What happens in photosythesis

Panel e shows moss gametophytes with sporophytes protruding from the ground. The gametophytes have small green leaves, and the sporophytes are thin, unbranched, brown stalks. Each sporophyte has a fluorescent orange, oviform capsule called a sporangia perched on top of its stalk. Panel f shows six clubmoss sporophytes emanating from the ground.


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Some stand vertically out of the soil, and some curve or have fallen horizontally. They have many stiff, protruding, spine-like, green leaves. The sporangia are small yellow balls at the base of the leaves. Panel g shows fern sporophytes with many stems covered with small, elongated, symmetrical green leaves.

Panel h shows a whisk fern sporophyte with long, straight, green stems beaded with yellow, round synangia along their lengths. 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.

The Power of Photosynthesis

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.

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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.

Other features of the cell include the nucleus N , mitochondrion M , and plasma membrane PM.

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DK Science: Photosynthesis

At right and below are microscopic images of thylakoid stacks called grana. Note the relationship between the granal and stromal membranes. Protein import into chloroplasts. Nature Reviews Molecular Cell Biology 5, doi Figure Detail. Photosynthesis consists of both light-dependent reactions and light-independent reactions. In plants, the so-called "light" reactions occur within the chloroplast thylakoids, where the aforementioned chlorophyll pigments reside. When light energy reaches the pigment molecules, it energizes the electrons within them, and these electrons are shunted to an electron transport chain in the thylakoid membrane.

Meanwhile, each chlorophyll molecule replaces its lost electron with an electron from water; this process essentially splits water molecules to produce oxygen Figure 5.

The light reactions take place in the thylakoid. There, water H 2 O is oxidized, and oxygen O 2 is released. The dark reactions then occur outside the thylakoid. The products of this reaction are sugar molecules and various other organic molecules necessary for cell function and metabolism. Note that the dark reaction takes place in the stroma the aqueous fluid surrounding the stacks of thylakoids and in the cytoplasm. The thylakoids, intake of water H 2 O , and release of oxygen O 2 occur on the yellow side of the cell to indicate that these are involved in the light reactions.

What is Photosynthesis?

The carbon fixation reactions, which involve the intake of carbon dioxide CO 2 , NADPH, and ATP, and the production of sugars, fatty acids, and amino acids, occur on the blue side of the cell to indicate that these are dark reactions. An arrow shows the movement of a water molecule from the outside to the thylakoid stack on the inside of the chloroplast. Another arrow shows light energy from the sun entering the chloroplast and reaching the thylakoid stack. An arrow shows the release of an oxygen molecule O 2 from the thylakoid stack to the outside of the chloroplast.

Once the light reactions have occurred, the light-independent or "dark" reactions take place in the chloroplast stroma. During this process, also known as carbon fixation, energy from the ATP and NADPH molecules generated by the light reactions drives a chemical pathway that uses the carbon in carbon dioxide from the atmosphere to build a three-carbon sugar called glyceraldehydephosphate G3P. Cells then use G3P to build a wide variety of other sugars such as glucose and organic molecules.

Many of these interconversions occur outside the chloroplast, following the transport of G3P from the stroma.

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The products of these reactions are then transported to other parts of the cell, including the mitochondria, where they are broken down to make more energy carrier molecules to satisfy the metabolic demands of the cell. In plants, some sugar molecules are stored as sucrose or starch. This oxygen is what we breathe and we cannot live without it. While it is important that photosynthesis provides food and oxygen, its impact on our daily lives is far more extensive. Photosynthesis is so essential to life on earth that most living organisms, including humans, cannot survive without it.

All of our energy for growth, development and physical activity comes from eating food from plants and animals. Animals obtain energy from eating plants. Plants obtain energy from glucose made during photosynthesis. Our major sources of energy such as natural gas, coal and oil were made millions of years ago from the remains of dead plants and animals which we already know got their energy from photosynthesis.