IGCSE enzyme

How do enzymes speed up chemical reaction?

• Increasing activation energy
• Decreasing activation energy
• Increasing deactivation energy
• Decreasing deactivation energy

Most enzymes work best at about 37°C, normal body temperature, and each one

• is usually specific to only one type of chemical reaction in the body.
• serves as a catalyst for several kinds of reactions.
• helps speed up reactions by a factor of 2.
• helps slow down reactions by a factor of 10.

The graph shows the effect of temperature on enzyme action. What characteristic do enzymes E₁, E₂, and E₃ share?

• Their activity increases between 20°C and 30°C.
• Their activity is greatest between 5°C and 10°C.
• Their activity is at a low level between 15°C and 25°C.
• Their activity is at a high level between 30°C and 40°C.

Enzymes provide a site where reactants called substrates can be brought together in an enzyme-catalyzed reaction. The site is called the

• enzyme substrate complex.
• reaction site.
• active site.
• lock and key.

A change in pH can change the shape of a protein. How might a change in pH affect the function of an enzyme? 

• A new enzyme may be required to speed up the reaction.
• The enzyme may no longer be able to function for the substrate as a catalyst.
• The enzyme and substrate may no longer fit together so the enzyme cannot speed up the reaction.
• All the other answers are correct.

The graph shows how enzymes affect reactions in cells. Which statement best summarizes the information shown in the graph?

• Enzymes increase the energy of the reactants.
• Enzymes decrease the energy level of the products.
• Enzyme decrease the activation energy of the reaction.
• Enzymes reverse the direction of the reaction.

A lock and key is sometimes used as a model to promote understanding of enzymes. Which characteristic of enzymes or their action is best illustrated by this model?

• The sensitivity of enzymes to changes in pH
• The change in activation energy the enzymes cause
• The specificity of fit between an enzyme and a substrate
• The increase in reaction rate due to the action of the enzyme

Which of the following conclusions can be drawn from this graph?

• The optimum pH of the enzyme is 6.6.
  
• The optimum pH of the enzyme is 5.8
  
• The enzyme’s activity increases as pH increases 5.0 to 9.0
  
• The enzyme’s activity is greater around pH of 8.0 .
  

How does an enzyme's activity change with increasing concentration of substrate?

• decreases
• stays the same
• no change
• increases 

What makes an enzyme substrate specific?

• Size
• Shape
• Name
• Location it is found in