Plant Life: April 2011

Deserts

Regions characterized by 10 inches or less of precipitation per year as considered deserts. Plants in desert biomes are typically specialized to endure the harsh conditions found there.

Deserts are regions, or biomes, too dry to support grasslands or forest vegetation but with enough moisture to allow specially adapted plants to live. In deserts, hot days alternate with cold nights.

Ninety percent of incoming solar radiation reaches the ground during the day, and 90 percent of that is radiated back out into space at night, the result of the absence of clouds, low humidity, and sparse vegetation.

Deuteromycetes

Deuteromycetes are an artificial group of fungi, of which there exist approximately fifteen thousand species, often referred to as “fungi imperfecti” because their only known reproductive mechanism is asexual.

Deuteromycetes—also known as Deuteromycota, Deuteromycotina, fungi imperfecti, and mitosporic fungi—are fungi that are unable to produce sexual spores and are therefore placed in their own separate phylum. The deuteromycetes are commonly called fungi imperfecti, that is, “imperfect fungi,” a term accepted by many mycologists.

Reproduction

Reproduction in the deuteromycetes occurs in several different forms. Spores, or conidia, may be produced directly on the mycelium (the mass of hyphae, or tubular filaments, forming the body of a fungus) or on a structure of specialized mycelial cell called a condiophore.

Diatoms

Diatoms are unicellular microorganisms of the phylum Bacillariophyta that are abundant in aquatic, semi aquatic, and moist habitats throughout the world, growing as solitary cells, chains of cells, or members of colonies.

Diatoms, algal organisms of the phylum Bacillariophyta, have more than 250 genera and about 100,000 species. A distinctive siliceous cell wall called a frustule surrounds each vegetative cell. Diatoms have an extensive fossil record, going back some 100 million years to the Cretaceous period.

Deposits of fossil diatoms, known as diatomite or diatomaceous earth, are mined commercially for use as abrasives and filtering aids. One subterranean marine deposit in Santa Maria, California, is about 900 meters in thickness. More than 270,000 metric tons of diatomaceous earth are quarried annually from a deposit in Lompoc, California.

Dinoflagellates

Dinoflagellates, phylumDinophyta, are unicellular and colonial algal organisms from the kingdom Protista named for the spinning motions that result from the movement of their flagella.

The two thousand to four thousand species that make up the Dinophyta phylum typically have two flagella. Dinokonts (Dinophyceae) have one flagellum running in a groove that cuts transversely across the cell and another flagellum, the sulcus, that runs backward in a longitudinal groove and is more or less perpendicular to the transverse one. In desmokonts (Desmophyceae), both flagella arise from a point at the front of the cell.

The motions of the flagella, which make dinoflagellates spin like a top, help give rise to the name, for dinos in Greek means “whirling,” and flagella means “whip.” Single-celled species are the most common, but colonial species exist. The largest dinoflagellate, Noctiluca, may grow as large as 2 millimeters in diameter.

Diseases and Disorders

The science and study of plant diseases is known as plant pathology, which can be briefly defined as the study of the nature, cause and control of plant disease.

Plant disease is as old as land plants themselves, as shown by the fossil record. Several biblical accounts of plagues have been attributed to plant diseases, and in Roman times cereal rust was so serious that an annual ritual, the Robigalia, was performed to appease the Rust God, Robigo.

In the mid-nineteenth century the Irish Potato Famine, a result of potato late blight disease, caused the deaths of some 800,000 persons and the emigration of about 1.5 million more, mostly to North America. Similarly, but to a lesser extent, brown spot disease of rice caused the Bengal famine of 1943 in India.

DNA in Plants

DNA is the hereditary or genetic material, present in all cells, that carries information for the structure and function of living things.

In the plant kingdom, DNA, or deoxyribonucleic acid, is contained within the membrane-bound cell structures of the nucleus, mitochondria, and chloroplasts. DNA has several properties that are unique among chemical molecules.

