Student Resources

Protozoans - Workbook Questions

What are the similarities and differences between sexual reproduction and conjugation?  (p. 2) 

In most cases, sexual reproduction involves two parent organisms that form gametes by meiosis, which decreases the genetic content of the gamete from diploid (2N) to haploid (N). A female gamete, the egg, is usually larger and non-motile compared to the smaller motile male gamete, sperm. Production of gametes has no affect on the parents that produce them, and the fusion product that results from the combination of the two gametes, the zygote, is a new organism.
Things are a little different with conjugation. The parent organism changes into the fusion product, and when conjugation is over the original parents no longer exist. During conjugation the micronucleus undergoes meiosis, and genetic material is swapped between the original organisms. The other nuclear material disappears and a new macronucleus and micronuclei form from the fusion product formed inside the original organism. Meiosis and recombination of two haploid products to form the new organism are common to both sexual reproduction and conjugation. But unlike sexual reproduction, conjugation doesn’t involve any gametes, and the original parent organisms disappear and are replaced by the new daughter organisms. 

What are the differences between cilia and flagella?  (p. 3) 

Structurally cilia and flagella are similar and are formed from the same 9+2 organization of microtubules. Flagellated animal cells have only one, and in some cases two, flagella on each cell. Ciliated cells have large numbers of these 9+2 structures on each cell. The two also differ in their lengths, with flagella being longer than cilia, and how they beat. Flagella move in helical spirals, like a power boat propeller, or back and forth in a single plane, like the dolphin kick or sculling when you swim. Cilia, on the other hand, beat with a distinct power and recovery stroke. The difference between the two is that in the power stroke the full surface of the cilium pushes against the water compared to the recovery stroke. To continue with our swimming analogy, the breast stroke is an example of the differences between power and recovery strokes. 

Describe the biochemical events involved in changing endoplasm to ectoplasm and back to endoplasm.  (p. 3) 

There is still some debate on how pseudopodia, and the cytoplasmic streaming inside them, work. There is agreement that the process involves converting the cytoplasm from fluid endoplasm, plasmasol, to solid ectoplasm, plasmagel, and there’s good evidence that the muscle proteins actin and myosin are involved. One of the more recent models proposes that actin is prevented from forming filamentous aggregates, actin filaments, by the presence of regulatory proteins attached to each actin molecule. When actin and regulatory protein stream forward and reach the hyaline cap, the regulatory proteins are removed and actin forms filaments connecting into a mesh that forms the ectoplasm. At the trailing edge of the cytoplasmic streaming, the presence of calcium dissolves the mesh and the actin filaments are now free to interact with myosin filaments. This causes the shape of the trailing edge of the pseudopod to change, or contract, and this propels the endoplasm toward the hyaline cap. 

How many different types of pseudopods can amoebas have?  (p. 4) 

The different types of pseudopods include:

1.      lobopodia with large, blunt ends;

2.      filopodia with thin, branching cytoplasmic pseudopods;

3.      reticulopodia that have cytoplasmic extensions that form meshes that connect and reconnect with each other; and

4.      axopodia, thin pseudopods with an internal supporting structure formed from microtubules. 

Describe the life cycle of the causative organism of sleeping sickness, Trypanosoma cruzi.  (p. 5) 

Trypanosoma cruzi is one of a variety of trypanosomes that infect humans and livestock around the world. One of the diseases caused by trypanosomes is African sleeping sickness with the tsetse fly as the vector that moves the disease between vertebrate hosts. Trypanosoma cruzi is the trypanosome species that causes a form of the disease in the tropical Americas, Chagas’ disease. Blooding sucking bugs are the vectors that move the disease between hosts, and if the insect feeds on an infected person they consume trypanosomes with the ingested blood meal and pass them to another person the next time they feed. These bugs are sneaky about getting their meal and inject an anaesthetic as they feed so the victim doesn’t feel the initial bite or the insect as it consumes its large blood meal. As the insect finishes feeding, fecal material often leaks out of the animal as it tries to make space for as much food as possible. The trypanosome is able to survive the digestive environment of an infected bug and is in the fecal material that drops from the insect at the end of its meal. Infection occurs by scratching the insect bite and introducing the contaminated fecal material into the wound. Darwin is thought to have died of Chagas’ disease, which he contracted during his explorations of the Galapagos Islands.

What are the different stages in the malarial organism’s life cycle, and what is the functional purpose of each?  (p. 6) 

To survive, a parasite must move between its different hosts, and each of the stages in the life cycle is either involved in increasing the numbers of the parasite inside the host or is modified for moving between hosts. Starting with the mosquito, sporozoites in the mosquito’s saliva are injected into the human host and migrate into liver cells where they undergo asexual multiple fission to become schizonts filled with merozoites. The infected liver cells break open, and merozoites are released into the blood to infect the red blood cells. As trophozoites, the parasite feeds on the contents of the red blood cells and then undergoes asexual multiple fission forming another schizont loaded with more merozoites. Merozoites burst from the red blood cells to infect other red blood cells, and the infection continues inside the host. In both the liver and red blood cells the process is referred to as schizogony.
But not all the merozoites infect new red blood cells. Some will differentiate into gametocytes, by gametogony. As the name implies, these form in preparation for the sexual reproductive stage of the life cycle. For gametocytes to become gametes they must be ingested by the mosquito to complete their differentiation. An egg and a motile male gamete fuse to form a zygote that forms a cyst embedded in the stomach wall of the mosquito.  Inside the cyst the parasite increases its numbers asexually in a process referred to as sporogony, and sporozoites escape from the cyst to accumulate in the salivary gland as sporozoites.

Protozoa || Porifera || Cnidaria || Platyhelminthes || Nematoda || Annelida || Mollusca || Arthropoda
Echinodermata || Chordate Origins || Jawed Fishes || Amphibia || Mammalia