Biology II: Seed Plants

In onions (Allium), cells of the sporophyte have 16 chromosomes within each nucleus. Match the number of chromosomes present in each of the following onion tissues. How many chromosomes should be in an endosperm nucleus?

24

Within a gymnosperm megasporangium, what is the correct sequence in which the following should appear during development, assuming that fertilization occurs? 1. sporophyte embryo 2. female gametophyte 3. egg cell 4. megaspore

4 → 2 → 3 → 1

Ecologists often build models to depict the relationships between organisms. In such models, an arrow is used to link two organisms in a relationship. The arrowhead is next to the organism that is affected. If the effect is positive, the arrow is labeled with (+), and if negative, then the label is (-). Capuchin monkeys have been known to use rocks to smash open the fruits of Brazil nut trees. On the rare occasions when this has been observed, the monkeys consume all of the Brazil nuts. Thus, which of the following correctly depicts the relationship between capuchin monkeys and Brazil nut trees?

Capuchin Monkeys +UP DOWN- Brazil Nut Trees

The cycads, a mostly tropical phylum of gymnosperms, evolved about 300 million years ago and were dominant forms during the Age of the Dinosaurs. Though their sperm are flagellated, their ovules are pollinated by beetles. These beetles get nutrition (they eat pollen) and shelter from the microsporophylls. Upon visiting megasporophylls, the beetles transfer pollen to the exposed ovules. In cycads, pollen cones and seed cones are borne on different plants. Cycads synthesize neurotoxins, especially in the seeds, that are effective against most animals, including humans. On the Pacific island of Guam, large herbivorous bats called "flying foxes" commonly feed on cycad seeds, a potent source of neurotoxins. The flying foxes do not visit male cones. Consequently, what should be true?

Flying foxes can be dispersal agents of cycad seeds if the seeds sometimes get swallowed whole (in other words, without getting chewed).

The Brazil nut tree, Bertholletia excels (n = 17), is native to tropical rain forests of South America. It is a hardwood tree that can grow to over 50 meters tall, is a source of high-quality lumber, and is a favorite nesting site for harpy eagles. As the rainy season ends, tough-walled fruits, each containing 8-25 seeds (Brazil nuts), fall to the forest floor. Brazil nuts are composed primarily of endosperm. About $50 million worth of nuts are harvested each year. Scientists have discovered that the pale yellow flowers of Brazil nut trees cannot fertilize themselves and admit only female orchid bees as pollinators. The agouti (Dasyprocta spp.), a cat-sized rodent, is the only animal with teeth strong enough to crack the hard wall of Brazil nut fruits. It typically eats some of the seeds, buries others, and leaves still others inside the fruit, which moisture can now enter. The uneaten seeds may subsequently germinate. Orchid bees are to Brazil nut trees as ________ are to pine trees.

breezes

Which of the following sex and generation combinations directly produces the fruit of angiosperms?

female sporophyte

In terms of alternation of generations, the internal parts of the pollen grains of seed-producing plants are most similar to a _____.

fern gametophyte bearing only antheridia

Many mammals have skins and mucous membranes that are sensitive to phenolic secretions of plants like poison oak (Rhus). These secondary compounds are primarily adaptations that _____.

inhibit herbivory

If one were to propose a new taxon of plants that included all plants that are pollinated by animals, and only plants that are pollinated by animals, then this new taxon would be _____.

polyphyletic

A botanist discovers a new species of land plant with a dominant sporophyte, chlorophylls a and b, and cell walls made of cellulose. In assigning this plant to a phylum, which of the following, if present, would be LEAST useful?

spores