Algae are a diverse group of photosynthetic eukaryotes in the kingdom Protoctista. Rhodomonas salina and Skeletonema costatum are two species of alga that live in seawater. Fig. 1.1 shows a scanning electron micrograph of $$\(R\)$$. salina, which is a unicellular organism. $$\(R\)$$. salina is red in colour. Fig. 1.1 Fig. 1.2 shows a scanning electron micrograph of $$\(S\)$$. costatum, which is also a unicellular organism. The individual cells can group together in a chain. S. costatum is yellow-brown in colour. Fig. 1.2 For each colour of light, the student carried out a statistical test to compare the pH of the samples taken from the small bottles that contained $$\(R\)$$. salina and $$\(S\)$$. costatum. The student decided that a $$\(t\)$$-test was the most appropriate test to use for these data. (i) Suggest one reason why a $$\(t\)$$-test was the most appropriate test to use for these data. ....................................................................................................................................... . ....................................................................................................................................... . ................................................................................................................................. (ii) State a null hypothesis for this test. ....................................................................................................................................... . ....................................................................................................................................... . .................................................................................................................................

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