EKU General Botany Lab

PLEASE BRING YOUR TEXTBOOK TO LAB THIS WEEK.
The illustrations on pp. 416--422 will be very helpful.

SUMMARY OF SEED PLANT CHARACTERISTICS

Our species, Homo sapiens, could not exist without seeds.

Basically, a seed plant is

      a heterosporous plant

      which forms only one functional megaspore in each megasporangium

            (the other 3 megaspore nuclei do not develop)

      the functional megaspore remains in the megasporangium

      when the functional megaspore divides and forms a gametophyte, the

      female gametophyte develops inside the megasporangium . . . so,

      Fertilization occurs within the megasporangium, and the embryo develops there.

The megasporangium plus its surrounding protective structures = an ovule.

The surrounding protective structures are the integuments . Integuments are

outgrowths from the megasporophyll. When an ovule matures, it becomes a seed; the fully matured integuments of a seed are called the seed coat.

Seed plants do not have free-swimming sperm. The young male gametophytes develop inside pollen grains. Pollen grains are transferred from the microsporangia to the megasporangia (in Gymnosperms) or to the tip of a sporophyll (in Angiosperms). This transfer of pollen is called pollination. After pollination, the pollen grain germinates and forms a tube that delivers the two sperm. (The sperm sometimes are flagellated, but they remain inside the pollen tube.)

These factors of (1) the female gametophyte developing on the sporophyte; (2) better protection of the female gametophyte; and (3) transferring the sperms more precisely; make reproduction less chancy.

(Please note: The word nucellus means the same thing as the megasporangium. Also note that for some reason, pollination is the correct spellingnot pollenation!)

GYMNOSPERMS

Gymnosperm means naked seed. Gymnosperm megasporophylls do not completely enclose the ovules. Note the examples of Gymnosperms in the PowerPoint supplement.

CONIFEROPHYTA

The most commonly recognized Gymnosperms are the cone-bearing plants or conifers.  Conifers include the spruces, firs, pines, yews, cypresses, redwoods, and others.  We will study pine as an example of a Gymnosperm life cycle.

PINE OVULE AND SEED DEVELOPMENT

Examine the series of microscope slides that show the development of seed cones, ovules, megaspores, female gametophytes, archegonia, fertilization, and development of the embryo.

Note and be able to identify all structures.

Which structures are diploid and which are haploid?

What is the function of each structure?

Describe how the female gametophyte develops.

Note the huge size of the egg cells (and their huge nuclei). Why would huge egg cells be advantageous?

What happens to the female gametophyte after fertilization?

How long does it take for pine ovules to develop into mature seeds?

Here is a list of structures or stages you should be able to identify from the microslides:  seed cone, megasporophyll, brack of megasporophyll, integuments, micropyle, megasporangium, megasporocyte, functional megaspore nucleus, free nuclear gametophyte, cellular gametophyte, archegonium venter, archegonium neck, egg, fertilization, suspensors, endosperm, embryo, cotyledons.

PINE POLLEN AND MALE GAMETOPHYTE DEVELOPMENT

Examine the series of microscopes that show the development of pollen cones, pollen grains, and gametophytes.

Note and identify all structures, including:   pollen cone, microsporophyll, microsporangium, microsporocytes, tapetum, microspores, male gametophytes, pollen tube, tube nucleus, tube cell, generative cell.

Please note that in the Powerpoint supplement, the pine images are not labelled. Therefore, you can use the images to test yourself!

                                                                          CYCADOPHYTA

During the lab period, we will be making a trip upstairs to the Biology greenhouse.  There are several species of cycads in the greenhouse.  You might want to take a few notes during the greenhouse visit.