Protozoa Honor

Nature Study

Requirements

What are the main characteristics of protozoa that place them in the protist kingdom? What similarities and differences do they have in relation to the other protists (algae)?
Answer: Protozoa are unicellular heterotrophic eukaryotes, with active locomotion and reproduction by division. That is why they fall into the kingdom Protista. They differ from bacteria (prokaryotes), fungi (chitin wall, absorption), plants (photosynthesis, cellulose wall), and animals (multicellular). — Protista was proposed by Haeckel in 1866 to house unicellular eukaryotic organisms; protozoa include amoebas, paramecia, and trypanosomes; the eukaryotic + unicellular + heterotrophic criterion is the basis — some, such as Euglena, perform photosynthesis, being mixotrophic, and generate modern taxonomic debates.
Be able to identify, by means of a drawing or picture, 5 common protozoa, giving their scientific name.
Answer: Five common protozoa: Amoeba proteus (amoeba), Paramecium caudatum (paramecium), Trypanosoma cruzi (Chagas disease), Plasmodium falciparum (malaria), and Giardia lamblia (giardiasis). Draw each one highlighting structures: pseudopods, cilia, flagella, or the absence of self-movement. — Chagas disease affects about 6 million people in Latin America according to the WHO; malaria kills 600,000 people a year worldwide; Giardia is a common cause of diarrhea from contaminated water; Paramecium has been a classic model in microbiology since Leeuwenhoek (1674); Amoeba is used to study pseudopodal cell movement.
Give the classification of protozoa, stating their distinctive characteristics and at least one example in each group and its importance.
Answer: Four groups: Sarcodina (movement by pseudopods — Amoeba); Ciliata (cilia for locomotion — Paramecium); Mastigophora/Flagellates (one or more flagella — Trypanosoma); Sporozoa (no self-locomotion, parasites — Plasmodium). The classification is based on the characteristic locomotor structure of each group. — This is the traditional classification still used in textbooks; modern (phylogenetic) classifications use up to 30 groups such as Excavata and Alveolata; Plasmodium is transmitted by the Anopheles mosquito and has a complex cycle in the human liver and red blood cells; Trypanosoma cruzi is transmitted by the kissing bug in Brazil.
What are pseudopods? What is their function?
Answer: Pseudopods ("false feet") are temporary extensions of the cell cytoplasm used by the amoeba and other sarcodine protozoa to move and capture food. They work by amoeboid movement: the cytoplasm flows in the desired direction and surrounds prey (bacteria, debris) by phagocytosis, forming digestive vacuoles. — Amoeboid movement involves the gel-sol change of the cytoplasm; it was discovered in 1755 by Rösel von Rosenhof; human macrophages use the same mechanism to engulf bacteria during the immune response; modern studies show that actin is the key protein of the process, discovered in the 1940s.
How does the reproduction of protozoa occur? How can they alter their genetic characteristics and become more resistant to aggressors?
Answer: Protozoa reproduce mainly by binary fission (asexual): the cell duplicates its DNA and organelles, then divides into two equal ones. Some have conjugation (sexual): they exchange genetic material with another cell. Conjugation increases genetic variability, generating descendants with new combinations that may be more resistant to drugs. — Paramecium is a classic model of conjugation, described by Sonneborn in the 1930s; the malaria Plasmodium develops resistance to chloroquine through mutation and genetic exchange, making treatment more difficult; the WHO has monitored antimalarial resistance worldwide since 2010 — the basis of current global drug resistance.
How does the feeding and respiration of protozoa occur?
Answer: Feeding: by phagocytosis (the amoeba surrounds prey with pseudopods, forming digestive vacuoles) or pinocytosis (it absorbs liquids through the membrane). Respiration: by simple diffusion through the plasma membrane — the oxygen dissolved in the water enters the cell and the CO₂ leaves without the need for specific lungs or gills. — Digestive vacuoles have lysosomal enzymes that break down the food; simple diffusion works because the protozoan is tiny (a high surface/volume ratio); the oxygen dissolved in the water is the limiting factor — in stagnant water there can be death from hypoxia; the process was described by Anton van Leeuwenhoek in the 17th century when observing microorganisms.
