Plantae: A Kingdom of Light
As you wake up in the morning, you set your feet over the edge of the bed and take a deep breath. Isn’t it magnificent to wake up to a striking sunrise, with the trees and plants in your front yard swaying in the breeze? On the third day of creation, God said, “Let the earth bring forth grass, the herb that yields seed, and the fruit tree that yields fruit according to its kind, whose seed is in itself, on the Earth.’… And God saw that it was good.” One day later, on the fourth day, God made the Sun and Moon. The reason you can take a profound gulp of air in the morning is because that beautiful Sun provides light for plants, so they can produce more of the precious oxygen needed to sustain life on the Earth. This ever-essential commodity is produced by a process called photosynthesis. The biochemical processes involved in photosynthesis are exceptionally complex, and yet an individual, diminutive cell can perform the complicated tasks many times over.
Our knowledge of the general workings of photosynthesis dates back to the 18th century, and, in some cases, even earlier. In 1772, an English chemist by the name of Joseph Priestly demonstrated that plants immersed in water give off a gas (oxygen), and that this gas is necessary for animals to live. Then, in 1779, Jan Ingenhousz discovered the essential aspects of what is known as the carbon cycle, a succession of events that allows the buildup of starch (a food storage product). Furthermore, Henri Dutrochet found that only plants containing a special, green substance called chlorophyll were able to form nutrient material (Garnder, 1972, pp. 381-383). Despite these discoveries, we still do not know some of the secrets of photosynthesis, even to this day. Does this life-sustaining process exhibit decisive design? Without a doubt, it does! Here are some of the facts that we know about photosynthesis:
Photosynthesis creates food by means of the following chemical equation:
6 CO2 + 6 H2O+ Sunlight + Chlorophyll → C6H12O6 + 6 O2
6 carbon dioxide molecules + 6 water molecules yields
glucose (energy for the cell) + 6 oxygen molecules (what we breathe)
Despite the complexity of these numbers and symbols, this equation is fairly easy to understand. As we exhale, we expel carbon dioxide into the air. Plants use this gas, along with water, sunlight, and a substance known as chlorophyll, to create glucose (the energy molecule that plant cells need to survive) and oxygen (around 90% of the oxygen we breathe comes from photosynthetic plants and algae in the oceans). Basically then, we are dependent on plants, and they are dependent on us. This interdependent unity of life seems to be more than just a chance happening, does it not?
There are two fundamental reactions that take place during photosynthesis—the light and dark reactions. We will begin with the light-dependent portion. Light’s voyage takes it from the Sun, through the Earth’s atmosphere, and to photosynthetic plants or algae. In the case of a plant with leaves, the light strikes the leaf, penetrates the outer covering of the plant’s cells, and arrives at the first checkpoint of photosynthesis—the chloroplast. Chloroplasts, which specialize in photosynthesis, are often oval or disk-shaped organelles about two to ten micrometers long. Like mitochondria (the energy-producing organelles in animal cells), they have a double-membrane system. In the most common types, the inner membrane is the site where sunlight energy is trapped, and where adenosine triphosphate (ATP) is produced. The inner membrane is arranged as a system of stacked disks, called grana, which are surrounded by a semifluid matrix called the stroma (Starr, et. al., 1987, p. 67). Imagine a miniscule, bean-shaped structure that contains stacks of miniature pancakes inside of it. The individual pancakes that make up the grana are called thylakoid disks. It is at this location where photosynthesis does much of its work.
The outer portion of the thylakoid disks is where light becomes useful to the plant. There are many structures that function in absorbing the energy and converting it to a form that is useful to the cells. The complexity of energy synthesis soon becomes almost inconceivable. Once the pure light energy reaches the thylakoid membrane, it starts a chain reaction that ultimately will result in the production of energy for the cell. The beginning of these reactions constitutes the electron transport chain. James Trefil explained it in this way:
The light reaction begins with Photosystem II, when light “hits” an electron in a specific chlorophyll molecule known as P680. The electron absorbs the light energy and becomes excited, meaning it has more energy than usual. The excited electron “jumps” to a higher energy level. Normally, the electron would immediately lose its additional energy and drop back down to its original position. However, it is met by an electron acceptor, Q, which sends the excited electron down a series of molecules known as a cytochrome chain. As the electron is passed from one molecule to the next, a series of coupled redox reactions occurs. The energy is immediately used to make ATP. The unexcited electron settles into a different chlorophyll molecule, known as P700, leaving behind a “hole” in P680. Photosystem I begins when a different electron in P700 also absorbs light energy and becomes excited. It too jumps to a higher energy level, where it is met by the electron acceptor Z. Z send the excited electron down a ferrodoxin chain, where coupled redox reactions occur. Meanwhile, back in Photosystem II, the ATP just formed supplies the energy used to split some water molecules into their component hydrogen and oxygen atoms. The oxygen is released into the air. One of its electrons is used to “plug” the hole in P680. The hydrogen atoms move over to Photosystem I, where they are picked up by the carrier molecule NADP+, along with the electron from P700 that went down the ferrodoxin chain and the energy that was released from the coupled redox reactions. The hydrogen and energy will be used to produce glucose in the dark reaction (2001, p. 383).
Your head may be spinning at all of the information packed into that quote, especially if you have never taken a biology course. Nevertheless, I hope you are beginning to see the complexity that is evident even at a microscopic level.
But we are not finished yet. As Trefil mentioned, the hydrogen and energy produced from the light reactions must now be transferred to the dark reactions (know as the Calvin-Benson cycle). If you refer to the description of the light-dependent reactions discussed by Trefil, two forms of energy are produced—ATP and NADPH. This energy, as well as an abundance of the carbon dioxide that we exhale, will now be needed by the dark reactions. The carbon dioxide is attached to a special molecule called RuBP. This combination will form a long chain of carbons (six carbons in length). This molecule, as it turns out, is extremely easy to break, and it will sever, forming two three-carbon chains. At this point, the ATP and NADPH are added to the mixture. This helps the three-carbon chain grab a few more molecules on its way to creating glucose. Finally, two separate molecules that have been created will form glucose—the energy molecule that the plant was working to produce all along. Purposeful design is seen in every aspect of this dazzling, life-giving cycle.
Could photosynthesis have occurred via chance processes? Scarcely. Biochemist Wayne Frair observed:
[F]or a cell to operate it must be able…to utilize this energy for the life of the cell. At the present time some single-celled organisms have chlorophyll such as is found in green leaves. This chlorophyll in cooperation with a whole host of other chemicals can utilize light energy which comes primarily from the sun. But these processes are very complex, and it is difficult to conceive how some simple functional device could have met the energy needs of any “first living cell” (2002, pp. 26-27).
Dr. Frair noted that it would be difficult to imagine how a “simple functional device” could have met the energy needs of any “first living cell.” How, then, could the “first cell” acquire the necessary energy without photosynthesis, and how could photosynthesis evolve without the energy? Those two questions present a paradox that is most likely insolvable. It is not reasonable to say that so many processes occurring in so many cells, over so small of a space, could have “evolved” merely as a result of time and chance. This natural wonder implies a supernatural origin. It needs a Designer.
Broom, Neil (2001), How Blind is the Watchmaker? (Downers Grove, IL: InterVarsity).
Frair, Wayne (2002), Biology and Creation: An Introduction Regarding Life and Its Origins (Creation Research Society).
Starr, Cecie and Ralph Taggart (1987), Biology (Belmont, CA: Wadsworth).
Trefil, James (2001), Encyclopedia of Science and Technology (New York: Routledge).