To portray this concept, imagine a pet store with a cage of baby mice. As the air randomly enters the stomata, proportionally less heavy 13C enters a plant than the lighter and faster 12C (meaning that the isotopes fractionate according to their relative masses). When plants photosynthesize carbon dioxide, they first capture air inside small openings in the leaves, called stomata, by a process called diffusion (diffusion is the random movement of particles from an area of higher concentration to an area with a lower concentration of that particular particle). There are two main reasons the first process is that 13C is heavier and moves less quickly. The terrestrial biosphere has a very different ratio of 13C to 12C than the atmosphere. Do these sinks take in a lot of 13C or very little relative to the amount of 12C they take up from the atmosphere? The ratio in the atmosphere is also affected by the isotopic fingerprint of carbon dioxide sinks. Some sources of carbon dioxide are “heavy” while others are “light”. This ratio is affected by the isotopic fingerprint of the source of new carbon dioxide to the atmosphere. The atmosphere has a certain ratio of 13C to 12C.
Let's look at the four main carbon pools with which climate scientists are concerned: the atmosphere, the terrestrial biosphere (land plants, animals, and soils), fossil fuels, and the ocean. Pools with relatively more 13C (less 12C) are called “heavy” and those with less 13C are called “light”. The differences are small - one carbon pool may have 98.8% 12C while another may have 99.2% 12C - but modern machines, called isotope ratio mass spectrometers, can detect these differences quite easily. Even so, different carbon pools have different ratios of 13C and 12C – called isotopic fingerprints. Recall that there is much, much more 12C than 13C in the world –almost 99% of all carbon atoms are 12C. So Why are There Differences in Ratios of 13C and 12C? Because they are stable isotopes, a 13C atom will always remain a 13C atom, and the same is true for 12C. Unlike 14C, the amount of 13C or 12C in an artifact does not change over time since both 13C and 12C are stable isotopes. discuss some of the science concepts that underlie the carbon cycle.The Basics: Stable Carbon and the Carbon Cycle A Little Background….use inference skills to answer some of the quiz questions.use reading literacy skills to locate information and answer the quiz questions.use scientific literacy skills to read and interpret features of the carbon cycle diagram.The quiz combines scientific literacy with reading literacy and provides students with an opportunity to practise the science capability ‘Interpreting representations’.Īlternatively, the quiz can be used as an introductory tool to gauge students’ prior knowledge or as a summative assessment.īy the end of this activity, students should be able to: In this activity, students use the interactive carbon cycle diagram to explore the global carbon cycle and to answer questions in an online or paper-based quiz. The carbon cycle is a visualisation of the processes that move and store carbon between living and non-living things. Carbon moves through the Earth’s system in many different ways.
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