1.	Barnacles are animals that live on rocky shores. The adults are fixed to the surface of rocks and do not move. The young larvae can swim freely in the sea. As they get older the larvae settle and attach themselves to a rock surface. Here they develop into adults which feed on microscopic plants and animals in the sea when the tide is in. In Britain two species of barnacle, Chthamalus stellatus and Balanus balanoides, commonly occur together on the same rocky shore.
	The diagram shows the typical distribution of the two in relation to the tide levels on a rocky shore.

(a)	In both species of barnacle few of the larvae which settle become adults. Explain how intraspecific competition could account for this.
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(1)
(b)	Suggest how interspecific competition could account for the difference in distribution of the adults of the two species.
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(2)
(c)	Suggest why there are larvae of C. stellatus above maximum high tide level, but no adults.
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(1)

(d)	In an investigation, it was found that the presence of adult barnacles stimulated larvae of the same species to settle in the same area of the shore.
(i)	Suggest a possible stimulus that encourages the larvae to settle.
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(1)
(ii)	Suggest an advantage of larvae settling in the same area as the adults.
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(1)
(Total 6 marks)

2.	Duckweed is a small plant that lives in ponds. As it grows it produces leaf-like structures.
	In an investigation, two species of duckweed, Lemna trisulca and Lemna minor, were grown in three beakers of pond water, X, Y and Z.
	Beaker X Contained only Lemna trisulca.
Beaker Y Contained only Lemna minor.
Beaker Z contained both Lemna trisulca and Lemna minor.
	The growth of each species was measured by counting the number of ‘leaves’. The results of the investigation are shown in the graph.

S	(a)	Give three abiotic factors that should be controlled in order to gain reliable data in this investigation.
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(3)
(b)	Describe the effects of interspecific competition on the growth of the two species.
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(2)
S	(c)	Lemna minor grows on the surface of the pond water. Lemna trisulca grows under the surface.
	Suggest one hypothesis to explain the results for Lemna minor.
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(2)
(Total 7 marks)

Ambrose College