Closely linked to resilience is adaptive capacity , which is the property of an ecosystem that describes change in stability landscapes and resilience. Godel's Theorem merely shows that any formalizable reasoning faculty could not correctly believe in its own consistency. FAO reports the proportion of the population whose daily food intake falls below that minimum energy requirement as 'undernourished'. Improper marketing and promotion of food products that compete with breastfeeding often negatively affect the choice and ability of a mother to breastfeed her infant optimally. Buddhism is the East Asian nontheistic mystical religion founded in India c BCE by the Buddha, who taught that existence is cyclical suffering caused by desiring and can be overcome by the " eightfold path " of right thought and deed.
Double Shredded Hardwood Mulch
The Sun Why would something so benign feel so scary? Christianity Today He had a benign smile and forearms like hams. Times, Sunday Times This is presumably not a trend being reflected in the relatively benign employment statistics.
Times, Sunday Times The curators of the exhibition take a more benign view. Times, Sunday Times Some benign tumours tend to become malignant. Mayes, Adrienne The Dictionary of Nutritional Health The privatisation programme is being launched against a relatively benign economic background. Times, Sunday Times These have been relatively benign and do not suggest any awful shocks to come.
Times, Sunday Times How do they come to such a benign view? Times, Sunday Times He was first diagnosed with a benign tumour nine years ago. The Sun The effects so far look relatively benign. Times, Sunday Times But benign tumours account for nine in ten lumps. The Sun An alternative view is that the liquidity squeeze is symptomatic of less benign changes in the financial landscape. Times, Sunday Times But it is a benign something. Times, Sunday Times My quarry is rather less benign.
Times, Sunday Times They are very common , entirely benign and harmless. The Sun His kind of Anglicanism is benign and pretty harmless. Times, Sunday Times The benign economic conditions now prevailing in the world could not last , he said. Times, Sunday Times Let's take a benign view of local conditions too. Times, Sunday Times The big question is what happens next year, when the outlook is much less benign. Times, Sunday Times The benign economic background since the mids is not inherently destined to continue.
Times, Sunday Times A love of the familiar and the secure is a harmless emotion ; benign, and yet powerful. Times, Sunday Times Translate your text for free.
Nearby words of 'benign'. Related Terms of 'benign'. Plants, unlike animals, can use inorganic forms of the element nitrogen N , such as nitrate and ammonia —which are made available to plants through the activities of microorganisms or through the industrial production of fertilizers —and the element sulfur S ; thus, they do not require an external source of protein in which nitrogen is a major constituent to survive. The life histories of plants include two phases, or generations, one of which is diploid the nuclei of the cells contain two sets of chromosomes , whereas the other is haploid with one set of chromosomes.
The diploid generation is known as the sporophyte , which literally means spore -producing plant. The haploid generation, called the gametophyte , produces the sex cells, or gametes. The complete life cycle of a plant thus involves an alternation of generations. The sporophyte and gametophyte generations of plants are structurally quite dissimilar. The concept of what constitutes a plant has undergone significant change over time.
For example, at one time the photosynthetic aquatic organisms commonly referred to as algae were considered members of the plant kingdom. The various major algal groups, such as the green algae , brown algae , and red algae , are now placed in the kingdom Protista because they lack one or more of the features that are characteristic of plants. The organisms known as fungi also were once considered to be plants because they reproduce by spores and possess a cell wall.
The fungi, however, uniformly lack chlorophyll, and they are heterotrophic and chemically distinct from the plants; thus, they are placed in a separate kingdom, Fungi. No definition of the kingdom completely excludes all nonplant organisms or even includes all plants. There are plants, for example, that do not produce their food by photosynthesis but rather are parasitic on other living plants. Some animals possess plantlike characteristics, such as the lack of mobility e. Despite such differences, plants share the following features common to all living things.
Their cells undergo complex metabolic reactions that result in the production of chemical energy, nutrients, and new structural components. They respond to internal and external stimuli in a self-preserving manner.
They reproduce by passing their genetic information to descendants that resemble them. They have evolved over geological time scales hundreds of millions of years by the process of natural selection into a wide array of forms and life-history strategies.
