Slide 1
As we continue our discussion of the protists, it is important to
remember that the taxonomy of protists is still changing.
Newer classifications attempt to present monophyletic groups based on ultrastructure, biochemistry, and genetics.
In this tutorial we will discuss the stramenopilans, the chlorophytes, and the rhodophytes.
Slide 2
Kingdom Stramenopila is a diverse group of organisms - some are
photosynthetic and plant-like (these are the diatoms, golden algae, and brown
algae - you can tell they are plant-like by the suffix phyta).
The other group - the water molds is heterotrophic and fungus-like (the suffix mycota means fungus-like).
Despite the diversity of these organisms, Kingdom Stramenopila is thought to be monophyletic and the diagnostic characteristic of these organisms is the presene of hair-like projects (known as stramen) on their flagella.
Slide 3
Phlym Bacillariophyta or the Diatoms consists of single-celled
individuals that have an elaborate silica shell. Most of the diatoms are
photosynthetic and they are found in virtually all environments - aquatic and
terrestrial.
There may be as many as 100,000 different species of diatoms and they are important components of plankton. As a group, they may be responsible for 20% of the global CO2 fixation - in other words, 20% of the photosynthesis ocurring on earth is the result of diatoms.
Slide 4
You can see here some of the beautiful and intricate shells made
by diatoms.
Slide 5
There are practical uses for diatoms and their fossilized remains.
Diatomaceous earth is the remains of fossilized diatoms, their silica shells give it an abrasive quality
Diatomaceous earth is used to make scouring powders, toothpastes, cat litter, and mechanical pesticides
Diatoms are also being used in nanotechnology studies - the goal is to get diatoms to produce silica structures to be used in optical systems, semiconductors, and use as a drug delivery system.
Slide 6
Our next group is the golden algae or Chrysophyta.
Most of
these organisms are photosynthetic and they use a pigment known as fucoxanthin
during photosynthesis.
You do not need to know the name of this pigment but I want you to recogize that chlorophyll is not the only photosynthetic pigment.
Some of the golden algae can turn heterotrophic when the environmental conditions are right. This is known as being facultatively heterotrophic or a mixotroph.
This group is an important component of food webs mainly in freshwater
systems such as lakes.
Slide 7
Phylum Oomycota is comprised of organisms knows as water molds,
downy mildews, and rusts). As you can probably tell from these common
names - these organisms are fungus-like.
Most members of this group are multicellular and they live in both terrestrial and aquatic environments.
They are all heterotrophic - the feed on complex organic molecules by asborbing them - this is the same way that the fungi feed. And like the fungi they are either decomposers - which means that they decompose already dead organic material - or they are parasites - which means they decompose living organic material.
They appear similar to the fungi not because they are closely related to the fungi - they are not. But rather because of convergent evolution.
Two features that let us know that they are not related to the fungi is that the oomycota have cell walls made of cellulose while fungi have cell walls made of chitin.
They are also diploid for most of their life cycle while fungi are haploid. We will learn more about the fungi in future tutorials.
Slide 8
The oomycota are important parasites. Some of the aquatic
forms cause diseases in fish and amphibians. If you have a fish tank -
you have probably had to treat your fish for an oomycete infection - they are
common in stagnat water like that found in fish tanks.
Slide 9
Phytophthora infestans is the organism which causes late blight of potato.
The potato is native to North America, but once it was introduced to Europe,
it quickly became an important food crop.
Late blight did not follow its
host plant across the Atlantic until much later; the disease organism grows
into the stem and leaf tissues, causing death, and may also infest the tubers,
which are the part of the plant that is eaten.
The disease spreads rapidly under cool and damp conditions, which are common in western Europe. In one week during the summer of 1846, this diease wiped out almost the entire potato crop of Ireland, a crop which was the primary food of the poor at that time. Nearly a million Irish died in the Great Famine, and an additional one-and-a-half million emigrated to other countries, including America.
Slide 10
Our final group of stramenopilans are the Brown algae or
phaeophyta.
This is a group of organisms that are found in marine environments and includes the organisms we usually refer to as seaweeds or kelps. They make up the kelp forests off the coast of southern California and other parts of the world.
This is a multicellular group of organisms and some of them get quite large.
Additionally, these organisms show tissue differentiation. This is the first group of organisms we have looked at that have had this feature. Tissue differentiation means that they have specialized tissues for carrying out specialized funcations. All the other organisms we have looked at thus far have either been unicellular or mutlticellular with a very simple body plan.
The bodies of the seaweeds show differentiation into holdfasts, stipes and blades. Holdfasts are similar to plant roots - they anchor the seaweed to the ocean floor.
Stipes are similar to the stems of plants and the blades are similar to the leaves of plants. Some of the brown algae even have conducting tissue which moves sugars produced via photosynthesis in the blades to other parts of the organism.
These brown algae look very plant like - but closer evaluation reveals this as another example of convergent evolution. Brown algae and plants appear similar but this similarity is due to similar selection pressues not evolutionary relatedness.
Slide 11
This image gives you an idea of how large some of the brown algae
can become.
You can also see the holdfast, stipes, and blades (labelled here as laminae because they are thin).