BSA's Classroom Plant Talking Point
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!
How important are plants?
Of course you recognized that sound! It’s popcorn popping, and people
in the United States consume nearly 17 billion quarts of popcorn each year.
But did you ever wonder why kernels of popcorn explode when heated? It’s
because of endosperm, a special tissue that you only find inside the seeds of
flowering plants. But most seeds still do not pop. Popcorn is different because
a core of soft, wet endosperm is surrounded by a layer of hard, stony endosperm.
When heated the water in the soft endosperm turns into steam, which expands.
When the pressure gets high enough, the kernel explodes, turning itself inside
out. The hard endosperm expands in volume turning the hard, inedible kernel
into a fluffy, white, edible nugget.
In Central America popping has been a familiar sound since before the dawn
of agriculture some 9,000 years ago. Teosinte, a wild ancestor of maize, was
considered inedible, and so people questioned how it could ever have been domesticated.
The kernels were just too hard to eat. But George Beadle, a famous botanist
who became Chancellor and President of the University of Chicago, rediscovered
that teosinte could pop. Ancestors of the native people of Central America were
sitting around campfires eating popped teosinte even before maize was domesticated.
And, of course, this means popcorn has been around for millenia before movies.
Have you ever heard of endosperm before? Endo-
means within, and sperm means seed, so endosperm means “within the seed”.
Endosperm results from a second fertilization event. The first fertilization
event results in an embryo, a baby plant. Endosperm functions as a nutritive
tissue for the growing embryo, and in some seeds, like beans and peanuts, the
growing embryo absorbs all the endosperm so at maturity no endosperm is evident.
In cereal grains the embryo sits beside the endosperm and absorbs it when the
embryo begins growing.
Endosperm may sound pretty esoteric, and you may wonder why you should know
about it. Endosperm is the most important plant product on Earth for humans.
Two thirds of all human calories come from endosperm. In one form or another
cereal grains, the one-seeded fruits of grasses, which include rice, wheat,
maize, rye, oats, and barley, constitute the majority of human food. Cereal
grains and their endosperm form the foundation of agriculture and human civilizations.
Without endosperm humans would starve, and yet something as important as endosperm
remains little known or appreciated.
Flour is finely ground endosperm. Coconut is shredded endosperm. White rice
and brazil nuts are solid endosperm. What makes endosperm so nutritious is starch,
the primary food storage molecule of flowering plants. Have
you had your endosperm today?
The next time you go to the movies, perhaps you will have a newfound appreciation
for popcorn and its exploding endosperm. Hold the butter, please!
Thanks for stopping by!!
The information contained in this "Plant
Talking Point" was supplied by Joseph E. Armstrong
of the BSA Economic Botany Section and is BSA