Chapter 31 Review: Seed Plants

The seed protects the embryo.

An extra layer of sporophyte tissue surrounds the embryo, creating the ovule, which later hardens. The seed protects the embryo, helps it resist drying out, and allows a dormant stage that pauses the life cycle until environmental conditions are favorable.

Angiosperms: The Flowering Plants

Angiosperms are distinct from gymnosperms and other plants because their ovules are enclosed within diploid tissue called the ovary at the time of fertilization, and they form fruits.

Specialized seed adaptations improve survival.

Before a seed germinates, its seed coat must become permeable so that water and oxygen can reach the embryo. Adaptations have evolved to ensure germination under appropriate survival conditions. In certain gymnosperms, seeds may be released from cones after a fire. Alternatively, seeds may require passage through a digestive tract, freeze-thaw cycles, or abundant moisture.

Conifers are the largest gymnosperm phylum.

Conifers include pines, spruces, firs, cedars, and many other groups. Both the tallest and the oldest vascular plants are conifers.

Flowers house the gametophyte generation of angiosperms.

Flowers are considered to be modified stems that bear modified leaves. Flower parts are organized into four whorls: sepals, petals, androecium, and gynoecium. The male andoecium consists of the stamens where haploid pollen, the male gametophyte, is produced. The female gynoecium consists of one of more carpels that contain the female gametophyte. The carpel has three major regions: the ovary, which later becomes the fruit; the stigma, which is the tip of the carpel; and the style, a stalk that connects the stigma and ovary.

Fruits allow angiosperms to colonize large areas.

Fruits exhibit a wide array of dispersal mechanisms. They may be ingested and transported by animals, buried in caches by herbivores, carried away by birds and mammals, blown by the wind, or float away on water.

Only one species of the ginkgophytes remains extant.

Ginkgo biloba is a gymnosperm with broad leaves that it sheds in the fall. It is dioecious, and the fleshy seeds of the female tree have a foul odor.

Gymnosperms: Plants with "Naked Seeds"

Gymnosperms have ovules that are not completely enclosed in sporophyte (diploid) tissue at the time of pollination. The four groups of gymnosperms are coniferophytes, cycadophytes, gnetophytes, and ginkgophytes; all lack flowers and true fruits.

Fruits are adapted for dispersal.

In angiosperms, a fruit is a mature ovary. Fruit development is coordinated with embryo, endosperm, and seed coat development. Angiosperms produce many types of fruit, which vary depending on the fate of the pericarp (carpel wall). Fruits can be dry or fleshy, and they can be simple (single carpel), aggregate (multiple carpels), or multiple (multiple flowers). A fruit is genetically unique because it contains tissues from the parents sporophyte (the seed coat and fruit tissue), the gametophyte (remnants in the developing seed), and the offspring sporophyte (the embryo)

Horizontal gene transfer occurred in land plants.

Moss genes have been found in the Amborella genome, possible transferred by parasitic plants, although it is unknown if they have a function in Amborella.

Cycads resemble palms, but are not flowering plants.

Most cycads can reach heights of 15m or more. Cycads, unlike palms, produce cones; in some species the female cones are huge. Their life cycle is like that of conifers.

Sorting out angiosperm origins is complicated.

No one is certain how the angiosperms arose, although the breakup of Pangea may have led to climate change that favored the expansion of the angiosperms. The earliest extant angiosperm appears to be Amborella trichopoda, found on the island of New Caledonia.

Pines are an exemplary conifer genus.

Pines have tough, needlelike leaves in clusters of two to five. They produce male and female cones. In the male cones, microspore mother cells in the microsporangia give rise to microspores that then develop into four-celled pollen grains, the male gametophytes. In the female cones, a megasporangium (nucellus) produces a single megaspore mother cell that becomes four megaspores; three of these break down, and the remaining one develops into a female gametophyte, which produes archegonia that carry eggs. Upon fertilization, a pollen tube emerges from the pollen grain and grows through the nucellus. Eventually two sperm cells migrate through the tube, and one unites with the egg; the other disintegrates.

Seeds protect the embryo

Seeds help to ensure the survival of the next generation by maintaining dormancy during unfavorable conditions, protecting the embryo, providing food for the embryo, and providing means for dispersal.

