What is the by-product of photosynthesis

am Puls Biologie 5, textbook

49 Cell metabolism 2.3 Photosynthesis Photosynthesis is one of the most important chemical processes on earth Glossary 1 Melvin Calvin: American biochemist, 1911–1997. He identified the chemical reactions of CO 2 fixation in photosynthesis and discovered how CO 2 is converted into organic molecules. For this he received the Nobel Prize in Chemistry in 1961. Task W 1 The accumulation of oxygen in the atmosphere 2.5 billion years ago led to a mass extinction known as the “great oxygen catastrophe”. Research which organisms became extinct and explain why we know about them today. You already know that plants can produce glucose from water and carbon dioxide. The energy required for this is provided by sunlight. This process is called photosynthesis. It is one of the most important chemical reactions for life on earth. All plants that carry out photosynthesis contain the green leaf pigment chlorophyll. All green parts of the plant are photosynthetically active. Most of the photosynthesis, however, is carried out by the green leaves, which serve to optimally capture the sunlight. During photosynthesis, plants produce oxygen (O 2) as a by-product. In the early days of life, about three billion years ago, the earth's atmosphere did not yet have any oxygen. Living beings that need oxygen to breathe, such as humans, would have suffocated in the air of that time. This only changed with the cyanobacteria. Cyanobacteria are blue-green bacteria that are among the oldest living things on earth and carry out photosynthesis. The massive production of oxygen as a by-product of photosynthesis led to a complete change in living conditions on earth 2.5 billion years ago. Suddenly there was oxygen to breathe. For many of the living things of that time, however, this oxygen was poisonous and they died out. At the same time, the oxygen-containing atmosphere enabled the emergence of many new species that could use the oxygen. When plants emerged in the course of evolution, the oxygen content of the atmosphere increased even further due to their photosynthesis. As you take your next breaths, think about it: Every single molecule of oxygen you breathe was created in photosynthesis. Plants make the sugar they feed on themselves. The photosynthesis process Photosynthesis takes place in two related steps: a light-dependent and a light-independent step. Here you get an overview of these two steps in photosynthesis, which are called the light reaction and the Calvin cycle 1. The first step requires sunlight. This part of photosynthesis is also known as photolysis of water, because it splits water into oxygen and hydrogen (k Fig. 12). This reaction is very energy-consuming. The splitting of the water molecules is made possible by the energy from the sunlight. The high-energy, released hydrogen is directly bound to a carrier molecule (coenzyme), the NADP +. In addition, in the first step, energy is released in the form of ATP. The second step is independent of light and can therefore also be carried out in the dark. Sugar is produced in the Calvin cycle: the energy-rich hydrogen from the split water reacts with CO 2 to form glucose (k Fig. 12). The ATP provides the energy required for this. The reaction equations of the two partial reactions as well as the overall reaction are given in Figure 12. The partial reactions of photosynthesis are discussed in more detail on the following pages. H 2 O CO 2 ADP ATP Sugar + Calvin cycle Light reactions NADP + NADPH e - e - Granum Stroma Light energy Light dependent reactions Light independent reactions Light energy Light energy 12 H 2 O 24 H + 6 O 2 6 CO 2 + 24 HC 6 H 12 O 6 + 6 H 2 O 6 CO 2 + 12 H 2 OC 6 H 12 O 6 + 6 O 2 + 6 H 2 O light-dependent: light-independent: overall equation: Figure 12: photosynthesis. The chemical processes of the light reaction and the Calvin cycle take place in the chloroplasts. Photosynthesis consists of a light-dependent and a light-independent step. For testing purposes only - property of the publisher öbv

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