Saturday, December 8, 2007

Concept 30.4

Q1: Explain why it is accurate to consider plant diversity to be a nonrenewable resource.

A1: Because extinction is irreversible, it decreases the total diversity of plants, many of which may have brought important benefits to humans. Such as in the field of medicine and agriculture.

Concept 30.3

Q1: It has been said that an oak tree is an acorn’s way of making more acorns. Write an explanation that includes these terms:

A1: In the oak's life cycel, the tree (the sporophyte) produces flowers, which contain gametophytes in pollen grains and ovules; the eggs in ovules are fertilized; the mature ovaries develop into dry fruits called acorns; and the acorn seeds germinate, resulting in embryos giving rise to seedlings and finally to mature trees, which produce flowers then acorns.

Q2: Compare and contrast a pine cone and a flower in terms of structure and function.

A2: Pine cones and flowers both have sporophylls , modified leaves that produce spores. Pine trees have separate pollen cones (with pollen grains) and ovulate cones (with ovules inside cone scales). In flowers, pollen grains are produced by the anthers of stamens, and ovules are within the ovaries of carpels. Unlike pine cones, many flowers produce both the pollen and the ovules.

Q3: Explain the use of the terms monocot, dicot and eudicot.

A3: Recent molecular evidence pointed out that while monocots are a clade, dicots are not. Based on phylogenetic relationships, most dicots form a clade, now known as eudicots.

Concept 30.2

Q1: Based on Figure 30.4, explain why the various types of gymnosperms can be described as being similar yet distinctive.

A1: Although gymnosperms are similar in having "naked" seeds, their seed bearing structure vary greatly. For instance, Cycads have larger cones compared to Ginkgo and Gnetum. Leaf shape also varies greatly, from the needles of many conifers to the palmlike leaves of cycads to Gnetum leaves that look like those of flowering plants.

Q2: Explain how the pine life cycle (see Figure 30.6) reflects basic characteristics of seed plant.

A2: The life cycle illustrates heterospory, as ovulate cones produce megaspores and pollen cones produce microspores. The reduced gametophytes are evident in the formof the microscopic pollen grains and the microscopic female gametophyte within the megaspore. The egg is shown developing within an ovule, and the pollen tube is shown conveying the sperm. The figure also shows the protective and nutritive features of a seed.

Concept 30.1

Q1: Contrast sperm delivery in seedless vascular plants with sperm deliver in seed plants.

A1: To have any chance of reaching the eggs, the flagellated sperm of seedless vascular plants must rely on swimming through a film of water, usually limited to a range of less than a few centimeters. In contrast, the sperm of seed plants are produced within durable pollen grains that can be carried long distances by wind or by animal pollinators. Although flagellated in some species, the sperm of most seed plants do not require water because pollen tubes convey them directly to the eggs.

Q2: What additional features of seed plants, not present in seedless plants, contributed to the enormous success of seed plants on land?

A2: The reduced gametophytes of seed plants are nurtured by sporophytes and protected from stress, such as drought conditions and UV radiation. Pollen grains have tough protective coats and can be carried long distances, facilitating widespread sperm transfer without reliance on water. Seeds are more resilient than spores, enabling better resistance to environmental stresses and wider distribution.

Concept 29.4

I. What are a few key differences between seedless vascular plants and bryophytes?

a) Bryophytes: have dominant gametophytes; are non-vascular plants. Seedless vascular plants: have dominant sporophyte; are vascular plants, and the evolution of true plants.

II. What is the major difference between most lycophytes and most ferns and their relatives?

a) Most lycophytes have microphylls, whereas ferns and most fern relatives have megaphylls.

Concept 29.3

I. How do bryophytes differ from other plants?

a) Bryophytes are described as non-vascular plants, meaning they do not have phloem or xylem. Another difference is that their life cycles is dominated by a gametophyte rather than sporophytes.

II. Give three examples how structure fits function in bryophytes.

a) protonema - large surface area enhances absorption of water and minerals; shape of archegonia - protects eggs during fertilization and transport nutrients to the embryos via placental transfer cells; seta - conducts nutrients form the gametophyte to the capsule where spores are produced.

Concept 29.2

I. Identify three derived traits that distinguish plants from charophyceans and facilitate life on land. Explain.

a) They have walled spores that are toughened by sporopollenin. They have multicellular, dependent embryos. And they have cuticle. All of which prevents land plants from drying out.

II. Identify each structure as either haploid or diploid:

sporophyte - diploid (2n)
spore - haploid (n)
gametophyte - haploid (n)
zygote - diploid (2n)
sperm - haploid (n)
egg - haploid (n)

Concept 29.1

I. Describe the evidence linking plants to a charophycean ancestry.

a) They share rosette cellulose-synthesizing complexes. They both have peroxisomes which minimize loss to photorespiration. They have similar structure of flagellated sperm.