on, and synthesis. Since the establishment of cultures and subsequent manipulations and observations are not time-consuming, other botanical or developmental topics can be integrated into these laboratory sessions.
In the first week, students receive written materials that provide goals for this investigation, sufficient background on the plant life cycle, and specific step-by-step instructions for completing this investigation. For the following weeks, students are prompted to make observations through questions.
Goal: To observe the development of the gametophytic generation of a fern. You will make observations on spore germination, gametophyte ontogeny, sexual maturation, fertilization, embryo growth, and the development of the young sporophyte. You should be able to relate all of these events to the complete life cycle of a fern as well as to plants in general.
Background: The life cycle of land plants is characterized by an alternation between two phases or generations that are morphologically and functionally distinct. The gametophyte generation is the sexual phase of the life cycle. Gametophytes produce eggs and/or sperm (gametes) and house and nourish the product of fertilization, the embryo. Gametophytes may be extremely small (seed plants) or the dominant phase of the life cycle (bryophytes). Although fern gametophytes are quite small, they are free-living and independent from the much larger spore-producing plant that you are familiar with, i.e. the sporophyte. In ferns, seed plants and other vascular plants, the sporophyte is the dominant phase of the life cycle and produces spores by meiosis. Spores are haploid cells and the plant that produces spores, the sporophyte, must be diploid. This contrasts from most animals, in which meiosis yields gametes.
After spores are dispersed from the sporophyte and germinate, what do they grow into? You will answer this question (if you do not already know the answer!) by observations of developing fern spores. You will inoculate C-Fern spores onto nutrient medium and use your sharpest powers of observation to see how fern spores develop. To do this investigation you will need: C-Fern spores, one cotton-tipped swab, one Petri dish containing agar-solidified nutrient medium, one plastic sandwich bag a marker and a place to grow your culture
A spore is a single cell. Under the right conditions, spores grow by mitotic divisions and differentiate into multicellular plants that eventually produce gametes. Look at the vial of C-Fern spores. These are spores of a tropical fern called Ceratopteris. you may have seen this fern sold as an aquarium plant named water sprite. How many spores do you think are in the vial? Are the spores dry? If they are dry, how can they survive? What do you think would be necessary for them to germinate?
Take a cotton-tipped swab and carefully dip it into the spores so that some spore adhere to the cotton. Take only a few spores! Since spores are very small, only a slight brown coloration on the cotton end is plenty. Tilt the Petri dish lid only enough to position the swab tip over the agar and tap off some of the spores onto the agar surface. After distributing the spores as sparsely and as evenly as possible, replace the petri dish lid. It is important to work quickly while the lid is up so that you reduce the chance that foreign air-borne spores and other contaminants enter your culture. Using the marker, write your initials, and date on the lid and bottom of the Petrid dish. Place your dish into a plastic sandwich bag.
Prepare a wet mount of some of the spores remaining on the swab. Sprinkle some spores into a small drop of water on a microscope slide and place a coverslip over them. Observe this wet mount of spores under the microscope at different powers. Can you see any patterns on the spore walls? What variations in the spore wall ornamentation occur on different surfaces of the spores? Draw a few spores showing the wall pattern or ornamentation.
Observe the spores on your dish with the microscope. Describe and record the general size and colo