Recombinant DNA technology result

Recombinant DNA technology makes use of science’s understanding of the molecular structure of DNA, the nucleic acid that encodes genetic information, to alter DNA in order to manipulate genetic traits. Such technology has immense implications for agriculture, horticulture, and the generation of medicinal compounds from plants.

Recombinant DNA technology has been essential for understanding DNA sequences. Because of their large, complex genomes, it was difficult to study one gene in eukaryotes, but recombinant DNA technology has allowed the isolation and amplification of specific DNA fragments facilitating the molecular analysis of genes. In addition, the tools of recombinant DNA technology have been used to create genetically modified plants.

Such modifications include the introduction of resistance to insects, herbicides, viruses, and bacterial and fungal diseases into plants. Plants have also been made to produce antibodies so that plants can serve as edible vaccines.

DNA replication

DNA, deoxyribonucleic acid, is the hereditary material of most living creatures. It carries genetic information that determines all types of plant lives. DNA replication is a process by which a single DNA molecule is copied, resulting in two identical molecules prior to the cell division. The accuracy and precision in DNA replication has ensured the continuity of life from generation to generation.

Following James Watson and Francis Crick’s landmark proposal for the structure of the deoxyribonucleic acid (DNA) molecule in 1953, many scientists turned their attention to how this molecule is replicated.

Plant dormancy

Dormancy is the state in which a plant or plant part exhibits little or no growth and in which most, if not all, metabolic activity ceases for a period of time.

The vast majority of plant life functions best when there is ample water and temperatures are well above freezing throughout the year. Except for those in moist, tropical regions, however, plants are exposed to dry periods and temperatures below freezing for varying lengths of time during the year. Plants, unlike animals, do not have the luxury of body insulation or locomotion.

Hence, plants cannot seek shelter or use other active ways to survive water shortages and cold weather. Consequently, many plants become dormant to avoid unfavorable environmental conditions. In dormancy, their metabolic activity either ceases or is drastically reduced.

Drought in Bangladesh

Drought is a shortage of precipitation that results in a water deficit for some activity. Droughts occur in both arid and humid regions.

One problem in analyzing and assessing the impacts of drought, as well as in delimiting drought areas, is simply defining “drought” itself. Conditions considered a drought by a farmer whose crops have withered during the summer may not be seen as a drought by a city planner.

There are many types of drought: agricultural, hydrological, economic, and meteorological. The Palmer Drought Severity Index is the best known of a number of indexes that attempt to standardize the measurement of drought magnitude. Nevertheless, there still is much confusion and uncertainty on what defines a drought.

Ecology: Concept

Ecology is the scientific study of ecosystems, which are generally defined as local units of nature, consisting of the aggregate of plants, animals, the physical environment, and their interactions.

Ecosystems consist of both biotic (living) and abiotic (nonliving) components. Biotic components include plants, animals, and microorganisms. The abiotic components are the physical factors of the ecosystem. The roots of ecology can be traced to the writings of early Greek philosophers such as Aristotle and Theophrastus, who were keen observers of plants and animals in their natural habitats.

During the nineteenth century, German biogeographer Alexander von Humboldt and English naturalist Charles Darwin wrote detailed descriptions of their travels. They recognized that the distribution of living things is determined by such factors as rainfall, temperature, and soil.

ecosystems

An ecosystem is made up of the complex interactions of a community of organisms of different species with one another and with their abiotic (nonliving) environment.

A biological community consists of a mixture of populations of individual species; a population consists of potentially interbreeding members of a species. Individual organisms interact with members of their own species as well as with other species. An ecosystem is formed by this web of interactions among species, along with the physical, chemical, and climatic conditions of the area.

Abiotic and Biotic Interactions

Abiotic environmental conditions include temperature, water availability, soil nutrient content, and many other factors that depend on the climate, soil, and geology of an area. Living organisms can alter their environment to some degree. A canopy formed by large forest trees, for example, will change the light, temperature, and moisture available to herbaceous plants growing near the forest floor.

