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Although a few protozoans are multicellular, the simplest are unicellular organisms, such as amoebas, bacte-
ria, sarcodina, ciliates, flagellates, and sporozoans, which can be amorphous in shape and smaller than .001
inch. Cytoplasm fills the cell membrane that en-Line closes it and functions as a barrier between cells. The
membrane serves as the outer tissue, and any compound that may destroy the cell has to penetrate it to reach
the cytoplasm.
Some types of organisms are termed colonial because they represent loosely assembled groups of structurally
similar and unifunctional cells. Colonial organisms maintain a symbiotic relationship within their particular
environments.
Unlike colonial organisms, almost all species of animals and plants are multicellular and include various
types of specialized or somatic cells, each with its own nucleus, genetic code, and RNA. The overall size of a
multicellular body is contingent on the total number of cells that comprise it, not the size of individual cells.
The simplest multicellular animals are hydras, sponges, and jellyfish, which have well-defined tissues, a cel-
lular nucleus, and an element of cell functions. Sponges have a few specialized cells but largely resemble
colonial organisms that can readily form a new individual group. If the cells of a sponge are separated, they
rejoin and continue as a newly formed colonial organism.
Text 2. Read, translate and retell.
When parchment, which was extraordinarily costly, was replaced by papyrus, it became feasible to establish
libraries. At the onset, they began as archives for record keeping and document storage. According to sec-
ond-hand reports, the most renowned papyrus library was the Alexandrian, founded by Alexander the Great
around 330 B.C. in Alexandria, Egypt.
His successors as rulers of Egypt, Ptolemy I and Ptolemy II, expanded the library into the greatest collection
of scrolls in the ancient world. To acquire this collection, the rulers borrowed scrolls and manuscripts from
libraries in Athens, Rome, and other localities and ordered them duplicated. At times, the library employed
more than 100 scribes and illustrators. Some historians claim that the Alexandrian library purchased entire
lesser libraries to contribute to and enhance the quality of its possessions.
The library owned a copy of every contemporary scroll known to the library's administrators and contained
more than 400,000 items, all of which were classified and organized. The contents of the papyrus rolls were
edited, and a bibliography of Greek literature was compiled and cross-referenced, reflecting the emergence
and dissemination of a highly developed Greek culture. Over time, a succession of leading scholars directed
this library, which was acclaimed for the scholarly undertakings it supported as well as for the size of its col-
lection. At one time, 72 scholars were engaged to translate religious testaments, historical annals, and mer-
cantile accounts. Although the library flourished, it was accessible to only a minority of the population be-
cause in ancient times the vast majority of urban dwellers were illiterate. Because papyrus was extremely
perishable, not a trace of the Alexandrian library remains today, and archaeologists have several hypotheses
as to what became of it.
Text 3. Read, translate and retell.
According to data obtained from radioactive dating, the oldest rocks found on earth are approximately 500
million to 4 billion years old. Similar ages have been determined for meteorites and the rocks gathered from
the moon's surface. Different methods of arriving at the earth's age generate very similar results. Modern
theories about the formation, development, and eventual burning out of stars suggest that the sun is about 5
billion years old. Experts contend that the earth and the sun were formed at almost the same time from a
cloud of dust and gas resulting from a cosmic explosion. The present rate of expansion of the galaxies can be
extrapolated to suggest that, if the universe began with a "big bang" about 15 billion years ago, an age of 5
billion years for both the earth and the sun can be considered plausible.
Long before radioactive dating was implemented, mythology and oral narratives alluded to a conjecture that
the earth was nearly 6,000 years old. The methods of computation based on the analysis of genealogical trees
in scant archaeological findings provide evidence that can be difficult to date accurately. Today, radioactive
dating of particles and whole objects has rejected this figure of the earth's age as unreliable.
Text 4. Read, translate and retell.
