Theme “General characteristics of protozoa.
7th grade biology
Topic: “General characteristics of protozoa. The origin of protozoa. The significance of protozoa in nature and in human life. L/R No.1 Study of the structure and movement of unicellular animals”.
Objective: to form an idea of the type of protozoa or unicellular animals, the peculiarities of their life activity in connection with their unicellularity, the classification and main representatives of this type
Concepts: unicellular, amoeba, infusoria-slipper, euglena green, photoreceptor, cabs, chemotaxis, phototaxis.
Type of lesson: combined lesson.
Subjects – generalization and consolidation of knowledge about the diversity and classification of unicellular animals, measures to combat and prevent infection by parasitic protozoa, the role of unicellular animals in nature and human life.
cognitive – the ability to highlight the main thing in the text, work with additional learning information structure the learning material, competently formulate conclusions;
communicative – the ability to work in pairs, to listen to the opinion of others, to express and defend their opinion
regulative – ability to organize the performance of the teacher’s tasks, develop skills of self-assessment and self-analysis
personal – development of communicative competence of communication and cooperation while doing learning tasks.
1. stage of organization.
2. Actualization of basic knowledge.
Discussion of a question.
How do unicellular organisms differ from multicellular organisms except for the number of cells?
3. Learning new material.
1.General characteristics of unicellular organisms
There are about 70,000 species of unicellular animals (Protozoa).
Their bodies consist of a single cell which performs all the vital functions of an integral organism: movement, feeding, breathing, excretion, etc.
The shape and size of protozoan cells are varied. They can be examined only with the help of magnifying devices. Protozoa are 0.1-0.5 mm in size on average (there are individuals about 0.01 mm, but larger organisms of several millimeters in size can also be found). There are also colonial forms of protozoa. Some protozoa do not have a constant body shape, while others have a relatively constant shape.
They inhabit unicellular animals mainly in the liquid medium – in sea and fresh water, in wet soil, in other organisms. Under unfavorable conditions (drying of water bodies, rise and fall of temperature) protozoa may form a dense protective shell, turning into cysts (Fig. A).
– is a temporary form of existence, adapted to survive unfavorable conditions.
When favorable conditions (Fig. B) arise, the animal leaves the cyst shell and continues its life activity.
A unicellular organism is separated from the external environment by a cell membrane; inside the cell there is cytoplasm with one or more nuclei and organelles.
Organelles are permanent structures of the cell that perform certain functions.
Organelles of protozoan movement are represented by spadefoot, flagella, cilia.
– are non-permanent outgrowths of cytoplasm without a dense cell membrane.
Pseudopodia are formed due to the flow of cytoplasm inside the cell and provide not only movement of a unicellular organism but also capture of food.
Cilia and flagella ensure faster movement than pseudopodia.
Digestive and contractile vacuoles are characteristic of protozoan cells.
Vacuoles are cellular cavities separated by a membrane and filled with fluid with dissolved substances.
The contractile vacuoles are found mainly in freshwater protozoa. They remove excess water from the protozoan organism. The concentration of salts in fresh water is much lower than in the protozoan cell cytoplasm. Therefore, according to the laws of physics, the water surrounding the protozoan organism enters the cell. To avoid cell rupture, excess water is removed from the cell by vacuole contractions. And together with water, metabolic products harmful to the organism are also eliminated.
Digestive vacuoles provide digestion of food that enters the cell. Undigested food remains in some organisms can be excreted in any place on the surface of the cell, in others they are excreted through special organelles.
Unicellular animals feed on finished organic matter (bacteria, unicellular algae and other unicellular organisms). This type of nutrition is called heterotrophic.
In addition to the heterotrophic type of nutrition, unicellular organisms are also characterized by the mixotrophic type. Forms with this type of nutrition are able to photosynthesize in the light – to create organic substances from inorganic ones (autotrophic nutrition), but in the darkness they turn to heterotrophic nutrition.
