Bio Tutorial 33 Q/a

Front 1

What is the dominant generation in non-vascular plants and in seedless vascular plants? Describe the relative sizes of the gametophyte and the sporophyte in each of these types of plants.

Back 1

The gametophyte is the dominant form in non-vascular plants. The sporophyte is smaller and is nourished by the gametophyte as it develops. In seedless vascular plants such as ferns, spores that are released from the undersides of fern fronds grow into the gametophytes (1n), which exist independently from the sporophyte. The sporophyte is much larger than the gametophyte in seedless vascular plants.

Front 2

Why is the sporophyte generation considered to be better suited for surviving on land?

Back 2

he sporophyte generation is diploid (2n), and has a “spare” copy of an intact chromosome if the sun’s radiation mutates its other chromosome. In water, the sun’s radiation is reduced, so haploid organisms are not in as much danger of being fatally mutated as they are on land.

Front 3

Are the gametophyte (n) and sporophyte (2n) present in all types of plants? What is one apparent trend relating to the relative sizes of the gametophyte and the sporophyte in plant evolutionary history?

Back 3

Yes, both the gametophyte and sporophyte forms are present in all types of plants. However, as plants become more evolutionarily advanced, the relative size of the gametophyte to the sporophyte decreases.

Front 4

What is the dominant generation of seed plants? What form does the non-dominant generation take?

Back 4

In seed plants, the sporophyte is the dominant generation. However, unlike the ferns, seed plants have gametophytes that are surrounded by sporophytic tissue. This sporophytic tissue nourishes the gametophyte and therefore, the gametophyte does not live independently from the sporophyte and is even more reduced in size (the gametophyte of seed plants is a structure composed of only eight cells.)

Front 5

In ferns, what are the advantages and disadvantages of using spores to reproduce?

Back 5

Using spores to reproduce allows ferns to take the best advantage of environmental conditions. If the conditions are suitable, the spore grows into a mature gametophytic generation. However, if the conditions are harsh, the spore will persist without germinating and will lie dormant until favorable conditions present themselves. However, spores contain very little storage tissue and they are released by the parent and must develop independently, instead of being nourished by the parent plant.

Front 6

How have the seeds of seeded plants evolved to take advantage of optimal environmental conditions? How is this similar to the way in which spores take advantage of environmental conditions?

Back 6

Like spores, many seeds are known for lying dormant until conditions are optimal for germination and growth. For example, some pine seeds actually require the heat of a fire to trigger germination. This is adaptive because just after a fire the seedling can grow quickly without competition from taller trees. Therefore, seeds and spores are similar in that they both are resistant to harsh conditions.

Front 7

How are seeds produced? Which generation (sporophyte or gametophyte) is responsible for producing seeds? Give an overview of seed production.

Back 7

Seeds develop within the parental sporophytic tissue. Both seedless plants and seed plants have female spores (megaspores) and male spores (microspores). The male microspore of a seed plant produces sperm within pollen, which are transported to the female megaspore. Seed plants have a haploid megaspore that is contained within a fleshy solid mass contained within an ovule. A seed is a fertilized mature ovule.

Front 8

How and why is pollen an example of how seed plants have adapted to a drier environment?

Back 8

The pollen grain is an important adaptation to dry environments. Pollen is a tough structure that contains the precursor to sperm cells. The tough outer coat of the pollen grain is able to survive very harsh conditions, so it can protect the cells for years. When the pollen grain finally lands on the female structure of a plant, it germinates and sperm cells travel to the egg cell through a pollen tube. Thus, the male gamete is protected rather than open to the environment, as is the case in seedless plants. This adaptation allows seed plants to live in such dry and harsh conditions as deserts.

Front 9

What are gymnosperms? When are they believed to have emerged?

Back 9

The gymnosperms are non-flowering seed plants which probably arose from a fern relative, appropriately named a progymnosperm, sometime between 409-363 million years ago.

