September
Photosynthesis
green machine
The most amazing thing happens on our planet each day. Sunlight, water and air are converted into energy. It’s an amazingly simple and simultaneously complex life-supporting event. Without it, life on earth could not exist. The simple side is: water, plus carbon dioxide – in the presence of sunlight – creates sugar and oxygen. While sunlight is not a directly usable form of energy, sugar – a form of chemical energy – is. And that’s where the simplicity ends. The complex set of systems, reactions, and processes that aid photosynthesis begins with the absorption of water and carbon dioxide. Plants have specialized cells and cellular structures for these jobs, including xylem, which moves water from the roots to the leaves, and stomata, which act as the gas-gateway to and from the leaf. Xylem uses transpirational pull to move water from the ground up: Transpiration occurs when plants “breath” out water molecules at their leaf surface. Transpiration pull occurs when water’s strong surface tension essentially pulls the water within the plant up as water evaporates at the leaf surface. Meanwhile, plant stomata are microscopic pores on the leaf surface that, thanks to guard cells, regulate when the pore is open or closed, allowing atmospheric CO2 to enter the leaf and H2O to leave. The process by which these guard cells function is in itself an amazing feat that includes osmotic pressure, potassium ions, ion channels and pumps, and turgor pressure. (Phew! More can be found on both these topics on Shmoop.) Now that water and carbon dioxide are in the leaf, let’s move on to chlorophyll.
Chlorophyll is the green pigment found in plants that is critical to the photosynthetic process. While the light from the sun is composed of a range of wavelengths – each with different energy levels and colors, – chlorophyll is best at absorbing red and blue light wavelengths while reflecting green. That reflected light/color is what our eyes perceive and is why we see leaves as green. Photosynthesis takes place in two steps, one that is light dependent and one that is not (although it does occur in the light). In the light-dependent reaction, light energy, in the form of photons, excites the chlorophyll pigment molecule, which uses this energy to create two products: ATP, the biological currency of energy, and O2, which is stripped from (or oxidized from) the H2O. Next, in the light-independent reaction, also known as the Calvin cycle, the energy from the ATP is used to convert atmospheric CO2 into a carbon molecule that can now be used to make glucose or other carbohydrates. As complex as this seems, it is an enormous simplification of the vastly complex chemical and cellular reactions taking place. For a more indepth look, check out this KhanAcademy Lecture or this straightforward write up from Chemistry Explained. Or consider the process not biologically, but vis-a-vis quantum mechanics, as described in this NOVA article on what author and MIT Professor, Seth Lloyd, calls “quantum biology.”
And now that we have glucose, a usable energy form, and oxygen, life on earth can continue to exist. That hasn’t stopped one group of scientists, however, from exploring the idea of “upgrading” or “hacking” photosynthesis. Check out this article from Gizmodo on how they plan to use this upgrade to feed the growing world population.
Did you know…
There’s a lot of trees out there! I just heard this fascinating article on NPR about scientists who, using satellite data and on-the-ground surveys of over 400,000 forests, estimate the world tree population at over three trillion. Take a listen to the full article on npr.org.
If you’re up for a little math, you might figure out how much carbon dioxide three trillion trees can take out of the active carbon cycle. This is called carbon sequestration. Trees can function as a storage space for atmospheric carbon dioxide and in fact, forests in the US have been calculated (by the US Forest Service) to sequester 10-20% of the country’s carbon emissions each year. Carbon sequestration rates differ by species and age of each tree but a rough estimate can be made by calculating the biomass (living material) of each tree and multiplying by 0.5 – this will give you an answer in kilograms of carbon. Use a tape measure and this species specific calculator to figure out the biomass of your favorite tree. Tweet us @WI_NatureNet if you complete the math – we’d love to know how much your tree (or three trillion trees) is helping the health of our planet.
To Do This Month:
Get hands-on with some green plants at Community GroundWorks’ Herb Garden Nights on Wednesday evenings or at their September 19th Garden Work Day.
The UW Arboretum also offers person-to-plant opportunities at each Saturday morning Ecological Work Party, or at the Arboretum’s Annual Native Gardening Conference on September 20th.
There’s also the Aldo Leopold Nature Center’s adult workshop for chainsaw safety or toddler programs focused on plants and animals on Tuesdays, Wednesdays, and Fridays.
Our Favorite Photosynthesis Books
September Events
Lussier Family Heritage Center
How Plants Breathe
For Educators:
Plants in the Classroom
Even without a garden bed, growing plants as a study specimen is easy to fit into classroom time with the Wisconsin Fast Plants Program. Fast Plants, developed by UW-Madison Professor Paul Williams, are a special genetic stock of brassica plants that grow, flower, and go to seed within 30 days. Brassica is a genus of plants in the mustard family, better known as cruciferous. Cruciferous vegetables your students might recognize include cabbage, broccoli, and cauliflower. The advantage of using Fast Plants in the classroom is not only the shortened growth period, but the lack required special equipment. A simple lighting system, a potting container, and the right soil and fertilizer are all you need. The Fast Plants website provides instructions for building your own potting containers from easy-to-find up-cycled materials (like water bottles and deli containers) and a step-by-step guide to getting started. Activities and resources are pre-sorted by grade level and “Reading Green” provides a detailed 2-week elementary level lesson plan with stories and activities geared toward both literacy and science learning. Fast Plants also foster science inquiry and critical thinking with AP Biology connections or, you may tie your plant-growing activities to other topics like the Brassica butterflies and Fast Plants in outer space. Check out the website for more info or to get started.
For other plant-related educator resources, check out this UK-based Science & Plants for Schools, including a photosynthesis “survival guide for teachers.” And there’s always Ms. Frizzle, who has fun facts and games as the Magic School Bus tackles the topic of photosynthesis.
For Families:
Chromatography Experiment
As we prepare for fall and the colored foliage, your children may wonder “what makes the leaves turn color?” The truth is, they don’t turn from green to orange, but the green fades and the yellow and orange pigments that were there all along are allowed to shine through. As the length of daylight abates, the photosynthetic process slows and the chlorophyll breaks down. Now the orange carotene and yellow xanthophyll pigments can be seen. These pigments don’t play a starring role in photosynthesis, but they do aid in the process by absorbing and using shorter light wavelengths (like ultraviolet) and by dissipating destructive, high-energy forms of oxygen that form in the process.
Chromatography is the separation of plant pigments. This little lab experiment will allow you and your budding botanist to see the differing pigments hidden in a green leaf. I remember this experiment from my days as young scientists – and it never gets old. Start by cutting or shredding several fresh, green leaves. Place them in a jar and completely cover with rubbing alcohol. Grind up the leaf shreddings, cover the jar, and let rest for up to 24 hours. Now cut strips of coffee filter paper and place just the tip of the paper in the solution and tape the other end to the top of your jar. The pigments will soak into the paper at differing rates, revealing the true existing colors. Try the experiment with different leaves or fruits and see what you get. We’d love to see your results so, send us your pictures on Facebook. Find more detailed instructions and step-by-step photos on Plants For Kids.
There’s a bit more info on fall foliage change on this site from the State University of New York, including what causes red coloration and how the weather can effect fall color. Be sure to check out Travel Wisconsin’s Fall Color Report to find out when and where to catch the best views, or try one of these suggested scenic drives to take in the dazzling landscape.