Mixotrophic type of nutrition is a mixed type of nutrition in which an organism is able to feed both autotrophically and heterotrophically at the same time.
Irritability is characteristic of protozoa. Reactions of protozoa appear in the form of movement towards the source of irritation or in the opposite direction. Such reactions are called cabs.
Irritability is the ability to react in a certain way to changes in the environment.
Cabs are motor reactions in response to a stimulus in the direction toward or away from it.
What features do these organisms have in common? First of all, all their living functions are performed by a single cell. Their unicellular body has the functions of a complete organism with its inherent physiological processes: respiration, digestion, excretion, reproduction and irritation.
The form of cells is diverse and can be permanent (flagellates, infusoria) and non-permanent (amoeba).
The covers of protozoa are represented either only by the plasma membrane or by a dense, sufficiently flexible and elastic membrane, the pellicle, which gives them a relative constancy of body shape. Two layers are clearly distinguished in cytoplasm: the surface, more dense, ectoplasm, and the inner, more fluid and granular, endoplasm, where organelles of protozoa are located.
Freshwater unicellular animals have contractile vacuoles that remove excess water from the cell. In marine and parasitic protozoa, contractile vacuoles are usually absent.
Organoids of motion: false legs, flagella, cilia. Nutrition: autotrophic (photosynthesis), heterotrophic (phagocytosis, pinocytosis, osmotic), saprotrophic (dead organics).
Reproduction: asexual (nucleus division by mitosis and then longitudinal or transverse cytokinesis); multiple division; sexual – conjugation (infusoria) and copulation (flagellates). Irritability: Responses of protozoa to various stimuli are called cabs. They manifest themselves mainly in the form of movement.
Cabs may be positive if the animal moves to the source of irritation and negative if it moves away from the irritant. For example, euglena greena is characterized by positive phototaxis – movement to the source of light, and infusoria slipper – negative chemotaxis – movement in the opposite direction from a salt crystal placed in water, etc. Cabs allows protozoa to find the most suitable conditions for their life and escape from adverse environmental influences.
Gas exchange in monocellular animals is carried out by the whole surface of the body. Modes of life: free-living and parasitic.
2.Significance: Sanitary, Soil-forming, Form chalk deposits, Exploration of minerals, Causes protozoan diseases of animals and humans.
Class flagellates (Lamblia, Trypanosomes)
Class Sarcodidae (dysentery amoeba)
Class Infusoria (Infusoria shoeba)
Class Sporobacteria (Malaria plasmodium)
Flagellates are unicellular organisms whose organoids are long outgrowths called flagella. The number of flagella in different species varies from one to several hundred. Most flagellates have a constant body shape because it is covered with a thin and elastic envelope – pellicle.
The pellicle is the outer dense layer of cytoplasm that ensures that the cell shape remains constant.
Green euglena is common in freshwater bodies of water. There is one flagellum at the front of its cell, and near the flagellum are: a contractile vacuole, which removes excess water from the body, and a bright red light-sensitive eye, the stigma, which senses changes in light exposure.
The stigma is a light-sensitive eye capable of detecting the source of light.
Closer to the back of the cell is the nucleus.
The cytoplasm of the euglena contains chloroplasts filled with chlorophyll. This ensures its ability to photosynthesize.
Euglena is able to change its feeding patterns depending on environmental conditions. It feeds autotrophically in the light and heterotrophically in the dark (it eats particles of organic matter, small animals, unicellular algae). This type of feeding is called mixotrophic (mixed).
Noxious substances (waste products) and excess water are expelled through the contractile vacuole.
Euglena breathes oxygen dissolved in water. Gas exchange occurs, as in the amoeba, through the entire surface of the body.
Reproduction. Euglena verde reproduces by longitudinal division in two:
More than 7000 species are classified as flagellates. According to the nature of their nutrition and metabolism, they are divided into plant and animal.
Animal flagellates include bodo, which lives in the same reservoirs as the plant euglena green flagellate.
