OCR GCSE Combined Science
A scientist is investigating the action of amylase enzymes on the digestion of starch into maltose.
What would increase the rate of reaction?
A Decreasing the enzyme concentration
B Decreasing the pH to 2
C Increasing the pH to 7
D Increasing the temperature to 70 
C
Many biological processes involve enzymes.
Explain how enzymes increase the rate of biological processes.
Explain how temperature affects the progress of an enzyme-controlled reaction.
Many lizards have a body temperature that matches the external temperature.
In the morning, these lizards often lie in the sun before they can become active and hunt.
Explain why they need to lie in the sun before they can hunt.
The graph shows the effect of pH on the activity of two enzymes.
Identify the pH where both enzymes are active.
The diagrams show stages in the hypothesis used to explain the mechanism of enzyme action.
Which term describes this hypothesis?
A Active site
B Denaturing
C Enzyme specificity
D Lock and key
New medicines are developed all the time.
Insulin is a protein used to treat diabetes. The human stomach contains an enzyme that is specific to proteins like insulin.
Suggest why it is difficult to develop an insulin medicine that is swallowed.
Which type of medicine has been developed to treat HIV?
antibiotic antigen antiseptic antiviral
Some diseases are treated by changes to lifestyle.
Complete these sentences about cardiovascular disease.
The risk of cardiovascular disease is reduced by a........ low in saturated fat.
This reduces the risk of blocked arteries therefore allowing more oxygen to be transported to the
........ muscle in the ventricle wall.
The diagrams show stages in the hypothesis used to explain the mechanism of enzyme action.
Which term describes the molecule labelled M?
A Active site
B Enzyme
C Lock and key
D Substrate
The pH inside the small intestine of the human digestive system is between pH 7 and pH 8.
The pH inside the stomach of the human digestive system is between pH 1 and pH 2.
The graph shows the effect of pH on the activity of two enzymes.
Which statement about the enzymes is correct?
A Both enzymes would be denatured inside the small intestine.
B Enzyme Q would be more efficient inside the small intestine compared to enzyme P.
C Neither enzyme would work at its highest activity inside the stomach or small intestine.
D Only enzyme P would be active in the stomach.
The picture shows the plant pathogen that causes powdery mildew.
Describe how powdery mildew is spread from one plant to another.
Powdery mildew reduces the efficiency of chloroplasts.
Explain how this might reduce the rate of respiration in a plant.
Plants resistant to powdery mildew are developed by genetic engineering.
Complete the sentences about genetic engineering.
The gene for resistance is cut out of DNA using a........ enzyme.
The gene is then joined to bacterial DNA using a........ enzyme.
To find out if the bacteria contain the gene, scientists use........
Explain why the process of cutting the DNA is prevented by high temperatures.
Use your knowledge of enzymes.
Powdery mildew can be controlled using chemicals.
Producing plants resistant to powdery mildew is better for biodiversity compared to using chemicals.
Suggest two reasons why.
The graph shows the effect of pH on enzyme activity.
What is the pH when enzyme activity is highest ?
A scientist investigates the effect of temperature on anaerobic respiration in yeast.
The diagram shows the apparatus they use.
This is the method they follow:
• Collect the gas produced by the yeast for five minutes.
• Increase the temperature of the water bath.
• Repeat the investigation with fresh sugar solution.
• Do each temperature three times.
Suggest why the scientist used fresh sugar solution each time.
Identify one variable the scientist should keep constant throughout the experiment.
Tick (✓) one box.
Which gas is collected by the scientist in the gas syringe?
When calculating the mean for 55 °C, they did not include Trial 1.
Give the reason why.
Plot the mean values from the table on the graph.
Draw a curve of best fit.
Anaerobic respiration is an enzyme-controlled reaction.
Explain the results between 15 °C and 35 °C. Include ideas about enzyme particles.
The scientist concludes that the best temperature for anaerobic respiration is approximately 40 °C.
How could they alter their investigation to identify a more accurate temperature?
A scientist investigates the effect of temperature on anaerobic respiration in yeast.
The diagram shows the apparatus they use.
This is the method they follow:
• Collect the gas produced by the yeast for five minutes.
• Increase the temperature of the water bath.
• Repeat the investigation with fresh sugar solution.
• Do each temperature three times.
Suggest why the scientist used fresh sugar solution each time.
Identify one variable the scientist should keep constant throughout the experiment.
Tick (✓) one box.
Which gas is collected by the scientist in the gas syringe?
When calculating the mean for 55 °C, they did not include Trial 1.
Give the reason why.
Plot the mean values from the table on the graph.
Draw a curve of best fit.
Anaerobic respiration is an enzyme-controlled reaction.
Explain the results between 15 °C and 35 °C. Include ideas about enzyme particles.
The scientist concludes that the best temperature for anaerobic respiration is approximately 40 °C.
