Investigating Decay in Biological Materials Flashcards

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What is decay in biological materials?

It is the breakdown of dead material by enzymes into simpler substances.

In a milk decay practical, which enzyme is used to model decay and what does it break down?

Lipase is used. It breaks down fats (lipids) into fatty acids and glycerol.

Which indicator is used, and what colour change shows the reaction has finished?

Phenolphthalein is used. It changes from pink to colourless when the pH falls as acids form.

Why do you add sodium carbonate to the milk before testing?

To make the mixture alkaline so the phenolphthalein starts pink.

What is the independent variable in this investigation?

Temperature in degrees Celsius (°C).

What is the dependent variable, and how can you calculate the rate?

The time for the pink colour to disappear. Rate = 1 ÷ time, in s⁻¹.

Give two control variables to keep the test fair.

Keep the volumes the same (milk mix and lipase) and use the same concentrations of solutions.

Why do you pre-warm both the milk mixture and the lipase in the water bath?

So the reaction starts at the set temperature, making it a fair test.

What trend with temperature do you expect and why?

It gets faster up to about 35–40 °C, then slows at higher temperatures as the enzyme denatures (changes shape).

What control setup could you use, and what would you expect to see?

Use boiled (denatured) lipase or no enzyme. The mixture stays pink, showing the enzyme causes the change.

How should you present your results?

In a table and a graph of rate (1/time) against temperature, with labelled axes and units.

Name two safety precautions for this practical.

Wear goggles, and take care with hot water baths and irritant chemicals like phenolphthalein and sodium carbonate.