The earliest plants undoubtedly evolved from an aquatic green algal ancestor as evidenced by similarities in pigmentation, cell-wall chemistry, biochemistry, and method of cell division , and different plant groups have become adapted to terrestrial life to varying degrees. Land plants face severe environmental threats or difficulties, such as desiccation, drastic changes in temperature , support, nutrient availability to each of the cells of the plant, regulation of gas exchange between the plant and the atmosphere, and successful reproduction.
Thus, many adaptations to land existence have evolved in the plant kingdom and are reflected among the different major plant groups. An example is the development of a waxy covering the cuticle that covers the plant body, preventing excess water loss. Specialized tissues and cells vascular tissue enabled early land plants to absorb and transport water and nutrients to distant parts of the body more effectively and, eventually, to develop a more complex body composed of organs called stems , leaves, and roots.
The evolution and incorporation of the substance lignin into the cell walls of plants provided strength and support. Informally known as bryophytes , nonvascular plants lack specialized vascular tissue xylem and phloem for internal water and food conduction and support. They also do not possess true roots , stems , or leaves. Some larger mosses , however, contain a central core of elongated thick-walled cells called hydroids that are involved in water conduction and that have been compared to the xylem elements of other plants.
Bryophytes are second in diversity only to the flowering plants angiosperms and are generally regarded as composed of three divisions: Bryophtya the mosses , Marchantiophyta the liverworts , and Anthocerotophyta the hornworts. Because bryophytes generally lack conducting cells and a well-developed cuticle that would limit dehydration , they depend on their immediate surroundings for an adequate supply of moisture.
As a result, most bryophytes live in moist or wet shady locations, growing on rocks, trees, and soil. Some, however, have become adapted to totally aquatic habitats; others have become adapted to alternately wet and dry environments by growing during wet periods and becoming dormant during dry intervals.
Although bryophytes are widely distributed, occurring in practically all parts of the world, none are found in salt water. Ecologically, some mosses are considered pioneer plants because they can invade bare areas. Bryophytes are typically land plants but seldom attain a height of more than a few centimetres. They possess the photosynthetic pigment chlorophyll both a and b forms and carotenoids in cell organelles called chloroplasts.
The life histories of these plants show a well-defined alternation of generations , with the independent and free-living gametophyte as the dominant photosynthetic phase in the life cycle.
This is in contrast to the vascular plants , in which the dominant photosynthetic phase is the sporophyte. The sporophyte generation develops from, and is almost entirely parasitic on, the gametophyte.
The gametophyte produces multicellular sex organs gametangia. Female gametangia are called archegonia ; male gametangia, antheridia. At maturity, archegonia each contain one egg , and antheridia produce many sperm cells.
Because the egg is retained and fertilized within the archegonium, the early stages of the developing sporophyte are protected and nourished by the gametophytic tissue. The young undifferentiated sporophyte is called an embryo. Although bryophytes have become adapted to life on land, an apparent vestige of their aquatic ancestry is that the motile flagellated sperm depend on water to allow gamete transport and fertilization.
Bryophytes are widely believed to have evolved from complex green algae that invaded land around million years ago. Bryophytes share some traits with green algae, such as motile sperm, similar photosynthetic pigments, and the general absence of vascular tissue.
However, bryophytes have multicellular reproductive structures, whereas those of green algae are unicellular, and bryophytes are mostly terrestrial and have complex plant bodies, whereas the green algae are primarily aquatic and have less-complex forms. Moss is a term erroneously applied to many different plants Spanish moss , a flowering plant; Irish moss , a red alga; pond moss, filamentous algae; and reindeer moss , a lichen.
True mosses are classified as the division Bryophyta. The moss gametophyte possesses leaflike structures phyllids that usually are a single cell layer thick, have a costa midrib , and are spirally arranged on a stemlike axis caulid.
Multicellular rhizoids anchor the gametophyte to the substrate. The sporophyte plant develops from the tip of the fertile leafy shoot. After repeated cell divisions, the young sporophyte embryo transforms into a mature sporophyte consisting of foot, elongate seta, and capsule.
The capsule is often covered by a calyptra, which is the enlarged remains of the archegonium. The capsule is capped by an operculum lid , which falls off, exposing a ring of teeth the peristome that regulates the dispersal of spores.
Liverworts , the second major division of nonvascular plants, are found in the same types of habitat as mosses, and species of the two classes are often intermingled on the same site.
