Photosynthesis and Carbon Input Quiz

Photosynthesis and Carbon Input in Ecosystems

• Photosynthesis directly supports plant growth and produces organic matter consumed by animals and soil microbes.
• Carbon from photosynthesis makes up almost half of the organic matter on Earth, while hydrogen and oxygen account for the remainder.
• Human activities have significantly modified the rate at which carbon enters the terrestrial biosphere, increasing atmospheric CO2 by 30%.
• The availability of water and nutrients is the major factor governing carbon input to ecosystems.
• Photosynthesis is the process by which most carbon and chemical energy enter ecosystems.
• The availability of reactants such as light energy and CO2, temperature, and nitrogen availability are the proximate controls over photosynthesis by a single leaf.
• Gross primary production (GPP) is the photosynthesis at the scale of ecosystems, which varies diurnally and seasonally.
• Differences among ecosystems in annual GPP are determined primarily by the quantity of leaf area and the length of time that this leaf area is photosynthetically active.
• Carbon and energy are linked as they move through ecosystems because the same processes govern their entry, transfer, and loss.
• The energy content of organic matter is relatively constant at about 20kJ g-1 of ash-free dry mass, while the carbon concentration is variable.
• The biochemistry of photosynthesis involves light-harvesting reactions that transform light energy into a temporary form of chemical energy and carbon-fixation reactions that convert CO2 into sugars.
• Chloroplasts, organelles inside the mesophyll cells of green leaves, are responsible for both groups of reactions in the light.