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Mar 20, 2024 · While there are many steps behind the process of photosynthesis, it can be broken down into two major stages: light-dependent reactions and light-independent reactions. The light-dependent reaction takes place within the thylakoid membrane and requires a steady stream of sunlight, hence the name light- dependent reaction.
- Overview
- Introduction
- What is photosynthesis?
- The ecological importance of photosynthesis
- Leaves are sites of photosynthesis
- The light-dependent reactions and the Calvin cycle
- Photosynthesis vs. cellular respiration
Conversion of light energy to chemical energy. Reactions of photosynthesis, where they take place, and their ecological importance.
Have you hugged a tree lately? If not, you might want to give it some thought. You, along with the rest of the human population, owe your existence to plants and other organisms that capture light. In fact, most life on Earth is possible because the sun provides a continuous supply of energy to ecosystems.
All organisms, including humans, need energy to fuel the metabolic reactions of growth, development, and reproduction. But organisms can't use light energy directly for their metabolic needs. Instead, it must first be converted into chemical energy through the process of photosynthesis.
Photosynthesis is the process in which light energy is converted to chemical energy in the form of sugars. In a process driven by light energy, glucose molecules (or other sugars) are constructed from water and carbon dioxide, and oxygen is released as a byproduct. The glucose molecules provide organisms with two crucial resources: energy and fixed—organic—carbon.
•Energy. The glucose molecules serve as fuel for cells: their chemical energy can be harvested through processes like cellular respiration and fermentation, which generate adenosine triphosphate—ATP , a small, energy-carrying molecule—for the cell’s immediate energy needs.
Photosynthetic organisms, including plants, algae, and some bacteria, play a key ecological role. They introduce chemical energy and fixed carbon into ecosystems by using light to synthesize sugars. Since these organisms produce their own food—that is, fix their own carbon—using light energy, they are called photoautotrophs (literally, self-feeders that use light).
Humans, and other organisms that can’t convert carbon dioxide to organic compounds themselves, are called heterotrophs, meaning different-feeders. Heterotrophs must get fixed carbon by eating other organisms or their by-products. Animals, fungi, and many prokaryotes and protists are heterotrophs.
[Read more about autotrophs and heterotrophs.]
Besides introducing fixed carbon and energy into ecosystems, photosynthesis also affects the makeup of Earth’s atmosphere. Most photosynthetic organisms generate oxygen gas as a byproduct, and the advent of photosynthesis—over 3 billion years ago, in bacteria resembling modern cyanobacteria—forever changed life on Earth1 . These bacteria gradually released oxygen into Earth’s oxygen-poor atmosphere, and the increase in oxygen concentration is thought to have influenced the evolution of aerobic life forms—organisms that use oxygen for cellular respiration. If it hadn’t been for those ancient photosynthesizers, we, like many other species, wouldn't be here today!
Plants are the most common autotrophs in terrestrial—land—ecosystems. All green plant tissues can photosynthesize, but in most plants, but the majority of photosynthesis usually takes place in the leaves. The cells in a middle layer of leaf tissue called the mesophyll are the primary site of photosynthesis.
Small pores called stomata—singular, stoma—are found on the surface of leaves in most plants, and they let carbon dioxide diffuse into the mesophyll layer and oxygen diffuse out.
Photosynthesis in the leaves of plants involves many steps, but it can be divided into two stages: the light-dependent reactions and the Calvin cycle.
•The light-dependent reactions take place in the thylakoid membrane and require a continuous supply of light energy. Chlorophylls absorb this light energy, which is converted into chemical energy through the formation of two compounds, ATP —an energy storage molecule—and NADPH —a reduced (electron-bearing) electron carrier. In this process, water molecules are also converted to oxygen gas—the oxygen we breathe!
•The Calvin cycle, also called the light-independent reactions, takes place in the stroma and does not directly require light. Instead, the Calvin cycle uses ATP and NADPH from the light-dependent reactions to fix carbon dioxide and produce three-carbon sugars—glyceraldehyde-3-phosphate, or G3P, molecules—which join up to form glucose.
