WJEC Biology for AS Level Student Book: 2nd Edition

Diagram of apparatus Apparatus ▪ 5, 10, 15, 20 and 25 vol hydrogen peroxide ▪ Distilled water ▪ Buffer pH 7 ▪ Conical flask fitted with a rubber bung, through which pass a syringe needle and a delivery tube ▪ 5 cm 3 syringe barrel ▪ 5 × 10 cm 3 syringe barrels ▪ Water trough ▪ Chopping board ▪ Potato ▪ Cork borers – 3 mm and 4 mm diameter are suitable ▪ Fine scalpel ▪ Forceps ▪ Ruler graduated in mm ▪ Timer ▪ 2 × 10 cm 3 measuring cylinders ▪ Tea strainer to prevent disks going down the drain when the flask is emptied Study point Reliability – several readings are made for each value of the independent variable and a mean is calculated from them. A mean is more reliable than an individual reading and the more readings, the more reliable the mean. Study point Some experiments require discs of plant material. The biological activity occurs over the discs’ surface area. It is assumed that they are cut uniformly, but this may not be the case: These discs have the same diameter but the faces are not parallel: both these cutting errors increase the surface area. A mechanical device for cutting discs accurately or a frame containing several mounted blades would be an improvement. potato disc oxygen water bu er at pH 7 and hydrogen peroxide perfect disc imperfect disc – one side too small imperfect disc – one side too big WJEC Biology for AS Level 88