The structure of the bodo flagellate
1 – cell mouth; 2 – flagella; 3 – membrane; 4 – cytoplasm; 5 – nucleus; 6 – mitochondrion; 7 – digestive vacuole.
Bodo moves in water with the help of two flagella located at the front end of the body. This animal has no chlorophyll, so only heterotrophic nutrition is characteristic of it. It feeds on bacteria, unicellular algae and microscopic animals that the bodo uses its flagella to drive to its mouth and swallow.
The bodies of colonial flagellates consist of many cells.
A volvox is a large spherical colony about 8 mm in diameter, with cells connected by cytoplasmic “bridges” in a single layer on its surface, and a liquid mucus occupies the inner cavity of the ball. The cells have flagella directed outward.
Animal flagellates include many human pathogens.
Trypanosoma, the causative agent of sleeping sickness, parasitizes in human blood.
At the front end of the cell begins a flagellum, which continues along the entire cell, connecting to it by a thin wave-like membrane.
The carrier of trypanosomes is the tsetse fly. The disease is common in Africa. When a sick person is bitten, the trypanosomes enter the intestines of the fly and begin to multiply there. They then enter the salivary glands of the insect. If such an insect bites a healthy person, the trypanosomes enter their bloodstream and cause sleeping sickness. Sleeping sickness is characterized by nervous and mental disorders, drowsiness and exhaustion. It leads to the death of the person.
Leishmanias are flagellate protozoa, human parasites that cause the disease, leishmaniasis.
The disease is spread by mosquitoes.
When a sick person is bitten, leishmania enter the digestive system of the female mosquito and begin to multiply there. They then enter the salivary glands of the mosquito. When a healthy person is bitten, the leishmanias enter their wound. The disease is manifested by skin ulcers and sometimes internal organ damage.
Leishmania life cycle
In the body of the mosquito, leishmanias have a long flagellum, spindle-like shape.
And in the human body, they have a short flagellum, round shape, they are immobile.
Lamblia are flagellate protozoa that parasitize in the human intestine.
Lamblia enter the human body with the consumption of contaminated water and food. In the human intestine, they eat digested food. Enter the environment with feces. While in the human body, giardia produce toxins that disrupt internal organs.
Trichomonads are flagellated protozoa that parasitize in the human intestine. They cause intestinal trichomoniasis. Trichomonads eat bacteria that live in the human intestines and cause diarrhea. Infection occurs through the consumption of food and water contaminated with trichomonas.
Infusoria, or ciliates, are the most highly organized protozoan animals.
Characteristic features of infusoria are:
They have cilia (organs of locomotion) on the surface of the body, which are in constant motion, allowing the infusoria to move rapidly.
There are two nuclei in the infusoria cell, different in size and function. The large (vegetative) nucleus, the macronucleus, is responsible for feeding, breathing, movement, and metabolism; the small (generative) nucleus, the micronucleus, is involved in the sexual process.
In the same reservoirs where live Proteus amoeba and Green Euglena, there is also found this unicellular animal, 0.5 mm long, with a body shape resembling a slipper – Slipper Infusoria.
Movement. Slipper infusoria swim rapidly with their blunt end first, moving forward with the help of cilia.
The body of the infusoria has a depression, the cellular mouth, which passes into the cellular pharynx. Larger cilia are located near the mouth. They drive bacteria – the main food of the shoe – into the pharynx together with the water flow. A digestive vacuole is formed at the bottom of the pharynx into which the food enters. The digestive vacuoles are moved in the body of the infusoria by the cytoplasmic current. Digestion of food occurs in the digestive vacuole, and the digested products enter the cytoplasm and are used for the infusoria’s life activity.
Undigested residues remaining in the digestive vacuole are ejected outside through a special structure at the posterior end of the body, the powders.
Excretion. There are two contractile vacuoles located at the anterior and posterior ends of the body.
