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general science#1


About soaps

  • Soaps are anionic surfactants used for washing and cleaning. Surfactants are wetting agents that lower the surface tension of a liquid
  • Soaps consist of sodium or potassium salts of fatty acids.
  • They are obtained by reacting common oils or fats with a strong alkaline solution
  • The earliest recorded evidence for use of soap is from Babylon c. 2800 BC
Mode of action

  • Soap molecules have both a hydrophilic end and a hydrophobic end
  • The hydrophilic end dissolves in water, while the hydrophobic end dissolves dirt and oil molecules
  • As a result, although water and oil don’t mix, soaps allow oil to dissolve in water, allowing them to be rinsed away
  • Thus, soaps allow water to remove normally insoluble matter by emulsification

  • Detergents are surfactants other than soap
  • Detergents are commonly used as industrial soaps, due to their heavy duty grease removal capabilities
  • Soaps differs from detergents in that in the case of former, excess of fat is used to consume the alkali and the glycerine is not removed, leaving a naturally moisturising soap
  • In general detergents are substances that have cleaning properties. By definition, even water is a detergent



  • Nutrition is the supply to cells and organisms, of the materials necessary to support life
  • Many common health problems can be prevented by a healthy diet
  • A poor diet can have injurious impact on health, leading to problems such as scurvy, beriberi and kwashiorkor
  • A healthy diet can also significantly prevent and mitigate systemic diseases like cardiovascular disease, diabetes and osteoporosis
  • Eating a wide variety of fresh, unprocessed food has proven favourable compared to monotonous diets of processed food
  • Consumption of whole plant foods slows digestion, allows better absorption and a more favourable balance of nutrients

  • There are six major classes of nutrients: carbohydrates, fats, minerals, proteins, vitamins and water
  • These can be classified into
    • Macronutrients: nutrients needed in large quantities. These include carbohydrates, fats, proteins and water. Fibre is another macronutrient whose functions have not been fully understood
    • Micronutrients: nutrients needed in smaller quantities. These include minerals and vitamins. Antioxidants and phytochemicals are micronutrients as well, but their functions are not well understood
  • Most foods contain a mixture of nutrients
  • Some nutrients may be stored internally (eg. Fat soluble Vitamins) while others are required more or less continuously

  • Carbohydrates are sugars, and are classified as monosaccharides, disaccharides or polysaccharides depending on the number of monomer (sugar) units they contain
  • Carbohydrates constitute a large part of foods such as rice, noodles, bread and other grain based products
  • In general, simple saccharides are easier to digest and absorb than polysaccharides
  • Since they are absorbed more quickly, simple carbohydrates lead to elevated levels of blood glucose

  • Dietary fibre is a carbohydrate (polysaccharide) that is incompletely absorbed in humans and some animals
  • Like all carbohydrates, when metabolised it produces energy
  • However, it does not contribute much energy due to limitations on its absorbability and digestion
  • Dietary fibre consists mainly of cellulose, a polysaccharide that is indigestible in humans
  • Whole grains, fruits and vegetables are good sources of fibre
  • Fibre provides bulk to intestinal contents and stimulates peristalsis – the rhythmic muscular contractions of the intestines that moves digesta along the digestive tract
  • For these reasons, fibre is important for digestive health. It helps alleviate constipation and diarrhoea and is said to reduce colon cancer

  • Fat consists of fatty acids bonded to glycerol. Fatty acids are carboxylic acids that contain long chains of carbon and hydrogen atoms
  • They are typically found as triglycerides
  • Fats are classified as
    • Saturated fats: have all the carbon atoms in the fatty acid chains bonded to hydrogen atoms
    • Unsaturated fats: have some carbon atoms double bonded to themselves, thereby have fewer hydrogen atoms
  • Studies have shown that unsaturated fats are preferable to saturated fats in terms of health effects
  • Saturated fats are usually solids at room temperature (eg butter) while unsaturated fats are liquids at room temperature (eg olive oil)
  • Trans fats are a type of unsaturated fat with trans-isomer bonds. These are rare in nature and usually created by an industrial process called hydrogenation. Trans fats are harmful to health (coronary heart disease) and their use is to be avoided

