Oryza is a genus of grass plants that includes the rice, Oryza sativa, a food crop.

1. (a)(i)Farmers flood fields of rice because this encourages faster growth and higher yields. An adaptation of rice plants that allows them to grow in water is the development of aerenchyma. State the function of aerenchyma.[2]
2. (a)(ii)State one other way in which the roots of rice are adapted to being submerged in water.[1]
3. (a)(iii)Another adaptation in some varieties of rice is the fast growth of stems. Describe how selective breeding could produce varieties of rice with fast-growing stems.[3]
4. (a)(iv)Auxin is a plant growth hormone that affects the growth of rice stems. Explain how auxin affects the growth of rice stems.[3]
5. (b)O. rufipogon and O. nivara are two species of wild rice. • O. rufipogon grows in places where water is always available. • O. nivara grows within the same geographical range as O. rufipogon. • The habitat of O. nivara can lack water for part of the year. • The two species flower at different times of the year. These two rice species may have evolved by sympatric speciation. Explain how O. rufipogon and O. nivara may have evolved through sympatric speciation.[3]