Front 10

Make a chart of the four major gymnosperms and their characteristics. Include unique structures, adaptations, typical shape of leaves, habitat, methods of reproduction, and examples of each. Be sure to include traits that distinguish them from other gymnosperms as well as other plants (especially flowering plants).

Back 10

Cycads are slow-growing and long-lived perennials (i.e., they live and reproduce year after year). They are considered woody, even though their wood does not look like that of a pine or oak tree. The leaves of cycads are large and appear feather-like, much like those of palm leaves. These leaves are arranged spirally at the top of the stem. Cycads are dioecious plants; their male and female reproductive structures reside on separate plants. One feature retained in cycads is motile sperm. Non-vascular plants and seedless vascular plants have sperm equipped with flagella for motility. However, like all non-flowering seed plants, the cycads have "naked" seeds.

Like cycads, ginkgos are dioecious and have motile sperm. The leaves are uniquely fan-shaped, with a split in the middle that makes them appear to have two lobes. Due to their broad leaves, ginkgos are often mistaken for a flowering seed plant. However, the pattern of veins in the leaves, termed dichotomous venation, is unlike any found in flowering seed plants.

There are three genera of gnetophytes: Weltwitschia, Ephedra, and Gnetum. These are probably the least familiar gymnosperms, however, they serve an important role in understanding the evolution of angiosperms. Although the precise relationships are not known, it is generally accepted that the gnetophytes are more closely related to angiosperms than any other non-flowering plants because they are the only gymnosperms to undergo a process known as double fertilization.

Pine trees, as well as, firs, spruces, larches, yews, junipers, cedars, cypresses, and redwoods are all conifers. Most of these are evergreen, but there are a few deciduous conifers, such as the cypress trees in the Florida everglades. The name conifer comes from the Latin word meaning cone bearing. Conifers can be either monoecious or dioecious (i.e., their male and female reproductive structures resides on the same or different plants, respectively), but unlike other non-flowering seed plants, their sperm are not flagellated. They are delivered directly via the pollen tube.

Front 11

What is double fertilization? What gymnosperm is this observed in and why does it make it unique?

Back 11

It is generally accepted that the gnetophytes are more closely related to angiosperms than any other non-flowering plants because they are the only gymnosperms to undergo a process known as double fertilization. In double fertilization, two sperm cells enter the ovule; one fertilizes the egg and the other fertilizes another cell within the ovary.

Front 12

Are all conifers “evergreen”?

Back 12

No. There are some deciduous conifers, like the cypress.

Front 13

Draw and discuss the lifecycle of non-flowering seed plants, using conifers as an example. Use the proper terminology to describe each step of the lifecycle.

Back 13

The male cones produce haploid pollen grains by meiosis. The pollen grains are immature microgametophytes. The female cones have scales that each contain two ovules. Each ovule has one opening called the micropyle. When the ovule is ready to accept pollen, it secretes a liquid to which the pollen grain can adhere. As the liquid dries, the pollen is pulled into the ovule through the micropyle. At this point, a megaspore within the ovule goes through meiosis to produce four haploid cells. Only one cell survives, growing and dividing to produce the immature megagametophyte. Several eggs can develop within the megagametophyte.

As the eggs are developing, two sperm cells are developing within the pollen grain. A third cell in the pollen grain begins to grow as the pollen tube moves towards the megagametophyte. Once the pollen tube reaches the megagametophyte, the sperm cells fertilize the egg cells. Note that pollination occurred when the pollen grain reached the ovule, but fertilization did not occur until the sperm reached the egg. In most cases, fertilization does not happen until at least one year after pollination.

Front 14

Describe the difference between pollination and fertilization.

Back 14

Pollination occurs when a pollen grain reaches the ovule, and fertilization does not occur until the sperm reached the egg. In most conifers, fertilization does not happen until at least one year after pollination.

Front 15

What is a seed (i.e. a plant embryo) composed of?

Back 15

The embryo is made up of a rudimentary root and several embryonic leaves. The seed consists of three types of tissue: the new generation sporophyte or diploid embryo; the haploid female gametophytic tissue that stores nutrients; and the parent sporophytic tissues of the seed coat.