Cereal Grains
--The biggest source of food is cereal grain crops, primarily wheat, rice, and maize (corn)
--Cereal grains are members of the grass family. They are monocots, with one cotyledon and parallel
leaf veins. They are wind-pollinated, and have small flowers with inconspicuous petals. Fruit is the grain:
single seed, dry and indehiscent. Embryo
called “germ”, outer coat called “bran”, starchy endosperm (most of what we eat)
--white flour and white rice are endosperm only: bran and germ removed. They store longer
(don’t go rancid), but aren’t as nutritious.
--some grasses have C4 photosynthesis, which means they take carbon dioxide in at night, then
convert it to sugar during the day. Advantage: don’t have to keep stomata open in hot daytime.
--Wheat was domesticated in western Asia, the Near East, about 10,000 years ago.
--Wheat domestication: start with diploid einkorn wheat. First domestication step: non-shattering head.
Hybridizes with a grass to form tetraploid emmer wheat. A chaffless tetraploid variety, durum wheta, is
still used for pasta flour today. Final step: another hybridization leads to hexaploid bread wheat.
--recent breeding for disease resistnace, dwarfism, and good fertilizer usage.
--became a good US crop when Russians from the Ukraine brough over varieties suited to the
Great Plains.
--winter wheat needs cold to germinate; spring wheat needs lengthening days.
--farming:
--plowing loosens the soil.
--Cultivating breaks up soil and removes weeds.
--Planting used to be down by broadcasting the seed, but now it si done with a seed drill that
opens a hole and drops a seed in at measured intervals. Invented by Jethro Tull.
--harvesting used to be done with a sickle. An improvement is the scythe, which uses full body
movement. Mechanical reapers cut the grain and bundle it.
--threshing is removing the grains from the stalks. Used to be done with by beating it with flails,
or allowing horses to trample it. Winnowing it removing the grain from the chaff: used to be done by
throwing the threshed grain up in the air: the grain falls down and the chaff blows away.
--Nowadays, harvesting, threshing, and winnowing are done with a combine.
--bread is an easily digested and stored form of grain. it is made by baking ground grain (flour) mixed
with salt and water.
--To make bread rise, yeast (leaven) is added. As it grows, it releases carbon dioxide, which is
trapped by gluten proteins, which are elastic. Only wheat and rye have enough gluten to make bread
rise.
--Maize is what we call corn. In other countries, corn can mean some other crop. Maize domesticated
in the New World. It is a C4 tropical grass with male and female flowers on different parts of the plant.
Domesticated from teosinte, which has only a few small seeds encased in hard shells.
--hybrid corn has greatly imporved the maize yield since 1900. It is made by first inbreeding
maize fro several generations: this eliminates many bad mutations. Then two inbred lines are cross,
producing a hybrid, which shows “hybrid vigor”: it is much larger and healthier than its parents.
--most corn in the US is dent corn, with a mixture of hard and soft endosperm. Popcorn has
hard outer endosperm surrounding soft inner endosperm, which bursts when th water inside boils.
Sweet corn has mutations that prevent sugar frpm being converted into starch.
--most corn in the US goes into animal feed, with ethanol being another major use. Only a small
portion is directly eaten by humans.
--Rice is probably the most important source of human nutrition. Nearly all of it is grown for human
consumption. Domesticated in China and in India. Also, another species domesticated in Africa. Has
hollow stems that allow it to be grown in water (which kills the weeds). An aquatic fern grow along with
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