Testing the biochemicals present in apple and green bean using specific chemical tests.

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Biology Experiment Report

Aim: To identify the biochemical and compare their contents in apple and green bean using specific chemical tests

Principle of method:

Carbohydrates, proteins and lipids are the major organic constituents of organisms. Thus they are often called biochemicals. The specific tests for reducing sugar, starch and protein are Benedict Test, Iodine Test and Biuret Test respectively.

Before a specific chemical test can be carried out, it is necessary to extract juice from the tissue under investigation. Extraction method is very common in biological investigation.

  1. Benedict’s test for reducing sugars

Benedict’s solution contains copper sulphate. Reducing sugars reduces copper(II) ions present in the blue copper sulphate solution into insoluble brick-red copper(I) oxide which is a precipitate.
Note.
The initial blue colouration of the mixture turns green, then yellow and may finally form a brick-red precipitate. The final colour and amount of precipitate gives a rough indication of the amount of reducing sugar present.

  1. Iodine test for starch

Iodine solution is a mixture of iodine and potassium iodide solutions. Starch combines with iodine to give the characteristic of blue-black colour.
Note.
The positive result may be confirmed by boiling the mixture in a hot water bath for a few minutes and the blue-black colour disappears. On cooling the mixture, the colour should appear again.

  1. Biuret test for proteins

When protein is mixed with the dilute alkaline cooper sulphate solutions, nitrogen atoms in the peptide bonds to form a violet complex with copper(II) ions.
Note.
The intensity of the colour developed is an indication of the quantity of peptide bonds present in the solution tested.

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Apparatus & materials:

  1.  Apparatus :

2.  Materials        :

Procedure:

  1. Preparation of extract from the plant structures
  1. 10 mL of distilled water was measured with a measuring cylinder.
  2. 10g of plant tissue was cut into small pieces by means of scalpel.
  3. The pieces are crushed in a mortar by pressing them with a pestle until they disintegrate. Then a small amount volume of water was added and the pieces are grinded for several times or until the crushed pieces of plants material change into paste. After that, the rest of the water was added ...

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***** This account is detailed and shows a clear understanding of the chemical basis for the tests carried out. A few minor details might have been better explained.