How could they alter their investigation to identify a more accurate temperature?
13* The pH of a soil will affect the crops that grow in the soil. When the soil pH is suitable, more crops will grow. This results in a higher yield (mass of crops).
The table shows data about the yield of four different crops, A, B, C and D, when grown in soils of different pH.
| pH range | Yield as a percentage of the highest yield obtained (%) | |||
| of soil | crop A | crop B | crop C | crop D |
| 4 – 4.9 | 25 | 3 | 14 | 65 |
| 5 – 5.9 | 74 | 8 | 34 | 75 |
| 6 – 6.9 | 100 | 98 | 100 | 100 |
A farmer measures the pH of the soil in their field. The soil is pH 4.5.
Which crop should the farmer grow in the field?
Explain your choice and give reasons why pH 4.5 prevents growth in some crops. Include ideas about enzymes and their function in plants.
*(i) Describe and explain the pattern in the results.
Use ideas about the lock and key hypothesis in your answer.
Describe how the student could improve their investigation to find a more accurate optimum pH for the enzyme.
Catalase is an enzyme found in potato. Catalase breaks down hydrogen peroxide to form water and oxygen.
A student investigates the activity of catalase.
This is the method they follow: – Cut equal sized pieces of potato. – Put one piece of potato into a conical flask. – Add 50 cm3 of dilute hydrogen peroxide. – Collect the oxygen produced in 15 minutes using a measuring cylinder full of water.
Fig. 15.1 shows the set-up of their investigation.
The student then repeats the investigation, increasing the number of potato pieces each time.
Each time the student repeats the investigation they use 50 cm3 of new dilute hydrogen (a) (i) peroxide.
Explain why they need to replace the dilute hydrogen peroxide.
Explain why the student does not need to replace the potato pieces already in the flask when repeating the investigation.
Plot a graph of the results and draw a line of best fit.
Use the graph to find the expected volume of oxygen produced when 4 pieces of potato are used.
Use the data in the table to calculate the rate of reaction when the student used 6 pieces of potato.
Give your answer to 2 significant figures.
Rate of reaction =........ cm3 / min
The reaction is exothermic.
Suggest how the student could improve their investigation to control the temperature.
Explain why the student leaves the test tubes in the water bath for 5 minutes before mixing them.
The table shows the student’s results.
| Temperature of water bath (°C) | Time when indicator stays orange (seconds) |
| 20 | 568 |
| 30 | 360 |
| 40 | 60 |
| 50 | 340 |
| 60 | Indicator still changes colour after 600 |
Explain the result for 20 °C.
Explain why amylase works slowly at 50 °C but no longer works at 60 °C.
The student has investigated the effect of temperature on the activity of amylase.
Describe how they could develop their investigation to find the effect of pH on the activity of amylase.
What type of molecules are Q and R ?
Molecule Q........
Molecule R........
Look at the graph. It shows the effect of pH on the activity of lipase enzyme.
Human lipase is most active in the small intestine.
The pH of the small intestine is pH7.5.
The lipase used to produce the results in the graph is not human lipase.
How can you tell this from the graph?
The lock and key hypothesis can explain the pattern in the graph.
Explain the lock and key hypothesis for enzyme specificity.
The diagram in Fig. 15.1 shows events that occur during human sperm production.
Cells in the germinal epithelium have the ability to turn into sperm cells.
Which term describes cells that have the ability to turn into specialised cells?
Compare the number of chromosomes in human germinal epithelium cells and human mature sperm cells.
Describe the events that occur at Stage 1 and Stage 2 in Fig. 15.1.
Sperm production occurs best at 35.0 °C due to the enzymes involved.
Explain why the testes are positioned outside of the body cavity.
Which gas makes the bubbles?
* The students think they could improve their method.
They will count the bubbles three times at each temperature. This would show up any anomalous results.
Describe other ways they could improve their method to obtain more precise and repeatable results.
For each improvement explain why it is needed.
The students count the bubbles three times at each temperature. They then calculate the mean number of bubbles at each temperature.
The table shows their results.
| Temperature (°C) | Mean number of bubbles per minute |
| 10 | 3 |
| 20 | 6 |
| 30 | 11 |
| 40 | 5 |
| 50 | 2 |
| 60 | 1 |
Plot the results on the grid.
Draw a line of best fit.
Respiration is an enzyme controlled reaction.
Use ideas about enzymes to explain the pattern in the results.
The diagram shows the position of the pituitary gland and hypothalamus in the body.
Two hormones released by the pituitary are involved in controlling the menstrual cycle.
Write down the names of these two hormones.
The graph shows the levels of these two hormones during the menstrual cycle.
Use the graph to explain how these two hormones work together to cause ovulation.
The hypothalamus is involved in the regulation of body temperature.
Explain why this function of the hypothalamus is important to the role of enzymes.
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Combined Science starter pack