Roundworms, pinworms, and hookworms are all nematodes. Many are scavengers, some are predators, and still others are parasites of different animals, including humans. Two of the roundworm parasites of humans are Ascaris and Trichinella spirilis.
The large, parasitic roundworm Ascaris has 20-35 cm-long adults that reside in their host's intestines, including those of humans. Reproduction occus there, and Ascaris eggs are passed along with feces. Eggs must mature in the soil and thus are restricted to survival only in warmer climates. A new host picks up this parasite when eggs are swallowed due to poor sanitation. Once inside the host's body, larvae hatch from their eggs and tunnel through the intestinal wall to the liver and eventually to the lungs. They molt in the lungs and crawl up the trachea. Once they reach the throat, they tend to be swallowed and once again end up in the intestinal tract. There they mature into adult worms and reproduce, completing their life cycle.
Ask your students what effect having a load of Ascaris worms in the intestines would have on the individual.
Hint: A good parasite does not kill its host but simply lives off it. Intestinal worms consume the food the host swallows, but having a few worms is unlikely to be greatly detrimental to the host unless the host is malnourished to begin with. Unfortunately, having worms and being malnourished often go hand in hand, since acquiring worms has to do with unsanitary conditions that are more commonplace in impoverished areas. Intestinal worms can lead to malnourishment, usually because of a heavy load of worms or having had worms for a long time. If protein consumption is insufficient, worms cause problems for the host. The worms eat the protein, making it unavailable to the host. The host then has problems making cells of the immune system and may also suffer liver damage. Another interesting fact is that, if caloric consumption is extremely low and inadequate for the host, it is even more detrimental to the parasite. Very healthy people tend to ward off parasites, and very malnourished or ill people cannot support them. It's those in the middle who are more likely to host intestinal parasites.
Trichinella spirilis is the cause of a disease known as trichinosis (not to be confused with trichomoniasis, the sexually transmitted disease). For humans, the most common way to get trichinosis is by eating rare pork infected with encysted larvae. When these larvae mature in human intestines, they tunnel through the intestinal wall and produce offspring that travel in the bloodstream. Eventually they reach skeletal muscles and encyst there. The larvae may survive in that condition for as little as six months or for as long as 30 years. Skeletal muscle is the preferred site, especially the muscles of the jaw, tongue, arms, chest, and legs. Symptoms appear about two weeks after the person has consumed infected and undercooked pork. Headache, difficulty breathing, muscle soreness, and edema result. A blood test can reveal the prevalence of eosinophils, which are a type of white blood cell produced in response to parasitic infections and allergies. Fully cooking meat, especially pork, is the best prevention for this disease. Ruminant animals such as cattle rarely host this parasite.
Many students new to biology are unaware of the numerical importance of all other kinds of animal species, other than humans and the animals with which we most frequently come into contact. Share with your students a listing of major animal phyla and the numerous sppecies in each. This also serves as a good review of the Kingdom Animalia.
| Name of the Phylum | Common Name | Estimated Number of Species |
| Porifera | Sponges | 5,000 |
| Cnidaria | Hydra, jellyfish | 9,000 |
| Ctenophora | Comb jellies | 90 |
| Platyhelminthes | Flatworms | 13,000 |
| Nematoda | Roundworms | 12,000 |
| Rotifera | Rotifers | 2,000 |
| Mollusca | Mollusks | 110,000 |
| Annelida | Segmented worms | 12,000 |
| Arthropoda | Arthropods, insects | 6,000,000+ |
| Echinodermata | Echinoderms | 6,000 |
| Hemichordata | Acorn worms | 90 |
| Chordata | Chordates | 45,000 |
| Subphylum Vertebrata | Vertebrates | 43,700 |
| Class Osteichthyes | Bony fishes | 20,000 |
| Class Amphibia | Amphibians | 3,900 |
| Class Reptilia | Reptiles | 6,000 |
| Class Aves | Birds | 9,000 |
| Class Mammalia | Mammals, humans | 4,500 |
We have all grown up knowing about dinosaurs, but sometimes it is fun to imagine having one walk down the street or to envision its immense size next to a building. Below are a few facts to share with your students to help them appreciate dinosaurs and their uniqueness. Other information can be found almost anywhere--many informative books about dinosaurs are currently on the market, and dinosaur facts can be found on everything from cereal boxes to toy and snack food labels.
The most fearsome of dinosaurs, Tyrannosaurus rex, was 50 ft long, the width of the average home yard, and weighed 6 tons, as much as 80 average human adults, combined.
The tallest dinosaur would have been able to peer over the top of a four-story building.
The smallest dinosaur was about the size of a beagle.
The fastest dinosaur, Gallimimus, could run 35 mph, much faster than a human can even ride a bicycle.
The largest dinosaur egg contained as much fluid as five dozen average chicken eggs.
When many of us encounter bats, it is an automatic (and probably learned) reaction to scream, grimace, or otherwise show displeasure and fear. The much maligned bat is now facing a rapid decline in numbers. Have students read the interesting, entertaining, and enlightening article by M.D. Tuttle entitled "Saving North America's Beleaguered Bats," in National Geographic, August 1995, pages 37-57. Discuss with them their own encounters with bats and reassure them that the vast majority of these flying mammals are insectivores.
Dian Fossey and Jane Goodall both made significant contributions to our knowledge of chimpanzee and gorilla behavior by doing something many other scientists refused to do: living in close proximity and observing these primates for years. Discuss the contributions of these two scientists. This is one of a number of excellent opportunities to focus on the contributions of women to the science of biology. Dian Fossey studied mountain gorillas and was eventually murdered by the poachers from whom she was trying to protect the gorillas. Jane Goodall has become an expert in chimpanzee behavior and has documented many different types of behavior, including those indicating close social bonds. National Geographic Educational Videos offers films about each of the se behavioral scientists.
One of the truly remarkable characters in the field of human evolution is Donald Johanson. Amidst the popularity of the Leakeys, this anthropologist has come up with his own, and sometimes controversial, ideas about the descent of modern man. He is amiable, a bit eccentric, and a delight to listen to. Share some of the evolutionary insight of this man with your students either through the video from Carolina Biological Supply or through his recent National Geographic article entitled "Face-to-Face with Lucy's Family," March 1996, pages 96-115.