Gender inequality index GII. The gospel authors never explicitly claim Jesus to be God, and the closest they come is the vague language of Jn 1: Primary producers, represented by trees , shrubs , and herbs, are a prolific source of energy in the form of carbohydrates sugars stored in the leaves. First, the limits to intelligence apply to artificial intelligence as much as to natural. Like teleportation, transferal of a human mind from a brain to an artifact is almost certainly impossible and would nevertheless not preserve personal identity.
This situation can also be depicted by placing the water molecule in a cube. This electronic structure leads to hydrogen bonding. We welcome suggested improvements to any of our articles.
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Please note that our editors may make some formatting changes or correct spelling or grammatical errors, and may also contact you if any clarifications are needed. Page 1 of 2. Next page Structures of ice. Learn More in these related Britannica articles: It includes all liquid and frozen surface waters, groundwater held in soil and rock, and atmospheric water vapour.
Water is the largest component of the body, accounting for more than half of body weight. To replace fluid losses, adults generally need to consume 2 to 4 litres of fluid daily in cool climates, depending on degree of activity, and from…. The range of organic molecules that organisms, especially microbes, can metabolize is very wide and occasionally includes foods such as formaldehyde or petroleum that seem unlikely from a human point of view.
Pseudomonas bacteria are capable of using almost any organic molecule as a…. Ninety-seven percent of all the water is in the oceans, and, of the fresh water constituting…. Water and most other volatile substances profoundly influence the properties and behaviour of magmas in which they are dissolved.
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Help us improve this article! Contact our editors with your feedback. Endosperm is the chief storage tissue in the seeds of grasses; hence, it is the primary source of nutrition in corn maize , rice , wheat , and other cereals that have been utilized as major food sources by humans and other animals. Many of the flowering plants are commonly represented by two basic groups, the monocotyledons and the dicotyledons , distinguished by the number of embryonic seed leaves cotyledons , number of flower parts, arrangement of vascular tissue in the stem, leaf venation, and manner of leaf attachment to the stem.
However, one of the major changes in the understanding of the evolution of the angiosperms was the realization that the basic distinction among flowering plants is not between monocotyledon groups monocots and dicotyledon groups dicots. This group of typical dicots is now known as the eudicots, and molecular-based evidence supports their having a single evolutionary lineage monophyletic.
Other angiosperm groups, such as the Magnoliids , do not fit the traditional paradigm of monocot and dicot and are considered to have more-ancient lineages. The plant body of angiosperms consists of a central axis of two parts, the shoot and the root. Shoots have two kinds of organs, the stem and the leaves , while roots have one type of organ, the root itself.
Systems of classification are often based upon the longevity of the portions of plant aboveground. Woody plants are trees and shrubs whose shoots are durable and survive over a period of years. They are further classified into deciduous and evergreen plants. Deciduous plants drop their leaves at the end of every growing season , whereas evergreens keep their leaves for up to several years.
Herbaceous plants have soft, flexible aerial portions and commonly die back each year. Another system of classification, based on the duration of the life history, is particularly applicable to angiosperms of the temperate region. Annuals are plants that complete the entire life history germinate from seeds, mature, flower, and produce seed in one growing season. Examples of annuals are corn , wheat , and peas. Biennials complete their life history in two seasons, blooming during the second season.
Beets , celery , cabbage , carrots , and turnips are biennials, but their flowers are rarely seen because they are harvested during the first season. Annuals and biennials are both generally herbaceous plants. Perennials are plants that live from year to year. Trees and shrubs are perennials , but some herbaceous plants are also perennials. A number of modifications of the stem occur in angiosperms, and many of these modifications provide a means for herbs to become dormant and survive for a period of years.
Rhizomes are horizontally growing underground stems that serve as organs of asexual reproduction and food storage. Similar to rhizomes, tubers are thickened underground stem portions that primarily serve as food storage for example, potato. Corms are short upright underground stems surrounded by a few thin scale leaves as in Crocus and Gladiolus.
