Plant Diversity II: The Evolution of Seed Plants

Why do you think there was more carbon-14 in the germinated seed?

Contrast how sperm reach the eggs of seedless plants with how sperm reach the eggs of seed plants.

What features not present in seedless plants have contributed to the success of seed plants on land?

If a seed could not enter dormancy, how might that affect the embryo’s transport or survival?

Use examples from Figure 30.7 to describe how various gymnosperms are similar yet distinctive. 

Explain how the pine life cycle in Figure 30.4 reflects the five adaptations common to all seed plants.

Early seed plants in the genus Elkinsia are a sister group to a clade consisting of gymnosperms and angiosperms. Draw a phylogenetic tree of seed plants that shows Elkinsia, gymnosperms, and angiosperms; date the branch points on this tree using fossil evidence. (See Figure 26.5.)

It is said that oak is an acorn's way of making more acorns. Write an explanation that includes these terms: sporophyte, gametophyte, ovule. In-plant species, the ovule is the megasporangium. It has an embryo sac generated by the functional megaspore, seed, ovary, and fruit.

WHAT IF? Do speciation rates in closely related clades of flowering plants show that flower shape is correlated with the rate at which new species form or that flower shape is responsible for this rate? Explain.

Compare and contrast a pine cone and a flower in terms of structure and function

Explain why plant diversity can be considered a nonrenewable resource.

How could phylogenies be used to help researchers search more efficiently for novel medicines derived from seed plants?

Where in an angiosperm would you find a megasporangium?

(A) in the style of a flower

(B) enclosed in the stigma of a flower

(C) within an ovule contained within an ovary 

of a flower

(D) packed into pollen sacs within the anthers found on a 

stamen

Key features of seed plants facilitating life on land include three of the following four traits. Select the exception.

(A) homospory

(B) pollen

(C) reduced gametophytes

(D) seeds

With respect to angiosperms, which of the following 

is incorrectly paired with its chromosome count?

(A) egg—n

(B) megaspore—2n

(C) microspore—n

(D) zygote—2n

Which of the following is not a characteristic that distinguishes gymnosperms and angiosperms from other plants?

(A) dependent gametophytes

(B) ovules

(C) pollen

(D) alternation of generations

Gymnosperms and angiosperms have the following in common except (A) seeds. (B) pollen. (C) ovaries. (D) ovules.

Use the letters a–d to label where on the phylogenetic tree each of the following derived characters appears. (A) flowers (B) embryos (C) seeds (D) vascular tissue.

History of life has been punctuated by several mass extinctions. For example, the impact of a meteorite may have wiped out most of the dinosaurs and many forms of marine life at the end of the Cretaceous period (see Concept 25.4). Fossils indicate that plants were less severely affected by this mass extinction. What adaptations may have enabled plants to withstand this disaster better than animals?

As will be described in detail in Concept 38.1, the female gametophyte of angiosperms typically has seven cells, one of which, the central cell, contains two haploid nuclei. After double fertilization, the central cell develops into endosperm, which is triploid. Because magnoliids, monocots, and eudicots typically have female gametophytes with seven cells and triploid endosperm, scientists assumed that this was the ancestral state for angiosperms. Consider, however, the following recent discoveries:

• Our understanding of angiosperm phylogeny has changed to that shown in Figure 30.14b.

• Amborella trichopoda has eight-celled female gametophytes and triploid endosperm.

• Water lilies and star anise have four-celled female gametophytes and diploid endosperm.

(a) Draw a phylogeny of the angiosperms (see Figure 30.14b), incorporating the data given above about the number of cells in female gametophytes and the ploidy of the endosperm. Assume that all of the star anise relatives have four-celled female gametophytes and diploid endosperm.

(b) What does your labeled phylogeny suggest about the evolution of the female gametophyte and endosperm in angiosperms?

WRITE ABOUT A THEME: ORGANIZATION Cells are the basic units of structure and function in all organisms. A key feature in the life cycle of plants is the alternation of multicellular haploid and diploid generations. Imagine a lineage of flowering plants in which mitotic cell division did not occur between the events of meiosis and fertilization (see Figure 30.12). In a short essay (100–150 words), describe how this change in the timing of cell division would affect the structure and life cycle of plants in this lineage.

This photograph shows a dandelion seed in flight. Describe how seeds and other adaptations in seed plants contributed to the rise of seed plants and their dominant role in plant communities today.