Lesson overview
Food tests: What is in this food?
Find out which elements and building blocks make up carbohydrates, proteins and fats, then test orange juice and five mystery solutions with iodine, Benedict's, biuret, the emulsion test and DCPIP.
Suggested sequence
- Lesson 1 · What food is made of. What food is made of: carbon, hydrogen, oxygen and nitrogen; big molecules from small ones. Read together and discuss (15–20 min), practise with self-checking (20–25 min).
- Lesson 2 · Testing foods. Testing foods: iodine, Benedict's, biuret, the emulsion test and DCPIP, each beside a water control. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- Lesson 3 · The structure of DNA. The structure of DNA: a double helix of two strands, with A paired to T and C to G (Supplement). Read together and discuss (15–20 min), practise with self-checking (20–25 min).
- End of module · final check. 7 new questions, 20–30 min, without hints or notes; pupils check their answers once they have answered them all.
- One to two weeks later · return questions. 7 questions, 15 min, lesson closed.
Learning goals
Part 1: What food is made of
- List the chemical elements that make up carbohydrates, fats and proteins (4.1.1)
- State that starch, glycogen and cellulose are made from glucose (4.1.2a)
- State that proteins are made from amino acids (4.1.2b)
- State that fats and oils are made from fatty acids and glycerol (4.1.2c)
Part 2: Testing foods
- Describe the use of iodine solution to test for starch (4.1.3a)
- Describe the use of Benedict's solution to test for reducing sugars (4.1.3b)
- Describe the use of biuret solution to test for proteins (4.1.3c)
- Describe the use of the ethanol emulsion test for fats and oils (4.1.3d)
- Describe the use of DCPIP to test for vitamin C (4.1.3e)
Part 3: The structure of DNA
- Describe a DNA molecule as two strands coiled together to form a double helix (Supplement 4.1.4a)
- Describe that each strand contains chemicals called bases (Supplement 4.1.4b)
- Describe that bonds between pairs of bases hold the strands together (Supplement 4.1.4c)
- Describe that the bases always pair up in the same way: A with T, and C with G (Supplement 4.1.4d)
Misconceptions to listen for
- “Proteins are made of carbon, hydrogen and oxygen, just like carbohydrates.” — Match protein to the option with four elements: every amino acid contains nitrogen as well as carbon, hydrogen and oxygen.
- “Fats contain nitrogen.” — Match fat or oil to carbon, hydrogen and oxygen only: fatty acids and glycerol contain no nitrogen.
- “Glycogen and cellulose are made from different sugars.” — All three carbohydrates are made from glucose; they differ in how the glucose units are joined and arranged.
- “Glucose is bigger than starch, because sugar is what starch breaks down into.” — Glucose is the small unit; starch is thousands of glucose units joined together.
- “Cellulose is made from fibre.” — Cellulose is the fibre, and it is made from glucose units.
- “Glycogen is made from glycerol.” — Glycerol is part of a fat. Glycogen is made from glucose.
- “A fat is a long chain of fatty acids.” — The three fatty acids are joined to the glycerol, not to each other.
- “A protein is one kind of unit repeated, like starch.” — A protein chain is made of many kinds of amino acid in an order that belongs to that protein.
- “The powder is a carbohydrate, because it contains carbon, hydrogen and oxygen.” — All three nutrients contain those; nitrogen is the clue, and of the three only protein has it.
- “Inulin is like a protein because it is a chain.” — A protein chain uses many kinds of amino acid; inulin repeats one kind of sugar, like starch.
Scope
The elements in carbohydrates, fats and proteins (4.1.1); starch, glycogen and cellulose from glucose, proteins from amino acids, fats and oils from fatty acids and glycerol (4.1.2); the iodine, Benedict's, biuret, ethanol emulsion and DCPIP tests (4.1.3) through the food-tests practical; the structure of DNA (Supplement 4.1.4) in the reading and practice. Colours and drop counts in the experiment come from a teaching model.