The effect of temperature on the rate of decomposition by an enzyme: practical | Exit Quiz | Oak National Academy

What is meant by pH?

• The colour that an indicator changes when added to a substance.

• How acidic or alkaline a substance is.

• The acidity of a substance.

Answer explanation

pH is how acidic or alkaline a substance is. Lower pHs are acidic substances, higher pH substances are alkalis.

In the practical looking at the decomposition of milk by an enzyme, the point at which a colour change indicates the change in pH is known as the ...

Answer explanation

The point at which a colour change indicates the change in pH is known as the end point.

Cresol red is a solution which changes colour. What are solutions that change colour called?

Answer explanation

Cresol red is an example of an indicator. It changes colour as the pH changes.

What pH does milk become when it decays?

• alkaline

• acidic

• neutral

• a gas

Answer explanation

Milk becomes acidic when it decays or decomposes. This is because the fats or lipids in the milk are broken down to form fatty acids and glycerol. As more fatty acids are formed, the conditions become more acidic.

When carrying out a practical activity, a precise, measurable and testable statement based on observations about how something works is called a ...

• prediction

• measurement

• observation

• hypothesis

Answer explanation

A hypothesis is a precise, measurable and testable statement based on observations about how something works. A hypothesis states what you would expect to happen and gives a reason, based on scientific knowledge, why it will happen.

In the practical where you looked at the effect of temperature on the decomposition of milk using an enzyme, which variable is the independent variable?

• milk volume

• milk temperature

• enzyme temperature

• pH of the milk

Answer explanation

The temperature of the milk is the variable that you will change. This is the independent variable. The time taken for the pH to change (using the indicator to determine the end point) is the dependent variable, the variable that you measure.