WJEC Biology for A2: Student Bk

Practical exercises To demonstrate the digestion of starch-agar using germinating seeds Rationale The food reserves in seeds are large, insoluble macromolecules. During germination enzymes are synthesised. The enzymes hydrolyse the macromolecules into small, soluble molecules that can move into the phloem of the embryo. They are translocated to the apical meristems where they are used as respiratory substrates or as metabolites in embryo development. One of the enzymes that seeds synthesise is amylase, which digests the starch in the endosperm or cotyledon into maltose. The maltose moves into the embryo where it is hydrolysed into glucose, which is respired to generate energy. In this experiment, amylase digests the starch in the agar plate. Iodine solution fails to turn blue-black in areas that lack starch. Design Name of variable Independent variable Live or dead seeds Dependent variable Width of halo around seed Controlled variables Starch concentration; temperature Control Boiled seeds Reliability 3 seeds per plate Hazard Seeds are maintained at 20ºC to reduce the risk of growing potentially harmful contaminants Apparatus – Broad bean seeds, soaked in water for two days at room temperature – 10% bleach – Sterile distilled water – 250 cm 3 beaker – Starch-agar plates – Sterile white tile – Sterile fine scalpel – Sterile fine forceps – Iodine–potassium iodide solution – Boiling tube – Boiling water bath – Timer WJEC A2 Biology: Chapter 10 190