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Organs of flowering plants
Plants are complex living organisms with interconnected and coordinated functioning organs. There are vegetative and generative organs. Vegetative organs (root, stem, leaf) serve to maintain the individual life of the plant, ensure its growth and development, generative organs (flower, fruit and seed) - for the sexual reproduction of plants.
Roots strengthen plants in the soil, give them stability, absorb from the soil the water necessary for plant life and nutrients dissolved in it, which are sent along the stem to the leaves. In addition, the root can serve as a reservoir for reserve nutrients. It synthesizes many organic compounds, a significant part of which is released into the soil and used by soil microflora (fungi, bacteria) and other plants. In root sucker plants, the roots perform the function of vegetative propagation. Distinguish main root, which is formed from the embryonic root, adventitious roots, developing on stems and leaves, and lateral roots, representing branches of any roots. The top of the growing root is covered with a kind of protective cover - root cap, whose cells are constantly renewed (Fig. 2). It creates passages for the roots in the soil. Under the cover is division zone (growth cone), represented by dividing cells of the apical educational tissue. Next is located stretch zone, in which cells grow intensively, stretching along the axis of the root, and begin to differentiate. Next one suction zone contains a large number of root hairs - external outgrowths of skin cells up to 20 mm long, the function of which is to absorb water and mineral salts from the soil solution. Conductive tissues of the root are also formed here, along which in the above venue area nutrients are transported. This zone does not have root hairs and is covered with suberized tissue. In some plants, the roots can be greatly modified. This is usually due to nutrient buildup. At the same time, the roots become thick and fleshy. Particularly common is a thickened storage main root, called a root vegetable (carrots, beets, turnips, radishes, radishes, etc.).
Rice. 2. Internal structure root:
1 - root cap; 2 - division zone (growth cone); 3 - stretch zone; 4 - suction zone; 5 - zone of conduction and formation of lateral roots.
The totality of all the roots of a plant is called the root system. They are distinguished by shape taproot system, in which the main root is strongly developed and stands out from the rest of the roots, and fibrous root system, in which the main root is absent or invisible among numerous adventitious roots (Fig. 3).
A leaf is a lateral vegetative organ of a plant that develops on the stem. The process of photosynthesis is carried out in the leaves, i.e., from water and minerals absorbed by the roots from the soil, as well as from carbon dioxide (carbon dioxide) of atmospheric air with the help of solar energy, which is captured by chloroplasts containing the green pigment - chlorophyll, organic substances are formed : starch, sugar, proteins, fats. These substances move along the stem to other parts of the plant: roots, flowers, seeds and fruits.
Rice. 3. Root system plants: A - rod; B- fibrous
The leaf usually consists of leaf blade and petiole, but the leaves of some plants lack a petiole (for example, plants of the Bluegrass family). Such leaves are called sedentary. U different plants leaves differ in the shape of the leaf blade (heart-shaped, lanceolate, oval, etc.), the shape of its edge (whole-edged, serrated, etc.), the arrangement of the veins (in the leaves of dicotyledonous plants the venation is usually pinnate or palmate, in the leaves of monocotyledons - parallel or arc). Leaves are also distinguished simple, having one leaf blade that falls entirely in the fall, and complex, disintegrating after dying into separate parts. Compound leaves are either palmate or pinnately compound.
The order in which the leaves are attached to the stem is called leaf arrangement. At next leaf arrangement leaves grow on the stem one at a time, alternating with each other, with opposite- two against each other, with whorled - are attached to the stem by bunches consisting of several leaves.
The stem is the axial vegetative organ of the plant, which connects the two poles of plant nutrition - roots and leaves, ensuring the exchange of necessary nutrients between them. It brings leaves to the light, serves as a support for generative organs, and can store nutrients. Stems are distinguished by location in space (erect, creeping, climbing, climbing, etc.), degree of lignification (herbaceous and woody), life expectancy, length (up to 300 m in some tropical vines).
The stem with leaves and buds located on it is called escape. The sections of the stem where leaves develop are called nodes, and the sections of the stem between two nodes are called internodes.
