Biological molecules
Cambridge IGCSE Biology (0610) · Unit 4: Biological molecules · 12 flashcards
Biological molecules is topic 4.1 in the Cambridge IGCSE Biology (0610) syllabus , positioned in Unit 4 — Biological molecules . In one line: Carbohydrates are composed of carbon, hydrogen, and oxygen. Examples include glucose (C6H12O6) and starch, which are vital energy sources for organisms like plants and animals.
This topic is examined in Paper 1 (multiple-choice) and Papers 3/4 (theory), plus Paper 5 or Paper 6 (practical / alternative to practical). Past papers from 2022 to 2025 show this topic across 14 questions worth 183 marks (around 2.7% of all Biology marks in those years).
The deck below contains 12 flashcards — 4 definitions, 3 key concepts and 5 process cards — covering the precise wording mark schemes reward. Use the 4 definition cards to lock down command-word answers (define, state), then move on to the concept and application cards to handle explain, describe and compare questions.
What chemical elements make up carbohydrates
Carbohydrates are composed of carbon, hydrogen, and oxygen. Examples include glucose (C6H12O6) and starch, which are vital energy sources for organisms like plants and animals.
What the Cambridge 0610 syllabus says
Official 2026-2028 specThese are the exact learning objectives Cambridge sets for this topic. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks.
- List List the chemical elements that make up: carbohydrates, fats and proteins
- State State that large molecules are made from smaller molecules, limited to: (a) starch, glycogen and cellulose from glucose (b) proteins from amino acids (c) fats and oils from fatty acids and glycerol
- Describe Describe the use of: (a) iodine solution test for starch (b) Benedict's solution test for reducing sugars (c) biuret test for proteins (d) ethanol emulsion test for fats and oils (e) DCPIP test for vitamin C
- Describe Describe the structure of a DNA molecule: (a) two strands coiled together to form a double helix (b) each strand contains chemicals called bases (c) bonds between pairs of bases hold the strands together (d) the bases always pair up in the same way: A with T, and C with G (full names are not required) Supplement
What chemical elements make up carbohydrates?
Carbohydrates are composed of carbon, hydrogen, and oxygen. Examples include glucose (C6H12O6) and starch, which are vital energy sources for organisms like plants and animals.
What chemical elements make up fats?
Fats are composed of carbon, hydrogen, and oxygen, but with a lower proportion of oxygen compared to carbohydrates. An example is triglycerides, which are important for energy storage in adipose tissue in mammals.
What chemical elements make up proteins?
Proteins are composed of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur.
What smaller molecules make up starch, glycogen, and cellulose?
Starch, glycogen, and cellulose are all made from glucose molecules. Starch is found in plants (
What smaller molecules make up proteins?
Proteins are made from amino acids. These amino acids link together via peptide bonds to form polypeptide chains. For instance, haemoglobin in red blood cells is a protein made from amino acids.
What smaller molecules make up fats and oils?
Fats and oils are made from fatty acids and glycerol. These combine to form triglycerides.
Describe the iodine solution test and its expected result for starch.
Add iodine solution to the sample. If starch is present, the iodine solution will change from brown to blue-black.
Describe the Benedict's solution test and its expected result for reducing sugars.
Add Benedict's solution to the sample and heat. If reducing sugars are present, the solution will change color from blue to green, yellow, orange, or brick red, depending on the concentration of sugar.
Describe the Biuret test and its expected result for proteins.
Add Biuret reagent to the sample. If protein is present, the solution will change from blue to purple.
Describe the ethanol emulsion test and its expected result for fats and oils.
Dissolve the sample in ethanol, then add water. If fats or oils are present, a cloudy white emulsion will form.
Describe the DCPIP test and its expected result for vitamin C.
Add the sample dropwise to DCPIP solution until the blue colour disappears. The volume of sample needed indicates the amount of vitamin C. Lemon juice will quickly decolourise DCPIP due to high vitamin C content.
Describe the structure of a DNA molecule.
DNA consists of two strands coiled together to form a double helix. Each strand contains bases (A, T, C, G). Bases pair up specifically: A with T, and C with G, held together by bonds between the base pairs. The sequence of these bases encodes genetic information in organisms, like eye colour in humans.
Key Questions: Biological molecules
What chemical elements make up carbohydrates?
Carbohydrates are composed of carbon, hydrogen, and oxygen. Examples include glucose (C6H12O6) and starch, which are vital energy sources for organisms like plants and animals.
What chemical elements make up fats?
Fats are composed of carbon, hydrogen, and oxygen, but with a lower proportion of oxygen compared to carbohydrates. An example is triglycerides, which are important for energy storage in adipose tissue in mammals.
What chemical elements make up proteins?
Proteins are composed of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur.
Describe the structure of a DNA molecule.
DNA consists of two strands coiled together to form a double helix. Each strand contains bases (A, T, C, G). Bases pair up specifically: A with T, and C with G, held together by bonds between the base pairs. The sequence of these bases encodes genetic information in organisms, like eye colour in humans.
Tips to avoid common mistakes in Biological molecules
- ● Create a table that pairs each cell structure — cell wall, cell membrane, vacuole — with its one primary function.
- ● For biological molecule tests, nail down the reagents and positive results for starch (iodine), glucose (Benedict’s), protein (biuret), fats (ethanol emulsion), and DCPIP.
- ● Link large molecules to their corresponding small building blocks: starch <--> glucose; protein <--> amino acids; fat <--> fatty acids and glycerol.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 0610 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Key terms covered in this Biological molecules deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
Related Biology guides
Long-read articles that go beyond the deck — cover the whole subject's common mistakes, high-yield content and revision pacing.
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