Bio - Biological molecules and food tests

Question 1

Structure of carbohydrates

Answer 1

Carbohydrates: contains carbon, hydrogen and oxygen

Starch and glycogen are large complex carbohydrates made up of small units in long chains

Question 2

Structure of protein

Answer 2

made of long chains of amino acids which all contain hydrogen, oxygen and carbon and nitrogen

Question 3

Structure of lipids

Answer 3

Contain fatty acids and glycerol, lipids also contain carbon, hydrogen and oxygen atoms

Question 4

How to prepare a food sample for food tests

Answer 4

Before starting a food test you should prepare the food in a suitable way:
Use pestle and mortar to break up food
Add distilled water to the food and allow some of the food to dissolve into the water - becoming a solution
Filter the solution through a filter paper into a conical flask - all the solid residue is separated

Question 5

Test for glucose:

Answer 5

Glucose: add benedict’s solution and heat it in a water bath at 75 degrees, if low concentrations of glucose is present it will turn from blue to green, if high concentrations: solution will turn brick red

Question 6

Test for starch:

Answer 6

Starch: Add iodine, if starch is present, solution turns blue, black

Question 7

Test for protein

Answer 7

Add Biuret solution, if protein is present solution will turn from blue to pink-purple

Question 8

Test for lipids

Answer 8

Lipids: Add and shake with ethanol and water, if lipids are present a cloudy emulsion will form

Question 9

Vitamin uses:

Answer 9

Vitamins:
A- Improves vision
found in guts
C- prevents scurvy
found in fruits
D- needed for calcium absorption
found in eggs, (or sunlight)

Question 10

How to investigate energy of food

Answer 10

Weight sample of food
Skewer sample food to a mounted needle
Fill test tube up with water and hold it aloof with a clamp, put thermometer in water to monitor the temperature
Measure temperature of water initially
Using Bunsen burner, light food sample on fire and hold it under test tube (where water is), keep relighting and placing under test tube until food is completely burnt out
Take temperature of water now and calculate the difference.
Repeat experiment 3 times to ensure reliability
Calculate energy transferred: energy transferred = 4.2 (specific heat capacity of water) x difference in temp. x mass of water (cm^3 or g)
Calculate amount of energy in joules per gram = energy in food/ mass of food; this is done so you can compare the energy values of different foods fairly
To increase accuracy add insulation around test tube to minimise heast loss and keep more energy in water