Shoots of some plant species, as well as roots, can be modified, adapting to perform additional, for example, storage functions. Particularly important are thickened underground shoots that serve for vegetative propagation. These include rhizome(creeping wheatgrass, lily of the valley), tuber(potato), bulb(onion, garlic).
Bud- This is a rudimentary shoot, consisting of a shortened stem with rudimentary leaves close together. At the top of the shortened bud stem there is a growth cone, consisting of an apical educational fabric. Due to the division of its cells, the stem grows in length and other organs are formed. There are buds vegetative, generative (floral) And mixed.
Flower- an organ of seed reproduction, a shortened modified shoot adapted for the formation of germ cells (gametes), pollination, fertilization and the formation of seeds and fruits. The flower includes the following parts: peduncle, on which there may be bracts (leaves accompanying flowers), expanded receptacle, calyx, corolla, stamens And pestle(Fig. 4). The calyx and corolla form perianth. In many wind-pollinated plants, the perianth is small and inconspicuous, while in insect-pollinated plants it is well developed, white or brightly colored. Stamens consist of filament And anther A large amount is formed in the anther pollen (male gametophyte). The pestle consists of a lower expanded part - ovaries and upper narrowed - column And stigma. Inside the ovary there is ovule (ovule), in which it is formed embryo sac(female gametophyte). The style carries the stigma out of the flower, which facilitates better pollen capture.
Rice. 4. Flower structure diagram:
1 - ovary; 2 - column; 3 - stigma; 4 - pollen grains that form pollen tubes; 5 - filament; 6 - cross section of the anther of the stamen; 7 - longitudinal section of the anther; 8 - ovule
According to their structure, plants are distinguished bisexual(potatoes, rye) and dioecious flowers that have either only stamens or only pistils. Plants with dioecious flowers can be monoecious, if there are male and female plants on the same plant female flowers(corn, cucumber), and dioecious, if male flowers develop on one plant, and female flowers on another (hemp, sea buckthorn, poplar).
Inflorescences. Flowers are often collected in inflorescences. In wind-pollinated plants, this allows for more efficient pollen capture. Inflorescences of insect-pollinated plants are more visible to insects than individual flowers. There are inflorescences simple And complex(Fig. 5). Simple ones include: brush(cabbage), simple ear(plantain), cob(corn), simple umbrella(onion, apple tree), head(clover), basket(sunflower), shield(pear). Complex inflorescences with a branching main axis include panicle(oats), complex ear(wheat, rye), complex umbrella(dill).
Seed- the reproductive organ of flowering plants, which is formed from the ovule as a result of double fertilization. It consists of a germ and a peel. Germ - it is a rudimentary plant, having a root, a stalk, a bud and cotyledons (the first leaves of the embryo). Monocots (cereals) have one cotyledon, and dicotyledons (grain legumes) have two. The seed of monocots also includes a special storage tissue - endosperm(bluegrass, nightshade, buckwheat). In dicotyledonous plants, the supply of nutrients is concentrated in the cotyledons.
Rice. 5. Schemes of the most common inflorescences:
1 - brush; 2 - panicle; 3 - simple ear; 4 - complex ear; 5 - cob; 6 - a simple umbrella; 7 - complex umbrella; 8 - head; 9 - basket
Fetus- container for seeds. The fruits consist of a pericarp, which is formed mainly from the walls of the ovary and seeds. The pericarp of some fruits is juicy and fleshy. These are juicy fruits. These include berry(fruits of grapes, tomatoes, potatoes), drupe(cherry, plum, bird cherry fruits), apple(fruits of apple, pear) pumpkin(watermelon melon). Another group consists of fruits with dry pericarp: bean(peas, beans), pod, pod(cabbage, radish, yarutka), box(poppy, flax), nut(hazel, linden), grain(rye, oats, wheat), achene(sunflower) (Fig. 6). Meet and complex (compound) fruits, formed from a flower with several pistils (collective drupe in raspberries, collective achene in strawberries, etc.). The spread of fruits and seeds of wild plant forms is facilitated by wind, insects, and animals.