THE CONTRACTILE VACUOLES EXCRETE EXCESS WATER.
Like other free-living unicellular animals, infusoria breathe through their body covers.
Root suckers are unicellular organisms that move with the help of false legs (pseudopodia). For the most part, root-feeders live in the same environment. They eat algae, bacteria and other protozoa. Reproduce mainly asexually.
is found in fresh water. Amoeba does not have a permanent body shape, its cell forms outgrowths – pseudopodia – by moving the cytoplasm. Cytoplasm consists of 2 layers: outer (ectoplasm) and inner (endoplasm). The cell has one nucleus, digestive vacuoles, a contractile vacuole, and other organelles. The amoeba reproduces by dividing in two (see previous section).
Amoeba feeds by phagocytosis.
Phagocytosis is a process in which cell pseudopodia envelop a solid food particle, after which it is absorbed and digested using the digestive vacuole.
1 – The nucleus of a unicellular organism;
2 – vacuole;
3 – bacterium;
4 – ingested bacterium
parasitizes in the human intestine and causes the disease amoebic dysentery. The disease occurs rarely. Basically, the amoeba lives in the intestine and feeds on bacteria there. But sometimes it injures the wall of the intestine, forming ulcers, penetrates the blood and begins to feed on blood cells, causing dysentery. At a certain stage of parasitization it enters the rectum, where it forms a cyst (incysts) and is released into the environment with the feces. It is spread by flies and can get on food.
Foraminifera (crustacean amoebae)
live exclusively in salt water. They concentrate calcium in their bodies, from which they form shells.
The shell has a protective function; its walls are pierced with tiny pores through which the pseudopodia emerge. Inside the shells are cytoplasmic organelles and a single nucleus. Foraminifera reproduce with alternating sexual and asexual generations. The adult foraminifera is asexual. It gives rise to the asexual generation, which gives life to the asexual generation. Ancient foraminifera took part in the formation of Cretaceous mountains.
Radiolarians (or Radiolarians) and Solanaceae are unicellular, less often colonial, protozoa that have a mineral skeleton (which includes silicon) that serves a protective function. The skeleton has pores through which pseudopodia in the form of thin filaments emerge. They are all planktonic organisms.
Planktonic organisms are organisms that drift freely in the water column closer to its surface.
Parasitic protozoa are single-celled animals that live at the expense of other organisms, called hosts.
Sporobacteria are unicellular organisms that live exclusively parasitic lives. There are about four thousand species of them. They parasitize in worms, insects, animals and humans.
Because of their parasitic lifestyle, sporozoans differ from other protozoans:
Adult sporozoans have no organoids of motion.
There are no digestive and contractile vacuoles, since nutrition is carried out by the entire surface of the cell.
Reproduction in most sporozoans is asexual. A parasite cell divides into many daughter cells – independent organisms.
About 30 species of protozoa can parasitize in the human body. The most dangerous to humans is malaria plasmodium – the causative agent of malaria.
The life cycle of malarial plasmodium is complex and proceeds with a change of hosts: the malaria mosquito (genus Anopheles) is the main host; humans are intermediate hosts.
The primary host is the organism within which the parasite reproduces sexually.
Intermediate host is an organism within which the parasite reproduces asexually. There can be several such hosts for a single parasite.
Asexual reproduction: When a female mosquito bites a parasite with the saliva of the mosquito enters the human bloodstream and penetrates into the liver cells. Here they divide to form forms which can settle in erythrocytes (red blood cells). The plasmodium actively multiplies in the erythrocytes, resulting in so many plasmodia that the blood cell bursts. The parasite enters the blood and infects its new cells. During the rupture of the blood cells, the person suffers an attack of fever (high body temperature).
Sexual reproduction: During the sucking of the blood of a sick person by the female mosquito, the plasmodium enters the digestive tract of the mosquito. There sexual reproduction takes place, as a result of which the next (asexual) generation is formed. During the bite they enter the human blood, and the cycle repeats.