1. 1
   A team of researchers is studying the growth of a group of laboratory mice from birth to eight weeks old. Each mouse is weighed weekly and its body length is measured. The researchers want to explain the biological processes that allow the mice to grow so much larger in just eight weeks, and how the mice's growth compares with children of the same age using standard reference data.

   (a)

   Which type of cell division is responsible for growth in animals?

   [1 mark]

   • AMitosis
   • BMeiosis
   • CBinary fission
   • DCytolysis

   (b)

   As the mice grow, some cells become specialised, for example into muscle cells or neurones. What is this process called?

   [1 mark]

   • AFertilisation
   • BDifferentiation
   • CTranscription
   • DTranslocation

   (c)

   The researchers plot each mouse's weekly weight on a percentile chart similar to those used for human infants. Explain how a percentile chart can be used to monitor whether an individual mouse is growing normally compared with the wider population.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student germinates cress seeds and measures the length of each root every day for five days. On day one, the roots are 2 mm long; by day five, they have grown to 30 mm long. The student marks equally spaced ink dots along one root on day one and observes where the dots have moved to by day five to work out which part of the root grew the most.

   (a)

   Which combination of processes allows the root of the seedling to lengthen?

   [1 mark]

   • ACytokinesis without cell division
   • BMeiosis and fertilisation
   • COsmosis and active transport only
   • DCell division and cell elongation

   (b)

   The student observes that the ink dots nearest the root tip are furthest apart by day five, while the dots near the base of the root have barely moved. Which region of the root is responsible for this pattern?

   [1 mark]

   • AThe mature vascular tissue near the stem
   • BThe root hair zone
   • CThe elongation zone just behind the root tip
   • DThe root cap

   (c)

   Describe how growth occurs in a plant root, referring to cell division, elongation and differentiation.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A paediatrician keeps growth records for a group of children attending a clinic, plotting each child's height and weight on standard percentile charts at every check-up. One 7-year-old boy has always tracked along the 50th percentile line for height since birth, but at his most recent check-up his height has fallen to the 5th percentile, prompting further investigation, while his weight has remained steady on the 60th percentile.

   (a)

   A doctor compares the height of a 7-year-old boy against a standard childhood growth chart. The boy's height has been on the 50th percentile line since birth, but at his most recent check-up his height has dropped to the 5th percentile. Explain why this drop is a cause for concern, even though the boy is still growing.

   [3 marks]

   (b)

   The paediatrician also notes that the boy's weight has stayed on the 60th percentile while his height has dropped to the 5th percentile. Suggest and explain two further pieces of information the paediatrician should gather to help work out the cause of the change in the boy's growth pattern.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A gardener grows two batches of tomato seedlings from the same seed stock. Batch A is grown in a warm, well-lit greenhouse and produces tall plants with broad leaves within four weeks. Batch B is grown in a cooler, shaded shed and after four weeks remains noticeably smaller, with thinner stems and smaller leaves, despite receiving the same watering and fertiliser as Batch A.

   (a)

   Explain, in terms of cell division, cell elongation and cell differentiation, how the difference in growing conditions could account for the difference in size between the two batches of seedlings.

   [6 marks]

   (b)

   The gardener then moves Batch B into the warm, well-lit greenhouse alongside Batch A for a further four weeks, keeping both batches under identical conditions from this point onwards. Discuss whether you would expect Batch B to fully catch up to the same size as Batch A, giving biological reasoning for your answer.

   [6 marks]

   Total for question 4: 12 marks

End of questions