Rice. 6. Variety of plant fruits:
1 - achene; 2 - leaflet; 3 - bean; 4 - pod; 5 - pod; 6, 8, 9- boxes; 7 - two-seed; 10 - drupe.
FLORAL, angiosperms (Angiospermae), the largest division of the plant kingdom, characterized by specialized reproductive organs that form the flower. Flowering plants have been known since the Jurassic period (about 150 million years ago): already at that time they were quite highly developed and widespread, so their first representatives undoubtedly appeared much earlier, perhaps on lands exposed after the retreat of the sea. Subsequently, flowering plants conquered the entire planet, greatly displacing the former dominants, in particular ferns and conifers. It is flowering plants that dominate the deciduous forests that once occupied significant areas in North America, and in the vast tropical forests of Central and South America, Africa and Asia. This department includes grasses covering the American prairies and pampas, African savannas and Eurasian steppes, as well as cacti and thorny bushes of deserts, many underwater and floating grasses of rivers, lakes and seas, moss-like species creeping along rocks and hanging from tree branches. Finally, it is flowering plants that people grow in fields, vegetable gardens and orchards; they are the main decoration of greenhouses and parks.
STRUCTURE OF FLOWERING PLANTS
Leaves.
The bulk of organic nutrients on Earth are produced in the leaves of flowering plants. Typically, a leaf consists of a flat leaf blade on a petiole, which is attached at its base to the stem. At the point of attachment there are two leaf-like outgrowths - stipules. However, each of these structures may be missing. The leaf blades of some flowering plants, for example many Lamiaceae and cruciferous plants, are sessile, i.e. arise directly from the stem without a petiole; in other species, all that remains of the leaves are their sheaths with plates reduced to thread-like structures (this can be observed in cereals). Inside the leaf there are relatively loosely packed cells rich in the green pigment - chlorophyll. Photosynthesis occurs in them. U top surface of the leaf, these cells are usually elongated and located side by side perpendicular to the surface: they form the so-called. palisade parenchyma. The underlying cells are less uniform in shape and are separated by air-filled intercellular spaces - this is the so-called. spongy parenchyma. Air exchange of internal leaf tissues with environment goes through small holes in the single-layer skin (epidermis) covering it: as a result, photosynthetic cells receive carbon dioxide, necessary for the formation of organic matter, and get rid of “production waste” - oxygen. The epidermis is usually covered on the outside with a waxy coating (cuticle) and is relatively impermeable to water and gases, and its cells are incapable of photosynthesis. Unfortunately, the leaf loses quite a lot of water through evaporation, which can sometimes threaten the existence of the entire plant. It is supplied with water through a system of internal veins, usually forming a dense branched network. The veins consist of cells of vascular tissues that deliver water and dissolved substances to the photosynthetic areas. mineral salts and spreading organic matter from there to all parts of the plant. Since some cells of this conducting system are thick-walled, the veins simultaneously play the role of the skeleton of the leaf, supporting it in a straightened state and ensuring a normal supply of light and air to all its parts.
Stem.
Through the conducting cells of the stem, water with mineral salts dissolved in it flows from the root to the veins of the leaf, which contain cells of the same type. In a young stem, this water-conducting system (xylem) usually forms a cylinder that begins underground, serving as a rigid support for leaves, flowers and fruits and over time capable of greatly thickening and becoming lignified, turning into a powerful multi-meter trunk. Outside the xylem there is a similar cylinder - phloem, consisting of cells through which the transport of organic substances occurs. Phloem also extends into the leaf veins. The rest of the stem consists of soft fabric, sometimes photosynthetic, in which excess nutrients are often stored. The central part of the stem - the core - can collapse, and then a cavity remains in the stem in its place. Stems with leaves (as well as flowers and fruits, which are thought to be derived from the leaves) are called shoots.
Root.
