1. 1
   A group of students studied a hedgerow ecosystem. They recorded every oak tree, every rabbit, and every blackbird in a marked-out field, and also noted the presence of soil, water and sunlight.

   (a)

   Which term describes all of the oak trees living in the field together?

   [1 mark]

   • AA population
   • BA community
   • CAn ecosystem
   • DA habitat

   (b)

   The students noticed that during a particularly cold winter, the number of rabbits in the field fell sharply, while the number of blackbirds stayed roughly the same. Which factor most likely explains the fall in rabbit numbers?

   [1 mark]

   • AA biotic factor (predation)
   • BAn abiotic factor (temperature)
   • CMigration to a warmer habitat
   • DAn increase in mutualism

   (c)

   The students also noticed that rabbits and oak seedlings both needed the same patch of open ground to grow and feed. Explain, using the term competition, why this might reduce the number of oak seedlings that survive.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A species of small fish called the cleaner wrasse removes and eats parasites from the skin of larger reef fish. The larger fish benefit by being kept free of parasites, and the cleaner wrasse gains a reliable source of food. A separate species, the tapeworm, lives inside the gut of some of these larger reef fish, absorbing digested nutrients directly from the fish's intestine and causing the fish to lose body condition.

   (a)

   What type of relationship exists between the cleaner wrasse and the larger reef fish?

   [1 mark]

   • APredation
   • BParasitism
   • CMutualism
   • DCompetition

   (b)

   Referring to the tapeworm living inside the gut of the reef fish, which statement correctly describes this relationship?

   [1 mark]

   • ANeither organism is affected
   • BBoth the tapeworm and the fish benefit
   • CThe tapeworm is harmed and the fish benefits
   • DThe tapeworm benefits and the fish is harmed

   (c)

   Explain why the survival of the cleaner wrasse population described above depends on interdependence with the larger reef fish.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A class carried out fieldwork in a school meadow to estimate the population of daisy plants. They placed a 0.5 m by 0.5 m quadrat at ten randomly chosen points across the meadow and counted the number of daisies inside each quadrat. Their ten counts were: 4, 6, 3, 5, 7, 4, 5, 6, 3, 7. The total area of the meadow was 200 m^2. A second group used a belt transect across the meadow, from the shaded edge near a hedge to the sunny centre, and found that daisy numbers increased steadily moving away from the hedge.

   (a)

   Calculate the mean number of daisies per quadrat, then use this to estimate the total number of daisies in the whole meadow. Show your working.

   [3 marks]

   (b)

   Using the belt transect results, explain why daisy numbers increased moving away from the hedge, and describe one improvement the class could make to increase the reliability of their quadrat data.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A lake ecosystem contains algae, small fish that eat the algae, and larger predatory fish that eat the small fish. Over several years, a nearby factory has been discharging warm water and small amounts of pollutants into the lake. Scientists have observed that algae numbers have increased, small fish numbers have fluctuated, and the top predatory fish have declined.

   (a)

   Describe the different levels of organisation present in this lake ecosystem, and explain how the levels of organisation, interdependence between species, and the abiotic factors described (temperature and pollutants) together determine the number of organisms found at each level.

   [6 marks]

   (b)

   The factory has proposed reducing the temperature of the water it discharges into the lake, but continuing to release the same amount of pollutants. Evaluate whether this single change is likely to restore the lake ecosystem to its original state, using ideas about abiotic factors, biotic factors and interdependence in your answer.

   [6 marks]

   Total for question 4: 12 marks

End of questions