Plant Respiration (page 2)
Try New Approaches
- Respiration occurs with or without the presence of light, but light is necessary for photosynthesis. Photosynthesis is the process by which light energy is absorbed and then converted to the chemical energy of glucose. This conversion occurs in plants that have chlorophyll (pigment that absorbs light). Photosynthesis is an anabolic process, in which energy is needed to build larger molecules from smaller ones. During photosynthesis, carbon dioxide and water in the presence of chlorophyll and light energy combine, forming glucose and oxygen. The general equation for photosynthesis is:
- Does the amount of light affect the results? Repeat the previous experiment twice by placing one set of uncovered test tubes closer to the light and a second set of test tubes farther away from the light.
- Does the source of light affect the results? Repeat the experiment by placing five uncovered test tubes near different light sources such as sunlight, incandescent bulbs, fluorescent bulbs, and plant grow-lights. When using artificial lights, place the test tubes an equal distance from the lights.
Determine how light affects the concentration of carbon dioxide released by plants into the environment around them. Do this by repeating the experiment but leave off the aluminum foil covering the test tubes. Then place the test tubes 8 inches (20 cm) from a desk lamp. Compare the color of the test tubes in the light with those from the previous experiment that did not receive light.
Design Your Own Experiment
- Seeds do not need light to germinate. Design an experiment to find out whether respiration occurs during seed germination. One method is to fill a small plastic soda bottle one-third full with dry pinto beans and cover the beans with distilled water. Place the jar in a refrigerator to reduce the production of bacteria while the beans soak. (Soaking the beans allows water to penetrate them, which encourages germination.) After soaking overnight, pour off the water and use modeling clay to secure one end of a flexible plastic drinking straw inside the mouth of the bottle. Insert the free end of the straw into a glass of bromthymol indicator (see Figure 15.3). Observe the color of the indicator solution near the end of the straw to determine whether carbon dioxide is exiting the straw.
- The chemical equations for photosynthesis and aerobic respiration are:
- The previous experiment can be performed by filling the jars about one-fourth full with soil. Use plants such as grass or ivy. Moisten the soil in each jar, then do not add any nutrients.
Aerobic Respiration:C6 H12 O6 + 6 O2→6 CO2 + 6 H2O + Energy
While photosynthesis requires light, aerobic respiration does not. Note that the products of one of the energy equations are the reactants for the other. Plants are autotrophs, which are organisms that can make their own food. So plants can live in a closed environment as long as they have access to sunlight, because they can recycle matter (transforming sugar and oxygen into carbon dioxide and water, and back again). They do need access to sunlight, however, because light energy cannot be recycled. Design an experiment to determine how long a plant can live in a closed container without any outside nutrient sources. One way is to prepare eight jars of distilled water and equal amounts of elodea sprigs. Use lids to close four of the jars. Then set all of the jars near a window with indirect sunlight or in a well-lighted area of a room. Observe the plants for one month or more. Compare the plants in the covered jars with those in the uncovered jars.
Get the Facts
- Cellular respiration is the process by which adenosine triphosphate, ATP ( a special energy-carrying molecule) is produced by respiration. How is ATP involved in energy production? What part do ADP molecules play in the production of ATP molecules? How much ATP is produced during aerobic respiration? What happens to the ATP molecules? Where does aerobic respiration take place in living organisms? For information about respiration, see a biology textbook.
- Photosynthesis is said to require light, but it actually involves two processes, one called the light reaction and the other the dark reaction. What is the difference between these two reactions? What is needed for these reactions to occur? A biology text can provide information about photosynthesis.
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