Key term
OCR A-Level Biology H420
Cell Structure
Biological Molecules
Nucleotides and Nucleic Acids
Enzymes
Biological Membranes
Cell Division, Cell Diversity and Cellular Organisation
Exchange Surfaces
Transport in Animals
Transport in Plants
Communicable Diseases, Disease Prevention and the Immune System
Biodiversity
Classification and Evolution
Communication and Homeostasis
Excretion as an Example of Homeostatic Control
Neuronal Communication
Hormonal Communication
Plant and Animal Responses
Topic overviewTropisms and plant responses to stress and herbivoryPlant hormones and their commercial usesThe nervous system and the brainReflex actions and the knee jerk reflexFight or flight and the control of heart rateThe structure of skeletal muscleThe neuromuscular junction and the sliding filament model
Photosynthesis
Respiration
Cellular Control
Patterns of Inheritance
Manipulating Genomes
Cloning and Biotechnology
Topic overviewNatural plant cloning and taking cuttingsMicropropagationAdvantages and disadvantages of plant cloningAnimal cloning: embryo twinning and nuclear transferAdvantages and disadvantages of animal cloningMicroorganisms in food productionAseptic techniqueFermentation and its conditionsThe microbial growth curveImmobilised enzymes
Ecosystems
Populations and Sustainability
Practical Skills and Mathematical Requirements
Biological Molecules
The biochemical tests
- 5 things to know
- Components 01, 02 and 03
Overview
Biuret for protein, Benedict's for reducing and non-reducing sugars, iodine for starch and the emulsion test for lipids, with the colour change each one gives.
What you need to know
Answer each one before you reveal it.
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Key term
What colour change indicates a positive result in Benedict's test for reducing sugars?
Key term
What colour indicates a positive result in the biuret test?
Key term
Why must you test for reducing sugars first when testing for non-reducing sugars?
Process
Compare four biochemical tests.
Questions from this subtopic
Each one with the model answer underneath.
- 1
In the biuret test, what reagent is added first to the sample?
Model answer
Sodium hydroxide solution.
- 2
In the biuret test, what reagent is added after sodium hydroxide?
Model answer
Dilute copper sulfate solution.
- 3
What colour indicates a positive result in the biuret test?
Model answer
Purple colour indicates protein is present.
- 4
What colour indicates a negative result in the biuret test?
Model answer
Blue colour indicates protein is absent.
- 5
Describe how to perform Benedict's test for reducing sugars.
Model answer
Add Benedict's reagent to the sample and heat in a water bath.
- 6
What colour change indicates a positive result in Benedict's test for reducing sugars?
Model answer
A colour change from blue through green, yellow, orange to brick red indicates reducing sugar is present.
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