with a buoyancy control device) or by releasing it. The more gas bubbles that accumulate over time, the more buoyant the leaves get. The oxygen gas bubbles change the buoyancy of the leaf. The oxygen bubbles are proof that photosynthesis is occurring inside the leaf disk! You might have seen the tiny bubbles of oxygen on top or underneath the leaf disks. ![]() As a result, oxygen gas was produced, which accumulated within the leaf disks or on its surface. Once you placed the cup with the leaf disks under the light, the chloroplasts within the leaves started to photosynthesize. Without the air pockets, the leaves should have all sunk to the bottom of the syringe. The vacuum you applied in the syringe sucked the air out of the leaves, which then got replaced with the solution in the syringe. This is because leaves have air pockets within their structure to facilitate gas exchange between different parts of the leaf. When you placed the leaf disks in your syringe, you probably noticed that they all floated on top of the solution. The leaf disk assay measures the rate of oxygen production in the leaf disks, which is a representation for the rate of photosynthesis. You can rinse and reuse the plastic cups and the syringe. Discard the solutions into your sink and throw the leaf disks into the trash.
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