1. lipids and carbs exam qu Flashcards
why is sucrose classed as a carbohydrate (1 mark)
carbon + hydrogen and oxygen in 2:1 ratio / same proportions in water
explain why sucrose will produce a positive result with benedict’s test only after it has been boiled with a dilute acid (2 marks)
needs to be hydrolysed / glycosidic bond needs to be broken
the product is a reducing sugar
explain why glucose and maltose both taste sweet but starch does not (1 mark)
glucose and maltose are soluble OR starch is insoluble
saccharin, cyclamates and sucrose are chemically different but they all taste sweet
suggest why (2 marks)
have a similar molecular shape/structure
so bind/fit to receptors
describe a biochemical test which could be used to show the presence of reducing sugars (2 marks)
benedict’s reagent and heat
goes from blue to brick red/orange/yellow/green
describe how you could use benedict’s reagent to test for the presence of glucose in a urine sample (2 marks)
add solution to urine sample and heat
turns brick red/orange/green/yellow
explain the difference between triglyceride and phospholipid (2 marks)
phopholipid has one phosphate group
replacing the fatty acid
explain the difference between saturated and unsaturated (2 marks)
saturated - all C-C single bonds / no double bonds
unsaturated - one or more C=C double bonds
give two features of starch molecules
and explain how each enables starch to act as an efficient storage substance (2 marks)
- coiled shape/compact/barnched
allows large amount to be packed in small space - insoluble
doesn’t affect water potential/osmosis
describe a chemical test you could carry out to show that a piece of coconut contains lipids (3 marks)
crush in ethanol/alcohol
add (to) water ORDER OF STEPS IS CRITICAL FOR MARK
milky white emulsion formed
describe how a phospholipid molecule differs in structure from a triglyceride molecule (1 mark)
phospholipid has a phosphate group OR phospholipid only has 2 fatty acids
name one chemical element present in a phospholipid that would not be present in a polysaccharide (1 mark)
phosphorus
suggest how 2 molecules can have the same formula but a different structure (1 mark)
atoms are arranged differently
OR
different isomers
how many molecules are produced when a triglyceride molecule is completely hydrolysed (1 mark)
4
explain why triglycerides are not polymers (1 mark)
not made of identical units/monomers
OR
made of fatty acids and glycerol