The root system anchors the plant in the substrate. The root also contains conducting tissues - xylem is closer to the center, phloem is further from the center. Large amounts of reserve substances can accumulate here, which is why some roots are very large. In addition to support and storage, the most important function of roots is absorption: water with salts dissolved in it must flow from the soil into the shoots and compensate for the costs and losses of the plant. Suction is carried out by the so-called. root hairs - numerous outgrowths of superficial root cells in a relatively narrow zone near its tip. It is the root hairs, penetrating between the smallest soil particles, that provide the enormous total absorbing surface of the underground part of the plant.
Angiosperms (Angiospermae), or flowering plants (Magnoliophyta) - the department of the most advanced higher plants having a flower. Previously they were included in the department of seed plants along with gymnosperms. Unlike the latter, the ovules of flowering plants are enclosed in an ovary formed by fused carpels.
The flower is a generative organ angiosperms. It consists of a peduncle and a receptacle. The latter contains the perianth (simple or double), androecium (collection of stamens) and gynoecium (collection of carpels). Each stamen consists of a thin filament and an expanded anther in which sperm mature. The carpel of flowering plants is represented by a pistil, which consists of a massive ovary and a long style, the apical expanded part of which is called stigma.
Angiosperms have vegetative organs that provide mechanical support, transport, photosynthesis, gas exchange, and nutrient storage, and generative organs that participate in sexual reproduction. The internal structure of tissues is the most complex of all plants; phloem sieve elements are surrounded by companion cells; Almost all members of angiosperms have xylem vessels.
Life cycle plants
Contained inside pollen grains male gametes fall on the stigma and germinate. Flowering gametophytes are extremely simplified and miniature, which significantly reduces the duration of the reproduction cycle. They are formed as a result of a minimum number of mitoses (three in the female gametophyte and two in the male). One of the features of sexual reproduction is double fertilization, when one of the sperm fuses with the egg, forming a zygote, and the second fuses with the polar nuclei, forming the endosperm, which serves as a supply of nutrients. The seeds of flowering plants are enclosed in the fruit (hence their second name - angiosperms).
For more information about the structure of roots, leaves, stems and the characteristics of reproduction of angiosperms, see Chapter 10.
The first flowering plants appeared at the beginning of the Cretaceous period about 135 million years ago (or even at the end of the Jurassic period). The question of the ancestor of angiosperms currently remains open; the extinct Bennettites are closest to them, however, it is more likely that, together with the Bennettites, the angiosperms separated from one of the groups of seed ferns. The first flowering plants were apparently evergreen trees with primitive flowers lacking petals; Their xylem still had no vessels.
In the middle of the Cretaceous period, in just a few million years, angiosperms conquered the land. One of the most important conditions The rapid spread of angiosperms was due to their unusually high evolutionary plasticity. As a result of adaptive radiation, caused by environmental and genetic factors (in particular, aneupolydy and polyploidization), great amount various types angiosperms belonging to a wide variety of ecosystems. By the mid-Cretaceous period, most modern families had formed. The evolution of terrestrial mammals, birds and, especially, insects is closely related to flowering plants. The latter play exclusively important role in the evolution of a flower, carrying out pollination: bright color, aroma, edible pollen or nectar are all means of attracting insects.
Flowering plants are distributed throughout the world, from the Arctic to the Antarctic. Their taxonomy is based on the structure of the flower and inflorescence, pollen grains, seeds, and the anatomy of xylem and phloem. Almost 250 thousand species of angiosperms are divided into two classes: dicotyledons and monocotyledons, differing primarily in the number of cotyledons in the embryo, leaf and flower structure.
Flowering plants are one of the key components of the biosphere: they produce organic matter, bind carbon dioxide and release molecular oxygen into the atmosphere; most pasture food chains begin with them. Many flowering plants are used by humans for cooking, building homes, making various household materials, and for medicinal purposes.
Flowering plants play a special role in the evolution of the organic world. The organs of flowering plants have reached sufficient high level development, providing this group of organisms with a dominant position on the planet. Today they are found on almost every continent. For comparison, we can cite the statistical data contained in the section of the school botany course “Organs of flowering plants” (grade 6). Namely: among all 850 species there are representatives of gymnosperms, and 250 thousand are flowering plants.
