Answer:
BIOLOGICAL IMPORTANCE OF SODIUM AND POTASSIUM
Both sodium and potassium
ions are essential constituents of biological fluids. It is observed that a
human being weighing about 70 kg contains about 90 g of Na and 170 g of K
respectively. Though \[N{{a}^{+}}\]and \[{{K}^{+}}\]ions are quite similar chemically
but they differ greatly in their biological activities. Their distribution in biological
systems is also different. The \[{{K}^{+}}\]ions are present in higher
concentrations inside the cells while \[N{{a}^{+}}\]ions are present in higher concentrations
outside the cells. \[N{{a}^{+}}\]ions are primarily found in blood plasma and
interstitial fluid which surrounds the cells. These ions participate in the
transmission of nerve signals, in regulating the flow of water across cell membranes
and in the transport of sugars and amino acids into cells. Potassium ions,
which are abundant within cell fluids, activate many enzymes which are
responsible for oxidation of glucose to produce ATP.
There is considerable
variation in the concentration of \[N{{a}^{+}}\]and \[{{K}^{+}}\]ions found on
the opposite sides of cell membranes. The cation gradients control the
development and the functioning of the nerve cells. These ionic gradients
called the sodium-potassium pump operate across the cell membranes. The energy
for this operation is provided by hydrolysis of energy rich molecules ATP.
Thus, both
sodium and potassium ions are essential ions for living organisms. The daily requirement
of sodium and potassium is about 2 g each.
BIOLOGICAL
IMPORTANCE OF MAGNESIUM AND CALCIUM
An adult
body contains about 25 g of magnesium and 1200 g of calcium. \[M{{g}^{2+}}\]ions
are concentrated in animal cells and \[C{{a}^{2+}}\]ions are concentrated in
body fluids outside the cells in the same way as \[{{K}^{+}}\] ions concentrate
inside the cells and \[N{{a}^{+}}\] ions outside the cells.
Magnesium serves a
variety of functions in metabolic processes and nerve action. All enzymes that utilize
ATP in phosphate transfer require magnesium as the cofactor. The recommended
daily intake of magnesium for adults is 350 mg. In plant life, magnesium plays
a critical role in photosynthesis, the process by which plants convert carbon
dioxide and water into sugars. The magnesium is present in the green pigment.
Chlorophyll, which is necessary for capture of energy from sunlight. Solar
energy is the energy source for the reactions of photosynthesis. Calcium is
essential to all living matter. About 99% of it is in the bones and teeth,
principally as the mineral hydroxyapatite,\[C{{a}_{5}}{{(P{{O}_{4}})}_{3}}OH\].
The other 1% is involved in several processes: clotting of blood, maintenance
of a regular heartbeat, proper functioning of nerves and muscles and various aspects
of metabolism. The calcium concentration in plasma is regulated at about\[100mg\,{{L}^{-1}}\].
It is maintained by two hormones: Calcitonin and parathyroid hormone. It is
important to know that bone is not an inert and unchanging substance but is continuously
being solubilised and re deposited to the extent of 400 mg per day in man. All
this calcium passes through the plasma.
Children require an adequate daily intake of calcium for the
proper development of bones and teeth. Adults especially older women require calcium
to prevent osteoporosis, a condition in which the bones become porous, brittle
and are easily broken. The recommended daily intake of calcium for adults is
1200 mg.
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