carbon fixation is a
metabolic pathway-Cellular respiration:Several distinct but linked metabolic pathways are used by cells to transfer the energy released by breakdown of fuel molecules to ATP...
for
carbon fixationCarbon fixation refers to any process through which gaseous carbon dioxide is converted into a solid compound. It mostly refers to the processes found in autotrophs , usually driven by photosynthesis, whereby carbon dioxide is changed into sugars...
in
photosynthesisPhotosynthesis is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of Bacteria, but not in Archaea...
. This process converts
carbon dioxideCarbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state...
and ribulose bisphosphate (RuBP, a 5-carbon sugar) into 3-phosphoglycerate through the following reaction:
- CO2 + RuBP → 2 3-phosphoglycerate
This reaction occurs in all plants as the first step of the
Calvin cycleThe Calvin cycle or Calvin-Benson-Bassham cycle is a series of biochemical reactions that take place in the stroma of chloroplasts in photosynthetic organisms. It was discovered by Melvin Calvin, James Bassham and Andrew Benson at the University of California, Berkeley by using the radioactive...
. In
C
4 carbon fixation is one of three biochemical mechanisms, along with C
3 and CAM photosynthesis, functioning in land plants to "fix" carbon dioxide for sugar production through photosynthesis...
plants, carbon dioxide is drawn out of malate and into this reaction rather than directly from the air.
PlantPlants are living organisms belonging to the kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The scientific study of plants, known as botany, has identified about 350,000 extant species of plants, defined as seed plants,...
s that survive solely on fixation (
plants) tend to thrive in areas where
sunlightSunlight, in the broad sense, is the total spectrum of the electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the atmosphere, and the solar radiation is obvious as daylight when the Sun is above the horizon. Near the poles in summer, the days are longer and the...
intensity is moderate,
temperatureIn physics, temperature is a physical property of a system that underlies the common notions of hot and cold; something that feels hotter generally has the higher temperature. Temperature is one of the principal parameters of thermodynamics...
s are moderate,
carbon dioxideCarbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state...
concentrations are around 200 ppm or higher, and ground water is plentiful. The plants, originating during
MesozoicThe Mesozoic Era is one of three geologic eras of the Phanerozoic eon. The division of time into eras dates back to Giovanni Arduino, in the 18th century, although his original name for the era now called the "Mesozoic" was "Secondary" The Mesozoic Era is one of three geologic eras of the...
and
PaleozoicThe Paleozoic or Palaeozoic Era is the earliest of three geologic eras of the Phanerozoic eon...
era, predate the
C
4 carbon fixation is one of three biochemical mechanisms, along with C
3 and CAM photosynthesis, functioning in land plants to "fix" carbon dioxide for sugar production through photosynthesis...
plants and still represent approximately 95% of Earth's plant biomass. plants lose 97% of the water taken up through their roots to transpiration.
plants cannot grow in hot areas because
RuBisCORibulose-1,5-bisphosphate carboxylase oxygenase, most commonly known by the shorter name RuBisCO, is an enzyme that is used in the Calvin cycle to catalyze the first major step of carbon fixation, a process by which the atoms of atmospheric carbon dioxide are made available to organisms in the...
incorporates more oxygen into RuBP as temperatures increase. This leads to
photorespirationPhotorespiration is the process by which RuBP, has oxygen added to it by the main enzyme involved in photosynthesis, rubisco, instead of carbon dioxide as happens during photosynthesis. Rubisco favours carbon dioxide to oxygen, approximately 3 carboxylations occur per oxygenation...
which leads to a net loss of carbon and nitrogen from the plant and can therefore limit growth. In dry areas plants shut their stomata to reduce water loss but this stops entering the leaves and therefore reduces the concentration of in the leaves. This lowers the :O
2 ratio and therefore also increases photorespiration. and
CAMCrassulacean acid metabolism, also known as CAM photosynthesis, is an elaborate carbon fixation pathway in some plants. These plants fix carbon dioxide during the night, storing it as the four carbon acid malate. The is released during the day, where it is concentrated around the enzyme...
plants have adaptations that allow them to survive in hot and dry areas and they can therefore outcompete plants.
The
isotopic signatureAn isotopic signature is a ratio of stable or unstable isotopes of particular elements found in an investigated material...
of plants shows higher degree of
13C depletion than the plants.