Unit 5 The History of Life on Earth

Introduction

Listen to the account of the history of ideas concerning the generation of life on Earth and discuss in pairs whether the following sentences are true or false.

1. Several centuries ago no one thought it difficult to answer the question of how living things had arisen. T / F

2. Earlier people thought that life had appeared spontaneously from nonliving things and other forms of life. T / F

3. In Medieval texts the authors suggested ways of creating nonliving things from living things. T / F

4. People thought that microorganisms had arisen from broth and wheat. T / F

5. Francesco Redi proved that maggots did not arise from rotting meat. T / F

6. Louis Pasteur’s ideas did not answer the question of how life on Earth had originated. T / F

7. Alexander Oparin thought that complex organic molecules could be formed spontaneously only if oxygen was around. T / F

8. Oxygen keeps molecules simple. T / F

9. Oparin and Haldane argued that the primordial atmosphere consisted of hydrogen gas, methane and ammonia and free oxygen. T / F

10. Prebiotic evolution means evolution of nonliving matter to become living matter. T / F

Reading

Prebiotic Conditions Would Allow Organic Molecules to Accumulate

Prebiotic synthesis would not have been very efficient or very fast. Nonetheless, in a few hundred million years, large quantities of organic molecules could accumulate, especially because they didn’t break down nearly as fast back then. On Earth today, most organic molecules have a short life; either they are digested by living organisms or they react with atmospheric oxygen. Primeval Earth lacked both life and free oxygen, so these sources of degradation were absent. However, the primordial atmosphere also lacked the ozone layer, a region high in the atmosphere that is enriched with ozone molecules, which absorb some of the sun’s high-energy ultraviolet (UV) light before it reaches Earth. During the early history of Earth, before the ozone layer formed, UV bombardment, which can break apart organic molecules, must have been fierce. Some places, however, such as those beneath rock ledges or at the bottoms of even fairly shallow seas, would have been protected from UV radiation. In these locations, organic molecules may have accumulated to relatively high levels.

Even in areas protected from the sun, however, it’s unlikely that molecules dissolved in a huge ocean could reach the concentrations necessary to form spontaneously the more complex molecules that arose in the next stage of prebiotic evolution. The chemical reactions in which simple molecules combined to form larger molecules such as RNA and proteins required that the reacting molecules be packed closely together. Scientists have proposed several mechanisms by which the requisite high concentrations might have been achieved on early Earth. One possibility is that shallow pools at the ocean’s edge were filled with water by waves crashing onto the shore. Afterward, some of the water in the pool might have evaporated, concentrating the dissolved substances. Given enough cycles of refilling and evaporation, the molecules in these pools could have become a concentrated “primordial soup” in which spontaneous chemical reactions could generate complex organic molecules. These molecules could then have become the building blocks of the first living organisms.

I. As in the example a, choose the definitions for the words in bold from the following list:

a related to the period when the universe or the Earth first began to exist - …primeval…

b the process of the change of a liquid into gas or steam - …………………

c necessary for a particular purpose - ……………………

d the process of changing into a worse condition - ………………………

e with only a short distance from the top or surface to the bottom - …………………..

f formed when the Earth or universe began - …………………..

g very strong or severe - …………………

h a narrow surface that continues out from the side of a cliff, wall or other surface - …………

II. List the conditions that prevented life from appearing on the primeval Earth. How do scientists solve the problems arising from these conditions?

Language focus 1

-Ing and –ed Participles

I. Translate the following word combinations:

a developing organism

a developed frog

a dividing cell

the divided world of the XXth century

intriguing results of latest experiments

intrigued observers of the advance of science

a misleading hypothesis

a proved theory

guided reactions

the guiding role of genes

failed attempts

to develop specialized structures

life-sustaining water

II. What is the general meaning of the –ed participles and of the –ing participles?

Fill in the gaps with a suitable form of an –ing or –ed participle

1. A …….……… (reproduce) organism can be called a ………………. (live) organism.

2. A ……………. (catalyze) reaction proceeds faster than a …………………. (non-catalyze) one.

3. The ideas ………………. (include) concerned not only the biological science but also other fields of knowledge.

4. In the 1980s, Thomas Cech and Sidney Altman offered an ………………. (intrigue) solution to the question of how self-reproducing molecules appeared.

5. A ……………….. (develop) human body needs more care than a …………………… (develop) one.

6. The ………………….. (intrigue) spectators waited for the outcome of the competition.

7. It is sometimes difficult to draw a ………………. (divide) line between living and non-living matter.

8. A house ……………….. (divide) cannot stand.

9. A …………….. (prove) hypothesis becomes a part of a scientific theory.

10. We don’t know how many ………………… (fail) experiments led to the discovery of many simple things.

Language focus 2

-Ing and –ed Participle Constructions

1 The photosynthetic reactions of the first cyanobacteria converted water and carbon dioxide to organic compounds, releasing oxygen as a by-product.

(The –ing participle construction is here an adverbial modifier and it modifies the whole of the main clause.)

2 Oxygen and nutrients going into the cell and waste products going out must diffuse through the plasma membrane.

(The –ing participle constructions are here attributes and they modify the words oxygen and nutrients and waste products.)

3 An organism may be multicellular - that is, it may consist of many small cells packaged into a large, unified body.

(The –ed participle construction is here an attribute, modifying the word cells.)

I. Say whether the –ing or –ed participle construction is an adverbial modifier or an attribute.

1. If an aerobe was captured by an anaerobe cell it could absorb half-digested food molecules residing in the cytoplasm of the anaerobe and its oxygen to complete its metabolism, gaining enormous amounts of energy as it did so.

