VII. Using additional sources of information prepare a report on one of the following topics and present it to the class

• Modern views on the problems of taxonomy and systematics in biology.

• The role of bacteria in ecology and in human lives.

• Modern virology. Recent investigations and discoveries.

Unit 4

Lesson 1

Vascular plants

PRE-READING TASKS

I. Answer the following questions

• What do you associate a plant with?

• What features distinguishing plants from other living organisms can you name?

• What part do plants play in ecology?

II. Listen to the following words and practice their pronunciation

Vascular plant, xylem, phloem, fern, gymnosperm, angiosperm, conifer, monocot, dicot, taproot, fibrous root, meristem, lateral bud, internode, petiole, axil, axillary bud, leaf primordia, protoderm, epidermis, procambium, cuticle, pith, cortex.

READING COMPREHENSION AND VOCABULARY DEVELOPMENT

I. Match each word on the left to its correct definition on the right

anchor, v comprise, v device, n dormant, adj erosion, n germinate, v principal, adj soil, n steep, adj tip, n twig, n

the upper layer of earth that may be dug or plowed and in which plants grow; the process by which rock or soil is gradually destroyed by wind, rain, or the sea; to hold firmly or fix; the usually pointed end of something; not active or not growing at the present time but able to be active later; a small shoot or branch usually without its leaves; to begin to grow or to sprout; most important or influential, chief; a mechanism designed to serve a special purpose or perform a special function; to consist of particular parts, groups, etc; making a large angle with the plane of the horizon.

II. Read the following text paying attention to the highlighted words. Explain or interpret the contextual meaning of the underlined phrases

The vascular plants, or Tracheophyta, differ from the evolutionary more ancient algae and mosses by the possession of conducting systems called vascular tissues. There are two types of vascular tissue: xylem and phloem. Xylem is concerned primarily with transport of water and dissolved minerals from the roots to the other parts of the plant, whereas the phloem transports food and certain other solutes from sites of production (such as leaves) to sites of utilization (such as roots).

The body of most vascular plants is divided into three principal organs: the leaves, the stem and the root system. A stem and its leaves, taken together, are called a shoot. The shoot system of a plant consists of all stems and all leaves. The leaves are the chief organs of food production (photosynthesis), whereas roots serve to anchor the plant in space and to absorb water and mineral nutrients from the soil. The stem may be regarded as a device for holding and displaying all leaves to the sun, so as to maximize the photosynthetic yield, as well as for providing transport connections between the roots and leaves.

The three principal groups of vascular plants are the ferns, gymnosperms (pines and other conifers), and angiosperms (flowering plants). The angiosperms, in turn, comprise two subclasses, the monocots and the dicots. Monocots are generally narrow-leaved flowering plants such as grasses, lilies, and orchids. Dicots are broad-leaved flowering plants such as beans, roses and oaks.

Roots. There is more than one type of root system. In many gymnosperms and dicots, there is typically a taproot system in which a single, large, deep-growing root is accompanied by less prominent secondary roots. The taproot itself may function as a food-storing organ, as in carrots and radishes. In contrast, monocots and some dicots have fibrous root system composed of numerous thin roots roughly equal in diameter. Such a root system holds soil very well, making grasses an ally on steep hillsides where runoff from rain could cause erosion. Fibrous root systems often have a tremendous surface area for absorption of water and minerals. The outer layer of cells in roots forms the epidermis. The flattened epidermal cells, called root hairs, produce amazingly long, delicate extensions that vastly increase the surface area of the root. At the tip of each root there is a root cap that protects the delicate growing region of the root as it pushes through the soil. Cells of the root cap are constantly damaged and scraped away and must therefore be replaced by the growing region, or meristem, of the root. The root cap is also the structure that detects the pull of gravity and thus causes the root to grow downward.

Stems. The vascular tissues run continuosly from root to stem, affording uninterrupted flow of water and food. Unlike the root, the stem may be green and capable of photosynthesis. The stem bears leaves, and, where each leaf meets the stem, there is a lateral bud, which develops into a branch if released from its dormant state. The branching patterns of plants are highly variable, depending upon the species, environment conditions and other factors.

The area, or region (not structure), of a stem where a leaf or leaves are attached is called a node, and a stem region between nodes is called an internode. A leaf usually has a flattened blade, and in most cases is attached to the twig by a stalk called the petiole. Each angle between a petiole and the stem contains a bud. The angle is called an axil, and the bud located in the axil is axillary bud. Axillary buds may become branches, or they may contain tissues that will develop into the next season’s flowers. Most buds are protected by one to several bud scales, which fall off when the bud tissue starts to grow.

At the tip of each stem there is an apical meristem which contributes to an increase in the length of the stem. The apical meristem is dormant before the growing season begins. It is protected by bud scales of the bud in which it is located and also to a certain extent by leaf primordia, the tiny embryonic leaves that will develop into mature leaves after the bud scales drop off and growth begins. The apical meristem in the embryonic stem of a seed is also dormant until the seeds begin to germinate.

When a bud begins to expand or a seed germinates, the cells of the apical meristem undergo mitosis, and soon three primary meristems develop from it. The outermost of these primary meristems, the protoderm, gives rise to the epidermis. Although there are exceptions, the epidermis is typically one cell thick and usually becomes coated with a thin, waxy, protective layer, the cuticle. A cylinder of strands constituting the procambium appears to the interior of the protoderm. The procambium produces water-conducting primary xylem cells and food-conducting primary phloem cells.

The remainder of the meristematic tissue, called ground meristem, produces two tissues composed of parenchyma cells. The parenchyma tissue in the centre of the stem is the pith. Pith cells tend to be very large and may break down shortly after they are formed, leaving a cylindrical hollow area. Even if they do not break down early, they may eventually be crushed as new tissues produced by other meristems add to the girth of the stem, particularly in woody plants. The other tissue produced by the ground meristem is the cortex. The cortex may become more extensive than the pith, but in woody plants, it, too, eventually will be crushed and replaced by new tissues produced from within. The parenchyma of both the pith and the cortex function in storing food or sometimes, if chloroplasts are present, in manufacturing it.