Some Learning Goals

Know features that the members of Kingdom Protista share with one another and note the basic ways in which they differ. Understand how a diatom differs in structure and form from other members of Phylum Chromophyta. Diagram the life cycles of Chlamydomonas, Ulothrix, Spirogyra, and Oedogonium; indicate where meiosis and fertilization occur in each.

Learn at least two features that distinguish the Chlorophyta, Chromophyta, Rhodophyta, Dinophyta, and Euglenophyta from one another.

Know the structure and function of holdfasts, stipes, blades, bladders, and thalli.

Learn the function of each of the three thallus forms of a red alga, such as Polysiphonia, and know at least 20 economically important uses of algae, in addition to the numerous uses of algin that are given.

Understand why the slime molds and water molds are not considered true fungi and what they have in common with other members of Kingdom Protista.

was once the sole passenger on a ship carrying

I cargo from a south Atlantic port to Boston. I had turned in early one night as we were nearing the equator, but awoke around 2:00 a.m. and went to the bathroom to get a glass of water. I had not turned on the light and was startled to notice that the water in the toilet bowl was "winking" at me. Scores of little lights in the water were flashing on and off! I remembered that ships in the open sea take in water from their surroundings for their sewage lines, and I hurried out on deck to see where we were headed. I was immediately treated to a beautiful display of bioluminescence (discussed in Chapter 11) caused by millions of microscopic algae called dinoflagellates. As the waves broke, both at the bow and in the wake, there was a sparkling, shimmering glow as the tiny organisms, through their respiration, produced light. The dinoflagellates comprise only one of several phyla of algae and other relatively simple eukaryotic organisms discussed in this chapter.

The fossil record indicates that less than 1 billion years ago, all living organisms were confined to the oceans, where they were protected from drying out, ultraviolet radiation, and large fluctuations in temperatures. They also absorbed the nutrients they needed directly from the water in which they were immersed. The fossil record also suggests that many times, beginning about 400 million years ago, green algae, which are important members of Kingdom Protista, began making the transition from water to the land, eventually giving rise to green land plants.

Coleochaete (Fig. 18.1), a tiny, freshwater green alga that grows as an epiphyte (an alga or plant that attaches itself in a nonparasitic manner to another living organism) on the stems and leaves of submerged plants, shares several features with higher plants and probably was an indirect ancestor of today's land plants. The features include cells that resemble parenchyma, the development of a cell plate and a phragmoplast during mitosis, a protective covering for the zygote, and the production of a ligninlike compound. Lignin adds mechanical strength to cell walls, and the discoverers of the substance suggest that it originated as a protection against microbes. The ligninlike compound was present 100 million years earlier than the presumed evolution of plant life from water to land, and its presence in algal cells could explain how such organisms adapted to land habitats.

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