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what are carbohydrates
organic molecules made of elements carbon, hydrogen and oxygen
ratio of hydrogen to oxygen is always 2:1
has a fixed proportion of C1:H2:O1
what are monosaccharides
simple sugars
basic unit of a carbohydrate
small enough to pass through cell membranes
examples of monosaccharides
glucose (found in plants and animals)
fructose (mainly found in plants)
what are polysaccharides
double sugars
formed when 2 single sugars are joined together
can be split into 2 single sugar molecules in the presence of an enzyme
examples of polysaccharides
-maltose
-sucrose
what are the 3 types of complex carbohydrates
starch
cellulose
glycogen
starch: role, occurrence and what it is
several thousand glucose molecules joined together
storage form of carbohydrates in plants
can be digested to form glucose to provide energy for cell activities.
found in the storage organs of plants
cellulose: what it is, role, and where its found
many glucose molecules joined together but bonded differently from starch
role: cellulose cell walls protect plant cells from damage or bursting
serves as dietary fibre that prevents constipation as it cannot be digested in our intestines
found in cell walls of plants
glycogen: what it is, role, and where its found
branched molecule of many glucose molecules
storage form of carbs in mammals
when needed, it is digested to glucose to provide energy for cell activities
stored in liver and muscle of mammals
why is glycogen and starch suitable as storage materials of glucose
insoluble in water
they are large molecules that cannot diffuse through cell membranes
easily hydrolysed to glucose when needed
made of molecules that have compact shapes so they occupy less space
function of carbohydrates
provide energy for cell activities
form supporting structures (eg cell wall)
for conversion into other organic compounds (eg amino acids and fats)
formation of DNA
synthesises lubricants (eg mucus)
synthesises nectar in flowers
what are fats
organic molecules made of carbon, hydrogen, oxygen
significantly higher amount of hydrogen to oxygen than carbs
no fixed proportion
function of fats
source and store of energy
acts as an insulating material to prevent excessive heat loss
solvent for fat soluble vitamins and some hormones
form cell membranes
help reduce water loss from skin surface
what are proteins
organic molecules made of carbon, hydrogen, oxygen and nitrogen
traces of sulfur may sometimes also be found in proteins
what are amino acids
basic building blocks of protein
how are polypeptides formed
peptide bonds link up amino acids to form polypeptide
how are proteins formed
2 or more polypeptide chains to form 3D molecule which is protein.
functions of protein
synthesis of
new protoplasm for growth and repair of worn out cells
enzymes and hormones
antibodies
how to carry out Biuret’s test and what it is tests for
tests for proteins
add 2cm3 of biurets solution to 2cm3 of food sample to a clean test tube. shake well and allow mixture to stand for 5 minutes
blue — no proteins
purple — protein present
how to carry out iodine test and what it tests for
tests for presence of starch
add a few drops of iodine to a food sample
brown — no starch
blue-black — starch
how to carry out ethanol emulsion test and what it is for
used to test for presence of fats
add 2cm3 of ethanol to 2cm3 of food sample to a clean test tube. shake contents vigorously. add 2cm3 of water into test tube and shake mixture.
cloudy mixture — presence of fats
clear mixture — no fats
how to carry out benedict’s test and what it is used to test
used to test for reducing sugars (glucose, fructose, maltose)
add 2cm3 of benedict’s solution to 2cm3 of food sample in a test tube. shake the mixture. heat the contents in a boiling water bath for 2-3 minutes.
red — green -presence of reducing sugars
blue — no reducing sugar
