1. lipids and carbs exam qu Flashcards

1
Q

why is sucrose classed as a carbohydrate (1 mark)

A

carbon + hydrogen and oxygen in 2:1 ratio / same proportions in water

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2
Q

explain why sucrose will produce a positive result with benedict’s test only after it has been boiled with a dilute acid (2 marks)

A

needs to be hydrolysed / glycosidic bond needs to be broken
the product is a reducing sugar

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3
Q

explain why glucose and maltose both taste sweet but starch does not (1 mark)

A

glucose and maltose are soluble OR starch is insoluble

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4
Q

saccharin, cyclamates and sucrose are chemically different but they all taste sweet
suggest why (2 marks)

A

have a similar molecular shape/structure
so bind/fit to receptors

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5
Q

describe a biochemical test which could be used to show the presence of reducing sugars (2 marks)

A

benedict’s reagent and heat
goes from blue to brick red/orange/yellow/green

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6
Q

describe how you could use benedict’s reagent to test for the presence of glucose in a urine sample (2 marks)

A

add solution to urine sample and heat
turns brick red/orange/green/yellow

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7
Q

explain the difference between triglyceride and phospholipid (2 marks)

A

phopholipid has one phosphate group
replacing the fatty acid

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8
Q

explain the difference between saturated and unsaturated (2 marks)

A

saturated - all C-C single bonds / no double bonds
unsaturated - one or more C=C double bonds

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9
Q

give two features of starch molecules
and explain how each enables starch to act as an efficient storage substance (2 marks)

A
  1. coiled shape/compact/barnched
    allows large amount to be packed in small space
  2. insoluble
    doesn’t affect water potential/osmosis
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9
Q

describe a chemical test you could carry out to show that a piece of coconut contains lipids (3 marks)

A

crush in ethanol/alcohol
add (to) water ORDER OF STEPS IS CRITICAL FOR MARK
milky white emulsion formed

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10
Q

describe how a phospholipid molecule differs in structure from a triglyceride molecule (1 mark)

A

phospholipid has a phosphate group OR phospholipid only has 2 fatty acids

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11
Q

name one chemical element present in a phospholipid that would not be present in a polysaccharide (1 mark)

A

phosphorus

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12
Q

suggest how 2 molecules can have the same formula but a different structure (1 mark)

A

atoms are arranged differently
OR
different isomers

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13
Q

how many molecules are produced when a triglyceride molecule is completely hydrolysed (1 mark)

A

4

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14
Q

explain why triglycerides are not polymers (1 mark)

A

not made of identical units/monomers
OR
made of fatty acids and glycerol

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15
Q

explain the meaning of saturated (1 mark)

A

no double bonds
OR
every carbon joined to 2 hydrogens/4 other atoms