There are two types of liverworts also called hepatics based on reproductive features and thallus structure. Thalloid thallose liverworts have a ribbonlike, or strap-shaped, body that grows flat on the ground. They have a high degree of internal structural differentiation into photosynthetic and storage zones. Liverwort gametophytes have unicellular rhizoids. Liverworts have an alternation of generations similar to that of mosses, and, as with mosses, the gametophyte generation is dominant.
The sporophytes, however, are not microscopic and are often borne on specialized structures. They sometimes resemble small umbrellas and are called antheridiophores and archegoniophores.
The third division of bryophytes comprises the hornworts , a minor group numbering fewer than species. The gametophyte is a small ribbonlike thallus that resembles a thallose liverwort. The name hornwort is derived from the unique slender, upright sporophytes, which are about 3—4 cm 1. Vascular plants tracheophytes differ from the nonvascular bryophytes in that they possess specialized supporting and water-conducting tissue, called xylem , and food-conducting tissue, called phloem.
The xylem is composed of nonliving cells tracheids and vessel elements that are stiffened by the presence of lignin , a hardening substance that reinforces the cellulose cell wall.
The living sieve elements that comprise the phloem are not lignified. Xylem and phloem are collectively called vascular tissue and form a central column stele through the plant axis. The ferns , gymnosperms , and flowering plants are all vascular plants. Because they possess vascular tissues, these plants have true stems, leaves, and roots.
Before the development of vascular tissues, the only plants of considerable size existed in aquatic environments where support and water conduction were not necessary. A second major difference between the vascular plants and bryophytes is that the larger, more conspicuous generation among vascular plants is the sporophytic phase of the life cycle.
The vegetative body of vascular plants is adapted to terrestrial life in various ways. In addition to vascular tissue, the aerial body is covered with a well-developed waxy layer cuticle that decreases water loss. Gases are exchanged through numerous pores stomata in the outer cell layer epidermis. The root system is involved in the uptake from the soil of water and minerals that are used by the root system as well as the stem and leaves.
Roots also anchor the plant and store food. The stem conducts water and minerals absorbed by the root system upward to various parts of the stem and leaves; stems also conduct carbohydrates manufactured through the process of photosynthesis from the leaves to various parts of the stem and root system.
Leaves are supported by the stem and are oriented in a manner conducive to maximizing the amount of leaf area involved in trapping sunlight for use in photosynthesis. Modifications of roots, stems, and leaves have enabled species of vascular plants to survive in a variety of habitats encompassing diverse and even extreme environmental conditions.
The ability of vascular plants to flourish in so many different habitats is a key factor in their having become the dominant group of terrestrial plants.
The vascular plants are divisible into the nonseed plants lower vascular plants , or cryptogams and those that reproduce by seeds higher vascular plants, or phanerogams. The ferns Polypodiopsida are a group of the lower vascular plants; other groups include the whisk ferns Psilotophyta , club and spike mosses Lycophyta , and horsetails Sphenophyta, or Arthrophyta.
Collectively, the latter four groups are sometimes referred to as pteridophytes, because each reproduces by spores liberated from dehiscent sporangia free sporing. Although the lower vascular plants have adapted to terrestrial life, they are similar to bryophytes in that, as an apparent vestige of their aquatic ancestry, all produce motile flagellated male gametes antherozoids, or sperm and must rely on water for fertilization to take place.
This division is represented by four or more living genera, with the principal genera being Lycopodium club mosses , Selaginella spike mosses , and Isoetes quillworts. Extant members of Lycophyta occur in both temperate and tropical regions and represent the survivors of a group of vascular plants that was extremely diverse and numerous. As a group, the lycopods were prominent in the great coal-forming swamp forests of the Carboniferous Period Although all living lycopods are small herbaceous plants, some extinct types were large trees.
Lycopods are differentiated into stem, root, and leaf microphylls. Sporangia are positioned on the upper adaxial surface of the leaf sporophyll. Some species form distinct cones or strobili, whereas others do not. Ferns are a diverse group of plants that are unranked at the division level in some taxonomies. Formerly, the group was designated as division Pteridophtya, but their phylogenetic relationships remain unresolved.
Although they have a worldwide distribution, ferns are more common in tropical and subtropical regions. They range in size and complexity from small floating aquatic plants less than 2 cm 0.
