1. 1
   A microbiologist samples a nutrient-rich pond. From the surface water she isolates Euglena, a single-celled protist that contains chloroplasts but also absorbs dissolved organic compounds from the water. From decaying leaves on the pond bottom she isolates three bacterial species, X, Y and Z. She grows each species in a separate tube of nutrient gel in which the oxygen concentration is high at the surface and falls to zero at a depth of 2 cm. Species X grows only in the top 0.5 cm. Species Y grows throughout the gel but most densely in the top 0.5 cm. Species Z grows only below a depth of 1.5 cm.

   (a)

   Which row correctly classifies species X, Y and Z?

   [1 mark]

   • AX obligate aerobe; Y obligate anaerobe; Z facultative anaerobe
   • BX facultative anaerobe; Y obligate aerobe; Z obligate anaerobe
   • CX obligate anaerobe; Y facultative anaerobe; Z obligate aerobe
   • DX obligate aerobe; Y facultative anaerobe; Z obligate anaerobe

   (b)

   Euglena grows in both light and darkness when dissolved organic compounds are present. Which term best describes its mode of nutrition?

   [1 mark]

   • ASaprotrophic
   • BHolozoic
   • CMixotrophic
   • DObligately autotrophic

   (c)

   Explain why species Y grows most densely near the surface of the gel.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An anthropology class examines casts of three hominid skulls. Skull 1, Paranthropus robustus, has very large, flat premolars and molars with thick enamel, small incisors and canines, a massive lower jaw and a bony ridge (sagittal crest) along the top of the skull where large jaw muscles attached. Skull 2, Homo sapiens, has small molars with moderately thick enamel and small canines that are similar in size to the incisors. Skull 3, Homo floresiensis, is small, with small molars and small canines; stone tools and animal bones with cut marks were found in the same cave deposits.

   (a)

   Which feature of skull 1 is most strongly associated with a diet of hard, tough plant material?

   [1 mark]

   • ASmall incisors
   • BLarge, flat molars with thick enamel
   • CLong, pointed canines
   • DCanines similar in size to the incisors

   (b)

   The diet of Paranthropus robustus cannot be observed. How have scientists reached conclusions about it?

   [1 mark]

   • ABy deduction from theories relating dentition to diet that were developed by observing living mammals
   • BBy direct observation of living Paranthropus populations
   • CBy analysing the preserved stomach contents of fossilised Paranthropus
   • DBy assuming that all hominids had the same diet as modern humans

   (c)

   Deduce, with a reason, whether Homo floresiensis was herbivorous or omnivorous.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Two barnacle species live on a rocky shore. Adults of Chthamalus stellatus are found only in the upper intertidal zone, which is exposed to air for long periods, while adults of Semibalanus balanoides occupy the middle and lower zones. Chthamalus larvae settle in both the upper and lower zones. In an experiment, Semibalanus was removed from some rocks in the lower zone. After one year, 90% of the Chthamalus that had settled on cleared rocks were still alive, compared with 25% on rocks where Semibalanus remained; many of these had been smothered, crushed or prised off by the faster-growing Semibalanus. Semibalanus transplanted into the upper zone died from drying out, whether or not Chthamalus was present.

   (a)

   Using the data, distinguish between the fundamental niche and the realized niche of Chthamalus.

   [3 marks]

   (b)

   Evaluate the claim that these results demonstrate competitive exclusion.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   In a lowland rainforest in Borneo, canopy trees reach 45–60 m and intercept about 95–98% of the sunlight, so plants on the forest floor receive only 2–5% of full sunlight. Woody lianas root in the soil and climb the trunks of trees. Orchids and ferns grow as epiphytes on high branches, and strangler figs germinate on branches before sending roots down to the soil. Shade-tolerant herbs with broad, thin leaves grow on the forest floor. Caterpillars and leaf beetles eat leaves, and many understorey plants have spines or leaves containing toxic alkaloids. Western tarsiers hunt insects at night; they have very large eyes, sensitive hearing, long hind limbs for leaping and grasping hands. Some of their prey are stick insects that resemble twigs and remain motionless during the day.

   (a)

   Explain how the forms of different plants in this forest are adapted for harvesting light.

   [6 marks]

   (b)

   Discuss how adaptations of herbivores and plants, and of predators and prey, influence feeding relationships in this forest.

   [6 marks]

   Total for question 4: 12 marks

End of questions