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PROTISTA

 

Protista constitutes a diverse kingdom containing thousands of species of single-celled organisms. Because many questions still persist concerning the ancestry of these organisms, deciphering which organisms should be classified in this kingdom is often a more arbitrary decision than most biologists would like. Because Protista is presented in the majority of biology texts as one of the five kingdoms, that's how the organisms are presented here.

Because multicellularity evolved many times, many multicellular organisms are more closely related to their ancestral unicellular lineages than they are to other multicellular organisms. This accounts for the reason that some members of the plant kingdom (such as the large multicellular algae) are sometimes considered to be multicellular protists. And certain members of the fungal kingdom (such as slime molds) are sometimes considered closer to the protistal lineage than to that of the fungi, and therefore are placed in the former. And in some classifications certain single-celled, heterotrophic protists are grouped with the animal kingdom. These are even respectable classifications in which all the major groups considered to be protists are placed in other kingdoms, and Protista is entirely dispensed with. The kingdom Protista as presented here, however, reflects the most widely accepted classification found in the majority of biology texts.

Discrepancies between different classifications are partially attributable to the way protists are defined. Rather than being grouped together by their shared characteristics, they are grouped by exclusion. That is, in addition to usually being unicellular, all protists are eukaryotes, so they are not included among the phylum Monera; since none develop from an embryo, they are not included among the phylum Plantae; since most do not develop from spores, they are not included among the phylum Fungi; and since none develop from a blastula, they are not included among the phylum Animalia. The organisms that remain tend to be those placed in this kingdom, Protista.

This kingdom includes the most simple, and often the most primitive, eukaryotic microorganisms and all their immediate descendants. Each protist cell has a nucleus and all the other eukaryotic properties. Members of this kingdom vary considerably in structure and physiology, ranging from heterotrophs (usually free-living, although there are parasitic forms) to photosynthetic autotrophs.

Protists appear to have evolved from a moneran type of ancestor. Protists possess specialized features such as endoplasmic reticulum, Golgi bodies, centrioles, chloroplasts, and mitochondria, as well as different kinds of vacuoles, granuoles, and fibrils. In addition, the average unicellular protist is considerably larger than the average moneran, and its cell division has become distinct from moneran cell division, having evolved mitotic and meiotic cell division.

It is theorized that the primitive protists were both plant-like and animal-like, having the capacity to obtain food by different mechanisms, as well as being able to photosynthesize additional food internally. There is considerable evidence that symbiotic relationships with prokaryotes living inside some early eukaryotes led to the development of chloroplasts and mitochondria. These organelles are contained in protists, as well as in many other more advanced eukaryotes.

Protista consists of several widely divergent phyla. Some of the unicellular, nonphotosynthetic protists are grouped as theProtozoa. These are subdivided into four classes: theMastigophora (flagellates), theSarcodina (amoebas), theCiliophora (ciliates), and theSporozoa (spore formers). The first three classes are identified according to their locomotor structures; however, sporozoans have no locomotor organelles, and instead they are characterized by their spores. To date, about 50,000 species of protozoans have been described.

Together, there are several other phyla that are often called true algae. They include about 25,000 described species, some of which belong to evolutionary lineages that were already well-developed more than 450 million years ago. Nearly all the members of these phyla are photosynthetic. They include forms that occur either as single cells, as filaments of cells, as plates or in planes of cells, or as a solid body. They range in size from unicellular microscopic organisms to giant multicellular forms such as the kelps, which often reach lengths exceeding 150 feet. A brief description of these photosynthetic groups is presented below.

There are three phyla of unicellular algae.Euglenophyta (euglenoids) live in fresh water, move by means of one to three flagella per cell, and have no cell wall.Chrysophyta usually include theyellow-brown algae, yellow-green algae, and thediatoms. They are mostly marine and contain pectic compounds, with siliceous materials providing the cell wall components. Pyrrophyta (dinoflagellates) live in marine environments, in fresh water, and in moist soil. They are characterized by having two flagella that beat in different planes, causing the organisms to spin. They often have distinctive, if not bizarrely shaped, cellulose walls. Like diatoms, the dinoflagellates are major components of the phytoplankton; they are aquatic, free-floating, photosynthetic, and usually microscopic.

