Task7. Read and translate the text about the structure of the eukaryotic cell.

Eukaryotes house an assortment of structures, called organelles, within the cytoplasm, a gel-like substance that fills the cell. Like the unique toolbox of a carpenter or electrician, the different organelles house different molecular tools, including the specialized proteins called enzymes needed to accomplish the cell’s work. With all the enzymes needed for a particular job clustered in one organelle, the eukaryotic cell can work efficiently.

The largest and most conspicuous organelle is the nucleus. The nucleus encloses and protects the cell’s genetic material, deoxyribonucleic acid (DNA), so that it is not damaged by biochemical reactions in the cell. Within the eukaryotic nucleus, DNA is wrapped around specialized proteins called histones, like a thread wound around a series of spools. Each DNA strand and its histones fold back and forth several times to form a compact, stick-shaped structure called a chromosome. Depending on the organism, the nucleus contains from one to over a thousand chromosomes. Surrounding the nucleus is the nuclear envelope, a membrane with numerous pores. The pores, ringed by special protein, regulate the flow of substances into and out of the nucleus.

The most extensive organelle in the cell is the cytoskeleton, a web of protein filaments that branches extensively throughout the cytoplasm and gives the cell its shape. The cytoskeleton proteins, as well as other proteins in the cell, are made by tiny spherical organelles known as ribosomes. Several other important organelles are found in the cells. Among them are the lysosomes, membranous sacs storing enzymes that digest and recycle worn out cell parts; and the mitochondria, sacs where the cell's energy is generated. The endoplasmic reticulum, another organelle, is an extensive network of membrane folds and tubes that serves in part as the cell's factory floor where large molecules, such as lipids, are manufactured. These large molecules are sent to another organelle, the Golgi apparatus, which consists of layers of membranes where the molecules are modified, sorted, and packaged for transport.

Plants, seaweeds, and microscopic algae are specialized eukaryotes that carry out photosynthesis, the process by which light is used to convert carbon dioxide and water into sugar. In addition to the organelles described above, photosynthetic eukaryotes contain chloroplasts. Chloroplasts house the green pigment chlorophyll that is used in photosynthesis. Photosynthetic eukaryotes also may house chromoplasts, sacs of yellow, orange, or red pigments responsible for color in flowers and fruits. Photosynthetic eukaryotes may also have organelles called amyloplasts, where energy-rich starch is stockpiled.

Passage of materials into and out of the cell is regulated by the plasma membrane. Plant cells and many algal cells are further surrounded by a tough cell wall composed of cellulose, a carbohydrate. Cells of fungi, on the other hand, are surrounded by a cell wall made of chitin, another type of carbohydrate. In addition, on the outside of the plasma membrane, many eukaryotic cells bear either cilia or flagella, slender filaments that propel cells through liquid. These slender filaments enable aquatic organisms, for example, to navigate through the water. Cilia and flagella may also move liquid past a stationary cell. For example, cilia on the cells that line the lungs and trachea push mucus and dirt particles up out of the lung.

Task8. Give definitions to these phenomena: organelle, DNA, histone, chromosome, cytoskeleton, ribosome, lysosome, photosynthesis, chloroplast, carbohydrate, aquatic organism.

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