Tropical tree ferns possess erect columnar trunks and large compound divided leaves more than 5 metres about 16 feet long. As a group, ferns are either terrestrial or epiphytic growing upon another plant. Fern stems never become woody composed of secondary tissue containing lignin , because all tissues of the plant body originate at the stem apex.
Ferns of the class Polypodiopsida typically possess a rhizome horizontal stem that grows partially underground; the deeply divided fronds leaves and the roots grow out of the rhizome. Fronds are characteristically coiled in the bud fiddleheads and uncurl in a type of leaf development called circinate vernation. Fern leaves are either whole or variously divided. The leaf types are differentiated into rachis axis of a compound leaf , pinnae primary divisions , and pinnules ultimate segments of a pinna.
Fern leaves often have prominent epidermal hairs and large chaffy scales. Venation of fern leaves is usually open dichotomous forking into two equal parts.
Each frond is a potential sporophyll spore-bearing leaf and as such can bear structures that are associated with reproduction. When growth conditions are favourable, a series of brown patches appear on the undersurface of the sporophylls. Each one of the patches called a sorus is composed of many sporangia , or spore cases, which are joined by a stalk to the sporophyll.
The spore case is flattened, with a layer of sterile, or nonfertile, cells surrounding the spore mother cells. Each spore mother cell divides by reduction division meiosis to produce haploid spores, which are shed in a way characteristic to the ferns.
Each fern spore has the potential to grow into a green heart-shaped independent gametophyte plant prothallus capable of photosynthesis.
In contrast to bryophytes , in which the sporophyte is nutritionally dependent on the gametophyte during its entire existence, the fern sporophyte is dependent on the gametophyte for nutrition only during the early phase of its development; thereafter, the fern sporophyte is free-living. In some ferns the sexes are separate, meaning a gametophyte will bear only male or female sex organs.
Other species have gametophytes bearing both sex organs. Features important in the identification of ferns include such aspects of the mature sporophyte plant as differences in the stem, frond, sporophyll, sporangium, and position of the sporangium and the absence or presence, as well as the shape, of the indusium a membranous outgrowth of the leaf covering the sporangia. Psilotopsida whisk ferns is a class represented by two living genera Psilotum and Tmesipteris and several species that are restricted to the subtropics.
This unusual group of small herbaceous plants is characterized by a leafless and rootless body possessing a stem that exhibits a primitive dichotomous type of branching: The photosynthetic function is assumed by the stem, and the underground rhizome anchors the plant. The vascular tissue is organized into a poorly developed central cylinder in the stem.
The family Ophioglossaceae , comprising four genera and some 80 species, is sometimes placed in the class Psilotopsida, though the taxonomy of the group is contentious. Equisetopsida also called horsetails and scouring rushes is a class represented by a single living genus Equisetum. It has a worldwide distribution but occurs in greater variety in the Northern Hemisphere. Like the lycopods, this group was a diverse and prominent group of vascular plants during the Carboniferous Period , when some genera attained great size in the coal-forming swamp forests.
Known as sphenophytes, these plants are differentiated into stem, leaf microphylls , and root. Green aerial stems have longitudinal ridges and furrows extending the length of the internodes, and stems are jointed articulated. Surface cells are characteristically filled with silica. Branches, when they occur, are borne in whorls at the node, as are the scale leaves. Sporangia are borne in terminal strobili. Equisetopsida had its origin in the Devonian Period Known as giant ferns, the class Marrattiopsida comprises a single extant family with four genera and some species of large tropical and subtropical ferns with stout erect stems.
The leaves fronds may be very large, some reaching 4. The Marattiaceae generally are considered to be one of the most primitive families of ferns still living.
Gymnosperms and angiosperms flowering plants share with ferns a dominant, independent sporophyte generation; the presence of vascular tissue; differentiation of the plant body into root, stem, and leaf derived from a bipolar embryo having stem and root-growing apices ; and similar photosynthetic pigments.
Unlike ferns, however, the seed plants have stems that branch laterally and vascular tissue that is arranged in strands bundles around the pith eustele. Among seed plants, as in ferns, the stem tissues that arise directly from the shoot apex are called primary tissues.
