OCR GCSE Combined Science B (21st Century) Paper 8 June 2024 question paper

Doctors select radioactive isotopes for imaging scans and for treatments very carefully.

The table shows the radiation emitted and half-lives of 6 radioactive samples.

Which sample is suitable to be used as a radioactive tracer for an imaging scan?

Explain your answer.

Use data from the table.

Sample........

Explanation........

Samples A and B emit alpha radiation.

Suggest two precautions that should be taken by hospital staff when handling samples A and B.

One of the samples in the table is radium-226.

Determine the number of neutrons in a nucleus of a radium-226 atom.

Use the Data and Equation Sheet.

How many outer shell electrons does each radium-226 atom have?

Explain your answer.

Use the Data and Equation Sheet.

Number of outer-shell electrons........

Another of the radioactive isotopes in the table is iodine-131.

Which element will most readily react with iodine-131 to form a salt?

Tick (✓) one box.

Some students are learning about radioactivity and radioactive half-life.

What is the definition for the activity of a radioactive source?

Tick (✓) one box.

What is the definition of half-life?

Tick (✓) one box.

The graph shows experimental data from a radiation detector, and a separate mathematical model of decay.

Complete the sentences about radioactive decay.

Use words from the list.

complete match random replace selective trend

Radioactive decay is a........ process.

Experimental data may not........ the model results due to chance

but the overall........ will be the same.

An antibiotic sensitivity test can help researchers to develop new antibiotics.

The test procedure is:

1. Spread bacteria on an agar plate.

2. Soak discs of paper in different antibiotics.

3. Place the discs of paper on an agar plate.

4. Incubate the agar plate so that the bacteria can grow.

There is a clear zone around each disc where no bacteria grow. This shows how effective an antibiotic is against the type of bacteria that is on the agar plate.

The image shows some test results. Some of the paper discs have been labelled B, C and D.

Draw a line to the least effective antibiotic disc and label it A.

Measure the diameter of the clear zone for antibiotic disc B.

Give your answer in mm.

Calculate the area of the clear zone for antibiotic disc B.

Use the equation: area = 3.14 × r²

At school, some students are studying rates of reaction.

They use this method to investigate how temperature affects the rate of reaction:

• Add 50 cm³ of sulfuric acid to calcium carbonate (CaCO₃) powder in a conical flask, at room temperature.

• Measure the change in mass of the reactants every 30 seconds for five minutes.

• Repeat the experiment at 80 °C.

Name one piece of equipment the students can use, instead of a Bunsen burner, to heat the reactants and conduct the experiment at 80 °C.

Explain your answer.

Equipment........

Explanation........

Suggest two improvements to this method. Explain each suggestion.

Carbon dioxide gas (CO₂) is produced in the reaction and escapes from the conical flask.

Calculate the relative formula mass of carbon dioxide.

Use the Data and Equation Sheet.

The reading on the balance at the start of the experiment and after two minutes is shown.

Calculate the number of moles of carbon dioxide produced in two minutes.

In another experiment, 0.006 moles of carbon dioxide is produced.

Calculate the number of molecules in 0.006 moles of carbon dioxide.

1 mole of a substance contains 6.0 × 10²³ molecules.

The student repeats the experiment again using a gas syringe to measure the volume of carbon dioxide gas produced.

They measure 92 cm³ of carbon dioxide which is equal to 0.184 g.

1 cm³ of carbon dioxide = 0.002 g.

If this 0.184 g of carbon dioxide was weighed on the balance shown in part (b)(ii), what would the balance display?

Tick (✓) one box.

Suggest one reason why the gas syringe method will give a more accurate number of moles of carbon dioxide than the balance method.

In the 1860s Gregor Mendel studied inheritance by crossing together pea plants with different characteristics.

Complete the Punnett square to show the possible genotypes when Mendel crossed homozygous tall pea plants with homozygous short pea plants.

The dominant allele causes plants to be tall.

Use T for the dominant allele. Use t for the recessive allele.

A student makes a statement about the genetic cross:

“If 100 pea plants were produced from this cross, then 50 of them should be tall pea plants.”

Explain why the student’s statement is incorrect.

The diagram shows a diver standing stationary at point X, several metres away from the diving board.

The diver takes a run up to the diving board.

The diver’s speed when they reach the diving board is 2.7 m / s. It takes 2.5 s for the diver to reach the diving board.

Calculate the acceleration between point X and the diving board.

Acceleration =........ m / s²

At point Y, the diver is no longer in contact with the diving board and is in free fall. At point Z under water, the diver has reached a constant speed.

Calculate the difference in acceleration between point Y and point Z.

Difference in acceleration =........ m / s²

Some students are investigating photosynthesis.

They measure the volume of gas produced by pondweed every 60 seconds.

Fig. 7.1 shows their results.

Calculate the rate of reaction.

Rate of reaction =........ cm³ / s

Describe the chemical test that the students can do to prove that the gas produced is oxygen.

The teacher gives the students the data shown in Fig. 7.2.

It shows how the intensity of light affects the volume of gas produced by pondweed in 10 minutes. The light intensity is varied by moving the lamp further away from the pondweed.

Distance from the lamp to the pondweed (m)

A student writes:

“The greater the distance of the lamp from the pondweed the slower the rate of photosynthesis.”

Evaluate the student’s statement.

State two factors that need to be controlled in this light intensity experiment.

Factor 1........

Factor 2........

Calculate the rate of photosynthesis when the lamp is 0.30 m from the beaker.

Rate of photosynthesis =........ cm³ / min

Fig. 7.3 shows how the rates of photosynthesis and respiration for a plant vary over a 24 hour period during the winter.

At which times of the day are the rate of respiration and the rate of photosynthesis equal in winter ?

Use Fig. 7.3.

In the summer the hours of daylight are longer and the temperature is warmer.

Sketch a curve on Fig. 7.3 for the rate of photosynthesis over a 24 hour period in the summer

Bungee jumping is an extreme sport that involves jumping off a high platform while attached to an elasticated ‘bungee’ cord.

A person’s weight needs to be measured before a bungee jump so that appropriate equipment can be used.

Describe how weight is measured.

In Fig. 8.1, the bungee cord is stretching.

Describe two forces that cause the cord to stretch.

In Fig. 8.2, the bungee jumper is at rest.

Draw two labelled arrows on Fig. 8.2 to represent the interaction pair of forces between the person and the bungee cord.

Fig. 8.3 shows the force-extension graph for a bungee cord at forces up to and beyond the forces experienced during a bungee jump.

Describe the relationship between force and extension in Fig. 8.3.

* A lifeboat organisation wants to buy a new tow rope.

The tow rope must:

• have a breaking force greater than 88 MN

• stretch easily to store energy as the boats go over waves

• sink in sea water.

The table shows some properties of three polymer ropes which all have the same dimensions.

The density of sea water is 1.02 g / cm³.

Explain which polymer is the most suitable to use for the tow rope.

Include in your answer:

• why you have not chosen the other polymers

• any other factors that may be considered when choosing the most suitable polymer.

Explain why carbon atoms can form a large variety of polymer ropes.

Use ideas about bonding.