Protists

Recap of Bacteria and Intro to Protists

• https://www.youtube.com/watch?v=vAR47-g6tlA

• The protist kingdom is the most challenging group of organisms to classify.

• There are 115 000 species of protists which display great variation.

• Protists have characteristics that are similar to organisms found in each of the other kingdoms. Some are unicellular which is similar to bacteria.

• However, one distinguishing characteristic that separates bacteria from protists is the presence of a nucleus.

• Remember, bacteria are prokaryotic because their DNA is free floating within the cytoplasm.

• All protists are eukaryotic which means they contain a distinct nucleus which surrounds their DNA.

• This evolutionary development generated the need for a distinct classification for these organisms.

• Classifying protists becomes challenging because of their vast differences.

• Most protists are unicellular, but there are some that are multicellular.

• Some are autotrophs while others feed on organic matter and are heterotrophic.

• Scientists have organized protists into three different groups: animal-like protists, plant-like protists, and fungi-like protists.

• In all, there are 11 phyla in the protist kingdom.

Animal-like Protists (Protozoa)• Protozoans are classified by their type of locomotion,

life cycle, reproduction, nutrition and whether the protist is parasitic or free-living.

• All animal-like protists are heterotrophs. Similar to organisms in the animal kingdom, these protists have to be motile to search out food.

• Protozoans can either absorb pre-digested materials through their cell membrane or they can engulf their food.

• Sarcodina, Mastigophora, Ciliophora, and Sporozoa are the four phyla of animal-like protists. You will now learn about each phylum in greater detail.

Sarcodina• The amoeba is probably the

most famous protist in this phylum. Perhaps you even had the opportunity to view an amoeba under a microscope.

• One of the interesting characteristics of protists in this phylum is the way they move.

• By extending and retracting its cytoplasm, an amoeba is able to create “false feet” called pseudopods.

• The image above shows an amoeba moving toward a group of cells. The movement of the cytoplasm forms the pseudopods as the amoeba moves towards the food.

• Pseudopods also enable an amoeba to capture and engulf its food by phagocytosis.

• Below is a sequence of pictures showing an amoeba engulfing an algal cell.

• In the fourth sequence you will notice the appearance of the pseudopods surrounding the algal cells.

Mastigophora• In the phylum Mastigophora, the protists contain

one or more flagellum (pl.flagella) for locomotion.

• A flagellum resembles a tail and is attached to the cell body of the protozoan. A protist will generate motion when the flagellum begins to rotate.

• Most of these protozoans are harmless. • However, Giardia lamblia, a parasitic

protozoan causes upset stomach and diarrhea in humans.

• This parasite lives in the digestive tract of animals, like cows.

• Humans can contract the parasite when they consume food or water that has come in contact with the feces of infected animals.

Ciliophora• Cilates contain cilia, tiny

hair-like structures, throughout the outer covering of their cell body.

• In the image on the right, the cilia appear clear. The dark spot in the centre of the paramecium is the macronucleus which functions like a nucleus.

• A micronucleus, not shown, is smaller and is involved in reproduction.

• Most paramecium reproduce by binary fission; however, they can also undergo conjugation.

Sporozoa• Sporozoans rely on other

organisms for movement. They lack cilia, pseudopods, and flagella. Therefore, these protists are all parasitic.

• Malaria is caused by Plasmodium. Symptoms include fever, headache, and vomiting: malaria can quickly become life-threatening if not treated.

• Malaria can be spread from person to person and through mosquito bites.

• Approximately 40% of the world's population, mostly those living in the world's poorest countries, are at risk of malaria.

• Every year, more than 500 million people become severely ill with malaria. (WHO, May 2007)

Homework• Giardia lamblia is a parasite that affects humans. Applying your

knowledge, how could you protect yourself from getting this parasite?

• Plasmodium vivax is the parasite responsible for malaria. Describe in detail how the parasite is spread via mosquitoes.

• In 1962 Rachel Carson published a book titled “Silent Spring” in which she condemned the use of DDT. DDT at the time was a pesticide used to destroy mosquitoes that transmitted malaria and it had been linked to cancer development in animals and humans. In 1969, Canada banned the use of DDT and subsequently so did the United States and other countries. It is highly unlikely that you will contract malaria while living in Ontario. However, 40% of the world's population is at risk of becoming infected with this parasite. What advantages do we have over these other populations?