chapter 3 - nutrients

Question 1

what are nutrients and what do they do?

Answer 1

they are chemical substances in food that release energy and raw materials to make new protoplasm.

Question 2

which chemical elements makes up carbohydrates?

Answer 2

carbon, hydrogen and oxygen, with hydrogen and oxygen in a ratio of 2:1

Question 3

which chemical elements make up fats?

Answer 3

• carbon, hydrogen and oxygen, where there is much less oxygen than hydrogen

Question 4

which chemical elements make up proteins?

Answer 4

carbon, hydrogen, oxygen, nitrogen and sulfur

Question 5

name the different carbohydrates and list some examples

Answer 5

monosaccharides : glucose, fructose and galactose

disaccharides : maltose, sucrose and lactose

polysaccharides : starch, glycogen and cellulose (made up of glucose)

Question 6

what are the functions of the polysaccaharides

Answer 6

• starch : storage form of carbohydrates in plants, found in storage organs
• cellulose : forms cell wall to protect cell wall and serves as dietary fibres to prevent constipation
• glycogen : storage form of carbohydrates in mammals in liver and muscles, digested to form glucose when needed

Question 7

condensation

Answer 7

chemical reaction which two smaller, simple molecules are joined together to form a larger, complex molecule with the removal of one molecule of water

Question 8

hydrolysis

Answer 8

chemical reaction in which a water molecule is needed to break down one larger, complex molecule into two smaller, simple molecules

Question 9

functions of carbohydrates

Answer 9

• broken down in respiration to release energy for cell activities
• form supporting structures eg. cell wall
• converted into organic compounds eg. amino acids and fats
• form part of nucleic acids eg. DNA
• synthesis of lubricants and nectar

Question 10

what are fats made up of?

Answer 10

1 glycerol molecule and 3 fatty acid chains

Question 11

differences between saturated and unsaturated fats

Answer 11

• the fatty acid chains in saturated fats and straight, but the fatty acid chains in unsaturated fats have kinks
• saturated fats are solid in room temp. but unsaturated fats are liquid in room temp.

Question 12

functions of fats

Answer 12

• source and store of energy
• insulating material to prevent excessive heat loss
• solvent for fat soluble vitamins and hormones
• forms main part of cell membranes
• reduce water loss from skin surface

Question 13

what are proteins made up of?

Answer 13

an amino group (NH2), acid group (COOH) and a side chain

Question 14

what bonds are present in a protein molecule?

Answer 14

peptide bonds link up amino acids to form polypeptide chains
hydrogen bonds link up polypeptide chains to fold to form a three-dimensional molecule, protein

Question 15

function of proteins

Answer 15

• synthesis of new protoplasm for growth and repair of worn out cell
• synthesis of enzymes and some hormones
• synthesis of antibodies

Question 16

importance of water in human body

Answer 16

• solvent in which chemical reactions can take place like hydrolysis
• essential component of cells’ protoplasm, tissue fluids, digestive juices and blood plasma
• regulate the human body temperature
• transport dissolved substances around the body

Question 17

how to test for starch

Answer 17

add 2cm3 of food sample and few groups of iodine solution into test tube

results :
blue black : starch is present
remain brown : starch is absent

Question 18

how to test for reducing sugars (what is not a reducing sugar?)

Answer 18

sucrose - not reducing sugar

using benedict’s solution

add 2cm3 of benedict’s solution + 2cm3 of food sample in test tube and heat in boiling water bath

results :
green : traces of reducing sugars
yellow : moderate amounts of reducing sugars
orange - red : large amount of reducing sugars
blue : reducing sugar absent

Question 19

how to test for proteins?

Answer 19

using biuret test

add 2 cm3 of sodium hydroxide solution to 2 cm3 of food sample into a test tube.
shake the mixture thoroughly and add 1% copper(II) sulfate solution drop by drop, shaking the mixture after each drop.

OR

add 2 cm3 of biuret solution and shake the mixture thoroughly.

results :
violet solution formed : proteins
solution remains blue : no proteins

Question 20

how to test for fats?

Answer 20

using ethanol emulsion test

add 2cm3 of ethanol to 2cm3 of food sample in a test tube
shake the contents vigorously and decant 2cm3 of water in test tube

results :
cloudy white emulsion : fats are present
remains clear and colourless : fats are absent