1. 1
   Marram grass (Ammophila arenaria) grows on mobile sand dunes along the coasts of north-west Europe. The sand holds little water and few nutrients, and the dunes are exposed to strong winds and salt spray and are often buried by blown sand. In dry weather the leaves roll into a tube, enclosing the stomata, which lie in grooves lined with hairs on the inner surface. When buried, its underground stems grow rapidly upwards, and its roots can extend more than 2 m deep.

   (a)

   How does rolling of the leaves reduce water loss in marram grass?

   [1 mark]

   • AIt increases the surface area exposed to the wind
   • BIt allows the leaf to absorb water from the air
   • CIt stops photosynthesis completely
   • DIt traps humid air around the stomata, reducing the concentration gradient for water vapour

   (b)

   Which of the following is an abiotic variable affecting the distribution of marram grass?

   [1 mark]

   • AGrazing by rabbits
   • BCompetition from other dune plants
   • CBurial by blown sand
   • DInfection by fungi

   (c)

   Outline the habitat of marram grass.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Red mangrove (Rhizophora mangle) forms forests in the intertidal zone of tropical coasts such as southern Florida. Its roots grow in soft mud that is waterlogged and contains almost no oxygen, and it is flooded twice a day by sea water. The tree has arching prop roots with many pores (lenticels) above the mud, root membranes that exclude most of the salt from the water taken up, and seeds that germinate while still on the parent tree. Red mangroves are absent from coasts where air temperatures regularly fall below freezing, and are rare on the dry land just behind the shore.

   (a)

   What is the main function of the lenticels on the prop roots?

   [1 mark]

   • ATo allow oxygen to reach root tissues growing in oxygen-free mud
   • BTo absorb mineral ions from sea water
   • CTo excrete excess salt
   • DTo carry out photosynthesis

   (b)

   Which conclusion about red mangrove is best supported by the information?

   [1 mark]

   • ATemperature has no effect on its distribution
   • BFreezing temperatures lie outside its range of tolerance
   • CIt can only survive in fresh water
   • DIts range of tolerance for salinity is narrower than that of most land plants

   (c)

   Suggest why red mangroves dominate the intertidal zone but are rare on the dry land just behind the shore.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student ran a 20 m transect from the shade of a beech wood out into an open meadow on a sunny day. At 5 m intervals she measured light intensity with a light sensor and estimated the percentage cover of dog's mercury (Mercurialis perennis) in a 1 m² quadrat. At 0 m light intensity was 2 klx and cover 60%; at 5 m, 8 klx and 35%; at 10 m, 20 klx and 10%; at 15 m, 45 klx and 0%; at 20 m, 60 klx and 0%. Soil moisture was highest under the trees and lowest in the meadow, where grasses covered almost all the ground.

   (a)

   Describe the relationship between light intensity and dog's mercury cover, and deduce the upper limit of its range of tolerance for light.

   [3 marks]

   (b)

   Evaluate the conclusion that light intensity determines the distribution of dog's mercury.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Climate data for four locations: P, mean annual temperature 26 °C and annual rainfall 2800 mm, spread through the year; Q, 24 °C and 120 mm; R, −1 °C and 500 mm, with long cold winters and a short summer; S, −12 °C and 200 mm, with the ground permanently frozen a short distance below the surface. The Sonoran Desert of North America and the Namib Desert of Africa both have climates like Q. Both contain succulent plants with swollen, water-storing stems and spines, although those in America are cacti and those in Africa belong to an unrelated family, the euphorbias.

   (a)

   Deduce, with reasons, the biome at each location, and explain how temperature and rainfall determine the distribution of biomes.

   [6 marks]

   (b)

   Compare and contrast the adaptations of named plant and animal species to life in hot deserts and in tropical rainforests.

   [6 marks]

   Total for question 4: 12 marks

End of questions