ASIM'S WEBWORLD View: Main School Main AP Biology Chapter Guides RELATED LINKS Chapter Outline		AP BIOLOGY: Chapter Thirty-Four Review Answers 1. All angiosperms are believed to be derived from a single ancestor because of the great number of common features, embryology, double fertilization, and endosperm; these make it unlikely that such features evolved in the same manner more than once. Gnetales are most closely related to the angiosperms. The earliest known definite angiosperm fossils are pollen grains, which are 123 million years old. 2. The two classes are the monocotyledones and dicotyledones. They differ in the following ways. Monocots have parallel venation in leaves, flower parts in threes, and embryos with one cotyledon seedling leaf. Dicots have netlike venation in leaves, flower parts in fours or fives, and embryos with two cotyledon seedling leaves. Monocots are derived from dicots by the suppression of one of the cotyledons. This is evident from the fact that monocots and primitive dicots have single-pored pollen, whereas more advanced dicot pollen is three pored. 3. Nine characteristics are flowers, gamete transfer (without requiring water), outcrossing, fruit dispersal, tough leaves, leaves with stomata, leaves with cuticles, specialized conducting elements, and production of natural insecticides. 4. A primitive angiosperm flower has numerous, free, spirally arranged sepals, petals, stamens, and carpels, with little visual differentiation between petals and sepals. Scientists can determine whether a flower is primitive or advanced by comparing the wood and pollen of the plant to those of known primitive plants, observing fusion and/or reduction in flower parts, and comparing the flower to fossil flowers. 5. Tissues that exhibit determinate growth (such as the apical meristem) do not continue to grow once a structure (i.e., a flower) is formed. Tissues with indeterminate growth (such as leafy shoots) continue to grow and differentiate. 6. The corolla is collectively made up of petals. The petals of most flowers are homologous with stamens in that both are affected by genes that do not affect either carpels or sepals. In a small number of flowers, petals evolved from sepals, which enlarged and developed color. 7. An androecium is the male reproductive structure, and it is composed of the stamens, which have probably evolved from the systems of small branches among which the microsporangia were borne. The anther produces pollen grains. 8. Pistillate flowers have only pistils and sterile or no stamens; staminate flowers have only stamens and no carpels. A dioecious sporophyte produces either ovules or pollen, whereas a monoecious sporophyte produces both ovules and pollen. These diverse characteristics promote outcrossing and reduce inbreeding. 9. Dichogamous plants are functionally staminate at one point in time and functionally pistillate at others; that is to say, the plant has both male and female parts, but they are not fertile at the same time. Genetic self-incompatibility refers to plants that cannot fertilize themselves due to incompatibility of pollen with stigma or inviability of the embryo. The advantage to this is that it promotes outcrossing, leading to more genetic diversity in the population. 10. Social bees have large colonies and must visit many types of flowers to get enough food; they produce several generations over a summer and must vary their flower choices over time as well; solitary bees have only a single brood to raise and use only a single type of flower. It is more likely that this flower will be visited by a solitary bee because it visits only a single type of flower; thus they can evolve together. Coevolution is advantageous to both parties as follows: plants get an efficient, reliable source of pollination and the bee gets a constant source of food. 11. Plants pollinated by birds must produce more nectar because birds use a lot more energy than insects. Deterring factors are red flowers, which attract birds but are not especially noticeable to insects; odorless flowers, because birds have strong visual, but weak, olfactory senses; and well-protected nectaries, which are available only to a strong beak. 12. Wind-pollinated flowers are small, greenish, and odorless; have reduced or absent corollas; and hang downward in tassels that wave in the wind. These plants have separate flowers, often even on separate plants. This promotes outcrossing. 13. Seeds were buoyant and floated to the island; seeds were carried by birds either on their bodies or inside their bodies as food; seeds were small and light and were blown to the island.