26.E: Seed Plants (Exercises)
26.1: Evolution of Seed Plants
The first plants to colonize land were most likely closely related to modern day mosses (bryophytes) and are thought to have appeared about 500 million years ago. They were followed by liverworts (also bryophytes) and primitive vascular plants—the pterophytes—from which modern ferns are derived.
Review Questions
Seed plants are ________.
- all homosporous.
- mostly homosporous with some heterosporous.
- mostly heterosporous with some homosporous.
- all heterosporous.
- Answer
-
D
Besides the seed, what other major structure diminishes a plant’s reliance on water for reproduction?
- flower
- fruit
- pollen
- spore
- Answer
-
A
In which of the following geological periods would gymnosperms dominate the landscape?
- Carboniferous
- Permian
- Triassic
- Eocene (present)
- Answer
-
C
Which of the following structures widens the geographic range of a species and is an agent of dispersal?
- seed
- flower
- leaf
- root
- Answer
-
A
Free Response
The Triassic Period was marked by the increase in number and variety of angiosperms. Insects also diversified enormously during the same period. Can you propose the reason or reasons that could foster coevolution?
- Answer
-
Both pollination and herbivory contributed to diversity, with plants needing to attract some insects and repel others.
What role did the adaptations of seed and pollen play in the development and expansion of seed plants?
- Answer
-
Seeds and pollen allowed plants to reproduce in absence of water. This allowed them to expand their range onto dry land and to survive drought conditions.
26.2: Gymnosperms
Gymnosperms, meaning “naked seeds,” are a diverse group of seed plants and are paraphyletic. Paraphyletic groups are those in which not all members are descendants of a single common ancestor. Their characteristics include naked seeds, separate female and male gametes, pollination by wind, and tracheids (which transport water and solutes in the vascular system).
Review Questions
Which of the following traits characterizes gymnosperms?
- The plants carry exposed seeds on modified leaves.
- Reproductive structures are located in a flower.
- After fertilization, the ovary thickens and forms a fruit.
- The gametophyte is longest phase of the life cycle.
- Answer
-
A
Megasporocytes will eventually produce which of the following?
- pollen grain
- sporophytes
- male gametophytes
- female gametophytes
- Answer
-
D
What is the ploidy of the following structures: gametophyte, seed, spore, sporophyte?
- 1 n , 1 n , 2 n , 2 n
- 1 n , 2 n , 1 n , 2 n
- 2 n , 1 n , 2 n , 1 n
- 2 n , 2 n , 1 n , 1 n
- Answer
-
B
In the northern forests of Siberia, a tall tree is most likely a:
- conifer
- cycad
- Gingko biloba
- gnetophyte
- Answer
-
A
Free Response
The Mediterranean landscape along the sea shore is dotted with pines and cypresses. The weather is not cold, and the trees grow at sea level. What evolutionary adaptation of conifers makes them suitable to the Mediterranean climate?
- Answer
-
The trees are adapted to arid weather, and do not lose as much water due to transpiration as non-conifers.
What are the four modern-day phyla of gymnosperms?
- Answer
-
The four modern-day phyla of gymnosperms are Coniferophyta, Cycadophyta, Gingkophyta, and Gnetophyta.
26.3: Angiosperms
From their humble and still obscure beginning during the early Jurassic period, the angiosperms—or flowering plants—have evolved to dominate most terrestrial ecosystems. With more than 250,000 species, the angiosperm phylum (Anthophyta) is second only to insects in terms of diversification.
Review Questions
Which of the following structures in a flower is not directly involved in reproduction?
- the style
- the stamen
- the sepal
- the anther
- Answer
-
C
Pollen grains develop in which structure?
- the anther
- the stigma
- the filament
- the carpel
- Answer
-
A
In the course of double fertilization, one sperm cell fuses with the egg and the second one fuses with ________.
- the synergids
- the polar nuclei of the center cell
- the egg as well
- the antipodal cells
- Answer
-
B
Corn develops from a seedling with a single cotyledon, displays parallel veins on its leaves, and produces monosulcate pollen. It is most likely:
- a gymnosperm
- a monocot
- a eudicot
- a basal angiosperm
- Answer
-
B
Free Response
Some cycads are considered endangered species and their trade is severely restricted. Customs officials stop suspected smugglers who claim that the plants in their possession are palm trees, not cycads. How would a botanist distinguish between the two types of plants?
- Answer
-
The resemblance between cycads and palm trees is only superficial. Cycads are gymnosperms and do not bear flowers or fruit. Cycads produce cones: large, female cones that produce naked seeds, and smaller male cones on separate plants. Palms do not.
What are the two structures that allow angiosperms to be the dominant form of plant life in most terrestrial ecosystems?
- Answer
-
Angiosperms are successful because of flowers and fruit. These structures protect reproduction from variability in the environment.
26.4: The Role of Seed Plants
Without seed plants, life as we know it would not be possible. Plants play a key role in the maintenance of terrestrial ecosystems through stabilization of soils, cycling of carbon, and climate moderation. Large tropical forests release oxygen and act as carbon dioxide sinks. Seed plants provide shelter to many life forms, as well as food for herbivores, thereby indirectly feeding carnivores. Plant secondary metabolites are used for medicinal purposes and industrial production.
Review Questions
Which of the following plant structures is not a defense against herbivory?
- thorns
- spines
- nectar
- alkaloids
- Answer
-
C
White and sweet-smelling flowers with abundant nectar are probably pollinated by
- bees and butterflies
- flies
- birds
- wind
- Answer
-
A
Abundant and powdery pollen produced by small, indistinct flowers is probably transported by:
- bees and butterflies
- flies
- birds
- wind
- Answer
-
D
Plants are a source of ________.
- food
- fuel
- medicine
- all of the above
- Answer
-
D
Free Response
Biosynthesis of nectar and nutrient-rich pollen is energetically very expensive for a plant. Yet, plants funnel large amounts of energy into animal pollination. What are the evolutionary advantages that offset the cost of attracting animal pollinators?
- Answer
-
Using animal pollinators promotes cross-pollination and increases genetic diversity. The odds that the pollen will reach another flower are greatly increased compared with the randomness of wind pollination.
What is biodiversity and why is it important to an ecosystem?
- Answer
-
Biodiversity is the variation in all forms of life. It can refer to variation within a species, within an ecosystem, or on an entire planet. It is important because it ensures a resource for new food crops and medicines. Plant life balances the ecosystems, protects watersheds, mitigates erosion, moderates climate, and provides shelter for many animal species.