Mechanism Concentrates Inorganic Carbon

a black and white microscopic view of three dimensional organic shapes

Biological Strategy

Diatoms

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Capture, Absorb, or Filter Chemical Entities

Living systems often require chemical elements and chemical compounds, including complex sugars, proteins, and odor-making compounds, to perform critical activities. These compounds exist in various states–solid, liquid, and gas–and are ubiquitous in soil, water, and air. This requires that living systems not only have ways to capture, absorb, or filter them, but also ways to differentiate among them, selecting those that are valuable or harmful. For example, mangrove trees live with their roots in salty water and sediments. Various mangrove species have different strategies for removing salt from the water they take in so that their tissues can use the fresh water.

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Capture, Absorb, or Filter Gases

Oxygen, carbon dioxide, and nitrogen are all gases of particular importance to living systems. Living systems obtain these gases from water and air by trapping them, absorbing them across surfaces, or filtering them. Gases are low in density and viscosity, and when dissolved in liquids, are very low in concentration–so extracting them requires specialized strategies. As a result, living systems use the properties of gases, liquids, and solids to assist in capture, absorption, and filtering. For example, fish gills have many filaments to create a large surface area to maximize how many blood vessels come in close contact with oxygen dissolved in the water.

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Plants

Phylum Plantae (“plants”): Angiosperms, gymnosperms, green algae, and more

Plants have evolved by using special structures within their cells to harness energy directly from sunlight. There are currently over 350,000 known species of plants which include angiosperms (flowering trees and plants), gymnosperms (conifers, Gingkos, and others), ferns, hornworts, liverworts, mosses, and green algae. While most get energy through the process of photosynthesis, some are partially carnivores, feeding on the bodies of insects, and others are plant parasites, feeding entirely off of other plants. Plants reproduce through fruits, seeds, spores, and even asexually. They evolved around 500 million years ago and can now be found on every continent worldwide.

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Diatoms assimilate inorganic carbon via a carbon concentration mechanism.

“Diatoms growing in their natural aquatic habitats operate inorganic C concentrating mechanisms (CCMs), which provide a steady-state CO2 concentration around Rubisco higher than that in the medium. How these CCMs work is still a matter of debate. However, it is known that both CO2 and HCO3– are taken up, and an obvious but as yet unproven possibility is that active transport of these species across the plasmalemma and/or the four-membrane plastid envelope is the basis of the CCM. In one marine diatom there is evidence of C4-like biochemistry which could act as, or be part of, a CCM. Alternative mechanisms which have not been eliminated include the production of CO2 from HCO3– at low pH maintained by a H+ pump, in a compartment close to that containing Rubisco.” (Roberts et al. 2007:79)

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