Interactions between organismsIB MYP Biology: Topic test

1. 1
   Clownfish live among the stinging tentacles of sea anemones on coral reefs in Fiji. The anemone's stings protect the clownfish from predators. The clownfish chase away fish that eat anemones, and their waste provides the anemone with nutrients. A small shrimp also shelters among the tentacles: it gains protection, but the anemone is neither helped nor harmed by the shrimp.

   (a)

   What type of relationship exists between the clownfish and the anemone?

   [1 mark]

   • AParasitism
   • BPredation
   • CCommensalism
   • DMutualism

   (b)

   What type of relationship exists between the shrimp and the anemone?

   [1 mark]

   • ACommensalism
   • BParasitism
   • CMutualism
   • DPredation

   (c)

   Explain how both the clownfish and the anemone benefit from their relationship.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Malaria is caused by a single-celled organism called Plasmodium. A female Anopheles mosquito becomes infected when she bites an infected person and takes in blood containing the parasites. When she later bites a healthy person, the parasites enter that person's blood and travel to the liver.

   (a)

   What is the role of the Anopheles mosquito in the spread of malaria?

   [1 mark]

   • AIt is the parasite that causes the disease
   • BIt is a vector that transfers the parasite between people
   • CIt is a predator of the parasite
   • DIt is a producer in the food chain

   (b)

   Which method would best reduce the spread of malaria?

   [1 mark]

   • AWashing hands before eating
   • BCooking meat thoroughly
   • CSleeping under insecticide-treated bed nets
   • DBoiling all drinking water

   (c)

   Explain how draining areas of stagnant water reduces the spread of malaria.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   In a greenhouse in the Netherlands, a grower introduces ladybirds to control aphids on pepper plants. The aphid population rises quickly at first. About two weeks later the ladybird population begins to rise, and as it does, the number of aphids falls. Later the number of ladybirds also falls.

   (a)

   Explain why the rise in the ladybird population comes after the rise in the aphid population.

   [3 marks]

   (b)

   The grower wants to investigate whether more ladybirds lead to fewer aphids. Write a testable hypothesis with a reason, and identify the independent variable and the dependent variable.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Lionfish are venomous fish from the Pacific that have been introduced to the Caribbean. They eat large numbers of young native fish and compete with native predatory fish, such as groupers, for food. Researchers on a reef in the Bahamas want to estimate the number of lionfish. They caught 60 lionfish, marked each with a harmless tag and released them. A week later they caught 45 lionfish, of which 15 carried a tag. Some divers suggest paying fishers to remove lionfish from reefs.

   (a)

   Calculate the estimated number of lionfish on the reef and evaluate the reliability of this method.

   [6 marks]

   (b)

   Discuss whether governments should pay fishers to remove lionfish from reefs.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   In 1990 a conservation group released 25 deer onto a large island in Chile that has no natural predators. For the first four years the population grew slowly. It then increased rapidly for about eight years and, after twelve years, levelled off at about 800 deer, where it has stayed since.

   (a)

   What term describes the largest population that the island can support for a long time?

   [1 mark]

   • ACarrying capacity
   • BSpecies richness
   • CPopulation density
   • DLag phase

   (b)

   Which is the most likely factor that limits the deer population once it has levelled off?

   [1 mark]

   • APredation by wolves
   • BCompetition from plants for light
   • CAn unlimited supply of food
   • DCompetition between the deer for food and shelter

   (c)

   Explain why the population grew slowly at first and then increased rapidly.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   Students are surveying the percentage cover of seaweed on a rocky shore in Cornwall. They use a 50 cm by 50 cm quadrat that is divided into 25 equal squares by string.

   (a)

   Seaweed completely fills 9 of the 25 squares. What is the percentage cover of seaweed in this quadrat?

   [1 mark]

   • A9%
   • B25%
   • C36%
   • D64%

   (b)

   Which method places the quadrats randomly?

   [1 mark]

   • APlacing each quadrat where the seaweed looks thickest
   • BUsing random numbers from a calculator as coordinates along two tape measures
   • CPlacing the quadrats at regular 5 m intervals
   • DChoosing places on the shore that are easy to reach

   (c)

   Explain why the students should place their quadrats randomly rather than on areas where the seaweed looks dense.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A school in Mexico City wants to estimate the number of dandelion plants on a lawn with an area of 600 m². The students place ten 1 m² quadrats at random positions and count the dandelions in each. Their counts are 4, 7, 5, 3, 6, 8, 2, 5, 6 and 4.

   (a)

   Calculate the mean number of dandelions per square metre and use it to estimate the number of dandelions on the whole lawn.

   [3 marks]

   (b)

   Evaluate the students' method by suggesting one way to make the estimate more accurate, explaining why, and identifying one source of error and how to reduce it.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   Avocado farmers in Kenya spray a pesticide that kills aphids but also harms honeybees. Honeybees visit avocado flowers to collect nectar and, as they do so, they pollinate the flowers, which are then able to form fruit. Since the spraying began, the number of honeybee colonies on the farms has fallen by a third and the harvest has dropped.

   (a)

   Explain how the fall in honeybee numbers has caused the fall in the harvest and how it could affect other organisms.

   [6 marks]

   (b)

   Discuss whether the farmers should continue to spray this pesticide.

   [6 marks]

   Total for question 8: 12 marks

End of questions