Primary tissues contribute to the longitudinal growth of the stem, or primary growth. Secondary growth, resulting in an increase in the width of the axis, is produced by meristematic tissue between the primary xylem and phloem called vascular cambium. This meristem consists of a narrow zone of cells that form new secondary xylem wood and secondary phloem secondary vascular tissues. Major evolutionary advancements of these plants are demonstrated by the generally more complex plant body and by reproduction via seeds.
Seeds represent an important evolutionary innovation within the plant kingdom. Each seed has an embryonic plant sporophyte , food-storage tissue, and hardened protective covering seed coat. The seed thus contains and protects the embryonic plant and, as the primary dispersal unit of the seed plants, represents a significant improvement over the spore, with its limited capacity for survival.
In comparing ferns and seed plants and their life histories, certain significant differences are seen. The gametophyte in seed plants has been reduced in size, usually consisting of a few to a dozen cells. Thus, it is no longer itself a plant body, as in the bryophytes and ferns. The gametophyte is not free-living but is embedded in the sporophyte and thus less vulnerable to environmental stress than the gametophytes of bryophytes and ferns.
Finally, the spores of seed plants are male and female, as are the sporangia that contain them. The spores are not dispersed as in the bryophytes and ferns but develop into gametophytes within the sporangia. In the most advanced seed plants, the male gametes sperm are carried to the egg by a later extension of the pollen grain called the pollen tube. The advantage of this system is that the nonflagellated sperm are no longer dependent on water to reach the egg. Another terrestrial adaptation of the seed plants not found in ferns is pollen dispersed by wind or animals.
Pollen is a unit of genetic material as well as part of the seed-formation process. The dispersal of pollen by wind or animals, in addition to dispersal of seeds, promotes genetic recombination and distribution of the species over a wide geographic area. The cone-bearing gymnosperms are among the largest and oldest living organisms in the world. They dominated the landscape about million years ago. Today gymnosperms are of great economic value as major sources of lumber products, pulpwood, turpentine, and resins.
Conifer stems are composed of a woody axis containing primitive water- and mineral-conducting cells called tracheids. Tracheids are interconnected by passages called bordered pits. Leaves are often needlelike or scalelike and typically contain canals filled with resin. The leaves of pine are borne in bundles fascicles , and the number of leaves per fascicle is an important distinguishing feature. Most gymnosperms are evergreen, but some, such as larch and bald cypress , are deciduous the leaves fall after one growing season.
The leaves of many gymnosperms have a thick cuticle and stomata below the leaf surface. The tree or shrub is the sporophyte generation. In conifers, the male and female sporangia are produced on separate structures called cones or strobili. Individual trees are typically monoecious male and female cones are borne on the same tree.
A cone is a modified shoot with a single axis, on which is borne a spirally arranged series of pollen- or ovule-bearing scales or bracts. The male cone, or microstrobilus , is usually smaller than the female cone megastrobilus and is essentially an aggregation of many small structures microsporophylls that encase the pollen in microsporangia.
The extant cycads division Cycadophyta are a group of ancient seed plants that are survivors of a complex that has existed since the Mesozoic Era They are presently distributed in the tropics and subtropics of both hemispheres.
Cycads are palmlike in general appearance, with an unbranched columnar trunk and a crown of large pinnately compound divided leaves. The sexes are always separate, resulting in male and female plants i. Most species produce conspicuous cones strobili on both male and female plants, and the seeds are very large.
The ginkgophytes division Ginkgophyta , although abundant, diverse, and widely distributed in the past, are represented now by a sole surviving species, Ginkgo biloba maidenhair tree. The species was formerly restricted to southeastern China, but it is now likely extinct in the wild.
The plant is commonly cultivated worldwide, however, and is particularly resistant to disease and air pollution. The ginkgo is multibranched, with stems that are differentiated into long shoots and dwarf spur shoots. A cluster of fan-shaped deciduous leaves with open dichotomous venation occurs at the end of each lateral spur shoot. Sexes are separate, and distinct cones are not produced. Female trees produce plumlike seeds with a fleshy outer layer and are noted for their foul smell when mature.
The gnetophytes division Gnetophyta comprise a group of three unusual genera. Ephedra occurs as a shrub in dry regions in tropical and temperate North and South America and in Asia, from the Mediterranean Sea to China.
Species of Gnetum occur as woody shrubs, vines, or broad-leaved trees and grow in moist tropical forests of South America, Africa, and Asia.