Water is not required to transport the male gametophyte to the female gametophyte.

The gametophytes of seed plants typically consists of only a few cells. Pollen grains are male gametophytes; each pollen grain contains sperm cells. Water is not required for fertilization. The female gametophyte develops within an ovule that forms the seed.

Double fertilization is a unique feature of the angiosperm life cycle

The megaspore produces eight haploid nuclei. The female gametophyte consists of a large embryo sac with the eight nuclei in seven cells. The egg and two polar nuclei (in a single cell) are most important. After landing on a receptive stigma, a pollen grain develops a pollen tube that grows toward the embryo sac. Eventually, two sperm pass through this tube. One fuses with the egg to form a zygote, and the other unites with the polar bodies to form a triploid endosperm nucleus that develops into endosperm to nourish the embryo.

Gnetophytes have xylem vessels.

Xylem vessels, a common feature in angiosperms, are highly efficient conducting cells. Gnetophytes are the only gymnosperms that have them. This group includes the strange Welwitschia genus of southwestern Africa and the numerous worldwide Ephedra species.

Which of the following terms is NOT associated with a male portion of a plant? a. Megaspore b. Antheridium c. Pollen grains d. Microspore

a. Megaspore

In a flower after fertilization, the following tissues are diploid: a. carpel, integuments, and megaspore mother cell b. carpel, integuments, and megaspore c. carpel, megaspore, and zygote d. carpel, megaspore mother cell, and endosperm

a. carpel, integuments, and megaspore mother cell

The lack of seeds is a characteristic of all: a. lycophytes b. conifers c. tracheophytes d. gnetophytes

a. lycophytes

The pericarp is the: a. ovary wall b. developing seed coat c. ovary d. mature endosperm

a. ovary wall

Comparing stems of two plant specimens under the microscope, you identify vessels in one sample and conclude the specimen: a. with vessels must be an angiosperm or a gnetophyte b. with vessels is either Ephedra or a cycad c. without vessels is a pterophyte d. without vessels must be a tracheophyte

a. with vessels must be an angiosperm or a gnetophyte

In double fertilization, one sperm produces a diploid ____, and the other produces a triploid ____. a. zygote; primary endosperm b. primary endosperm; microspore c. antipodal; zygote d. polar nuclei; zygote

a. zygote; primary endosperm

An example of a drupe is a: a. strawberry b. plum c. bean d. pineapple

b. plum

Apply your understanding of angiosperms to identify which innovations likely contributed to the tremendous success of angiosperms. a. Homospory in angiosperms b. Fruits that attract animal dispersers c. Cones that protect the seed d. Dominant gametophyte generation

b. Fruits that attract animal dispersers

Which of the following gymnosperms possesses a form of vascular tissue that is similar to that found in the angiosperms? a. Cycads b. Gnetophytes c. Ginkgophytes d. Conifers

b. Gnetophytes

Which of the following adaptations allows plants to pause their life cycle until environmental conditions are optimal? a. Stomata b. Phloem and xylem c. Seeds d. Flowers

c. Seeds

Reproduction in angiosperms can occur more quickly than in gymnosperms because: a. gymnosperm sperm requires water to swim to the egg b. flowers always increase the rate of reproduction c. angiosperm pollen tubes grow more quickly than gymnosperm pollen tubes d. angiosperms have nectaries

c. angiosperm pollen tubes grow more quickly than gymnosperm pollen tubes

Which of the following potentially represents the oldest known living species of angiosperm? a. Cooksonia b. Archaefructus c. Chlamydomonas d. Amborella

d. Amborella

Fruits are complex organs that are specialized for dispersal of seeds. Which of the following plant tissues does NOT contribute to mature fruit? a. Sporophytic tissue from the previous generation b. Gametophytic tissue from the previous generation c. Sporophytic tissue from the next generation d. Gamteophytic tissue from the next generation

d. Gametophytic tissue from the next generation

In a pine tree, the microspores and megaspores are produced by the process of: a. fertilization b. mitosis c. fusion d. meiosis

d. meiosis

The integuments of an ovule will develop into the: a. embryo b. endosperm c. fruit d. seed coat

d. seed coat