This unit is designed to be part of the Ecology course which is taught by High School in the Community at the West Rock Nature Center for four hours a day during the last quarter of the school year, The present ecology course involves both theoretical and practical studies relating to the earth and how it works. We will trace calcium in the biosphere from its location in igneous rocks in the early history of the earth to its location in the skeletons of high school students at the Nature Center. In the process of studying the transport and deposition of calcium we have a vehicle which touches on many of the important concepts we are teaching and relates to some of the hands-on activities the students are involved in.
Some of the connections between the calcium cycle and the Ecology course are:
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Geology: Many of the students have no idea of the age and history of the earth and the great changes which it has gone through. How the calcium stored in the rocks in northwestern Connecticut came to be there touches on much of this chemistry: Most of the students have had very little exposure to chemistry, yet it is important in the study of ecology. Using the study of calcium, some simple chemical principles can be introduced such as the fact that calcium is intimately associated with carbon dioxide (CO2), as the solid calcium carbonate (CaCO3), and therefore is involved with life and life forms.
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Cycles: The concept that all materials on earth come from somewhere and must go somewhere is central to ecology. Calcium has its own biogeochemical cycle which is not treated in the materials we currently use.
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Agriculture: Growing a garden and raising animals, including chickens, are important practical activities in this course. Calcium relates to soil fertility and to the ability of chickens to produce eggshells. Also, since humans can’t move a muscle without the presence of calcium in the muscle, it relates to the students’ ability to do agricultural work.
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Nutrition: Calcium is an essential element in human nutrition. As such it relates to the selection of which foods to produce. (.Nutritionists often call calcium a mineral; while a geologist or mineralogist will insist this is not correct. See the chemistry section below.)
“Drink your milk and go play in the sunshine,” generations of mothers have told their children. In doing this they have shown an understanding of:
The importance of calcium in the diet of growing children,
The importance of milk as a source of calcium,
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and
The importance for proper calcium nutrition of vitamin D, developed on the skin in the presence of sunlight, and exercise.
Science News3
reported early in 1985 three studies which relates calcium to diseases of older people, osteoporosis, atherosclerosis, and colorectal cancer.
One
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study showed that milk may be better than calcium supplements at slowing or curbing bone loss or osteoporosis in postmenopausal women because milk doesn’t suppress bone renewal the way the calcium supplements, which are calcium carbonate, do.
Another study,
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done with goats, showed that the calcium in milk, in the absence of excess vitamin D, may impart some protection against atherosclerosis (hardening of the arteries) and clogging of blood vessels with plaque. The third study
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showed that a group of men who had higher intake of calcium rich foods and vitamin D had lower rates of colorectal cancer than those who ingested less calcium and vitamin D.
From birth to death calcium is an essential element for human beings. Besides its presence in bones and teeth, the mineralized tissues which contain 99% of the body’s calcium, it is present in ionized form in the blood, extracellular fluids and within the cells of soft tissues such as muscles. It is necessary for the release of energy in muscular contraction, for nerve transmission and the regulation of heart beat, must be present for blood to clot, and influences the transport function of cell membranes. The proper balance of calcium with sodium, potassium and magnesium ions maintains muscle tone and controls irritability.
Shortages of calcium in the diet can lead to stunting of growth or abnormal development of bones such as rickets in the young.
