Biology - Nutrition

Biology – Nutrition Nutrition is the assimilation and absorption of nutrients, which are raw materials and mineral ions containing energy for growth and tissue repair. ● ● ● ● provides energy and keep us warm provides raw materials for growth and repair maintains health and regulates metabolism obtain food from other organisms – mode of nutrition : heterotrophic nutrition Primary Food Substances (essential to life) Carbohydrates 1. Monosaccharides ● ● ● ● ● simplest form of carbohydrates small and soluble in water have reducing power (can’t be oxidised) immediate source of energy eg. glucose, fructose, galactose 2. Disaccharides ● ● ● ● ● ● ● ● ● formed by condensation—the joining of two monosaccharide molecules—in the presence of an enzyme. during condensation, one water molecule is released can be broken down into monosaccharides through hydrolysis sweet and soluble in water have reducing power except sucrose provide energy eg. glucose + fructose -> sucrose + water glucose + galactose -> lactose + water glucose + glucose -> maltose + water 3. Polysaccharides ● ● ● ● ● ● ● ● ● long chain of monosaccharides joined together eg. starch : food storage in plant glycogen : food storage in animal -> muscle and liver cellulose : structural component in plant the most complex form of carbohydrates large and insoluble in water have no reducing power food storage in plants and animals strucutral components (eg. cell wall) Test for reducing sugars using Benedict’s test 1. mix equal volumes of glucose solution and Benedict’s solution 2. put the mixture in a hot water bath for 5 minutes 3. brick red precipitate indicates the presence of reducing sugar ; blue solution indicates the absence of reducing sugar Functions of carbohydrates ● ● ● main energy source eg. glucose undergoes respiration to release energy cellulose as dietary fibre – no energy value but can prevent constipation ● storage of energy – glycogen is stored in liver and muscles , some excess carbohydrates will be converted into fats which is stored under skin or around some internal organs Fats ● ● ● insoluble in water but soluble in organic solvents semi solid form -> fats liquid form -> oils Functions of fats ● ● ● ● ● as a food reserve and stored in adipose tissues (under skin) subcutaneous fat reduces heat loss as a shock absorber for protection help transport fat-sluble vitamins A and vitamin D important in forming cell membranes Emulsion Test (Emulsification) 1. shake some of the test sample with about 4 cm3 of ethanol 2. decant the liquid into a test tube of water, leaving any undissolved substances behind 3. tiny oil droplets in water and colourless solution to cloudy white emulsion Spot Test 1. 2. 3. 4. take a filter paper drop an oil droplet onto the pater wait for 10 minutes a permanent translucent spot is left Proteins ● ● ● ● ● ● ● ● ● basic units : amino acids functional grous : amino and carboxyl two amino acids condense to form a dipeptide a peptide bond is formed to link two amino acids 12 non-essential amino acids – can be produced in the body 8 essential amino acids – must be obtained from food soluble in water denatured at high temperatures and extreme pH values excess amino acids cannot be store – converted into urea through deamination Functions of proteins ● ● ● for growth and repair – important to new body cells, important component of cell membranes and cytoplasm used to make enzymes, hormones, antibodies, haemoglobin serve as a source of energy and heat Biuret Test 1. 2. 3. 4. put 2 cm3 of sample into a clean test tube add 2 cm3 of dilute sodium hydroxide to test tube and shake well add drops of copper sulphate solution and shake the test tube after each drop is added a colour change from blue to violet indicates the presence of proteins Vitamins ● ● ● ● ● organic food substance needed in small amounts no energy value help control various metabolic reactions for maintaining good health Vitamin C ● ● ● ● for healing of wounds the synthesis and repair of connective tissues deficiency diseases : scurvy, bleeding gums present in citric fruits and green vegetables Vitamin D ● ● ● ● ● ● helps the absorption of calcium and phosphorus in small intestine fat soluble the uptake of calcium and phosphate ions from blood into the cells the formation of bones and teeth deficiency diseases : rickets in young children, bone fractures in elderlies present in milk, cheese, fish-liver oil, egg yolk, sunlight (produced by skin) Minerals ● ● ● ● ● inorganic food substances needed in small amounts no energy value important in regulating metabolism and building body tissues for maintaining good health Calcium ● ● ● ● ● for formation of bones and teeth for blood clotting for muscle contraction deficiency diseases : rickets, bleeding present in dairy products Iron ● ● ● ● to make haemoglobin menstruation deficiency disease : anaemia present in green leafy vegetables, liver, red meat Dietary Fibre ● ● ● ● ● ● known as roughage consists mainly of cellulose from the cell walls of vegetables and fruits cannot be digested in human since we have no such enzyme adds bulk to undigested food passing through the intestines, maintaining peristalsis stimulates muscular movements along the alimentary canal (peristalsis) prevents constipation and bowel cancer Water ● ● ● ● ● ● ● ● ● ● inorganic food substance no energy value prevents dehydration main composition of the body dissolve substances as a solvent a component of blood and body fluid for transporting provides a medium for chemical reaction to take place helps to regulate body temperature dilutes waste products and poisonous substances contributes to urine formation