Practical (bio) Flashcards
What is the Benedict’s test used for?
Test for presence of reducing sugar
Color changes: green (low), yellow, orange (moderate), brick red (large), solution remains blue.
What is the Iodine test used for?
Test for starch
Blue-black colouration is observed; iodine remains brown.
What is the Ethanol emulsion test used for?
Test for fats
White precipitate is formed.
What does the Biuret’s test detect?
Test for proteins
Violet colouration.
What are reducing sugars?
All monosaccharides and some disaccharides are reducing sugars.
Sucrose is the only common non-reducing sugar (no change when test conducted).
What are the steps for conducting the Benedict’s test?
- To 2cm³ of solution, add equal volume of Benedict’s solution (CuSO₄). 2. Shake mixture. 3. Boil in water bath for max 5 minutes. 4. Observe any colour changes/precipitate.
What are the steps for conducting the Iodine test?
- Place food on white tile. 2. Add 2-3 drops of dilute iodine solution. 3. Observe any colour change.
What are the steps for conducting the Ethanol emulsion test?
- Sample must be dissolved in ethanol first before adding water. 2. Add 2cm³ of ethanol to 2cm³ of food solution in a test tube. 3. Shake well. 4. Add 2cm³ of water to solution, shake to mix and observe for any changes.
What are the steps for conducting the Biuret’s test?
- To 2cm³ of food solution, add 1cm³ of sodium hydroxide. 2. Shake thoroughly. 3. Add 1% copper(II) sulfate solution drop by drop and shake after every drop to observe colour changes.
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Reducing-sugar → substrate for respiration to release energy
Starch → digested into glucose → stored or broken down and used for respiration to release energy
Best foods for building muscle
Protein → repair and growth of damaged muscles and build new muscle tissue
Diff tissues diff water potential, concentration of nutrients, etc
Take samples from the same part of the plant to ensure they have the same …
Time for end of experiment/Colour change of solution is subjective/colour intensity of food test is subjective
Compare to a standard colour chart
Temp of water bath not kept constant → affect rate of reaction
Use thermometer to measure temp of water bath + add hot/cold water to keep temp constant
Experimental set-up will gain heat from lamp
Transparent heat shield/ place in water bath → add cold/hot water
Stopwatch only started after last sample added → not all solutions immersed in the solution for the same period of time
Stagger experiments
Counting bubbles inaccurate measurement for rate of reaction (diff sizes)
Use gas syringe/ inverted measuring cylinder filled with water
Colour of food sample interferes with observations of results
Use food solution instead of actual food sample
Starting mass of food sample not kept constant
Crush food sample and weigh out a fixed mass for testing
Using a dropper to measure out 2cm3 of food solution is imprecise
Replace dropper with syringe which gives more precise measurements
Volume of water added to dissolve solution not kept constant
Use measuring cylinder to measure out exact volume of water for both samples
Degree of swirling/mixing may not be consistent → diff extents of nutrients dissolving → inaccurate
Place mortar on mechanical shaker for a fixed duration → equal mixing
Magnification
1m - precision; cm (1d.p.); mm (whole number)
1m - measurement of longest length shown in drawing to correct precision
1m - correct calculated answer to 1d.p.
Magnification = X size of drawing/size of actual specimen
