Plants Use the Energy of Sunlight to Plants Use the Energy of Sunlight to Easy Notes Cards
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Catalyze Chemical Breakdown
Life depends upon the building up and breaking down of biological molecules. Catalysts, in the form of proteins or RNA, play an important role by dramatically increasing the rate of a chemical transformation––without being consumed in the reaction. The regulatory role that catalysts play in complex biochemical cascades is one reason so many simultaneous chemical transformations can occur inside living cells in water at ambient conditions. For example, consider the 10-enzyme catalytic breakdown and transformation of glucose to pyruvate in the glycolysis metabolic pathway.
Chemically Assemble Organic Compounds
Part of the reason that synthesis reactions (chemical assembly) can occur under such mild conditions as ambient temperature and pressure in water is because most often, they occur in a stepwise, enzyme-mediated fashion, sipping or releasing small amounts of energy at each step. For example, the synthesis of glucose from carbon dioxide in the Calvin cycle is a 15-step process, each step regulated by a different enzyme.
Transform Chemical Energy
Life's chemistry runs on the transformation of energy stored in chemical bonds. For example, glucose is a major energy storage molecule in living systems because the oxidative breakdown of glucose into carbon dioxide and water releases energy. Animals, fungi, and bacteria store up to 30,000 units of glucose in a single unit of glycogen, a 3-D structured molecule with branching chains of glucose molecules emanating from a protein core. When energy is needed for metabolic processes, glucose molecules are detached and oxidized.
Transform Radiant Energy (Light)
The sun is the ultimate source of energy for many living systems. The sun emits radiant energy, which is carried by light and other electromagnetic radiation as streams of photons. When radiant energy reaches a living system, two events can happen. The radiant energy can convert to heat, or living systems can convert it to chemical energy. The latter conversion is not simple, but is a multi-step process starting when living systems such as algae, some bacteria, and plants capture photons. For example, a potato plant captures photons then converts the light energy into chemical energy through photosynthesis, storing the chemical energy underground as carbohydrates. The carbohydrates in turn feed other living systems.
Plants
Phylum Plantae ("plants"): Angiosperms, gymnosperms, green algae, and more
Plants have evolved by using special structures within their cells to harness energy directly from sunlight. There are currently over 350,000 known species of plants which include angiosperms (flowering trees and plants), gymnosperms (conifers, Gingkos, and others), ferns, hornworts, liverworts, mosses, and green algae. While most get energy through the process of photosynthesis, some are partially carnivores, feeding on the bodies of insects, and others are plant parasites, feeding entirely off of other plants. Plants reproduce through fruits, seeds, spores, and even asexually. They evolved around 500 million years ago and can now be found on every continent worldwide.
By absorbing the sun's blue and red light, chlorophyll loses electrons, which become mobile forms of chemical energy that power plant growth.
Introduction
For the first half of Earth's life to date, oxygen was all but absent from an atmosphere made mostly of nitrogen, carbon dioxide, and methane. The evolution of animals and life as we now know it owe everything to .
About 2.5 billion years ago, —the first organisms that used sunlight and carbon dioxide to produce oxygen and sugars via photosynthesis—transformed our atmosphere. Later, algae evolved with this ability, and about 0.5 billion years ago, the first land plants sprouted.
Algae, plankton, and land plants now work together to keep our atmosphere full of oxygen.
The Strategy
Photosynthesis occurs in special plant cells called s, which are the type of cells found in leaves. A single chloroplast is like a bag filled with the main ingredients needed for photosynthesis. It has water soaked up from the plant's roots, atmospheric carbon dioxide absorbed by the leaves, and contained in folded, maze-like organelles called s.
Chlorophyll is the true of photosynthesis. Cyanobacteria, plankton, and land plants all rely on this light-sensitive molecule to spark the process.
Chlorophyll molecules are so bad at absorbing green light that they reflect it like tiny mirrors, causing our eyes to see most leaves as green. It's usually only in autumn, after chlorophyll degrades, that we peep those infinite shades of yellow and orange produced by s.
