The sea otter, Enhydra lutris, is a marine mammal that lives on the coasts of the North Pacific ocean. Fig. 6.1 shows a sea otter. [Figure 6.1] Table 6.1 shows part of the classification of the sea otter. Table 6.1 taxonomic group name phylum Chordata class Mammalia order Carnivora family Mustelidae genus Enhydra species lutris

1. (a)Complete Table 6.1 by adding the correct taxonomic groups in the two spaces provided.[2]
2. (b)There were estimated to be about 300000 sea otters in the year 1700. • Extensive hunting for their fur resulted in the numbers of sea otters falling to about 1000 by the year 1911, when most hunting was banned. • The population size then increased to about 125000 by the year 2012. All of the sea otters alive today are descended from the 1000 individuals alive in the year 1911. Outline the genetic consequences to a species, such as the sea otter, of having a large population that is descended from a very small number of individuals.[3]
3. (c)Seaweeds, such as kelp, are large algae that can grow to be over 30 metres in length. In the ocean along the coasts of California, USA, there are very dense areas of kelp called kelp forests. Kelp forests are very productive and diverse ecosystems. Fig. 6.2 shows a kelp forest. [Figure 6.2] The sea otter is a keystone species in kelp forests along the coasts of California. This means that sea otters have a larger than expected effect on other organisms in these kelp forests. The loss of the sea otter would cause major changes to the kelp forest ecosystem and a reduction in biodiversity. Fig. 6.3 shows part of a food web in a kelp forest. The arrows show the direction of energy flow. sea otters large fish sea urchins starfish crabs other small invertebrates sea slugs molluscs kelp other algae small fish animal plankton plant plankton [Figure 6.3] Using Fig. 6.3, suggest and explain what would happen to the numbers of sea urchins, animal plankton and crabs if sea otters in this kelp forest became extinct. sea urchins animal plankton crabs[3]
4. (d)Sea otters may spend up to five minutes under water while searching for food. During this time, respiration in anaerobic conditions takes place. When a sea otter first returns to the surface of the ocean, its breathing is faster and deeper than normal. Explain why its breathing is faster and deeper than normal.[3]
5. (e)The striated muscle of the sea otter is composed of fibres called myofibrils. Myofibrils are made of units called sarcomeres. Describe the proteins that are involved in the contraction of a sarcomere.[4]

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