2. The oxygen expelled by cyanobacteria reacted with iron atoms in Earth’s crust, or surface layer, forming huge deposits of iron oxide, known as rust.

3. Mitochondria, chloroplasts and centrioles each contain their own minute supply of DNA, which some researchers interpret as a remnant of the DNA originally contained within the symbiotic bacterium.

4. Waterproof coatings on the aboveground parts reduced water loss by evaporation, and rootlike structures delved into the soil, mining water and minerals.

5.Specialized cells formed tubes called vascular tissues to conduct water from roots to leaves.

6. Extra-thick walls surrounding certain cells enabled stems to stand erect.

7. A wide variety of Precambrian invertebrate animals (animals lacking backbones) appear in rocks laid between 650 million and 544 million years ago.

8. A new and different set of fossil animals appears just as suddenly in strata from the Cambrian period, marking the beginning of the Paleozoic era, about 544 million years ago.

9. Most invertebrates in the Silurian period possessed either an internal hydrostatic skeleton, much like a water-filled tube (worms) or an external skeleton covering the body (arthropods such as trilobites).

10. Soon a more efficient means of feeding evolved: A separate mouth and anus, found today in almost all animals, was developed.

II. Translate into Russian, using participle constructions.

1. Анаэробный организм не нуждается в кислороде для метаболизма, используя другие метаболические механизмы.

2. Земная кора содержит значительные по объему залежи минералов, используемые как источник энергии и строительный материал большим количеством организмов.

3. Реакции фотосинтеза, происходящие в хлоропластах, превращают энергию солнечного света в другие формы энергии.

4. Митохондрии, находящиеся в цитоплазме эукариотических клеток, играют важную роль в их метаболизме.

5. Водоотталкивающие покрытия, сформированные на поверхности листьев, предотвращают потерю воды путем испарения.

6. Организмы, у которых нет хорды, называются беспозвоночными.

7. Цианобактерии, содержащие хлорофилл прямо в цитоплазме, варьируют в цвете от сине-зеленого до фиолетового.

8. Цианобактерии, поглощенные клеткой-хозяином, развились в первые хлоропласты.

9. Согласно общепризнанной гипотезе, первые хищники были специализированными прокариотическими клетками, у которых не было клеточных стенок и которые, следовательно, были способны поглощать целые бактерии.

10. Кислород, освобожденный цианобактериями, реагировал с железом, образуя соединение, известное как ржавчина.

Words, Words, Words

I. Prepare to discuss the development of: a) microspheres and their qualities, and b) the first living things and their qualities, using some of the expressions given.

- to create favorable conditions for the formation of complex organic compounds

- to possess significant stability

- to form microspheres

- to absorb various substances

- to be transformed in a series of reactions

- to be expelled into the environment

- to be only partially similar to living things

- to control the synthesis of specific compounds

- to develop the mechanism of reproduction and inheritance

- to determine the order of amino-acids in the synthesis of proteins

- to gain energy from the environment

- to give off energy in the process of decay of organic compounds

- to lead to giving off oxygen into the atmosphere and water

II. Render the following extract into English, using the expressions from I.

Большое количество данных говорит о том, что средой возникновения жизни могли быть прибрежные районы морей и океанов. Здесь, на стыке моря, суши и воздуха, создавались благоприятные условия для образования сложных органических соединений. Например, растворы некоторых органических веществ (сахаров, спиртов) обладают большой устойчивостью и могут существовать неограниченно долгое время. В концентрированных растворах белков, нуклеиновых кислот могут образовываться сгустки подобно водным растворам желатина. Такие сгустки называют коацерватными каплями, или коацерватами (зд. microspheres). Коацерваты способны адсорбировать различные вещества. Из раствора в них поступают химические соединения, которые преобразуются в результате реакций, проходящих в коацерватных каплях, и выделяются в окружающую среду.

Коацерваты – это еще не живые существа. Они проявляют лишь внешнее сходство с такими признаками живых существ, как рост и обмен веществ с окружающей средой. Поэтому возникновение коацерватов рассматривают как стадию развития преджизни.

Коацерваты претерпели очень длительный отбор на устойчивость структуры. Устойчивость была достигнута вследствие создания ферментов, контролирующих синтез тех или иных соединений. Наиболее важным этапом в происхождении жизни было возникновение механизма воспроизведения себе подобный и наследования свойств предыдущих поколений. Это стало возможным благодаря образованию сложных комплексов нуклеиновых кислот и белков. Нуклеиновые кислоты, способные к самовоспроизведения, стали контролировать синтез белков, определяя в них порядок аминокислот. А белки-ферменты осуществляли процесс создания новых копий нуклеиновых кислот. Так возникло главное свойство, характерное для жизни, - способность к воспроизведению подобных себе молекул.

Живые существа представляют собой так называемые открытые системы, то есть системы, в которые энергия поступает извне. Без поступления энергии жизнь существовать не может.

По способам потребления энергии организмы делятся на две большие группы: автотрофные и гетеротрофные. Очевидно, первые организмы были гетеротрофными, получающими энергию путем бескислородного расщепления органических соединений. На заре жизни в атмосфере Земли не было свободного кислорода. Возникновение атмосферы современного химического состава теснейшим образом связано с развитием жизни. Появление организмов, способных к фотосинтезу, привело к выделению в атмосферу и воду кислорода. В его присутствии стало возможным кислородное расщепление органических веществ, при котором получается во много раз больше энергии, чем при бескислородном.