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The process of photosynthesis in plants involves a series of steps and reactions that use sunlight, water, and carbon dioxide to produce sugars that the plant uses to grow. Oxygen is released from the leaves as a byproduct.
The Strategy
But chlorophyll's superpower isn't the ability to reflect green light—it's the ability to absorb blue and red light like a sponge. The sun's blue and red light energizes chlorophyll, causing it to lose electrons, which become mobile forms of chemical energy that power plant growth. The chlorophyll replenishes its lost electrons not by drinking water but by splitting it apart and taking electrons from the hydrogen, leaving oxygen as a byproduct to be "exhaled".
The electrons freed from chlorophyll are utilized in at least two ways. First, they are used to build up a high concentration of protons in the space inside the thylakoid (called the lumen), which in turn drives the transformation of ADP into —nature's energy carrier molecule. Secondly, they reduce NADP+ to . These transformations take place in the , the area outside of the thylakoid folds but still inside the chloroplast "bag." The energy brought by ATP and NADPH fuels a series of reactions in which carbon dioxide is persuaded to give up its precious cargo of carbon to build and other key metabolic compounds. As these reactions (known as the Calvin Cycle) occur, the molecules are depleted back to ADP and NADP+ returning to the thylakoid folds to replenish their store of energy through sunlight-stimulated chlorophyll.
When plants have enough sunlight, water, and fertile soil, the photosynthesis cycle continues to churn out more and more glucose. Glucose is like food that plants use to build their bodies. They combine thousands of glucose molecules to make , the main component of their cell walls. The more cellulose they make, the more they grow.
The Potential
Nature, through photosynthesis, enables plants to convert the sun's energy into a form that they and other living things can make use of. Plants transfer that energy directly to most other living things as food or as food for animals that other animals eat.
Humans also extract this energy indirectly from wood, or from plants that decayed millions of years ago into oil, coal, and natural gas. Burning these materials to provide electricity and heat has, through overexploitation, led to dire consequences that have upset the balance of life on Earth.
What if humans could harness this power in a different way? Imagine green chemistry that's catalyzed by sunlight instead of having to mine for heavy metals like copper, tin, or platinum. Think of the potential that chemical processes requiring little heat have to reduce energy consumption. With a better understanding of photosynthesis, we may transform agriculture to consume less water and preserve more land for native plants and forests. As we continue to grapple with climate change, listening to what plants can teach us can shine a light down a greener path.
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Last Updated June 9, 2021
References
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"Light is captured by a set of light-harvesting complexes (LHCs) that funnel light energy into photochemical reaction centres, photosystem (PS) I and PSII (Fig. 1) (see review by Ort and Yocum, 1996). Special subsets of chlorophyll molecules in these photosystems are excited by light energy, allowing electrons on them to be transferred through a series of redox carriers called the electron transfer chain (ETC), beginning from the oxygen evolving complex (OEC) of PSII (which oxidizes H 2 O and releases O 2 and protons) (Diner and Babcock, 1996), through the plastoquinone (PQ) pool, the cytochrome (cyt) b 6 f complex (Sacksteder et al., 2000) and plastocyanin (PC), and finally through PSI (Malkin, 1996). Electrons from PSI are transferred to ferredoxin (Fd), which, in turn, reduces NADP + to NADPH via ferredoxin:NADP + oxidoreductase (FNR) (Knaff, 1996). This linear electron flux (LEF) to NADP + is coupled to proton release at the OEC, and 'shuttling' of protons across the thylakoid membrane by the PQ pool and the Q-cycle at the cyt b 6 f complex, which establishes an electrochemical potential of protons, or proton motive force (pmf) that drives the synthesis of ATP by chemiosmotic coupling through the chloroplast ATP synthase (McCarty, 1996; Mitchell, 1966)." (Cruz et al. 2005:395)
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Source: https://asknature.org/strategy/how-plants-transform-sunlight-into-food/
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