Leaves, Photosynthesis, Compost
The Value of Leaves
Our lives would be entirely different if we didn’t have leaves. In reality, we could not exist without leaves. Leaves are the manufacturing center for all plants. They collect the energy from the Sun through the process of photosynthesis and store the energy throughout the plants.
This manufacturing process basically uses the energy in sunlight to convert carbon dioxide (CO2) from the atmosphere to organic compounds that can be utilized by the plants. In this process, not only is carbon dioxide taken from the atmosphere, oxygen (O2) is returned into the atmosphere.
This process is critical to life as we know it, because animals, including humans, breathe in oxygen and exhale carbon dioxide through the process of respiration. In addition, all oxidation processes, such as burning gasoline in our cars and burning natural gas, coal, and oil for heat and electricity, produce carbon dioxide. This cycle is called the carbon dioxide–oxygen cycle and is illustrated in Figure 11.1
The carbon dioxide–oxygen cycle acts as a buffer to keep the earth’s level of carbon dioxide at a reasonably constant 0.03%. Throughout the history of the earth, the level of CO2 has fluctuated. This fluctuation is critical, because the amount of CO2 in the atmosphere affects the world’s climate through the greenhouse effect.
We often divide plants into annuals, which live for only one year, and perennials, which live for more than one year. Many of our garden-variety flowers grow from seed to flower and die in one year. Other plants such as trees and shrubs grow for many years. Bristlecone pine trees live for as long as 3,500 years. Each year and in some cases, such as for evergreens, every two or more years, the plant will shed its leaves. In the spring of each year, new leaves will be formed.
Photosynthesis is the process by which plant cells, located predominantly in the leaves, convert carbon dioxide (CO2) to organic material by reducing this gas to carbohydrates in a rather complex set of reactions. Energy for this process is supplied by light absorbed by plant pigments (primarily chlorophyll). The pigments absorb blue and red light. Green and yellow light are not effectively absorbed by the pigments and are reflected by leaves—this is why plants look green.
Leaves also contribute to soil development. When leaves drop in the fall, over a period of time they break down. This decomposition is caused predominantly by microorganisms. The compost, or basic organic materials that are formed, helps plants grow. We can contribute to this process by making compost piles from grass clippings, leaves, and plant material from our garden. Information on making compost piles can be obtained from your county extension agents, books, and the Internet.
© ______ 2009, Merrill, an imprint of Pearson Education Inc. Used by permission. All rights reserved. The reproduction, duplication, or distribution of this material by any means including but not limited to email and blogs is strictly prohibited without the explicit permission of the publisher.
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