Studies ecosystems

The study of ecosystems defines a specific area of the earth and the attendant interactions among organisms and the physical-chemical environment present at the site.

Ecosystems are viewed by ecologists as basic units of the biosphere, much as cells are considered by biologists to be the basic units of an organism. Ecosystems are self-organized and self-regulating entities within which energy flows and resources are cycled in a coordinated, interdependent manner to sustain life.

Disruptions and perturbations to, or within, the unit’s organization or processes may reduce the quality of life there or cause its demise. Ecosystem boundaries are usually defined by the research or management questions being asked.

Gel electrophoresis

Electrophoresis is a biochemical technique used to separate charged molecules in an electric field. Gel electrophoresis is one of the most common forms of this method, used to separate DNA, proteins, enzymes, and other molecules from the cell for laboratory investigation and manipulation.

Electrophoresis is widely used to separate, visualize, or purify charged biological molecules such as deoxyribonucleic and ribonucleic acids (DNA and RNA) and proteins, including enzymes.

It is also used to estimate the size of DNA fragments and the molecular weight of proteins. Most biological molecules are electrically charged in solution; hence, when subjected to an electric field, they migrate as zones toward an electrode (a terminal source of electricity) of opposite electrical polarity.

Endocytosis and Exocytosis

Endocytosis is used by cells to move water, macro molecules, or larger objects, such as cell fragments or even whole cells, from outside a cell to the inside of the cell. Exocytosis is the reverse of endocytosis, that is, the movement of materials from the inside to the outside of the cell. Both types of transport move the materials using membrane-bound vesicles.

Endocytosis

In endocytosis, during which materials are moved into a cell, the cell’s plasma membrane engulfs material and packs it into saclike structures called vesicles. The vesicles then detach from the plasma membrane and move into the cell.

Once the vesicle is in the cytoplasm, it will typically fuse with some other membrane-bound organelle, such as a vacuole or the endoplasmic reticulum, and release its contents into the organelle. There are three types of endocytosis: phagocytosis (transport of actual particles), pinocytosis (transport of water, along with any solutes in the water), and receptor-mediated endocytosis (explained in detail below).

The endomembrane system is a collective term applied to all of the membranes in a cell that are either connected with or are derived from the endoplasmic reticulum (ER), including the plasma membrane but not the membranes of chloroplasts or mitochondria.

The membrane-bound organelles considered to be part of the endomembrane system are the vacuole, nuclear envelope, endoplasmic reticulum, Golgi complex, and various types of vacuoles.

Some components of the endomembrane system have direct, permanent connections with the endomembrane system (such as between the endoplasmic reticulum and the nuclear envelope), whereas other components share membrane and contents by trafficking vesicles (membrane-bound packages) from one component to another (for example, the ER sends numerous vesicles to the Golgi complex) across the cytosol.

Endophytes

Fungi that spend at least a part of their lives within the above ground parts of living plants—in leaves, stems, and in some cases reproductive organs—but cause no outward signs of infection are called endophytes. Some endophytes protect the host plant by deterring grazing animals or pathogenic fungi.

In the 1980’s scientists began to realize that a great variety of microscopic fungal species live benignly within plants, as endophytes (from the Greek words endos, meaning “inside,” and phyton, for “plant”), in contrast to fungi living on the surfaces of plants, as epiphytes (from the Greek epi, meaning “upon,” plus phyton). Most endophytic fungi are ascomycetes. Many appear to be close relatives of plant pathogens.

Most endophytic fungi live and feed between the host plant’s cells. Those endophytes that provide a benefit to the plant in return for their keep are considered to be partners with their host, in a symbiotic relationship called mutualism. Endophytic mutualism is well developed in some grasses, in which the fungal partner produces alkaloid substances that deter herbivores and pathogens.

Endoplasmic Reticulum

The endoplasmic reticulum is a network of sacs in the cytosol of eukaryotic cells that manufactures, processes, transports, and stores chemical compounds for use inside and outside of the cell.