Bulbs have a greatly reduced stem with thick fleshy scale leaves surrounding it as in the onion. Runners and stolons are surface stems characteristic of such plants as strawberries ; new plants may form on the runner or stolon as it spreads along the ground.
Many of the most prolific weeds have runners or stolons by which they propagate asexually. In herbaceous dicotyledonous stems, the vascular conducting tissue xylem and phloem is organized into discrete strands or vascular bundles , each containing both xylem and phloem. The cells between the vascular bundles are thin-walled and often store starch. The peripheral region of cells in the stem is called the cortex ; cells of the central portion make up the pith. The outermost cells of the stem compose the epidermis.
No bark is formed on the herbaceous stem. In contrast, woody dicot stems develop an outer layer of dead thick-walled cells called cork cells, which together with the underlying phloem compose the bark of the tree. The water-conducting cells that make up the xylem are nonliving. The accumulated xylem often forms annual rings composed of two zones: Such rings may be absent in tropical trees that grow all year round.
Xylem rays, radiating like spokes of a wagon wheel, are formed in the xylem and connect with the peripheral phloem. Stems of monocotyledons are composed of numerous vascular bundles that are arranged in a seemingly scattered manner within the ground tissue. Monocot vascular bundles lack a vascular cambium, and monocot stems thus do not become woody in a manner similar to dicots. Leaves are the other plant organ that, along with stems, constitutes the shoot of the vascular plant body.
Their principal function is to act as the primary site of photosynthesis in the plant. Leaves of dicots possess a network of interconnecting veins and minor veins between the larger veins of the leaf a pattern called net venation. Leaves of monocots possess major veins that extend parallel to the long axis of the leaf parallel venation. Leaves are classified on the basis of leaf arrangement and whether they are simple or compound. A leaf may be deeply lobed but still simple; a compound leaf is composed of two or more distinctly separate leaflets.
Structurally, leaves are composed of an outermost layer of cells called the epidermis. Epidermal cells secrete a waxy substance cutin that forms a cuticle impermeable to water. The pores stomata in the epidermis that allow for gas exchange are formed between specialized epidermal cells called guard cells.
Vascular bundles veins are embedded in the mesophyll , the tissue that includes all of the cells between the upper and lower epidermis. The cells of the mesophyll contain the photosynthetic pigments. The root system begins its development from the embryonic root radicle , which grows out of the seed after the seed has absorbed water. This is the primary root of a new plant. The tip of the root is covered by a mass of loose cells called the root cap.
Just beneath the root cap is the region of cell division of the root. Epidermal outgrowths just above the root tip are root hairs that are active in water and mineral absorption. Two types of root systems are commonly distinguished, fibrous roots and taproots. Fibrous root systems are composed of large numbers of roots nearly equal in size; root systems of this type are found, for example, in the grasses. A taproot system is one in which the primary root remains the largest, and a number of smaller secondary roots are formed from it; taproots are found in such plants as carrots and dandelions.
Roots that arise other than by branching from the primary roots are called adventitious roots. The prop roots of corn, for example, are adventitious. As noted above, a primary distinction between the gymnosperms and the angiosperms is that the latter have flowers.
Flowers represent modified shoots that have become differentiated for reproduction. The flower bears whorls of floral organs attached to a receptacle, the expanded end of a flower stalk on which the flower parts are borne. Sepals collectively called the calyx are modified leaves that encase the developing flower. They are sterile floral parts and may be either green or leaflike or composed of petal-like tissue. Petals collectively called the corolla are also sterile floral parts that usually function as visually conspicuous elements serving to attract specific pollinators to the flower.
The calyx and the corolla together are referred to as the perianth. Flowers that lack one or both of the above perianth parts are called incomplete. Stamens collectively called the androecium are the male parts of the flower. Stamens are composed of saclike anthers microsporangia and filaments, which are stalks that support the anthers. Anthers are usually compartmentalized and contain the pollen grains microgametophytes. The pistil , or female part of the flower, is composed of one or a number of carpels collectively called the gynoecium that fuse to form an essentially enclosed chamber.