There is another group of algae, sometimes called the true algae. In a recent classification by Margulis and Schwartz, the true algae are grouped with the protists, along with the water molds, slime molds, and slime nets, forming a kingdom they callProtoctista.

 

COMPREHENSION CHECK

 

1. Choose the right variant for the multiple-choice statements.

 

1. All protists

 

a. together represent a kingdom b. are eukaryotic organisms

c. are unicellular d. are multicellular

e. a and b.

 

2. All protists

 

a. Photosynthesize b. are heterotrophs

c. have tissue differentiation d. all of the above

e. none of the above.

 

3. The following are protists:

 

a.blue-green bacteria b. bacteria

c. bryophytes d. euglenoids

e. lycopsids.

 

4. Unlike monerans, protists possess

 

a. endoplasmic reticulum b. mitochondria

c. Golgi bodies d. chloroplasts

e. all of the above.

 

5. The nonphotosynthetic protists are known as

 

a. Thallophytes b. Bryophytes

c. chlorophytes d. protozoa

e. Chrysophyta.

 

6. All of the following are protozoans, except for

 

a. Sarcodina (amoebas) b. Ciliophora (ciliates)

c. Mastigophora (flagellates) d. Sporozoa

e. Tracheophyta.

 

7. Which of the following is prokaryotic?

 

a. Dinoflagellates b. blue-green bacteria

c. brown algae d. red algae

e. diatoms.

 

2. Ask questions revealing the main points of the text.

 

3. Think of 5-7 statements that would contradict the contents of the text.

 

 

LANGUAGE FOCUS

 

1. Find synonyms to the following words in the text:

 

lineage random to explain considerable
difference offspring lineal differ
elementary simultaneously single-celled strange, odd, unusual

 

2. Complete the table (where possible):

 

Noun Verb Adjective
protista    
  to persist  
    multicellular
ancestry    
lineage    
    divergent
    bizarre

 

3. Define the following terms:

 

protista unicellular multicellular kingdom
phylum classification ancestor true algae

 

4. Match the first half of a sentence in column A with the appropriate second half in column B:

 

A B
1. Protista constitutes a diverse kingdom a) having the capacity to obtain food by different mechanisms.
2. Members of the kingdom Protista vary b) giant multicellular forms such as the kelps.
3. It is theorized that the primitive protists were both plant-like and animal-like, c) considerably in structure and physiology.
4. True algae range in size from unicellular microscopic organisms to d) containing thousands of species of single-celled organisms.

 

5. Put the parts of the sentences in the right order:

 

a. To, unicellular, their, lineages, many, are, closely, organisms, related, multicellular, ancestral.

b. Protists, to be, some, of, plant, the, kingdom, sometimes, are, considered, multicellular, members.

c. Properties, each, cell, protist, has, and, a, all, the, eukaryotic, nucleus, other.

d. Appear, from, to, protists, evolved, a, have, moneran, ancestor, type, of.

e. Algae, there, several, phyla, other, are, that, often, are, true, called.

f. Million, they, already, ago, 450, were, more, well-developed, than, years.

 

FOLLOW-UP ACTIVITIES

 

1. Prepare dialogues discussing: a) general information about the kingdom Protista; b) primitive protists; c) true algae; d) unicellular algae.

2. Prepare a report on the topic under discussion.

 

 

GRAMMAR EXERCISES

Ex. 1. Translate the sentences into Russian paying attention to the Zero Conditional.

a)

1. If you boil water it evaporates.

2. If the soil is dry pradically very little water absorption takes place.

3. If glycogen is in solution, and it there is some sodium chloride present the glycogen colors itself a deep brownish – red color.