Organs and functions of a flowering plant
Angiosperms are plants that produce flowers and fruit.
All plant organs can be combined into two groups. Vegetative plants include a shoot consisting of a stem and a leaf, as well as an underground part - the root. Flower, fruit and seeds are generative. Only flowering plants have them. The organs of flowering plants, depending on their structural features, perform certain functions. All of them play an important role in the functioning of organisms, determining their viability and adaptation to living conditions.
The organs and functions of a flowering plant are interconnected. Let's look at the structure of each of them in more detail.
Root
In the biology textbook, in the topic “Organs of flowering plants” (grade 6), a definition of the concept “root” is given. This is an underground organ that provides anchorage in the soil and nutrition. minerals, water supply, upward flow and vegetative propagation.
Various have flowering plants. The organs of flowering plants are diverse. There are main roots, subordinate and lateral roots. They combine special structures. Their name is root systems.
Types of root systems
Taxonomists distinguish the tap root and the first is formed by a single main root and lateral roots extending from it. It is typical for representatives of the Dicotyledonous class.
Fibrous grows in a bunch immediately from the shoot. It is characteristic of all representatives of the Monocot family. These are, for example, Cereals, Lilies and Onions. Each system has a number of advantages. For example, plants with a long main root can easily obtain moisture from great depth. And the fibrous system provides large area suction.
Escape and its modifications
It is flowering plants that are characterized by a large variety of above-ground parts. The organs of flowering plants sometimes change depending on environmental conditions. This is the adaptive ability of escape.
Its axial part is called the stem. The areas where leaves develop are called nodes, and the distances between them are called internodes. The angle between the blade and the stem forms the leaf axil.
The lateral parts of the stem are also very diverse. Leaves with one leaf blade are called simple, while leaves with several are called compound. They can be located differently on the plant. For example, the leaves of birch and sunflower are alternately in a spiral, while those of lilac and maple are opposite each other. Whorled is a leaf arrangement in which the blades develop in numbers of three or more in one node.
All vegetative organs perform functions asexual reproduction, mineral nutrition, photosynthesis and transpiration.
Organs of seed reproduction of flowering plants
A special organ of a flowering plant where sexual reproduction cells are formed is the flower. Its main parts are the pistil and stamen. The formation of germ cells occurs in them. The result of their fusion is the seed. It consists of an embryo formed by a root, a stalk, a leaf and a bud, and a shell.
The process of fertilization in flowering plants is preceded by pollination - the transfer of pollen from the stamen to the pistil. This happens with the help of insects, humans or the wind. Next, when the female reproductive cell and one sperm merge, an embryo is formed. The second unites with the central germ cell, forming the endosperm. This is a spare nutrient, which the embryo uses to carry out the processes of growth and development.
A seed surrounded by shells is called a fruit. They are also varied. According to the structure of the pericarp, they are divided into dry and juicy, and according to the number of seeds - single- and multi-seeded. With the help of fruits, plants spread and disperse. Humans, in turn, use them as food. He also controls the number of plants used for his own purposes.
Unusual plants
The organs of flowering plants are often impressive in their shape and size.
A representative of the gymnosperms, the amazing Welwitschia visually resembles a ball of snakes. This is exactly what its long, wide leaves look like, reaching a length of up to two meters. The plant grows in deserted open landscapes, where strong wind currents tear the leaves of Welwitschia along. This creates the effect of a snake's nest. And the escape itself is underground.
Under the supporting roots of the ficus banyan tree, which number about 4 thousand, 5,000 people can easily fit.
The modified leaves of sundew and bladderwort are very sticky and have specialized digestive glands or closing traps. The thing is that they are predatory plants capable of assimilating proteins of animal origin. They can feed on small insects, crustaceans and fish fry.
Vegetative and flowering plants have complex structure, which determines the performance of functions and ensures their predominance on Earth.