The three regions of the pistil from the base up are the ovary , which contains the ovules; the style , a stalked structure atop the ovary that elevates the stigma ; and the stigma, a sticky knob whose surface receives the pollen during pollination. Flowers may contain both male and female parts a condition called perfect or parts related to just one sex imperfect , or they may have no sexual parts sterile. Female and male flowers may be located on separate plants dioecious or on the same plant monoecious.
Flowers can also be borne singly or in aggregations called inflorescences. Primitive flowers are radially symmetrical actinomorphic and are characterized by numerous spirally arranged floral parts. Floral parts are free unfused and are borne on an elongated floral axis.
Sepals, petals, and stamens are attached below the ovary. Advanced flowers are bilaterally symmetrical and are characterized by a reduction in the number of floral parts. Floral parts are fused often forming a long floral tube. Sepals, petals, and stamens are attached to the floral tube above the ovary. Pollination is the transfer of pollen to the stigma of the same or another flower.
Agents of pollination encompass a vast and diverse array of animals, including insects , birds , bats , honey possums, and slugs. Flowers exhibit various adaptations to pollinators, such as showy corollas, the production of nectar a sugary liquid , and even visual cues visible only to insects that can perceive ultraviolet wavelengths of light.
Flowers pollinated by wind generally are small and lack petals. The stigma is the pollen receptor site and must be chemically compatible with any pollen that lands on it for the pollen grain to germinate. This ensures that only genetically compatible sperm are transferred to the egg. In flowering plants, ovules are enclosed and protected in an ovary. As the ovule develops into a seed, the ovary matures into a fruit.
The formation of fruits is a characteristic feature of the flowering plants. Fruits are extremely variable. In some fruits, the ovary wall pericarp is thick and fleshy; in others, it is thin and dry. Angiosperms have evolved many adaptations for seed dispersal involving such agents as wind, water, and animals. Adaptations to wind dispersal include wings or plumules attached to the seed or as part of the fruit or simply very minute seeds that are easily windborne. Adaptations to water dispersal are seeds that float or fruits that float and carry the seeds with them.
Some seeds are a source of food to animals, which bury the seeds in the ground, where they later germinate. Other plants produce a fleshy fruit that is eaten along with the seeds inside it by animals, which pass the seeds through their digestive tracts unharmed. Another adaptation for animal dispersal is the development of barbed fruits or seeds that stick to the coats or skins of wandering animals. Some plants, such as witch hazels or jewelweed, can project their seeds through the air some distance from the parent plant.
Seeds have many adaptations that enable them to survive long periods of harsh conditions. Seeds can remain viable in a dormant condition for a few days or, in some species, for hundreds of years.
For further information on seeds and fruits, see Reproductive system, plant. We welcome suggested improvements to any of our articles. You can make it easier for us to review and, hopefully, publish your contribution by keeping a few points in mind.
Your contribution may be further edited by our staff, and its publication is subject to our final approval. Unfortunately, our editorial approach may not be able to accommodate all contributions. Our editors will review what you've submitted, and if it meets our criteria, we'll add it to the article. Please note that our editors may make some formatting changes or correct spelling or grammatical errors, and may also contact you if any clarifications are needed.
Woodwell Hans Lambers Rudolf Schmid. Aug 9, See Article History. Page 1 of 4. Next page Reproduction and life histories. Learn More in these related Britannica articles: Animals and plants have played important roles in the oral traditions and the recorded myths of the peoples of the world, both ancient and modern. This section of the article is concerned with the variety of relationships noted between humans and animals…. The cold desert climate of Antarctica supports only an impoverished community of cold-tolerant land plants that are capable of surviving lengthy winter periods of total or near-total darkness during which photosynthesis cannot take place.
Growth must occur in short summer…. Growth in plants is regulated by a variety of plant hormones, including auxins, gibberellins, cytokinins, and growth inhibitors, primarily abscisic acid and ethylene.
During the ongoing struggle for survival, organisms have evolved toxic compounds as protection against predators or simply to gain competitive advantage. At the same time, these organisms have evolved mechanisms that make themselves immune to the effects of the toxins that….
