BSA's Classroom "Plant
Imagine a world where the plants of
the planet are harnessed to help its inhabitants find sustainable
solutions for some of their most pressing needs – clothing,
food, housing, jobs, clean air …
clean water. Welcome to planet earth!
Plants are the air-purifiers for planet earth. They clean it, and in doing so produce
the oxygen we, and all animals need to survive. This happens through one of the most amazing chemical reactions you can imagine, photosynthesis. More on this a bit further down, but as a lead in to the story we'll ask a question whose answer may astound you... Imagine the largest tree you've ever seen (even in a picture) - where does the matter come from that forms the mass of wood, branches and leaves?
The earth itself is a "closed
system" in that it produces everything it needs to ensure the survival
and development of its inhabitants. Within the system there is a delicate balance
that must be maintained. In the page below we will explore one relationship within that balance, the air-purifying
plants, man and Carbon Dioxide (CO2).
We'll do so looking at things most of us use everyday as examples of mans part in this relationship (as a producer of CO2).
At present there is much debate about people's impact on the planet. This debate is most
pronounced in the discussions around global warming and our responsibility for
the continued increase in CO2 and other "greenhouse gases"
released into, and consolidating in, the earth's atmosphere. Tying in directly
to this problem are topics such as deforestation and the 1994 Kyoto protocols.
When you look around, it's a bit hard to comprehend we are really
the newcomers on the planet. We've built so much and seem to be expanding everywhere.
With our building and expansion, we use ever more fossil fuel to run our homes, our
cars and the planes we fly in. Burning these fuels creates CO2 as one byproduct of the process. Even the batteries that run our cell phones, Ipods
and other gadgets use electricity for charging, which in most instances creates more CO2.
As it turns out, CO2 is also a very important gas in the life processes. Plants use CO2 in the chemical process
mentioned above, photosynthesis.
Photosynthesis is an extremely complex process.
In its simplest form, this important reaction convert CO2
[carbon dioxide] and H2O
[water] plus energy [sunlight] into
[glucose]. The oxygen goes into the air you breathe.
6CO2 + 6H2O
(+ light energy) -->-->-->-->
six molecules of carbon dioxide plus six molecules of water produce one molecule of glucose plus six molecules of oxygen
Taking the chemistry a bit further, we note that water supplies
the oxygen atoms (indicated below as O.)
required for the formation of molecular oxygen. We now write the
equation as: 6CO2
+ 12H2O. (+
light energy) -->-->-->-->
And a wee bit further, photosynthesis produces carbohydrates
other than glucose - cellulose and starch. They can be represented
A better representation of our equation becomes 6nCO2
+ 12nH2O. (+
light energy) -->-->-->--> (C6H12O6)n
+ 6nO2. +
Why is this important you ask? Cellulose (C6H10O5)n
is a long-chain polymeric polysaccharide carbohydrate, of beta-glucose.
What in the world is that you say... This forms the primary structural
component of green plants. The green plants primary cell wall
is made largely of cellulose and the secondary wall contains cellulose
with variable amounts of lignin. Lignin and cellulose, considered
together, are termed lignocellulose, which, in the form of wood,
is the most common biopolymer on Earth. Now, once again, where
does the matter come from that forms the mass of wood, branches
Trees store carbon, sequestered from the air, as the wood and plant material that makes up their mass.
OK, so plants (most) use carbon in as a part of their life processes... Knowing this, how much CO2 is sequestered by an average tree? Well, it very much
depends on type of tree. For our example we'll use a mature pine tree (Pinus
radiata). An acre of pine trees (~120 trees) has the potential
to sequester roughly 5 tons of CO2 per year.
Let's look at part of your "carbon imprint",
your home, and make an estimate for the CO2 it might
be producing each year. To do this estimate we'll make a few assumptions.
Let's say your house is about 2,000 square feet, you have a heater,
an air conditioner and a water heater. Check the boxes below for
the items that fit your family situation.
Think about this problem for a moment. This problem is one small component
in a much larger issue. Trees have a limited life span and also
create CO2 when the die and decay or are burned in
a fire. And where do the aquatic plants fit in? Did you know the
ocean plants are estimated to take in as much or more CO2
each year than the land plants? It is thought that CO2
sequestered in plants on the oceans surface that die and descend
to oceans depths may be released back into the atmosphere over
a much longer timeframe than that stored in trees. Have you ever
consider this as a reason for keeping the oceans clean and ensuring
a thriving environment for plants? How important is this?
Interesting "Plant Talking Point"
isn't it. How far can you stretch the point? We'd love to hear
your thoughts on the subject and share them with others. If you'd
like, please send your class discussion to: PlantingScience@botany.org.
Remember, solutions are all around us. Talking
about and considering options helps us develop and build on new
ideas. No matter how hard it seems, think long term. What kind
of world do you want for your grandchildren’s children?
Thanks for stopping by!!
The information contained in this "Plant
Talking Point" was supplied by Bill Dahl of
the BSA Staff Team.