Overall, the light-dependent reactions capture light energy and store it temporarily in the chemical forms of ATP and NADPH . There, ATP is broken down to release energy, and NADPH donates its electrons to convert carbon dioxide molecules into sugars. In the end, the energy that started out as light winds up trapped in the bonds of the sugars.
At the level of the overall reactions, photosynthesis and cellular respiration are near-opposite processes. They differ only in the form of energy absorbed or released, as shown in the diagram below.
At the level of individual steps, photosynthesis isn't just cellular respiration run in reverse. Instead, as we'll see the rest of this section, photosynthesis takes place in its own unique series of steps. However, there are some notable similarities between photosynthesis and cellular respiration.
For instance, photosynthesis and cellular respiration both involve a series of redox reactions (reactions involving electron transfers). In cellular respiration, electrons flow from glucose to oxygen, forming water and releasing energy. In photosynthesis, they go in the opposite direction, starting in water and winding up in glucose—an energy-requiring process powered by light. Like cellular respiration, photosynthesis also uses an electron transport chain to make a H+ concentration gradient, which drives ATP synthesis by chemiosmosis.
If those things don't sound familiar, though, don't worry! You don't need to know cellular respiration to understand photosynthesis. Just keep reading and watching, and you'll learn all the ins and outs of this life-sustaining process.
There are two main stages of photosynthesis: the light-dependent reactions and the Calvin cycle.
- If you heavily breath on a plant, will it help growth considering it needs CO2, water, sunlight?In an open environment, probably not by any noticeable amount. However, if you put the plant in a sealed container such as a greenhouse and sit in...
- what is NADPH?the electron carrier for photosynthesis. NADH(without the P for photosynthesis :) ) is used in cellular respiration. They carry electrons to and fr...
- how does the plant reléase the oxgenthrough stomata on the back of it's leaves
- Calvin Cycle: ATP is used to create sugars that the plant will use to grow and live. My question is ...The Calvin cycle is dependent on the Light-dependent reactions, and almost in the same way Light-dependent reactions are dependent on "The Calvin C...
- How do trees survive when they lose their leaves in the winter? How can photosynthesis still occur w...Deciduous trees store energy and resources within their bark, which can be used during the winter months when they have no leaves. Additionally, th...
- "Light energy is captured by chloroplasts and stored as ATP" ATP is need to make sugar, BUT ATP is a...ATP is not sugar, it is a nucleotide. The carbon atoms needed to build sugar molecules are taken from the CO2 that the plant absorbs. CO2 is conver...
- How often do they(plants) produce the Oxygen?? Is it a continuing process, I mean.. Don't they stop ...Every time that the process of photosynthesis happens, it produces 1 molecule of oxygen along with the ATP and NADPH. However, only one molecule of...
- "Light energy is captured by chloroplasts and stored as ATP" ATP is need to make sugar, BUT ATP is a...ATP itself is not composed of sugar. When light energy is captured by the chloroplast, it, along with carbon dioxide and water, gets converted to A...
The Two Parts of Photosynthesis. Photosynthesis takes place in two stages: the light-dependent reactions and the Calvin cycle. In the light-dependent reactions, which take place at the thylakoid membrane, chlorophyll absorbs energy from sunlight and then converts it into chemical energy with the use of water. The light-dependent reactions ...
Sep 21, 2021 · Photosynthesis takes place in two stages: the light-dependent reactions and the Calvin cycle. In the light-dependent reactions, which take place at the thylakoid membrane, chlorophyll absorbs energy from sunlight and then converts it into chemical energy with the use of water.
Skills to Develop. Explain the relevance of photosynthesis to other living things. Describe the main structures involved in photosynthesis. Identify the substrates and products of photosynthesis. Summarize the process of photosynthesis. Photosynthesis is essential to all life on earth; both plants and animals depend on it.
The chloroplast is involved in both stages of photosynthesis. The light reactions take place in the thylakoid. There, water (H 2 O) is oxidized, and oxygen (O 2 ) is...
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