More About Plant 73 references found in Britannica articles Assorted References cause of genetic damage In human genetic disease: Plants, fungi, and bacteria chemoreception and plant chemicals In chemoreception: Plant chemicals In chemoreception: Between the most significant worldwide coral bleaching event was recorded which corresponded with the El Nino Southern Oscillation, with significant damage to the coral reefs of the Western Indian Ocean.
Depletion of fish stocks results in lowered biodiversity and consequently imbalance in the food chain, and increased vulnerability to disease. In addition to overfishing, coastal communities are suffering the impacts of growing numbers of large commercial fishing vessels in causing reductions of small local fishing fleets. Many local lowland rivers which are sources of fresh water have become degraded because of the inflows of pollutants and sediments.
Dumping both depends upon ecosystem resilience whilst threatening it. Dumping of sewage and other contaminants into the ocean is often undertaken for the dispersive nature of the oceans and adaptive nature and ability for marine life to process the marine debris and contaminants.
However, waste dumping threatens marine ecosystems by poisoning marine life and eutrophication. According to the International Maritime Organisation oil spills can have serious effects on marine life. The OILPOL Convention recognized that most oil pollution resulted from routine shipboard operations such as the cleaning of cargo tanks.
In the s, the normal practice was simply to wash the tanks out with water and then pump the resulting mixture of oil and water into the sea. In the limits were extended by means of an amendment adopted at a conference organized by IMO. The threat of oil spills to marine life is recognised by those likely to be responsible for the pollution, such as the International Tanker Owners Pollution Federation:.
The marine ecosystem is highly complex and natural fluctuations in species composition, abundance and distribution are a basic feature of its normal function.
The extent of damage can therefore be difficult to detect against this background variability. Nevertheless, the key to understanding damage and its importance is whether spill effects result in a downturn in breeding success, productivity, diversity and the overall functioning of the system.
Spills are not the only pressure on marine habitats; chronic urban and industrial contamination or the exploitation of the resources they provide are also serious threats. The Woods Hole Oceanographic Institution calls nutrient pollution the most widespread, chronic environmental problem in the coastal ocean. The discharges of nitrogen, phosphorus, and other nutrients come from agriculture, waste disposal, coastal development, and fossil fuel use.
Once nutrient pollution reaches the coastal zone, it stimulates harmful overgrowths of algae, which can have direct toxic effects and ultimately result in low-oxygen conditions. Certain types of algae are toxic. Overgrowths of these algae result in harmful algal blooms , which are more colloquially referred to as "red tides" or "brown tides".
Zooplankton eat the toxic algae and begin passing the toxins up the food chain, affecting edibles like clams, and ultimately working their way up to seabirds, marine mammals, and humans. The result can be illness and sometimes death. There is increasing awareness that a greater understanding and emphasis of ecosystem resilience is required to reach the goal of sustainable development.
And, as more and more people move into densely populated cities, using massive amounts of water, energy, and other resources, the need to combine these disciplines to consider the resilience of urban ecosystems and cities is of paramount importance. The interdependence of ecological and social systems has gained renewed recognition since the late s by academics including Berkes and Folke  and developed further in by Folke et al.
This is a movement which causes wide concern in environmental and social forums and which Clive Hamilton describes as "the growth fetish". The purpose of ecological resilience that is proposed is ultimately about averting our extinction as Walker cites Holling in his paper: Folke et al state that the likelihood of sustaining development is raised by "Managing for resilience"  whilst Perman et al.
The challenge of applying the concept of ecological resilience to the context of sustainable development is that it sits at odds with conventional economic ideology and policy making. Resilience questions the free market model within which global markets operate.
Inherent to the successful operation of a free market is specialisation which is required to achieve efficiency and increase productivity. This very act of specialisation weakens resilience by permitting systems to become accustomed to and dependent upon their prevailing conditions. In the event of unanticipated shocks; this dependency reduces the ability of the system to adapt to these changes.