Amebiasis and giardiasis are gastrointestinal diseases caused by protozoa that are very similar. Cite 3 differences that distinguish them and how we can prevent them.
Answer: Differences between amebiasis and giardiasis: 1) Causative agent — amebiasis is caused by Entamoeba histolytica; giardiasis by Giardia lamblia. 2) Site of action and symptoms — the amoeba attacks the large intestine (colon), causing diarrhea with blood and mucus (amoebic dysentery); Giardia attacks the small intestine, causing fatty, foul-smelling diarrhea without blood, with gas and malabsorption. 3) Complications — Entamoeba can cross the intestinal wall and form abscesses in the liver and other organs; Giardia generally remains restricted to the intestine. Prevention (common to both, since both are transmitted through water/food contaminated with cysts): drink only treated, filtered, or boiled water; wash your hands well before meals and after using the bathroom; wash and sanitize fruits and vegetables; have adequate basic sanitation (proper sewage and septic tank); avoid food of dubious origin; and control flies and cockroaches that carry the cysts. — Entamoeba pode invadir fígado causando abscesso; Giardia se prende ao epitélio com disco adesivo; ambas se transmitem por água ou alimentos contaminados (rota fecal-oral); são doenças negligenciadas no Brasil segundo Ministério da Saúde, com prevalência maior no Norte e Nordeste em águas não tratadas.
Talk about leishmaniasis and how dogs are related to the spread of this protozoan disease.
Answer: Leishmaniasis is caused by the protozoan Leishmania (several species) and transmitted by the bite of the sandfly (phlebotomine). Dogs are the main reservoirs — they keep the parasite and infect more mosquitoes that bite people. That is why control includes euthanasia or treatment of infected dogs, the use of a repellent collar, and screens on windows. — In Brazil there are 200,000 cases per year (Ministry of Health 2023); visceral leishmaniasis kills if untreated (7% mortality); collars with deltamethrin reduce canine infection by 80%; the ethical debate over canine euthanasia is strong — some countries use only treatment (allopurinol) in infected dogs, according to the WHO.
Malaria is a disease that causes many deaths in the Amazon region and in Africa. Describe its form of contagion, its main symptoms, and how we can prevent and treat this disease.
Answer: Malaria is caused by the protozoan Plasmodium (P. falciparum, vivax, malariae, ovale) and transmitted by the bite of the infected female Anopheles mosquito. The parasite invades the human red blood cells and the liver, causing cycles of high fever, chills, anemia, and sweating. Without treatment (chloroquine, artemisinin), it can be fatal. — The WHO estimates 250 million cases and 600,000 deaths annually worldwide, mainly in sub-Saharan Africa; the Plasmodium cycle was described by Ronald Ross in 1897 (Nobel 1902); falciparum is the most lethal species; insecticide-treated bed nets have reduced deaths by 50% in Africa according to recent official WHO data.
Draw the cycle of Chagas disease, explaining each phase. What does it cause in human beings? How is it transmitted? How can we prevent it? Is there treatment?
Answer: Cycle: Trypanosoma cruzi lives in the kissing bug (Triatoma); it bites a human and defecates near the bite; the parasite enters through the scratched skin; it invades the heart, esophagus, and colon causing arrhythmia (acute phase) and chagasic cardiomyopathy (chronic phase). Prevention: improve rural housing, screen houses, and control kissing bugs with insecticides. — Carlos Chagas described the disease in 1909 (the only one identified by a single researcher); 6 million infected in Latin America; transmission also through blood, transplant, and the ingestion of contaminated açaí; treatment with benznidazole works only in the acute phase — the chronic phase is treated only for symptoms, in effect today.