In panel i, a horsetail sporophyte is shown. It has a single long stem, which is surrounded by a skirt of green leaves at its base and an elongated, yellow cone at the top. In Panel j, a large Cycas seed plant sporophyte is shown. Long fronds emanate upwards from the plant's trunk, and in the center of them there is a large mass called the cone.
Panel a is a photomicrograph of a gametophyte of a microscopic green alga called Coleochaete orbicularis. Most living things depend on photosynthetic cells to manufacture the complex organic molecules they require as a source of energy. Photosynthetic cells are quite diverse and include cells found in green plants, phytoplankton, and cyanobacteria. During the process of photosynthesis, cells use carbon dioxide and energy from the Sun to make sugar molecules and oxygen. These sugar molecules are the basis for more complex molecules made by the photosynthetic cell, such as glucose.
Then, via respiration processes, cells use oxygen and glucose to synthesize energy-rich carrier molecules, such as ATP, and carbon dioxide is produced as a waste product. Therefore, the synthesis of glucose and its breakdown by cells are opposing processes. Figure 2 2 in the sky represents the process of photosynthesis.
Two arrows are directed outwards from the trees towards the atmosphere. One represents the production of biomass in the trees, and the other represents the production of atmospheric carbon dioxide CO 2. Arrows emanating from a tree's roots point to two molecular structures: inorganic carbon and organic carbon, which may decompose into inorganic carbon.
Inorganic carbon and organic carbon are stored in the soil. This CO2 can return to the atmosphere or enter rivers; alternatively, it can react with soil minerals to form inorganic dissolved carbonates that remain stored in soils or are exported to rivers. B The transformations of organic to inorganic carbon through decomposition and photosynthesis continue in rivers; here, CO2 will re-exchange with the atmosphere degassing or be converted to dissolved carbonates.
These carbonates do not exchange with the atmosphere and are mainly exported to the coastal ocean. Organic carbon is also exported to the ocean or stored in flood plains. C In the coastal ocean, photosynthesis, decomposition, and re-exchanging of CO2 with the atmosphere still continue.
Solid organic carbon e. Dissolved inorganic and organic carbon are also exported to the open ocean, and possibly deep-ocean waters, where they are stored for many centuries. Indeed, the fossil fuels we use to power our world today are the ancient remains of once-living organisms, and they provide a dramatic example of this cycle at work. The carbon cycle would not be possible without photosynthesis, because this process accounts for the "building" portion of the cycle Figure 2. However, photosynthesis doesn't just drive the carbon cycle — it also creates the oxygen necessary for respiring organisms.
Interestingly, although green plants contribute much of the oxygen in the air we breathe, phytoplankton and cyanobacteria in the world's oceans are thought to produce between one-third and one-half of atmospheric oxygen on Earth. Photosynthetic cells contain special pigments that absorb light energy. Different pigments respond to different wavelengths of visible light.
Chlorophyll , the primary pigment used in photosynthesis, reflects green light and absorbs red and blue light most strongly. In plants, photosynthesis takes place in chloroplasts, which contain the chlorophyll.
Chloroplasts are surrounded by a double membrane and contain a third inner membrane, called the thylakoid membrane , that forms long folds within the organelle. In electron micrographs, thylakoid membranes look like stacks of coins, although the compartments they form are connected like a maze of chambers.
The green pigment chlorophyll is located within the thylakoid membrane, and the space between the thylakoid and the chloroplast membranes is called the stroma Figure 3, Figure 4. Chlorophyll A is the major pigment used in photosynthesis, but there are several types of chlorophyll and numerous other pigments that respond to light, including red, brown, and blue pigments.
These other pigments may help channel light energy to chlorophyll A or protect the cell from photo-damage. For example, the photosynthetic protists called dinoflagellates, which are responsible for the "red tides" that often prompt warnings against eating shellfish, contain a variety of light-sensitive pigments, including both chlorophyll and the red pigments responsible for their dramatic coloration.
Figure 4: Diagram of a chloroplast inside a cell, showing thylakoid stacks Shown here is a chloroplast inside a cell, with the outer membrane OE and inner membrane IE labeled. Black pigments absorb all wavelengths of visible light that strike them. White pigments reflect most of the wavelengths striking them. Each pigment has a characteristic absorption spectrum describing how it absorbs or reflects different wavelengths of light. Wavelengths absorbed by chlorophyll and other photosynthetic pigments generate electrons to power photosynthesis.
Carotenoids reflect orange, yellow and red light waves. In a leaf, carotenoid pigments cluster next to chlorophyll a molecules to efficiently hand off absorbed photons.
Carotenoids are fat soluble molecules, also believed to play a role in dissipating excessive amounts of radiant energy. Xanthophyll pigments pass along light energy to chlorophyll a and act as antioxidants. The molecular structure gives xanthophyll the ability to accept or donate electrons. Xanthophyll pigments produce the yellow color in fall leaves. Anthocyanin pigments absorb blue-green light and aid chlorophyll a.
Apples and autumn leaves owe their vibrancy to reddish, violet anthocyanin compounds. Anthocyanin is a water-soluble molecule that can be stored in the plant cell vacuole.
What Is the Role of Carotenoids in Photosynthesis? Leaf Cell Structure. The Three Stages of Photosynthesis. Leaves, stems and roots also contain a variety of pigments. Such pigment molecules include anthocyanins, flavanoids, flavines, quinones and cytochromes, just to name a few. However, none of these should be considered a photosynthetic pigment.
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