4. If the skin of an earthworm gets dry the animal dies.

5. If a tapeworm’s eggs are eaten by animals they penetrate through the alimentary canal into the muscles.

b)

1. If I have any problems I ask my friends for help.

2. If it rains I take an umbrella.

3. If I go to bed late I have a headache next day.

4. If I need a visa I go to the Embassy.

5. We usually go to the country on Saturday if the weather is good.

6. If he wants to go to the theatre he buys tickets in advance.

7. If he has to translate a text he uses a dictionary.

 

Ex. 2. Translate the sentences into Russian paying attention to the First Conditional.

a)

1. If we use the method I propose we shall obtain an entirely different result.

2. Unless mold spores have an opportunity to germinate, they will die.

3. The cells will shrink if the osmolarity of their cytoplasm is reduced to one-half or less normal.

4. The chilled slices will swell unless they are placed in medium of almost twice the osmolar concentration of the extracellular fluids.

5. Unless purely artificial limits are drawn, the definition “alga” will include all holophytic organisms.

6. If we examine a very thin piece of a plant under a microscope we shall see that it has a honeycomb structure.

7. If you compare the structure of the Tapeworm with that of the Earthworm you will notice that the Tapeworm’s body is more rudimentary.

b)

1. You wont regret if you see this film.

2. If you don’t hurry you will miss the train.

3. If he has his car repaired we’ll be able to go to the country.

4. It will be wise if you consult a dentist twice a year.

5. If you put salt on ice it will melt.

6. Providing that we get up early we’ll reach the place of destination in time.

7. If she works hard she will pass all exams successfully.

 

Ex. 3. Translate the sentences into Russian paying attention to the Second Conditional.

 

a)

1. A seed would not germinate if the soil wasn’t warm enough.

2. If I were a botanist I should know the difference between these roots.

3. If these new methods were applied we should succeed in obtaining better results.

4. If it were not for the roots, the plant would not be able to absorb water and mineral substances.

5. If the ozone were suddenly withdrawn from the atmosphere, we should all be killed by the sun’s ultra-violet light.

6. If there were no air, the stone and the piece of paper would fall together.

7. The plant would not develop so quickly if the soil were not fine.

8. Were the intensity of all the beams alike, we should get an opposite result.

9. The heating elements could be easily exchanged should the need arise.

10. Were the Earth stationary, the movements of the atmosphere would be controlled almost entirely by temperature differences.

b)

1. If he were a true friend he wouldn’t fail you.

2. If this was dangerous they would warn us.

3. We would accept their invitation if we were free.

4. If he was a wise man he would find a way out of the situation.

5. If I were you I wouldn’t go to Egypt in summer.

6. If I were in your place I wouldn’t worry about it now.

7. We would stay for an hour if it wasn’t so late.

 

Ex. 4. Translate the sentences paying attention to the Third Conditional.

a)

1. If the potential had been suddenly increased, very little current would have flown through the membrane.

2. The migration of the placental animals into Australia must have been blocked and this could only have happened if Australia had become isolated from the rest of the world.

3. If anoxia had hindered active expulsion of water, it would have led to excessive accumulation in cells.

4. If the F-zygote had been similarly poisoned, a viable zygote might not have been formed.

5. If we had given the culture the very high dose initially, we should most likely have killed it completely.

6. Their communication would have been more vivid if it had been illustrated with examples.

7. Had it not been for the powerful microscope our investigation of minute particles of the living organism would have been limited.

8. Stimulation would have produced different results could some of the experimental conditions have been changed.

b)

1. Even if I had phoned them, it would have been too late to change their minds.

2. He wouldn’t have been able to pass the exam if you hadn’t helped him.

3. If the ambulance had come sooner, the man might have been saved.

4. If I had known there was no more work to do, I could have left earlier.

5. If I had realized how late it was I wouldn’t have phoned you.

6. If he had experimented alone he would never have finished the work.

7. If he had followed his father’s advice he wouldn’t have got in trouble.

 

Ex. 5. Put the verbs in brackets into the appropriate conditional forms.