The endoplasmic reticulum (ER) is an extensive, complex system of a more or less continuous distribution of convoluted membrane-bound cavities that take up a sizable portion of the cytosol.

The internal space of the ER is called the lumen. The ER is attached to the double-layered nuclear envelope and provides a connection, or bridge, between the nucleus and the cytosol.

Transformation of sunlight into biochemical energy

Life on earth is dependent on the flow of energy from the sun. A small portion of the solar energy, captured in the process of photosynthesis, drives many chemical reactions associated with living systems.

In living organisms, energy flows through chemical reactions. Each chemical reaction converts one set of substances, called the reactants, into another set, the products.

All chemical reactions are essentially energy transformations, in which energy stored in chemical bonds is transferred to other, newly formed chemical bonds. Exergonic reactions release energy, whereas endergonic reactions require an input of energy for a reaction to occur.

Estrogens From Plants

While the female hormones called estrogens are common in mammals, only a few plants contain estrogens. Others synthesize compounds which are chemically unrelated to estrogens but resemble them in their molecular size and shape. These compounds are called phytoestrogens (plant estrogens) and may, when ingested by animals or humans, have properties similar to those of mammalian estrogens.

The precursor of estrogens in plants and animals is the linear (straight-chain) triterpene known as squalene. Cyclization of squalene, via the intermediate cycloartenol in plants and via the intermediate lanosterol in animals, forms a group of very important compounds known as the steroids.

Steroids include cholesterol, mammalian sex hormones (including the estrogens and androgens), corticosteroids, insects’ molting hormones, and plant brassinosteroid hormones.

Ethanol

Ethanol, sometimes called grain alcohol, is an alcohol produced by fermentation of carbohydrates from a broad range of plant matter for many uses in the chemical industry. It has potentially significant use as a gasoline replacement and is also the primary alcohol component of alcoholic beverages.

Ethanol is produced by carbohydrate fermentation processes, hydration of ethylene, and, to a lesser extent, reduction of acetaldehyde obtained from acetylene. Also called ethyl alcohol, alcohol, and grain alcohol, ethanol is a colorless liquid with a mild and distinct aroma and taste.

It has a boiling point of 78.3 degrees Celsius and a melting point of 114.5 degrees Celsius. Ethanol is completely soluble in water and most organic solvents. It has a flash point of 8 degrees Celsius and is thus highly flammable.

Eudicots

The eudicots, class Eudicotyledones (literally “true dicots”), are descended from a common ancestor and comprise three-quarters of all flowering plants. It is one of the two main classes of the angiosperms, the other being the monocots, or Monocotyledones.

Eudicots, the common name used for class Eudicotyledones, are the most common group of flowering plants, comprising 75 percent of all angiosperms. The other 25 percent, monocots (Monocotyledones), are often characterized by pollen grains that have a single aperture (or line of weakness).

Eudicots have pollen grains that typically possess three apertures, referred to as triaperturate pollen. Thus, there is no monocot-dicot division among the flowering plants.

Euglenoids

Organisms called euglenoids, the algal phylum Euglenophyta in the kingdom Protista, make up a large group of common microorganisms numbering between 750 and 900 known species.

Euglenoids can be found in both fresh and stagnant water. Some genera of euglenoids can also be found in marine habitats. Euglena and Phacus are representative common genera. Euglenoids are unicellular, except for those of the colonial genus Colacium.

Because euglenoids have flexible cell coverings, move about freely, and ingest their food through a structure called a gullet, many scientists have classified the euglenoids as animals. Some species of euglenoids, however, have chloroplasts and are able to supply at least some of their food needs through photosynthesis.

The Eukarya form one of the domains of life in the three-domain classification system. Eukarya consists of the advanced, complex organisms, formed by eukaryotic cells (cells with nuclei), including fungi, algae, plants, and animals. The other two domains of life, Archaea and Bacteria, consist of simpler organisms formed by prokaryotic (nucleus-free) cells.

