Syllabus Edition
First teaching 2023
First exams 2025
1 markThe following diagram shows the process of oogenesis in a human ovary.
Identify the structure present at stage 2 in the diagram.
2 marksDescribe what is happening to the structure identified in a) between steps 3 and 4 in the diagram in part a).
3 marksIdentify three similarities between the processes of oogenesis and spermatogenesis.
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Some scientists investigated the uptake of magnesium ions in rice plants. They divided the plants into two groups and placed their roots in solutions containing radioactive magnesium ions.
Group Y: plants had a substance that inhibited respiration added to the solution
Group Z: plants did not have the respiratory inhibitor added to the solution
The scientists calculated the total mass of magnesium ions absorbed by the plants every 5 minutes. Their results are shown in the graph below:
Calculate the ratio of the mean rate of uptake of magnesium ions in the first 20 minutes to the mean rate of uptake of magnesium ions in the second 20 minutes for group Z.
Using the graph in part (a), calculate the rate of uptake of magnesium ions for group Y plants after 40 minutes. Give suitable units.
Consider the graph in part (a). Explain the results of the investigation.
State two differences between the processes of facilitated diffusion and active transport.
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Crops absorb and use light energy for the production of photosynthetic products.
Describe how light energy is used by crop plants during the light-dependent reaction.
The diagram below depicts the light-independent reactions of photosynthesis.
Describe the mechanism of these reactions and explain how they allow for the continuous synthesis of 6-carbon sugars.
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2 marksThe table below shows the genome size and haploid chromosome number of different organisms.
| Organism | Genome size / base pairs | Chromosome number / n |
| Polychaos dubium (single celled eukaryote) | 6.7 x 1011 | > 100 |
| Trumpet lily (plant) | 9.0 x 1010 | 12 |
| Mouse | 3.5 x 109 | 20 |
| Human | 3.2 x 109 | 23 |
| Carp (fish) | 1.7 x 109 | 49 |
| Chicken | 1.2 x 109 | 39 |
| Housefly | 9.0 x 108 | 6 |
| Tomato plant | 6.6 x 108 | 12 |
Calculate the percentage difference in the chromosome number found in the zygotes of chickens compared to those of humans.
Show your working and give your answer to three significant figures.
2 marksThe diploid number in an organism is always an even number.
Using your knowledge on the behaviour of chromosomes during meiosis, explain the importance of the diploid number in an organism.
3 marksScientists hypothesised that a high chromosome number leads to the development of a more complex organism.
Discuss this hypothesis using the data provided in part a).
1 markBased on your knowledge of chromosomes, suggest a reason why the genome size of a species does not always seem to correlate with the chromosome number.
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