2cStructures and Functions in Living Organisms
Biological molecules — Edexcel Linear - OL Revision Notes & Topical Questions
5 min read 7 parts Lesson 3 of 25 1 quiz
Lesson summary
Biological molecules Edexcel O Level Linear Biology notes: identify the chemical elements present in carbohydrates, proteins and lipids (fats and oils)Haemoglobin is a globular protein with 4 chains and haem groups (quaternary).Collagen is fibrous3 chains in a triple helix, stron…
- Biological molecules Edexcel O Level Linear Biology: what to do next
- Condensation
- Hydrolysis
- Glycosidic bond
- Ester bond
- Peptide bond
Section 1 of 7Process & sequence
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Primary: amino acid sequence
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Secondary: α-helix / β-sheet (H-bonds)
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Tertiary: 3D folding (ionic, disulfide, H, hydrophobic)
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Quaternary: several chains
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Heat sample with Benedict’s – no colour change: no reducing sugar.
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Boil a new sample with dilute HCl (hydrolysis).
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Neutralise with sodium hydrogencarbonate.
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Heat with Benedict’s again.
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Brick-red now → non-reducing sugar present.
Section 2 of 7Keep going
Biological molecules Edexcel O Level Linear Biology: what to do next
These Biological molecules Edexcel O Level Linear Biology notes covered the key ideas, worked examples and exam technique for this topic. Check your Biological molecules Edexcel O Level Linear Biology understanding with the practice questions below, then reread any Biological molecules Edexcel O Level Linear Biology point you were unsure about before moving on.
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Previous lesson: 2b Cell structure — Notes
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Course: Edexcel Linear - OL — all units
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Official syllabus: Pearson Edexcel International GCSEs
Section 3 of 7Compare
| Molecule | Monomer | Bond | Structure | Function | Test |
|---|---|---|---|---|---|
| Starch (amylose) | α-glucose | α-1,4 glycosidic | Unbranched helix | Energy store in plants – compact | Iodine → blue-black |
| Amylopectin / glycogen | α-glucose | α-1,4 and α-1,6 | Branched (glycogen more) | Rapid glucose release | Iodine |
| Cellulose | β-glucose | β-1,4 glycosidic | Straight chains, H-bonds → microfibrils | Cell wall strength | — |
| Triglyceride | Glycerol + 3 fatty acids | Ester | Hydrophobic | Energy store, insulation | Emulsion test |
| Phospholipid | Glycerol + 2 fatty acids + phosphate | Ester | Hydrophilic head, hydrophobic tails | Membrane bilayer | — |
| Protein | Amino acids | Peptide | Primary → quaternary | Enzymes, haemoglobin, collagen | Biuret → purple |
| Water | — | Hydrogen bonds | Polar molecule | Solvent, coolant, high SHC | — |
Section 4 of 7Key terms
Section 5 of 7Syllabus checklist
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identify the chemical elements present in carbohydrates, proteins and lipids (fats and oils)
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describe the structure of carbohydrates, proteins and lipids as large molecules made up from smaller basic units
- starch and glycogen from simple sugars
- protein from amino acids
- and lipid from fatty acids and glycerol
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practical: investigate food samples for the presence of glucose, starch, protein and fat
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understand the role of enzymes as biological catalysts in metabolic reactions
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understand how temperature changes can affect enzyme function, including changes to the shape of active site
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practical: investigate how enzyme activity can be affected by changes in temperature
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understand how enzyme function can be affected by changes in pH altering the active site
Section 6 of 7Command terms
Command terms
Give / State / Name
Recall a fact; one idea per mark.
Define
Give the exact meaning using the specification keywords.
Describe
Give an account of what happens / the pattern in data, quoting values; no reasons needed.
Explain
Give reasons with linked statements (cause → effect). Each linked step is usually a separate marking point.
Suggest
Use knowledge in a new context; more than one answer may be accepted.
Compare
Similarities and differences; each point must refer to both items.
Calculate
Show working; include units; check significant figures. Method marks are given even if the final answer is wrong.
Discuss
Explore the issue from different angles and link the points.
Evaluate / Assess
Weigh strengths and weaknesses and reach a supported judgement.
Deduce
Draw a conclusion from the information given.
Justify
Support a statement/choice with evidence.
Section 7 of 7Exam technique
Keywords the mark scheme looks for in this lesson
Keywords the mark scheme looks for in this lesson
Monomer · Condensation · Hydrolysis · Glycosidic bond · Ester bond · Peptide bond · Reducing sugar · Hydrogen bond
Learn each definition in the Key words tab exactly; a missing keyword in a definition usually loses the mark.
How to get full marks (examiner guidance)
How to get full marks (examiner guidance)
Use specification keywords exactly (e.g. eukaryotic/prokaryotic, enzyme–substrate complex, active site, complementary).
Link ideas
Link ideas for “explain” each marking point is usually a cause → consequence step; unlinked facts often score nothing.
Use the information in the question
“discuss/evaluate” answers must use the data provided and match the number of marks.
Convert units carefully (mg → g, cm³ → dm³) and show working for calculations.
Avoid vague words
“it”, “stuff”, “things”, “goes up”, “energy is made”. Name the substance and the process.
Do not extrapolate a graph line beyond the data or to zero unless asked.
Six-mark extended responses are marked on content AND a logical, linked line of reasoning.
Marked practiceQuizzes for this lesson
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