Question

1. What would be some of the possible positive and negative controls of the effect of pH in potato enzyme lab?

2. What would be the positive and negative controls of the effect on temperature in a potato enzyme lab experiment?

3. Positive and negative controls on the effect of salt in potato enzyme lab?

Answer 1

Ans. I. Negative control – It is a reaction mixture that lacks a specific component that is responsible for desired/ specific negative result. A negative result would be the one as if the enzyme did NOT catalyze the reaction, so NO product would be formed, too.

II. Positive control: A reaction mixture that gives the desired/ specific positive result is called a positive control. A positive result is obtained when enzyme catalyzes the reactants into product.

Note: Both the positive and negative controls are specific to the aim of experiment. To determine the specific factor, only that factor shall be missing in negative control. For example, if you want to see the effect of pH, both the positive and negative controls have identical composition EXCEPT change in pH- the positive control would be at optimum pH, and the negative control would be at extreme pH.

#1. Aim of experiment: Effect of pH on enzyme activity (potato enzyme, probably amylase)

Positive control- A reaction mixture containing all the reaction components and buffered at optimum pH (say, 7.0 is optimum pH). When at pH 7.0, the reaction mixture gives a positive result- starch is hydrolyzed into glucose – so, you get a positive result for Benedict’s test indicating that amylase (your potato enzyme) has catalyzed the reaction to form glucose (product).

Negative control- A reaction mixture containing all the reaction components and buffered at an extreme pH (say, 2.0) at which enzyme becomes catalytically inactive. Under this condition, no positive result (NO positive Benedicts’ test) would be observed- indicating that enzyme has NOT catalyzed the reaction (hydrolysis of starch).

#2. Aim of experiment: Effect of temperature on enzyme activity

Positive control- A reaction mixture containing all the reaction components, and incubated at optimum temperature (say, 37⁰C is optimum temperature). Positive result would be obtained.

Negative control - A reaction mixture containing all the reaction components and incubated at extreme temperature (sat 4⁰C) at which enzyme does not catalyze the reaction within the specified reaction time. Negative result would be obtained.

#3. Aim of experiment: Effect of salt on enzyme activity

Positive control- A reaction mixture containing all the reaction components- plus, the specified salt added to it. Positive result (desired result in presence of salt) would be obtained.

Negative control - A reaction mixture containing all the reaction components- except the specified salt. Negative result (desired result in absence of salt) would be obtained.

Note that the desired result would depend on the type of salt. If the salt enhances enzyme catalysis, the desired positive result in presence of salt would be ‘a positive Benedict’s test’. However, if the salt inhibits enzyme activity, the desired positive result would be ‘a negative Benedict’s test’.