Nutrition, Diseases, Vaccines, Plants and Heredity

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Nutrients

Carbohydrates are the main source of energy and proteins build and repair the body, each giving about 4 kcal per gram; fats give about 9 kcal per gram. Vitamins and minerals protect the body, and roughage (dietary fibre) prevents constipation. Lack of protein causes kwashiorkor (swollen belly and limbs) and lack of both protein and energy causes marasmus (wasting). Iodine solution turns starch blue-black. Casimir Funk coined the word vitamine in 1912.

Vitamins and minerals

Vitamins A, D, E and K are fat-soluble and stored in the body; B-complex and C are water-soluble. Deficiencies: A (retinol) causes night blindness and xerophthalmia; B1 (thiamine) beri-beri; B2 (riboflavin) cracked lips; B3 (niacin) pellagra; B9 (folic acid) anaemia; B12 (cobalamin, which contains cobalt) pernicious anaemia; C (ascorbic acid, from amla and citrus fruits) scurvy with bleeding gums; D (calciferol), made in the skin in sunlight, rickets in children and osteomalacia in adults; and K, made by gut bacteria, poor blood clotting. Vitamin E (tocopherol) is an antioxidant. Vitamin C is destroyed by cooking. Iron deficiency causes anaemia and iodine deficiency goitre; calcium builds bones and teeth; excess fluoride causes fluorosis.

Communicable diseases

Bacterial diseases include tuberculosis (Mycobacterium tuberculosis, discovered by Robert Koch in 1882), cholera (Vibrio cholerae; treated with ORS), typhoid (Salmonella typhi; Widal test), tetanus, diphtheria, whooping cough, leprosy and plague (spread by rat fleas). Viral diseases include the common cold, influenza, measles, mumps, chickenpox, polio, rabies, hepatitis, dengue and chikungunya (both spread by the Aedes mosquito) and AIDS (HIV; ELISA test); smallpox was declared eradicated in 1980. Protozoan diseases include malaria (Plasmodium, spread by the female Anopheles; Alphonse Laveran discovered the parasite in human blood in 1880, and in 1897 Ronald Ross found it developing inside an Anopheles mosquito, the key step in proving that mosquitoes spread malaria), kala-azar (Leishmania, sandfly), amoebic dysentery (Entamoeba) and sleeping sickness (tsetse fly). Ringworm and athlete's foot are fungal; filaria is caused by a worm spread by the Culex mosquito.

Vaccines and discoverers

A vaccine contains killed or weakened germs or their parts and trains the body to make antibodies and memory cells (active immunity). Edward Jenner made the first vaccine, against smallpox, in 1796 using cowpox; the word comes from the Latin vacca, cow. Louis Pasteur made the rabies vaccine in 1885 and devised pasteurisation. Jonas Salk developed the injectable polio vaccine and Albert Sabin the oral polio drops; BCG against tuberculosis is named after Calmette and Guérin. Alexander Fleming discovered penicillin, from the mould Penicillium, in 1928. Ready-made antibodies, as in anti-venom, give passive immunity.

Photosynthesis

Green plants make food from carbon dioxide and water using sunlight absorbed by chlorophyll in chloroplasts: 6CO2 + 12H2O gives C6H12O6 + 6O2 + 6H2O. Water is split in the light reaction, so the oxygen released comes from water; carbon dioxide is turned into glucose in the dark reaction and stored as starch. Chlorophyll absorbs mainly red and blue light. Gases pass through stomata, which guard cells open and close, and the water lost through them (transpiration) pulls water up the xylem. Cuscuta (amarbel) is a parasite with no chlorophyll.

Plant hormones and movements

Auxins promote cell elongation and rooting of cuttings and cause phototropism, as a shoot bends towards light because auxin gathers on its shaded side; the synthetic auxin 2,4-D is a weedicide. Gibberellins lengthen stems and enlarge grapes; cytokinins promote cell division and delay the ageing of leaves; abscisic acid inhibits growth, closes stomata and causes dormancy; ethylene, the only gaseous plant hormone, ripens fruit. Roots grow towards gravity and water and shoots towards light. The folding of touch-me-not (Mimosa pudica) leaves is a quick movement, not growth.

