Biological molecules
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Which statement correctly pairs a molecule group with its main role?
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Fat provides long-term energy storage and insulation.
Fats contain carbon, hydrogen and oxygen, but differ in structure from carbohydrates.
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Which list correctly gives the smaller units for protein and fat?
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Protein: amino acids; fat: glycerol and fatty acids.
Keep both components when describing the basic units of a fat.
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Benedict's solution stays blue after being added to glucose solution, but the mixture was not heated. What is the best next step?
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Repeat correctly with water-bath heating and appropriate controls.
Missing heating makes the method incomplete. A known positive control checks that the method and reagent work.
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Invented results for four foods: P: iodine blue-black, Benedict's blue. Q: iodine brown, Benedict's brick-red. R: iodine blue-black, Benedict's green. S: iodine brown, Benedict's blue. Which food contains starch and a small amount of reducing sugar?
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R
Blue-black iodine shows starch, and a green Benedict's result shows a small amount of reducing sugar.
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Which sequence is appropriate for the ethanol emulsion test?
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Mix the sample with ethanol, then add the ethanol extract to water.
A cloudy white emulsion indicates fat. Keep ethanol away from flames and heat sources.
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A student adds biuret solution to egg white, milk, glucose solution and cooking oil. Which pair would turn violet?
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Egg white and milk
Both contain protein, which gives a violet colour with biuret solution.
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Which change explains how an enzyme increases reaction rate?
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It lowers activation energy when a suitable substrate forms a complex.
Binding at a complementary active site enables catalysis, and the enzyme remains available for reuse.
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An enzyme is slow at 5 degrees C but becomes active when warmed to 30 degrees C. Which explanation fits?
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Cold slowed collisions without permanently changing its active site.
The recovered activity supports a reversible effect of cooling rather than permanent denaturation.
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Invented data: amylase takes 120 s to digest starch at 20 degrees C, 40 s at 40 degrees C and 300 s at 60 degrees C. Which statement fits the data?
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The rate is highest at 40 degrees C and falls at 60 degrees C.
The shortest time means the fastest rate, so 40 degrees C is fastest; 300 s at 60 degrees C is much slower.
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Which method best isolates the effect of pH on amylase activity?
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Use different pH buffers but keep temperature and enzyme and substrate amounts constant.
A consistent endpoint and repeated measurements then support a fair comparison of pH conditions.
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Why does an amylase experiment include a tube of boiled and cooled amylase with starch?
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To show that starch disappears only when active enzyme is present.
Boiling denatures the enzyme. If starch remains in that tube, the change in the test tubes was caused by active amylase.
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Write a short answer, then compare it with a sample and check for missing ideas.