 

1. Mr. Davidson says he (to come) to give a talk at the conference if we (to play) him a reasonable fee.

2. If I (can get) a job, life here (to be) perfect.

3. If you (to have) a lot of money do you think you (to give up) work?

4. If the train (to arrive) on time, they (to be) here long ago.

5. What (to happen) to them if the helicopter (to be) there to save them?

6. If father (to get) this promotion, we (to have) enough money for a holiday abroad this year.

7. She (to do) a very good managing director if she (to get) this job.

8. He (to do) really well if he (to work) hard.

9. He (to be able) to live on his own if his parents (to help) him.

10. If you (to tell) her the truth I’m sure she (to forgive) him long ago.

 

Ex. 6. Match the clauses together to make mixed conditional sentences.

 

1. If you had told me about A. he probably won’t be at

this problem earlier, the meeting.

2. If you were a more B. you could always ring them up.

sensitive person,

3. If they don’t contact C. he wouldn’t have fallen ill.

you soon,

4. If he hadn’t died so D. you wouldn’t have said that

young, to her.

5. If he didn’t work so E. I would have had it by now.

hard all the time,

6. If the train hadn’t been F. everything would be all right now.

delayed,

7. If he was feeling ill G. would you hurry up and get ready?

this morning,

8. If you are coming H. you wouldn’t be so busy

with us, this month.

9. If I really wanted to I. we would be there by now.

have a car,

10. If you had worked harder J. I am sure he would be a

last month, famous musician now.

 

Ex. 7. Translate into English.

 

1. Ты едва ли узнал бы её, если бы встретил.

2. Если бы прохожий не помог нам, мы бы не нашли дорогу.

3. Если бы не ветер, не было бы так холодно.

4. Если пойдет снег, станет теплее.

5. Он не вел бы себя так глупо вчера, если бы был умнее.

6. Если бы я хорошо знала английский, я уже бы перевела этот текст.

7. Если ты решишь принять мое предложение, дай мне знать.

8. Если бы он не приехал на машине встретить нас, нам пришлось бы взять такси.

9. Если бы я была на твоем месте, я не стала бы никому рассказывать об этом.

10. Если бы он вел машину осторожно, никакой бы аварии не произошло.

11. Если ты поспешишь, то успеешь на восьмичасовой поезд.

12. Если ты будешь больше читать на английском, ты быстрее овладеешь языком.

 

Ex. 7. Choose the right variant and translate the sentences into Russian.

 

1. She wished at that moment she (had not sent/ did not sent) for him.

2. “I wish I (had been/ were) there with you”, - he said with deep regret.

3. I wish you (had not looked/ didn’t look) so sad.

4. The professor wishes I (had studied/ studied) harder.

5. We wished he (had not come/ did not come) so late yesterday.

6. I wish he (had seen/ saw) the play, it was a great success.

7. I wish they (introduced/ would introduce) their friends to me.

8. He wished they (hadn’t noticed/ didn’t notice) his embarrassment.

9. I wish you (wouldn’t leave/ didn’t leave) so soon.

10. The patient wished he (had fulfilled/ fulfilled) all the doctor’s instructions.

 

 

UNIT 12

 

GRAMMAR: PARTICIPLE.

TEXT: FUNGI

 

PRE-READING AND READING TASKS

 

1. Make sure you know the following words and word combinations:

 

ascus (pl. asci) ['xskqs] ['xskaI] аск
basidium [bq'sIdIqm] базидий
fungus (pl. fungi) ['fANgqs] ['fANg(a)I] гриб
mold [mqVld] плесень, плесенный гриб
mutual ['mju:tSVql] взаимный
hypha (pl. hyphae) ['haIfq] ['haIfi:] гифа, нить грибницы
lichen ['laIkqn, 'lItS(q)n] лишайник
mycelium [maI'si:lIqm] грибница
sac fungus [sxk] ['fANgqs] сумчатый гриб
septum (pl. septa) ['septqm] ['septq] перегородка
slime mold [slaIm] [mqVld] слизистый гриб
water mold ['wO:tq] [mqVld] водная плесень

 

Exercise 2. Read and translate the text.

 

FUNGI

 

There is some evidence that the organisms classified as fungi arose from protists along several different evolutionary lines. In fact, depending on the classification, fungi are sometimes placed within the kindgom Protista, or within the kingdom Plantae, or in their own kingdom,Fungi.