Reproduction in plants

Vegetative propagation produces new plants from stems (potato tubers, ginger rhizomes, sugarcane and rose cuttings), roots (sweet potato, dahlia) and leaves (Bryophyllum); yeast reproduces by budding and ferns and fungi by spores. In a flower the stamens (male) make pollen in their anthers, and the carpel (female) has a stigma, a style and an ovary with ovules. Pollination carries pollen to the stigma by wind, water, insects or birds. Fertilisation in flowering plants is double: one male gamete fuses with the egg to form the zygote and another with the polar nuclei to form the endosperm. The ovule becomes the seed and the ovary the fruit.

Mendel, heredity and DNA

Gregor Mendel, the father of genetics, crossed garden peas for seven pairs of contrasting traits and published his work in 1866; it was rediscovered in 1900. Crossing pure tall (TT) and dwarf (tt) plants gave only tall plants in F1, as tall is dominant, and tall and dwarf plants in the ratio 3:1 in F2, with genotypes in the ratio 1:2:1; a dihybrid cross gives 9:3:3:1. His laws are dominance, segregation and independent assortment. James Watson and Francis Crick proposed the double-helix model of DNA in 1953, using X-ray work by Rosalind Franklin and Maurice Wilkins; adenine pairs with thymine and guanine with cytosine, and RNA has uracil instead of thymine. Humans have 23 pairs of chromosomes, 22 pairs of autosomes and one pair of sex chromosomes (XX in females, XY in males), so the father's sperm decides the sex of the child. Haemophilia and colour blindness are sex-linked; Down syndrome results from an extra chromosome 21.

Key facts

Energy per gram: carbohydrate and protein about 4 kcal, fat about 9 kcal; kwashiorkor = protein deficiency, marasmus = protein and energy deficiency.
Fat-soluble vitamins: A, D, E, K; water-soluble: B-complex and C. D is made in the skin in sunlight, K by gut bacteria; B12 contains cobalt.
Deficiency diseases: A night blindness; B1 beri-beri; B3 pellagra; B12 pernicious anaemia; C scurvy; D rickets (osteomalacia in adults); K poor clotting; iron anaemia; iodine goitre.
Bacterial: TB (Koch, 1882; BCG vaccine), cholera (Vibrio; ORS), typhoid (Salmonella; Widal test), tetanus, diphtheria, whooping cough, leprosy, plague.
Viral: polio, measles, mumps, chickenpox, rabies, dengue, hepatitis, influenza, AIDS (HIV; ELISA). Protozoan: malaria (parasite found by Laveran, 1880; mosquito link shown by Ronald Ross, 1897), kala-azar, amoebic dysentery, sleeping sickness.
Vaccines: Jenner - smallpox (1796); Pasteur - rabies (1885); Salk - injectable polio vaccine; Sabin - oral polio vaccine; BCG - Calmette and Guérin; Fleming - penicillin (1928).
Photosynthesis: the oxygen released comes from water; it takes place in chloroplasts; gases pass through stomata; iodine turns starch blue-black.
Plant hormones: auxin (phototropism, rooting; 2,4-D weedicide), gibberellin (stem elongation, bigger grapes), cytokinin (cell division), abscisic acid (stress, closes stomata), ethylene (ripening; the only gaseous one).
Vegetative propagation: potato (stem tuber), ginger (rhizome), sweet potato (root), Bryophyllum (leaf); after fertilisation the ovule becomes the seed and the ovary the fruit.
Mendel's peas: F2 monohybrid ratio 3:1 (genotypes 1:2:1), dihybrid 9:3:3:1; DNA double helix by Watson and Crick (1953); A pairs with T, G with C; the father's sperm decides the child's sex.

Quick revision

Fat 9 kcal/g, carbohydrate and protein 4; kwashiorkor protein deficiency; A, D, E, K fat-soluble; B1 beri-beri, C scurvy, D rickets, K clotting, B12 has cobalt; TB Koch 1882; typhoid Widal; HIV ELISA; malaria Plasmodium (Laveran 1880), female Anopheles (Ross 1897); smallpox eradicated 1980; Jenner 1796, Pasteur rabies 1885, Fleming penicillin 1928; oxygen of photosynthesis from water; ethylene ripens fruit; ovule becomes seed; Mendel 1866, 3:1 and 9:3:3:1; DNA double helix 1953; XY male.

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