Photosynthesis is the chemical process by which plants, algae, and some bacteria use the energy from sunlight to transform carbon dioxide (a greenhouse gas) from the atmosphere, and water, into organic compounds such as sugars. These sugars are then used to make complex carbohydrates, lipids, and proteins, as well as the wood, leaves, and roots of plants. The amount of organic matter made by photosynthesizing organisms in an ecosystem is defined as the productivity of that ecosystem. Energy flows through the biosphere as organisms (including some animals) eat photosynthesizing organisms (called herbivores), and as organisms then eat those herbivores (carnivores), etc., to get their energy for growth, reproduction, and other functions. This energy is acquired through the process of cellular respiration, which usually requires oxygen. Oxygen is a byproduct of photosynthesis. About 70% of the oxygen in the atmosphere that we breathe comes from algae in the ocean. Atmospheric oxygen from photosynthesis also forms the ozone layer, which protects organisms from harmful high-energy ultraviolet (UV) radiation from the Sun. Because photosynthesis also requires water, the availability of water affects the productivity and biomass of the ecosystem, which in turn affects how much and how rapidly water cycles through the ecosystem. Fossil fuels are derived from the burial of photosynthetic organisms, including plants on land (which primarily form coal) and plankton in the oceans (which primarily form oil and natural gas). While buried, the carbon in the organic material is removed from the carbon cycle for thousands of years to hundreds of millions of years. The burning of fossil fuels has dramatically increased the exchange of carbon from the ground back into the atmosphere and oceans. This return of carbon back into atmosphere as carbon dioxide is occurring at a rate that is hundreds to thousands of times faster than it took to bury it, and much faster than it can be removed by photosynthesis or weathering. Thus, the carbon dioxide released from the burning of fossil fuels is accumulating in the atmosphere, increasing average temperatures and causing ocean acidification. The rate of photosynthesis in ecosystems is affected by various environmental conditions, including:
Humans have altered the rate of photosynthesis, and in turn productivity, in ecosystems through a variety of activities, including:
Earth system model about photosynthesisThe Earth system model below includes some of the processes and phenomena related to photosynthesis. These processes operate at various rates and on different spatial and temporal scales. For example, carbon dioxide is transferred among plants and animals over relatively short time periods (hours-weeks), but the deforestation alters ecosystems over decades to centuries, or longer. Can you think of additional cause and effect relationships between photosynthesis and other processes in the Earth system? Explore the Earth SystemClick the bolded terms (e.g. respiration, productivity and biomass, and burning of fossil fuels) on this page to learn more about these process and phenomena. Alternatively, explore the Understanding Global Change Infographic and find new topics that are of interest and/or locally relevant to you. InvestigateLearn more in these real-world examples, and challenge yourself to construct a model that explains the Earth system relationships.
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