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  • By comparing some features of fossilised plants with the same features of plants living today, scientists hope to be able to learn more about the effect of changing carbon dioxide (CO2) levels in our atmosphere and to understand what effect climate change might have on life on Earth in the long term.

    This project involves citizens categorising two types of cell on images taken by electron microscopes of the underside of gingko tree leaves.

    Rights: Zooniverse

    Zooniverse logo

    Zooniverse is a platform for citizen science projects that bring together researchers and volunteers to assist with data analysis and image identification.


    Reach: Worldwide

    Nature of science focus: Online citizen science (OCS) projects can be used to develop any of the Nature of Science (NoS) substrands. Identify aspects of NoS that your students need to get better at or understand more fully and then frame your unit to be very clear about these things when you do them.

    Science capability focus: Gather and interpret data, Interpret representations

    Science focus: climate change, fossils, plant cell structure, atmosphere

    Some suggested science concepts:

    • Fossils are the preserved remains of living organisms or of traces of their activities.
    • Fossils provide a record of previous life and living conditions on Earth.
    • Some features of plants can only be observed with microscopes.
    • The living and non-living things that make up planet Earth are closely interlinked and delicately balanced. Changes to one thing can result in changes to others.
    • Some cells have specialised jobs to do (Living World level 5).

    Many concepts could be learned – focusing on a few can often be more powerful. Develop your learning outcomes and success criteria from these concepts as well as the Nature of Science strand and the science capabilities.

    Some examples of learning outcomes:

    Students can:

    • describe how fossils are formed
    • explain how fossils provide a record of previous life and living conditions on Earth
    • explain the purpose of stomata
    • compare and contrast the stomatal index at varying CO2 levels
    • comment on the meaning of CO2 variation in our atmosphere for our world
    • critique aspects of the method used in the Fossil Atmospheres project.

    About stomata

    Stomata are microscopic pores found on the surfaces of plant leaves and some plant stems. The pores are surrounded by specialised cells called guard cells. When the guard cells are swollen (contain a lot of water), they enlarge into a bean shape and the pore opens. When the guard cells are flaccid (contain less water), their more oval shape means that the pores are closed.

    Rights: Stephen Hill, 123RF Ltd

    Stoma open and closed

    A diagram showing the parts of the plant guard cell and stoma. Stomata open to receive carbon dioxide for photosynthesis and to release oxygen. The stomata close to reduce water loss through evaporation.

    Stomatal pores are important for plants because they enable CO2 to enter the plant. CO2 is used for photosynthesis. This means that stomata open during the day when there is sunlight (which is also needed for photosynthesis). The downside to open stomata is water loss: water vapour exits through the open pores. To reduce the amount of evaporation from the plant, there needs to be a balance between keeping the stomata open for CO2 to get in and reducing the amount of water vapour being lost. Excess oxygen produced during photosynthesis also exits the plant through the stomata.

    When there is more CO2 in the atmosphere, plants tend to have fewer stomata. They are able to easily get the CO2 they need and conserve water. Paleoclimatologists are interested in changes to the number of stomata in fossilised plants because they are very sensitive indicators of past CO2 levels. Increased levels of atmospheric CO2 are currently contributing to climate change.

    This project would offer a useful application for knowing about cell structure at level 5 and above or as a link to the effect of changing CO2 levels in relation to climate change.

    About Fossil Atmospheres

    In Fossil Atmospheres, citizen scientists classify the cells in images as either a stomata or a normal cell. What scientists are looking for is the ratio between stomata and normal cells – called the stomatal index – to give clues about the atmosphere at the time the plant was growing.

    Rights: Richard S. Barclay

    Gingko stomata

    These two microscopic images show a fossilised gingko with stomata on the left and the stomata of a living gingko on the right.

    Images are taken using an electron microscope and are either of fossilised gingko leaves or current gingko leaves.

    Gingko trees have survived three mass extinctions, including the one that eventually caused the dinosaurs’ demise. Although there have been many different species of ginkgo, they all belong to one genus and the leaves are recognisably similar in all the different species. This makes them an ideal plant to study because they can provide a record from 300 million years ago through to the present.

    Rights: Thin Ice/University of Waikato

    Fossil plants as paleoclimate proxies

    Professors Jane Francis and Matt Huber explain how fossilised plants are one of several proxies used to form a picture of past climates and ecosystems.

    The categorising of cells is very easy. Although it is not possible to view the ratios of the images you analyse, you can view some results achieved to date.

    Extensive explanation is provided to support both teachers and students. Alongside citizen scientists contributing to the analysis of images, there is a live experiment taking place in which gingko trees are being grown in chambers with a different controlled amount of CO2 in each one.

    The sensitivity of climate to CO2 has enormous economic and societal implications because of the effect climate change will have on sea level, food production, storm strength, water availability, and many other factors. By improving our ability to quantify the effects of CO2 on climate, you will be contributing to the basic science underlying projections of future environmental change.

    Fossil Atmospheres
    Rights: Richard S. Barclay

    Experimental gingko trees at the Smithsonian

    In an experiment, gingko trees are being grown in their natural environment in specific concentrations of CO2. This will allow scientists to measure how stomatal index varies with environmental conditions.

    Nature of science

    The actual classification of the images in this project is relatively simple. The real opportunities for development lie in discussions about how scientists work and why they might need assistance from citizen scientists. There is also considerable scope for developing students’ abilities to understand the meaning of the stomatal index and relate that to possible meanings for our world again with regard to climate change.

    Related content

    The article Clues to the past discusses how microfossils and stomata help climate scientists build up a picture of what the world once looked like when atmospheric CO2 levels were higher. It includes the video Fossil plants as paleoclimate proxies.

    The video Evaporation and transpiration provides insight into how plants use stomata to control the transpiration process.

    New research into the DNA from moa bones is not only unlocking the secrets of their survival during the last ice age but it is also providing lessons for species currently threatened by climate change.

    Here are some planning tips for when you intend to use a citizen science project with your students.

    The Ministry of Education’s Connected series includes Global action with teacher support material.

    Useful links

    The Ministry of Education’s Building Science Concepts series includes:

    Learn more about stomata and the balancing act to meet the demands of plant transpiration and gas exchange in The costs of transpiration.

    The following articles highlight ongoing research regarding the link between rising CO2 levels and plant stomata numbers:

    Stomatal density is just one of the clues that experts use to build up a picture of past CO2 levels. This article from Skeptical Science compares the precision of stomatal density (an indirect measurement) with air bubbles in ice cores (a direct measurement).


    This project outline was written as part of Victoria University of Wellington’s Citizen Scientists in the Classroom project funded by the Ministry of Education’s Teaching & Learning Research Initiative.

      Published 8 April 2019 Referencing Hub articles
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