Click the following link to learn more about photosynthesis. Some organisms can carry out photosynthesis, whereas others cannot. An autotroph is an organism that can produce its own food. Plants are the best-known autotrophs, but others exist, including certain types of bacteria and algae Figure 5. Oceanic algae contribute enormous quantities of food and oxygen to global food chains.
Plants are also photoautotrophs, a type of autotroph that uses sunlight and carbon from carbon dioxide to synthesize chemical energy in the form of carbohydrates. All organisms carrying out photosynthesis require sunlight. Heterotrophs are organisms incapable of photosynthesis that must therefore obtain energy and carbon from food by consuming other organisms.
Even if the food organism is another animal, this food traces its origins back to autotrophs and the process of photosynthesis.
Humans are heterotrophs, as are all animals. Heterotrophs depend on autotrophs, either directly or indirectly. Deer and wolves are heterotrophs. A deer obtains energy by eating plants. A wolf eating a deer obtains energy that originally came from the plants eaten by that deer. The energy in the plant came from photosynthesis, and therefore it is the only autotroph in this example Figure 5. Using this reasoning, all food eaten by humans also links back to autotrophs that carry out photosynthesis.
Major grocery stores in the United States are organized into departments, such as dairy, meats, produce, bread, cereals, and so forth. Each aisle contains hundreds, if not thousands, of different products for customers to buy and consume Figure 5. For carrying out photosynthesis in low light conditions, cyanobacteria have the help of proteins called phycobiliproteins , which are found buried in the cell membranes the outer covering of the cyanobacteria. Phycobiliproteins play the role of assistants to Chl in aquatic water environments.
Since light has a difficult time penetrating into the oceans, phycobiliproteins make this job easier by absorbing whatever light is available; they absorb the green portion of the light and turn it to red light, which is the color of light required by Chl [ 2 ]. However, changing the color of light is not as easy as it seems.
The green light has to pass through different phycobiliprotein molecules, which absorb light of one color and give out light of another color. The color that is given out is then taken up by a second phycobiliprotein, which turns it into a third color.
This process continues until the emitted light is red, which can finally be taken up by Chl. For this whole process to take place, we have three different kinds of phycobiliprotein molecules arranged as a sort of a hat over the Chl molecule, as you can see in Figure 3. These three kinds of phycobiliproteins are:.
The reason phycobiliproteins absorb light of different colors is that they contain chemical molecules called bilins inside them, which give them their bright colors. These bilins are responsible for absorbing light of one color and emitting light of another color, thus causing a change in the color of light.
Advanced instruments have let us analyze the arrangement of these molecules and proteins in the cyanobacteria. We know that phycobiliproteins are shaped like disks [ 3 ], and the disks are stacked on top of each other to form the hat-like structure. This assembly joins to the core, made of APC.
This entire structure is linked to Chl, which accepts the red light emitted by APC. The arrangement of the hat-like structure has been shown in Figure 3. The change in light color from green to red takes place through a process known as fluorescence. In plants, for example, light energy is transferred to chlorophyll pigments.
The conversion to chemical energy is accomplished when a chlorophyll pigment expels an electron, which can then move on to an appropriate recipient. The pigments and proteins, which convert light energy to chemical energy and begin the process of electron transfer, are known as reaction centers.
The reactions of plant photosynthesis are divided into those that require the presence of sunlight and those that do not. Both types of reactions take place in chloroplasts : light-dependent reactions in the thylakoid and light-independent reactions in the stroma. Light-dependent reactions also called light reactions : When a photon of light hits the reaction center, a pigment molecule such as chlorophyll releases an electron.
The released electron manages to escape by traveling through an electron transport chain , which generates the energy needed to produce ATP adenosine triphosphate, a source of chemical energy for cells and NADPH.
The "electron hole" in the original chlorophyll pigment is filled by taking an electron from water. As a result, oxygen is released into the atmosphere. Light-independent reactions also called dark reactions and known as the Calvin cycle : Light reactions produce ATP and NADPH, which are the rich energy sources that drive dark reactions.
Three chemical reaction steps make up the Calvin cycle: carbon fixation, reduction and regeneration. These reactions use water and catalysts. These sugars are then used to make glucose or are recycled to initiate the Calvin cycle again.
Photosynthetic organisms are a possible means to generate clean-burning fuels such as hydrogen or even methane. Recently, a research group at the University of Turku in Finland, tapped into the ability of green algae to produce hydrogen. In plants, the process of photosynthesis takes place in the mesophyll of the leaves, inside the chloroplasts.
Chloroplasts contain disc-shaped structures called thylakoids, which contain the pigment chlorophyll. Chlorophyll absorbs certain portions of the visible spectrum and captures energy from sunlight. Key Terms chloroplast : An organelle found in the cells of green plants and photosynthetic algae where photosynthesis takes place. Overview of Photosynthesis Photosynthesis is a multi-step process that requires sunlight, carbon dioxide, and water as substrates.
Oxygen is generated as a waste product of photosynthesis. In reality, the process includes many steps involving intermediate reactants and products. Glucose, the primary energy source in cells, is made from two three-carbon GA3P molecules.
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