OCR AS Biology (F212) - May 2014

Can someone do an overview of the biomol tests, I havent looked up on them and it seems people are confident theyre gonna come up

Can someone do an overview of the biomol tests, I havent looked up on them and it seems people are confident theyre gonna come up

Outline the main steps by which disease resistance could be selectively bred into commercially grown papaya (3)

Starch- Test with iodine, positive result is blue-black

Reducing sugar- test with Benedict solution, positive result is orange-red

Non reducing sugars- if Benedict test is unsuccessful, boil with hydrochloric acid which hydrolyses and sucrose present. Then add an alkali to neutralise it such as Sodium hydrogen-carbonate solution and carry out the reducing sugar test again. Positive result will be orange-red

Protein- Test with Biuret reagent, positive result is lilac

Lipids- Mix sample with ethanol, pour mixture into water in another test tube. positive result is a cloudy white emulsion forming near the top of the water.

Good luck!

Starch: add iodine solution. Postive result- amber==> blue-black

Reducing sugar: add Benedict's Reagent and heat in a water bath over 80o'C, observe colour changes (qualitative) or use a colourimeter (quantitative). Positive result- clear blue ==> opaque red.

Non reducing sugar: add warm dilute HCL(aq) (to hydrolyse the glycosidic bonds) then add NaHCO3(s) (to neutralise the acid). Perform Benedict's test as above.

Protein: add Biuret Reagent. Positive result- blue ==> purple

Lipid: add ethanol and shake well. Decant liquid into a clean test tube and add a few drops of water. Positive result- milky white emulsion

Hope that helps

Starch test - Add iodine and test piece will go blue/black from yellow/brown if starch is present

Reducing sugar test - Add Benedict's solution and heat to 80 degrees celsius. Solution goes from blue to green to orange to red (With precipitate) if reducing sugar is present (In increasing concentrations)

Non-Reducing sugar - Add dilute HCl and boil, cool and add alkali and then carry out benedict's test. Any colour change indicates non-reducing sugar instead of reducing sugar.

Protein test - Add Copper (II) Sulphate and solution goes from blue to lilac if proteins are present.

Lipid test - Add ethanol to crushed material and filter with cold water. Discard residue and leave filtrate to separate. If a milky emulsion forms in water layer, lipid present.

Would we have to know the specific name of the tests? I remember lipid test was also called the emulsion test if I remember correctly

In enzymes when it asks about competive inhibitors do you say the competitive inhibitor has a simillar shape with the substrate so it competes with the substrate for the enzymes active site to form an enzyme-inhibitor complex. What else do i need to add to get 3 marks in this question.

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You diamond!


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why do we need to know that

why do we need to know that

Whats an inorganic ion cofactor

Is water translucent or transparent in terms of photosynthesising plants underwater?

Whats an inorganic ion cofactor

Is water translucent or transparent in terms of photosynthesising plants underwater?

What are the differences between cellulose and glycogen and haemoglobin and collagen