  • Proteins are the basis of many animal body structures and form enzymes that control chemical reactions in the body
  • Proteins are composed of amino acids, which contain nitrogen atoms
  • The body requires amino acids to produce new proteins and replace damaged proteins
  • Since the body cannot store protein, amino acids must be present in the daily diet
  • Diet with adequate proteins is especially important during early development and maturation, pregnancy, lactation or injury
  • A complete protein source is one that contains all essential amino acids
  • Sources of protein include meat, tofu, soy, eggs, grains, legumes and dairy products
  • A few amino acids can be converted into glucose for energy (called gluconeogenesis). This process mainly happens only during starvation

  • Dietary minerals are the chemical components required by living organisms other than the four elements carbon, oxygen, nitrogen, hydrogen that are present in nearly all organic molecules
  • Dietary minerals include some metals as well (sodium, potassium) which are usually found in ionic state
  • Minerals are recommended to be supplied in the daily diet
  • Most famous dietary mineral is iodine (added to salt) which prevents goitre
  • Macrominerals (required more than 200 mg/day) include
    • Calcium: electrolyte, also needed for structural growth (teeth, bones)
    • Chlorine: electrolyte
    • Magnesium: required for processing ATP (energy)
    • Phosphorous: required component of bones, essential for energy processing
    • Potassium: electrolyte (heart and nerve health)
    • Sodium: common electrolyte, needed in large quantities. Most common source is common salt. Excess sodium depletes calcium and magnesium leading to high BP an osteoporosis
    • Sulphur: essential for certain amino acids and proteins
  • In addition to the macrominerals, many other minerals are required in trace amounts. These include cobalt, copper, chromium, iodine, iron, manganese, molybdenum, nickel, selenium, vanadium, zinc

  • A vitamin is an organic compound required as a nutrient in tiny amounts by an organism
  • A compound is called a vitamin when it cannot be synthesised in sufficient amounts by an organism, and must be obtained from the diet
  • Thus, the term “vitamin” is conditional both on the circumstance and the organism. For instance ascorbic acid is termed Vitamin C for some organisms but not for others, and Vitamins D and K are required in the human diet only under certain circumstances
  • Vitamins must be supplied in the diet (except Vitamin D, which can be synthesised by the skin in the presence of UV radiation)
  • Fresh fruits and vegetables are good sources of vitamins
  • Vitamin deficiencies may results in diseases like goitre, scurvy, osteoporosis, impaired immune system etc
  • Excess of some vitamins can also be dangerous: excess Vitamin A can cause jaundice, nausea, blurry vision, vomiting, muscle pain etc

  • About 70% of non-fat mass of the body is water
  • To function properly, the body requires between one and seven litres of water every day
  • It is recommended that daily water intake for an adult male be 3.7 l and for females be 2.7. However, these requirements vary with climate, activity level and other factor
  • Too little water can lead to dehydration
  • Too much water can lead to water intoxication, a potentially fatal disturbance to the brain. However, this is very rare in normal humans and usually only occurs during water drinking contests or intense bouts of exercises when electrolytes are not replenished

Nutrients Deficiency Excess
Carbohydrates Low energy Diabetes, obesity
Fats None Cardiovascular disease, obesity
Cholesterol none Cardiovascular disease
Protein Kwashiorkor
(edema, anorexia, inadequate growth)
Rabbit starvation (diarrhoea, headache, low BP, low heart rate
Discomfort/hunger that can only be satisfied by eating fats and carbohydrates
Sodium Hyponatremia
(electrolyte imbalance)
Hypernatremia, hypertension
Iron Anaemia Cirrhosis (chronic liver disease), heart disease
Iodine Goitre, hypothyroidism Iodine toxicity
Vitamin A Night blindness, xeropthalmia (dry eyes) Hypervitaminosis A (birth defects, liver problems, osteoporosis)
Vitamin B1 Beri-beri
Vitamin B2 Cracking of skin
Vitamin B12 Pernicious anaemia
Niacin (Vitamin B3) Pellagra (diarrhoea, dermatitis, dementia, death) Dyspepsia (indigestion), cardiac arrhythmias
Vitamin C Scurvy Diarrhoea
Vitamin D Rickets Hypervitaminosis D (dehydration, vomiting, constipation)
Vitamin E Nervous disorders Hypervitaminosis E (anticoagulant)
Vitamin K Haemorrhage
Calcium Osteoporosis Fatigue, vomiting, depression, cardiac arrhythmias
Magnesium Hypertension Weakness, nausea, vomiting
Potassium Hypokalaemia, cardiac arrhythmias Hyperkalaemia, palpitations


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