Fungi are eukaryotic organisms; most exist in multicellular form, although some go through an amoeba-like stage, and others, such as yeast, exist in a unicellular form. Unlike the photosynthetic algae and plants, fungi do not photosynthesize but absorb food through their cell walls and plasma membranes.

Theslime molds are different from most other fungi in that they are mobile during part of their life history. Some slime molds exist as a plasmodium, which is amultinuclear (coenocytic) mass of cytoplasm lacking cell walls. The plasmodium moves about and feeds in an amoeboid manner. The amoeboid mass is a slime mold's diploid phase.

Other slime molds have separate feeding amoebas that occasionally congregate into apseudoplasmodium that then sprouts asexual fruiting bodies. Because they pass through an amoeba-like stage, slime molds are occasionally classified as protists. Slime molds are usually found growing on such decaying organic matter as rotting logs, leaf litter, or damp soil, where these viscous, glistening masses of slime are usually white or creamy in appearance, though some are yellow or red.

During its vegetative phase, the slime mold plasmodium moves about slowly, phagocytically feeding on organic material. Under certain conditions, the plasmodium stops moving and growsfruiting bodies, from whichsporesare released that upon germination produceflagellated gametes. The gametes fuse, forming zygotes that lose their flagella and become amoeboid. The diploid nucleus continually undergoes mitotic divisions without any cytokinesis, and the organism develops into a multinuclear plasmodium that usually reaches a total length of five to eight centimeters.

Most fungi secrete digestive enzymes that hydrolyze nearby organic matter into minerals and compounds that can then be absorbed. Chemicals that don’t get absorbed, as well as the fungal waste products, enrich the surrounding area and become available to plants and other nearby organisms.

Fungi obtain their nutrition in any of three ways, or in any combination of these three ways: assaprophytes, living on dead organic matter; asparasites,attacking living plants or animals; and inmycorrhizal associations, in which they have a symbiotic relationship with plants, usually tree or shrubs.

Fungal spores are tiny haploid cells that float through the air, dispersing the fungi to new habitats. They are relatively resistant to high and low temperatures as well as to desiccation, and can survive long periods in an unsuitable habitat. When conditions become right, however, the spores germinate and grow. They absorb food through long, threadlikehyphae. The mass of branching hyphae creates the body of the fungus, called themycelium. Mycelia grow, spreading throughout their food source. Some hyphae arecoenocytic, having many nuclei within the cytoplasm. Others are divided bysepta into compartments containing one or more nuclei. The rigid cell walls of the hyphae and fruiting bodies are composed of cellulose, or other polysaccharides, although some are composed of chitin.

The mycelium constitutes the largest part of the fungal body, yet few ever see mycelia because they are usually hidden within the source of food they are eating. Sometimes, however, they can be seen on the forest floor spreading over moist logs and dead leaves. When mycelia break into fragments, fungi can reproduce vegetatively. Each fragment may grow into a new individual fungus. Other methods of fungal reproduction involve the production of spores, which can be formed asexually or sexually. The spores are usually produced on structures that extend above the food source, where they can be blown away and travel to new environments. Slime molds send up spore-bearing fruiting bodies. The mycelia of mildew send up aerial hyphae that form spores. The fruiting bodies that most people are familiar with, those associated with such fungi as mushrooms, are huge compared to the tiny fruiting bodies that cover moldy bread and cheese.

Most fungi are either parasitic or symbiotic. Parasitism occurs when one individual benefits while the other is harmed, and symbiosis is a mutually beneficial relationship between two individuals. By far the majority of fungal species are terrestrial and reproduce both sexually and asexually. Many have mycelia that grow in a close, intimate manner with plant roots. In such a relationship, the plant benefits by receiving nitrogen and phosphorus, while the fungus benefits by receiving nutritious carbohydrates.

Thewater molds and their relatives include the molds that grow on dead animals in the water. The powdery mildew found growing on Concord grapes is also a member of this group.

Zygomycota represent a group of fungi that, like the Oomycetes, have coeno-cytic hyphae. They also have chitinous cell walls. Although there are hundreds of species in this group, few people recognize any of them.

