Task18. Read the text about cyanobacteria.

Unlike other algae, the cyanobacteria are prokaryotes—single-celled organisms with characteristics that cause biologists to debate whether they are really algae or bacteria. Cyanobacteria are found nearly everywhere, occurring in typical aquatic and terrestrial habitats as well as in such extreme sites as hot springs with temperatures as high as 71° C (160° F) and crevices of desert rocks. Cyanobacteria make up the phylum Cyanophyta, and this phylum contains about 150 genera and 2000 species worldwide.

Like other bacteria, cyanobacteria do not have organelles such as nuclei, mitochondria, or chloroplasts. Cyanobacteria are distinguished from bacteria by the presence of internal membranes, called thylakoids, that contain chlorophyll and other structures involved in photosynthesis. While higher plants have two kinds of chlorophyll, called a and b, cyanobacteria contain only chlorophyll a. Cyanobacteria color varies from blue-green to red or purple and is determined by the proportions of two secondary pigments, c-phycocyanin (blue) and c-phycoerythrin (red), which tend to mask the green chlorophyll present in the thylakoids.

Cyanobacteria reproduce asexually by binary fission, spore production, or fragmentation, forming singular cells, colonies, filaments, or gelatinous masses. Although most lack flagella and are nonmotile, filamentous forms such as Oscillatoria rotate in a screwlike manner, and the gelatinous forms glide along their slimy mucus.

Cyanobacteria may be both beneficial and harmful to humans: Some act as natural fertilizers in some habitats, especially rice paddies, whereas others produce toxins. Mild cyanobacteria toxins in lakes and oceans cause a rash known as swimmer’s itch, while powerful neuromuscular toxins released by other cyanobacteria can kill fish living in the water or the animals that drink the water. In certain conditions, cyanobacteria may form dense blooms, which may produce toxins that make seafood poisonous to humans. Even if the cyanobacteria do not produce toxins, blooms can cause water to have an unpleasant taste and odor.

Task19. Prove the statements.

1. Cyanobacteria can be found nearly everywhere.

2. Cyanobacteria are distinguished from bacteria.

3. Cyanobacteria reproduce asexually.

4. Cyanobacteria may be both beneficial and harmful to humans.

Task20. Sum up the information given in the text.

Task21. Translate the following word combinations into English and memorize them.

структурные и физиологические отличия

анаэробные организмы

световая энергия

внутренняя мембрана

вращаться подобно пропеллеру

вырабатывать белок

бинарное поперечное деление

испытывать недостаток атмосферного кислорода

частые извержения вулканов

постоянно изменять химический состав

сине-зеленые водоросли

содержание кислорода в атмосфере

преобразовывать атмосферный азот в азотсодержащие соединения

водные экосистемы

синтезировать витамины, органические кислоты, ферменты

зуд купальщика

GRAMMAR SECTION

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