2022 Topic 3 Revision

State what is meant by the term catalyst. Select more than 1 option.

• A catalysts decreases the rate of reaction

• It helps to decrease the activation energy of a reaction

• A catalysts increases the rate of reaction

• Is it not changed by the reaction can be reuse

Explain how the shape of an enzyme molecule and its substrate is important to enable a reaction to occur. Select more than 1 option.

• The shape of active site must be complementary / specific to the substrate like a lock and key

• Specific shape of active site and substrate allows the molecules to bind together forming

  an enzyme-substrate complex

• The shape of active site must not necessarily be complementary / specific to the substrate

• Active site is found in both the enzyme and substrate

Explain why each type of enzyme can only catalyse a specific reaction. Select more than 1 correct option.

• Specific shape of active site and substrate allows the molecules to bind together forming enzyme-substrate complex

• The shape of active site and substrate is like lock and key. Shape of active site have different shapes which fits different substrates

• Wrongly shaped substrates cannot fit into active site

• The shape of active site and substrate is like lock and key. Shape of active site have are all the same but only substrates shape are different.

Explain why rate of enzyme reaction descreases to zero at very high temperature. Select more than 1 correct option.

• Active site has denatured and changes shape and cannot fit substrate.

• Rate of reaction is reduced or becomes zero because no enzyme-substrate complex is formed.

• Substrate site has denatured and changes shape and cannot fit enzyme.

• Because too many enzyme-substrate complex is formed when active site changes shape.

Explain the effects of temperature on the rate of enzyme reaction. Select more than 1 correct option.

• At very low temperature enzymes denature, substrate can no longer fit active site

• At 20 °C, the molecules have less kinetic energy. Fewer collisions between the enzyme and substrate occur.

• At 40 °C molecules gain more kinetic energy. More collisions occur. Rate is at its optimum.

• At 80 °C enzyme denatured. Active site changes shape. Substrate cannot fit into active site. Yeast is killed.

Select the correct properties of enzymes.

• All enzymes are proteins, Affected by temperature, Affected by pH

• Specific in their action,

  Remains unchanged at the end of the reaction,

  Reusable many times

• Each enzyme catalyse more than one reaction,

  Inactive at very high temperature

• Each enzyme catalyse one reaction,

  Inactive at very low temperature

Enzymes are affected by pH. Select the correct explanations below.

• Protease works best in stomach because of the acidic condition produced by hydrochloric acid

• Enzyme works only at very narrow pH range.

  Enzymes denature beyond these ranges.

• Amylase works best at neutral pH (optimum pH for amylase is pH 7)

• Amylase works best at all pH range