Embedded Files
Introduction:
Earth is awash in energy streaming from the sun. The energy powered by the sun gives life to plants, algae, and bacteria through the process of photosynthesis. Only about 1% of this huge supply of energy is captured by photosynthesis, using it to provide the energy that drives all life.
Photosynthesis can be described as the process that allows some living organisms to convert light energy into chemical energy, which is used to synthesize organic compounds. The chemical energy provided by photosynthesis is also used in other processes such as nitrogen or sulfur assimilation.
The process of photosynthesis:
During photosynthesis, plants take in carbon dioxide (CO2) and water (H2O) from the air and soil. Oxygenic photosynthesis is found in plants, algae, and cyanobacteria. Within the plant cell, the water is oxidized (loses electrons), while the carbon dioxide is reduced (gains electrons). A process transforms water into oxygen and carbon dioxide into glucose. The plant then releases the oxygen back into the air, and stores energy within the glucose molecules.
CO2 + H2O + light→ CH2O + O2
Despite the fact that plants are not regularly ordered systems and that photon energy comes in broad distribution, photosynthesis is nearly 100% efficient. That means nearly 100% of that absorbed energy gets converted into electron energy, which then creates those sugars via photosynthesis.
Here's how quantum physics does it. When a photon from the sun strikes a leaf, it sparks a change in a specially designed molecule. The energy knocks loose an electron. The electron, and the “hole” where it once was, can now travel around the leaf, carrying the energy of the sun to another area where it triggers a chemical reaction to make sugars for the plant. Together, that traveling electron and hole pair is referred to as an “exciton”. To simplify the process of photosynthesis, chlorophyll, which is a light-absorbing pigment within the thylakoid membranes of small organelles called chloroplasts, absorbs energy from blue- and red-light waves, and reflects green-light waves, making the plant appear green.
The chlorophyll found in plants is the only molecule capable of absorbing and using sunlight over two particular narrow wavelength ranges: blue light that peaks at around 430 nanometers in wavelength and red light that peaks at around 662 nanometers in wavelength and reflects green-light waves, making the plant appear green. The chlorophyll is a light-absorbing pigment within the thylakoid membranes of small organelles called chloroplasts, that absorbs energy. Chlorophyll is the molecule that makes photosynthesis possible and is found in all photosynthetic organisms: plants, algae, and cyanobacteria among them.
When photosynthetic cells absorb light from the sun, packets of energy called photons leap between a series of light-harvesting proteins until they reach the photosynthetic reaction center. There, cells convert the energy into electrons, which eventually power the production of sugar molecules.
This transfer of energy through the light-harvesting complex occurs with extremely high efficiency. Nearly every photon of light absorbed generates an electron, a phenomenon known as near-unity quantum efficiency.
This photograph shows chloroplasts within the plant cells of the organism Plagiomnium affine. In terms of transferring absorbed sunlight energy into the photosynthetic reaction centers where sugars are created, that energy transport is nearly 100% efficient: an anomaly among nearly all biological processes.
As we know, in the spring and summer months leaves make food for the tree through photosynthesis and appear in green color. During photosynthesis, chlorophyll, as highlighted above, absorbs energy from blue- and red-light waves and reflects green-light waves, making the plant appear green. But that does not mean other colors are not in the leaves. Thus, in summer, the overwhelming amounts of chlorophyll in the leaves mask the other colors.
During the transition season from summer to fall, the change in temperatures and amount of sunlight cuts off the food-making process from the leaves to the tree. That means chlorophyll breaks down, the greens fade away, and other colors become visible!
The electromagnetic spectrum. Light is a form of electromagnetic energy conveniently thought of as a wave. The shorter the wavelength of light, the greater its energy. Visible light represents only a small part of the electromagnetic spectrum between 400 and 740 nanometers.
To perform photosynthesis, plants must open stomatal pores to let in carbon dioxide from the air. Water is absorbed through the roots of the plant. Light energy is converted to chemical energy during the first stage of photosynthesis, which involves a series of chemical reactions known as light-dependent reactions.
Therefore, two major reactions in the photosynthesis process that are important to understand:
1. The light-dependent reactions: Occurs during the day and takes place within the thylakoid membrane and requires a steady stream of sunlight (daylight), and the chlorophyll absorbs energy from the light waves, which is converted into chemical energy in the form of the molecules ATP (adenosine triphosphate) and NADPH (the reduced form of nicotine adenine dinucleotide phosphoric acid). During this stage, energy from the ATP and NADPH molecules is used to assemble carbohydrate molecules, like glucose, from carbon dioxide. At this stage, water is spilt into its elements – oxygen and hydrogen ions. Then, the ions go through a series of electron carriers, eventually leading to the accumulation of hydrogen ions. As electrons get transferred from one electron carrier to another, energy is released.
2. The light-independent reactions, known as the Calvin Cycle: take place in the stroma, the space between the thylakoid membranes and the chloroplast membranes, and do not require light. During this stage, energy from the ATP and NADPH molecules is used to assemble carbohydrate molecules, like glucose, from carbon dioxide.
C3 and C4 as other photosynthesis processes:
- C3 photosynthesis is used by the majority of plants and produces a three-carbon compound called 3-phosphoglyceric acid during the Calvin Cycle, which goes on to become glucose.
- C4 photosynthesis produces a four-carbon intermediate compound, which splits into carbon dioxide and a three-carbon compound during the Calvin Cycle. A benefit of C4 photosynthesis is that by producing higher levels of carbon, it allows plants to thrive in environments without much light or water. Producing higher levels of carbon allows plants to thrive in environments without much light or water.
Finally, chlorophylls and related pigments play central roles in light-harvesting and primary charge separation reactions of photosynthesis. There are several types of chlorophylls, among which, chlorophyll has long been believed to be the common species that absorbs the longest wavelength light in oxygenic photosynthesis. The diversity of chlorophylls is an important factor for oxygenic photosynthetic organisms to adapt to various light environments.
Page updated
Google Sites
Report abuse