TheAscomycota, orsac fungi, form another group of fungi that is widespread although just a few species are familiar. Among this group's 30,000 orsospecies are the yeasts, certain bread molds, and the fungi that produce penicillin, as well as the species involved in making Roquefort and Camembert cheeses.

The yeasts are unicellular, but the Ascomycetes also include many multicellular types that form hyphae with perforated septa, allowing the cytoplasm and organelles such as ribosomes, mitochondria, and nuclei to flow from one cell to another.

Asexual reproduction is common among the Ascomycetes. It occurs whenever the projections known asconidia form and the asexualconidiosporespinch off. The sexual part of the life cycle involves two hyphae growing together so that the two nuclei become housed within the same cell. When these cells, calleddikaryons, develop into the fruiting bodies known asasci,which are characteristic of the Ascomycetes, the two nuclei fuse inside each ascus (singular of asci). This is the process of fertilization. Then the diploid nucleus undergoes meiosis, forming four haploid nuclei. These undergo mitosis, forming eight haploid nuclei that become theascospores. When the ascus ruptures, the ascospores are liberated.

The Basidiomycota, orclub fungi, include most of the commonmushrooms.Their fruiting bodies are known as mushrooms,basidia, or clubs; they are formed when two hyphae fuse. This is fertilization. A diploid nucleus is formed that undergoes meiosis, forming four haploid nuclei that move along thin extensions created by outgrowths of the cell walls. These nuclei are pushed to the edge of the club, where thesebasidiospores (spores) easily break off from their delicate stalks and are carried away by the slightest breeze. If they land in a suitable location, the spores germinate and grow hyphae, which form a mycelium that eventually sends up more fruiting bodies.

Theimperfect fungi represent about 25,000 fungal species for which sexual reproduction has either been lost or has yet to be observed. Without information about their sexual stages, it has not been possible to identify the characteristic structures that would help specialists classify them appropriately. Accordingly, they have all been lumped together and called imperfect. Members of this group are responsible for ringworm and athlete's foot; both are fungi that infect people without ever sprouting fruiting bodies.

Mycorrhizal associations occur when the hyphae of a fungus grow around, between, and sometimes even into living plant root cells. Such associations have been found to occur in at least 90 percent of all the different plant families. Eighty percent of all the angiosperms (flowering plants) may have such associations. These relationships are symbiotic.

Plants benefit because the mycorrhizae mobilize nutrients by secreting enzymes that help to decompose the litter in the soil. And then, by acting as root hairs, they help to absorb the nutrients, especially nitrogen and phosphorus, by moving these nutrients from the soil into the root tissue. Mycorrhizae also secrete antibiotics that help reduce the plant's susceptibility to infection by pathogens. The mycorrhizae benefit by absorbing the chemicals and carbohydrates that constantly leak through the roots.

Many of the mushrooms seen under trees and shrubs are the fruiting bodies of the fungi that have a mycorrhizal relationship with the roots of the neighboring plants. One often sees certain species of mushrooms associated with certain species of plants because mycorrhizal relationships are often quite specific.

Lichens are symbiotic combinations of organisms living together intimately. The species involved are always a fungus and either a chlorophyte (green algae) or a cyanobacteria (blue-green bacteria). The fungi are always either members of Ascomycetes or Basidiomycetes. Although the fungi involved in lichens are usually not found growing alone, the photosynthetic portion of the lichens sometimes does live on its own. It is clear that the fungus living in a lichen benefits from the organic compounds obtained from the photosynthesizing member of the association. The algae may obtain water and minerals from the fungus, but this part of the interaction isn’t well understood.

Because lichens are so tolerant of drought, heat, and cold temperatures, they are often the most important autotrophs found on recent lava flows, as well as on the stones used to construct buildings and gravestones. Lichens are also associated with dry, exposed soils, such as those in some deserts, and they also commonly occur in cold, exposed regions.

Most lichens reproduce either byfragmentation, when pieces break off and are blown elsewhere, or by spores produced by the fungal part of the lichen. The spores are blown or washed elsewhere, where they may grow and come in contact with an appropriate algal species. This marks the beginning of another lichen.

COMPREHENSION CHECK

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