Lab 3 :: Gymnosperms & Angiosperms, and Primary Growth I



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		Ephedra

‹ Gymnosperms ›

Gymnosperms include plants whose seeds are not enclosed in an ovule, hence why they’re called “naked seeds” (Think of a pine cone). Gymnosperms normally have needles instead of broad leaves. These types of plants are sometimes referred to as “softwoods” and usually stay green throughout the entire year. Examples of those that stay green are spruce trees, firs and pines. It is important to remember that there are exceptions to this, but it is sometimes a good way to distinguish between those that are gymnosperms and those that aren’t. Gymnosperms are NOT flowering plants and commonly occur naturally here in the desert.

Links:

http://glossary.gardenweb.com/glossary/nph-ind.cgi?scrug=16677&k=gym

Pinus

The specific species of Pinus that you looked at in lab (Pinus monophylla) is easily distinguished from other species of Pinus in that the needles are grouped singly into their fascicles, unlike Pinus edulis, where they occur in bundles of two. The species you looked at in lab is the most common pinyon pine in California. The desert mountains of Utah, Idaho, Colorado, Nevada and California are home to this tree, growing between the elevations of 2,000 to 10,000 feet. Another interesting fact is that Pinus monophylla is one of the slowest growing pines; it may grow only 2 to 6 inches in an entire year!

Links:

Juniperus

Juniperus osteosperma (what you looked at in lab) is a short tree that may live to as long as 650 years. These trees grow less than 27 feet and are often as short as 10-15 feet. Juniper trees begin to produce seeds only when they are about 30 years old. Accordingly, these seeds are extremely long-lived. In one study, 17% of Utah Juniper seeds germinated after 45 years! In general, however, about 8 to 49% of Juniper seeds germinate.

Links:

http://www.fs.fed.us/database/feis/plants/tree/junost/

Ephedra

Ephedra shrubs normally grow up to a height of 5 feet. Its numerous stems point upward, and look somewhat like a broom. The fragile, deep rooting system of Ephedra consists of numerous taproots that extend almost straight down from the plant’s base. Unlike some of the other gymnosperms we have studied, this one is dioecious, meaning that male and female structures occur on separate plants.

Links:

http://www.fs.fed.us/database/feis/plants/shrub/ephvir/

‹ Angiosperms ›

Angiosperms include plants whose mature seeds are enclosed in an ovule (think of an apple). This group is sometimes referred to as “hardwood”. Angiosperms usually have broad leaves, and they normally change color and die every autumn, unlike normal gymnosperms. Angiosperms ARE flowering plants and are especially dominant in the Mojave Desert. Oaks, maples and dogwoods are examples of angiosperms.

Links:

http://www.cnr.vt.edu/dendro/forsite/idtype.htm

Composite Flowers

These types of angiosperms are quite possibly the most mistakenly named by the untrained eye. Although they appear to be one large flower, they are actually dense clusters of many tiny flowers in the center (disk flowers), and their “petals” are actually not petals at all, but ray flowers. Examples of these types are sunflowers, daisies, dandelions, and ragweeds. If you look at one of these plants closely, you will be able to see the individual flowers located in the center.

Links:

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/Angiosperm.html
http://www.hcs.ohio-state.edu/hcs300/angio2.htm

Angiosperm Life Cycle

FYI: As with all plants, outside of liverworts and mosses, the dominant phase of flowering plants is the sporophyte (2n) condition.

Male Development

1. If we look at a cross section of a developing anther (male), we can see four microspore mother cells (2n).
2. Those microspore mother cells undergo meiosis to produce a tetrad (4) of microspores (1n)
3. Those microspores (1n) divide mitotically to develop immature male gametophytes (1n), a.k.a. pollen grains.

Female Development

1. If we look at a cross section of an ovary (female), we can see three ovules (megaspore mother cell, 2n).
2. Each megaspore mother cell under meiosis to produce megaspores (1n), but only one of them survives.
3. Those megaspores undergo mitosis three times (producing 8 nuclei) and then each nucleus specializes to form the egg, polar nuclei, etc.

Pollination and Fertilization

1. Pollen grains land on the (female) stigma.
2. Pollen undergoes mitosis, forming two sperm nuclei (1n).
3. Both sperm nuclei (1n) travel down the pollen tube and into the female gametophyte via an opening called the microphyle.
4. One sperm nucleus fuses with the egg forming the zygote (2n).
5. The other sperm nucleus fuses with the polar nuclei, forming the endosperm. Since most angiosperms have two polar nuclei (each 1n), the endosperm becomes triploid (3n).

Seed, Fruit and Plant Development

1. Each fertilized ovule now undergoes mitosis and becomes a seed (a dormant embryo sporophyte with stored food and protective coats).
2. As the seeds mature, they secrete a hormone to stimulate the ovary wall to develop into a fruit (mature ovary). Each seed inside the fruit now contains an embryo (2n), endosperm (3n), and a seed coat for protection.
3. As the fruit matures, the seeds eventually leave (whether by vector, wind, or by some other means), and germinate. The seed eventually undergoes mitosis and becomes a flowering sporophyte (2n), to produce both male and female structures and begin the cycle over again.
FYI: Remember, most plants have mechanisms in which to avoid self-fertilization

‹ Primary Growth and Development ›

Primary growth (growth in length) consists of two processes:

1. Cell Division (mitosis)

a. This occurs at the apical meristem.
b. This creates an exact copy of the cell, resulting in doubling. One copy will stay where it started and not differentiate, while the other copy will differentiate into a specialized cell.

2. Cell Enlongation

a. This normally occurs below the zone of active cell division.
b. This allows the cell to become enlarged and specialized for specific functions

During primary growth, cell divisions occur at the apical meristem, which is located near the apex (tip) of stems and roots. Growth does NOT occur from the bottom-up, but rather from the top. For example, if you were to carve your initials in a tree at eye level, and you traveled back to that same tree 10 years later, the initials would still be at eye level (although they will look spread out width-wise, because of secondary growth, but you will learn about that in lab 5!). This is important to remember! Primary growth occurs ONLY at the apical meristems!

Links:

http://oak.cats.ohiou.edu/~trivett/courses/pbio100/growth.pdf

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updated 3-12-06