Chapter 42

Summary		Questions		Media Resources
42.1 Angiosperms have been incredibly successful, in part, because of their reproductive strategies.
• Angiosperms have been successful because they can be relatively drought-resistant, and smaller herbaceous angiosperms have relatively short life cycles. Most important, however, are their flowers and fruits. Flowers make possible the precise transfer of pollen and, therefore, outcrossing, even when the stationary individual plants are widely separated. Fruits, with their complex adaptations, facilitate the wide dispersal of angiosperms. • Modification of floral parts, especially petals, has been key in facilitating pollination. Bilateral symmetry has evolved independently, multiple times.		1.  What characteristics of early angiosperms are thought to contribute to their success. 2.  What flower whorl is collectively made up of petals? With which other plant parts are the petals of most flowers homologous? 3.  What is an androecium? Of which flower parts is it composed?		•Angiosperms
42.2 Flowering plants use animals or wind to transfer pollen between flowers.
• Bees are the most frequent and constant pollinators of flowers. Insects often are attracted by the odors of flowers rather than color. Birds are attracted to red flowers, but not odors. • Self-pollination reduces genetic variability among offspring. Outcrossing increases genetic diversity. • Outcrossing in different angiosperms is promoted by the separation of stamens and carpels into different flowers, or even into different individuals.		4.  What does it mean if a plant is dichogamous? Of what advantage is it to the plant? 5.  Is it more likely that a flower visited by a social or a solitary bee will become highly specialized toward that bee? Why?		•Gamete Formation •Fertilization
42.3 Many plants can clone themselves by asexual reproduction.
• In asexual reproduction, plants clone new individuals from portions of adult roots, stems, leaves, or ovules. • The progeny produced by asexual reproduction are all genetically identical to the parent individual, even when they are produced in the ovules (apomixis).		6.  Why would a plant capable of sexual reproduction reproduce asexually? 7.  You have just cloned a gene responsible for apomixis. Several corn breeders are very interested in your gene. Why?		•Asexual Reproduction
42.4 How long do plants and plant organs live?
• Plants can live for a single season or thousands of years. • For annual and biennial plants, reproduction triggers senescence and death. • Asexually reproducing plants can form clones that cover huge areas and/or live for many thousands of years. • Plant organs and shoots can senesce and die while the whole plant thrives. Organ senescence is an efficient way to maximize the use of energy resources.		8.  Some plants flower once and die; others flower multiple times, reaching great heights and diameters. What are the relative advantages of the two strategies? 9.  How and why does leaf abscission occur?

•  Scientists on Science •  How Scientists Think •  Student Papers

•  Bioethics Case Studies •  General Biology Weblinks

• Essential Study Partner

• Multiple Choice Quiz