Pearson Science Double Award Practical 5: Biology Contexts

Double Award Biology practical questions embed investigation design, observations and interpretation within the written Biology paper. This note maps the explicit 4SD0 practical points without turning them into a separate laboratory examination.

Food tests and enzymes

For reducing sugar, add Benedict's reagent and heat in a water bath. A positive result progresses from blue toward green, yellow, orange or brick-red according to amount. For starch, add iodine solution; orange-brown turns blue-black. For protein, use the Biuret test; blue turns lilac or purple. For lipid, shake with ethanol and add water; a cloudy white emulsion is positive.

Use separate samples and clean droppers to prevent cross-contamination. Include a known positive and water negative control when evaluating an unfamiliar method. Record the actual observation, not merely “positive.”

To investigate enzyme temperature, use a defined substrate and endpoint, equal enzyme and substrate quantities, controlled pH and a water bath. Allow solutions to equilibrate before mixing. Repeat at several temperatures. Rate may be gas volume per time or reciprocal time to a colour endpoint. Temperature can increase successful collision frequency until active-site shape changes and activity falls.

Diffusion and osmosis

Diffusion is net particle movement down a concentration gradient. Osmosis is net water movement through a partially permeable membrane from higher water potential to lower water potential.

Living systems can include potato cylinders or plant tissue; non-living systems can include dialysis tubing. Cut equal initial dimensions, blot consistently and record initial and final mass. Percentage change permits comparison when starting masses vary:

$$\text{percentage mass change}=\frac{\text{final mass}-\text{initial mass}}{\text{initial mass}}\times100$$