Day 3 Frog Text Set

What makes text complex?

Excerpt from Life Sciences

Text 1:

Frogs, toads, and salamanders are amphibians. Amphibian comes from a Greek word that means double life. Amphibians begin their life cycle as water animals. They develop into air-breathing animals as they grow up.

Female amphibians lay their eggs in wet places. The eggs are covered with a jelly-like material to protect them. The eggs hatch into larvae, or tadpoles. Tadpoles swim in the water and grow legs. When they are adults, amphibians live on land and breathe air. Toad tadpoles grow up quickly. It takes them only a few months to lose their tails and become small toads. After that, it may take as long as three years for them to become full-grown adults! Toads have been known to live 30 to 40 years.

When frog eggs hatch into tadpoles it takes them a very long time to grow up. Several years can go by before the tadpoles become frogs.

What makes text complex?

Excerpt from Life Sciences

Text 2:

Frogs and toads have an aquatic larval stage, the familiar tadpole. The fish-like tadpole has gills which are later lost in metamorphosis. The moist skin of frogs and other amphibians contains mucous glands that assist in maintaining the moisture. Moreover, the eggs of amphibians, laid in water or other moist areas, are usually covered with a gelatinous substance. Thus amphibians remain dependent on aquatic (or at least wet) environments in many ways.

This group also shows adaptations for living on land. Most importantly, adults have lungs adapted for air breathing and are therefore no longer dependent on water for gas exchange. (It can occur through the skin when amphibians are in water.) Furthermore, the two nostrils are connected to the mouth cavity to facilitate breathing through the lungs. Almost all amphibians have two pair of jointed appendages that permit locomotion both on land and in water. Frogs and toads also have sound-sensitive membranes (“external eardrums”) on their bodies; such specialized sense organs are essential for land dwellers, because air does not transmit sound waves as efficiently as water. Finally, amphibians have a more efficient type of circulatory system than fish, including a heart with three chambers rather than two.

What makes text complex?

Excerpt from Life Sciences

Text 3:

It is possible to calculate that, if a frog oocyte (a developing egg cell) had the same number of ribosomal RNA genes as a body cell of the frog, it would take many years—far longer than a female frog lives—to make an egg with so many ribosomes.

Early in the development of the frog oocyte, however, the genes for ribosomal RNA undergo amplification: They are selectively replicated many hundredfold or thousandfold, while the rest of the nuclear DNA undergoes no further replication. These extra copies do not remain with the chromosome from which they are copied; they are “extrachromosomal” pieces of DNA that float free in the nucleus. They are all transcribed to yield ribosomal RNA, and egg development is completed in a matter of weeks instead of years. Amplification of ribosomal genes has been observed in other species. Amplification of nonribosomal genes—of structural genes coding for specific proteins, for example—has not yet been seen, despite intensive and critical search.

Rearrangement of structural genes has, however, been detected as a specific event in eukaryotic development. In the development of lymphocytes (the line of white blood cells that make antibodies in vertebrates), two genes that were originally located in different parts of the chromosome are physically combined to form a single functional structural gene that codes for one antibody polypeptide chain.

DMU Timestamp: February 17, 2017 01:10