The life sciences comprise all fields of science that involve the scientific study of living organisms, like plants, animals, and human beings. However, the study of behaviour of organisms, such as practised in ethology and psychology, is only included in as much as it involves a clearly biological aspect. While biology remains the centerpiece of the life sciences, technological advances in molecular biology and biotechnology have led to a burgeoning of specializations and new, often interdisciplinary, fields.
PHOTOSYNTHESIS (English pronunciation: /foʊtoʊˈsɪnθəsɪs/; from the Greek φώτο- [photo-], "light," and σύνθεσις [synthesis], "putting together", "composition") is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight.[1] Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can create their own food. In plants, algae, and cyanobacteria, photosynthesis uses carbon dioxide and water, releasing oxygen as a waste product. Photosynthesis is vital for all aerobic life on Earth. As well as maintaining the normal level of oxygen in the atmosphere, nearly all life either depends on it directly as a source of energy, or indirectly as the ultimate source of the energy in their food[2] (the exceptions are chemoautotrophs that live in rocks or around deep sea hydrothermal vents). The rate of energy capture by photosynthesis is immense, approximately 100 terawatts,[3] which is about six times larger than the power consumption of human civilization.[4] As well as energy, photosynthesis is also the source of the carbon in all the organic compounds within organisms' bodies. In all, photosynthetic organisms convert around 100–115 petagrams of carbon into biomass per year.[5][6]
Although photosynthesis can happen in different ways in different species, some features are always the same. For example, the process always begins when energy from light is absorbed by proteins called photosynthetic reaction centers that contain chlorophylls. In plants, these proteins are held inside organelles called chloroplasts, while in bacteria they are embedded in the plasma membrane. Some of the light energy gathered by chlorophylls is stored in the form of adenosine triphosphate (ATP). The rest of the energy is used to remove electrons from a substance such as water. These electrons are then used in the reactions that turn carbon dioxide into organic compounds. In plants, algae and cyanobacteria, this is done by a sequence of reactions called the Calvin cycle, but different sets of reactions are found in some bacteria, such as the reverse Krebs cycle in Chlorobium. Many photosynthetic organisms have adaptations that concentrate or store carbon dioxide. This helps reduce a wasteful process called photorespiration that can consume part of the sugar produced during photosynthesis.
Overview of cycle between autotrophs and heterotrophs. Photosynthesis is the main means by which plants, algae and many bacteria produce organic compounds and oxygen from carbon dioxide and water (green arrow).
The first photosynthetic organisms probably evolved about 3,500 million years ago, early in the evolutionary history of life, when all forms of life on Earth were microorganisms and the atmosphere had much more carbon dioxide. They most likely used hydrogen or hydrogen sulfide as sources of electrons, rather than water.[7] Cyanobacteria appeared later, around 3,000 million years ago, and drastically changed the Earth when they began to oxygenate the atmosphere, beginning about 2,400 million years ago.[8] This new atmosphere allowed the evolution of complex life such as protists. Eventually, no later than a billion years ago, one of these protists formed a symbiotic relationship with a cyanobacterium, producing the ancestor of many plants and algae.[9] The chloroplasts in modern plants are the descendants of these ancient symbiotic cyanobacteria.[10]
Evolution (also known as biological or organic evolution) is the change over time in one or more inherited traits found in populations of organisms.[1] Inherited traits are particular distinguishing characteristics, including anatomical, biochemical or behavioural characteristics, that are passed on from one generation to the next. Evolution may occur when there is variation of inherited traits within a population. The major sources of such variation are mutation, genetic recombination and gene flow.[2][3][4][5] Evolution has led to the diversification of all living organisms from a common ancestor, which are described by Charles Darwin as "endless forms most beautiful and most wonderful
PHOTOSYNTHESIS (English pronunciation: /foʊtoʊˈsɪnθəsɪs/; from the Greek φώτο- [photo-], "light," and σύνθεσις [synthesis], "putting together", "composition") is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight.[1] Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can create their own food. In plants, algae, and cyanobacteria, photosynthesis uses carbon dioxide and water, releasing oxygen as a waste product. Photosynthesis is vital for all aerobic life on Earth. As well as maintaining the normal level of oxygen in the atmosphere, nearly all life either depends on it directly as a source of energy, or indirectly as the ultimate source of the energy in their food[2] (the exceptions are chemoautotrophs that live in rocks or around deep sea hydrothermal vents). The rate of energy capture by photosynthesis is immense, approximately 100 terawatts,[3] which is about six times larger than the power consumption of human civilization.[4] As well as energy, photosynthesis is also the source of the carbon in all the organic compounds within organisms' bodies. In all, photosynthetic organisms convert around 100–115 petagrams of carbon into biomass per year.[5][6]
Although photosynthesis can happen in different ways in different species, some features are always the same. For example, the process always begins when energy from light is absorbed by proteins called photosynthetic reaction centers that contain chlorophylls. In plants, these proteins are held inside organelles called chloroplasts, while in bacteria they are embedded in the plasma membrane. Some of the light energy gathered by chlorophylls is stored in the form of adenosine triphosphate (ATP). The rest of the energy is used to remove electrons from a substance such as water. These electrons are then used in the reactions that turn carbon dioxide into organic compounds. In plants, algae and cyanobacteria, this is done by a sequence of reactions called the Calvin cycle, but different sets of reactions are found in some bacteria, such as the reverse Krebs cycle in Chlorobium. Many photosynthetic organisms have adaptations that concentrate or store carbon dioxide. This helps reduce a wasteful process called photorespiration that can consume part of the sugar produced during photosynthesis.
Overview of cycle between autotrophs and heterotrophs. Photosynthesis is the main means by which plants, algae and many bacteria produce organic compounds and oxygen from carbon dioxide and water (green arrow).
The first photosynthetic organisms probably evolved about 3,500 million years ago, early in the evolutionary history of life, when all forms of life on Earth were microorganisms and the atmosphere had much more carbon dioxide. They most likely used hydrogen or hydrogen sulfide as sources of electrons, rather than water.[7] Cyanobacteria appeared later, around 3,000 million years ago, and drastically changed the Earth when they began to oxygenate the atmosphere, beginning about 2,400 million years ago.[8] This new atmosphere allowed the evolution of complex life such as protists. Eventually, no later than a billion years ago, one of these protists formed a symbiotic relationship with a cyanobacterium, producing the ancestor of many plants and algae.[9] The chloroplasts in modern plants are the descendants of these ancient symbiotic cyanobacteria.[10]
Evolution (also known as biological or organic evolution) is the change over time in one or more inherited traits found in populations of organisms.[1] Inherited traits are particular distinguishing characteristics, including anatomical, biochemical or behavioural characteristics, that are passed on from one generation to the next. Evolution may occur when there is variation of inherited traits within a population. The major sources of such variation are mutation, genetic recombination and gene flow.[2][3][4][5] Evolution has led to the diversification of all living organisms from a common ancestor, which are described by Charles Darwin as "endless forms most beautiful and most wonderful
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