Single-Celled Animals: The Protozoa (1962)

hundreds of millions of years ago the first animals to live on earth were probably tiny similar to those We Now call protozoa these animals are all Tropic protozoa may be as small as a human red blood cell or as large as the letter o in your textbook these are paramia swimming among fibers that are about the same thickness as one hair from your own head originate biologists do not know to this question however one Theory suggests that protozoa evolved from extremely simple single celled organisms perhaps an ancient plant-like form of life similar to a modern ugina was the first organism to develop animall likee structures such as a light sensitive eyes in a situation where the ugina can choose its environment the ey spot can detect light and the flagellum provide a means of moving into the lighted area where photosynthesis can be carried on in the course of evolution from plant to animal an ancient single celled plant may have lost its photosynthetic pigments and yet survived because of its ability to use absorbed food such an hypo hesis can be tested by experiment for example we can demonstrate the loss of chlorophyll in these modern ugina to do this we add an antibiotic to culture fluid containing a large ugina population first the antibiotic is diluted to a concentration that will not kill the ugina but only interfere with the ugena production of chlorophyll the diluted antibiotic is left in contact with the Active Green ugina until the pigment chlorophyll entirely disappears as we see by the change in color here such animals are incapable of making their own food now since they have lost their chlorophyll we can demonstrate their need for chemical food by an experiment we divide this bleached ugina population into two test tubes to one we add organic food in the form of a solution of sodium acetate food is not added to the other tube it acts as the control tube both tubes are kept in total darkness after a few days we find that the population in the tube on the left containing organic food has grown while the population in the tube on the right without food has died out ugina without chlorophyll such as we see here are no longer plant-like since they cannot photosynthesize instead they must feed upon organic matter to survive they have become more animall likee for animals that do not absorb food material from solution Locomotion provides a greater chance of coming in contact with food particles this dileptus appears to actively search for food when it finds food it very efficiently eats it as you can see for convenience in identifying the thousands of kinds or species of the philm protozoa they are classified generally by the kind of structure they use for movement and food Gathering protozoans which move by means of whip-like flagella are called flagellates protozoa such as the amoeba move by means of the flowing of their cellular material into pseudopods or false feet some amas such as this atinos sporium do not use their thin rodlike pseudopods for movement only for the capture of food particles some amibas have hard shells over most of their bodies but active pseudopods can be seen where they project from a hole in the Shell as in this arella other amibas have hard internal structures these skeletons are from Marine amibas called radiolarians protozoa like this blue green stentor move by means of tiny hairlike cyia which beat in a coordinated manner these protozoa are called Cates they control the direction of the beating of their cyia and thereby change direction of locomotion very efficiently the shape of ciliates varies widely but all show Movement by means of cyia this blepharisma and this long lean spirostomum are fast swimmers in this upes ayate we find the Celia fused together to form the larger leg-like structures called Siri other Cates such as vorticella use their modified Celia to create water currents to bring food their way vorticella are attached to solid objects by stalks which contract when the animal is Disturbed another group The suctoria are also attached they capture food with their tentacles but their stocks cannot contract they obtain food by chance contact of ayate then as their name suctoria implies they suck the contents out of the captured Cate some protozoa have no means of locomotion because they have non motal sporik bodies they are called sporozoa here we see the sporozoan called plasmodium in the live red blood cells of a chick if we add a drop of acid to a population of paramia as here the paramia will move away from the high acidity and congregate in water that is only slightly acid this shows sensitivity to the to further explore sensitivity of protozoans to environmental factors we can demonstrate that paramia are able to react to differences in temperature we cool the left side of the glass slide on which the paramia are swimming after a period of time the paramia have moved to the right away from cold a heated iron is applied to the right side of the same glass Slide the paramia now move to the center of the glass slide thereby congregating in the region of most favorable temperature to demonstrate the avoidance reaction of a parami we place them in a tangle of glass fibers after bumping into an object the parami backs up and moves off in another Direction This Is trial and error Behavior the Amoeba's reaction to light can be demonstrated quite easily by placing it between between bright light and darkness as in this culture dish which is half dark and Half Light we can see that the amoeba moves out of the strong light into the dark it is possible to show some aspects of digestion in protozoa by laboratory experimentation for example we can demonstrate some of the chemical activity which occurs in a food vacuo during digestion we will take a small quantity of food for parami such as this yeast to the yeast an indicator dye is added the dyed yeast cells are then added to the environment of a population of paramia we will then be able to follow color change in the pink dyed yeast cells after they have been eaten by paramia after a half hour some of the paramia are observed under a microscope in this parami from the test population we can see both pink and red food vacu the change to red color is an indication of digestive activity by the parami the indic Ator Dy added to a tube of plain water shows by the resulting color that the reaction is neutral that is the solution is neither acid nor alkaline this color is comparable to the color of the D stained yeast before digestion began adding a drop or two of acid will change the color from pink to Red thus the red color in the parami food vacuo indicates a Aid conditions in the vacu adding a drop or two of alkali to the indicator causes it to change to Blue thus blue vacuoles in the parami would indicate an alkaline condition in the vacuoles to identify these color changes in the paramia again let's look at the food vacuoles we infer that very soon after eating the yeast the parami secretes acid into to its vacuoles thus accounting for the red food vacuoles later the parium secretes Alkali into its vacu changing the color to Blue in this specimen the change from acid to alkaline condition is just occurring as shown by the blue vacu among several red ones other paramia show Blue vacuoles an indication of fur digestion when a parium has grown to a particular size it will then divide this is an asexual form of reproduction since the offspring are derived from only one parent by division of the parent's body under favorable conditions paramia will divide as many as four times a day if all the paramia so produced were to survive it would take only a few days until the mass of paramia would equal the mass of the Earth some one-celled organisms fail to separate after cell division and remain together forming a colony such as these vvox colonies by means of this Association some of the cells specialize for reproduction within the larger colonies are daughter colonies formed by some members of the parent Colony that migrated inside the sphere the importance of the nucleus to continuing life of a protozoan can be demonstrated readily by using amoeba we support a micro needle on a mound of Clay on the microscope an amoeba in a drop of water on the slide is cut into two parts this half with a nucleus will move about and feed the other without a nucleus soon will die and degenerate here we see the sexual process of conjugation in the ciliate blepharisma the two animals fuse and the exchange of nuclear material between the two cells occurs after separation each animal divides asexually most protozoa are free living but some have adapted to a parasitic way of life life some single celled protozoan parasites cause diseases Timba hyola lives in the intestinal tract of man and causes Amic disent these live gregarines from the intestine of a beetal larvae move about in the intestinal content and at some stages of their life cycle invade intestinal cells plasmodium causes malaria the parasites live within the red blood cells of their host although a protozoan is composed of only a single cell it is capable of carrying on all of the basic functions of animal life it senses it moves it ingests food as this didinium eating a parium the parium having eaten bacteria it assimilates the products of digestion and grows and it reproduces protozoa have been an existence for a greater length of time than any other animal group they also make maintain the largest animal population and they are adapted to a tremendous variety of habitats h