Two Types of Cell

The domain concept of biological organization is relatively new. As recently as the mid-twentieth century, two kingdoms—plant and animal—were widely accepted as describing the most significant split in the biological world. Every living thing was classified as either a plant or an animal. Subsequently, three additional kingdoms were recognized.

Only in the late twentieth century did it become clear, based on molecular and other evidence, that distinctions at the level of the kingdom did not acknowledge the most fundamental differences among organisms. A higher category, the domain, was therefore posited.

Eukaryotic cells (as opposed to prokaryotic cells) have internal, membrane-bound organelles and a distinct nucleus that physically separates the genetic material of the cell from the all of the other parts of the cell. All protists, fungi, plants, and animals are composed of eukaryotic cells.

The cells of all organisms can be divided into two broad categories: prokaryotic cells and eukaryotic cells. Prokaryotic cells are cells with a relatively simple structure, having no internal, membrane-bound organelles. The most striking feature of prokaryotic cells is that they lack a distinct nucleus, hence the name prokaryotic, literally translated from its Greek roots as “before nucleus.”

The prokaryotic organisms comprise two domains of the three domains of life: the ancient bacteria, Archaea; and the modern bacteria, Bacteria or Eubacteria. The Archaea are single-celled organisms that often inhabit extreme environments, such as hot springs. The remainder of bacteria are classified as Eubacteria.

Yellow rapeseed field

European agricultural practices are affected by the policies of the European Union, in addition to global conditions which influence farming everywhere.

Agriculture in Europe goes back to classical times. The development first of the Greek city states, then of the Roman Empire, created urban centers that required substantial amounts of food to be imported from as far away as Egypt. In the year 2000 European agriculture was dominated by two major groups: the European Union (EU), with fifteen member states, and those European states outside the EU.

The EU, which began with the Common Market created by the Treaty of Rome, signed in 1957, initially comprised France, West Germany, Italy, Belgium, the Netherlands, and Luxembourg. By the year 2000 it had expanded to include Great Britain, Ireland, Denmark, Greece, Spain, Portugal, Finland, Sweden, and Austria.

European flora

Flowering plants in Europe vary from those growing in mediterranean to alpine to Arctic regions.

Many of Europe’s flowering plants are similar to those in North America, belonging to many of the same genera but to different species. Some of the most common North American flowering plants have cousins in Europe, but their location varies according to their latitude and altitude.

Climate and Soil

Themost important factor determining the location of plants is climate. The continent of Europe ranges from the coastal areas on the northern shores of the Mediterranean Sea and Black Sea to the Arctic Ocean north of the Scandinavian peninsula. Although most of Europe is in the temperate climate zone, the areas that border the Mediterranean Sea are nearly all frost-free.

Some of the most dramatic examples of natural selection are the result of adaptation in response to stressful climatic conditions. Such selection may cause unrelated species to resemble one another in appearance and function, a phenomenon known as convergence.

In other situations, subpopulations of a single species may split into separate species as the result of natural selection. Such divergence is best seen on isolated islands.

Convergent Evolution

Convergent evolution occurs when organisms from different evolutionary lineages evolve similar adaptations to similar environmental conditions. This can happen even when the organisms are widely separated geographically.

Evolution: Gradualism vs. Punctuated Equilibrium

The gradualism model of evolution proposes that a progenitor species gradually gave rise to many new species, with no special mechanisms accounting for the origins of new genera or groups of higher classifications—only the accumulation of many small changes in the frequencies of alleles in gene pools. The punctuated equilibrium model of evolutionary change supposes long periods of little or no change interspersed with short intervals of rapid change.

Charles Darwin, author of On the Origin of Species by Means of Natural Selection (1859), believed that morphological change was inevitable and proceeded slowly, encompassing slight, successive, and gradual changes within lineages.

Speciation, therefore, was the result of the gradual accumulation of changes within ancestral populations over time, ultimately leading to the formation of recognizably new and different species.

Miller's spark discharge experiment

The earliest cells evolved sometime early in the Precambrian era,which includes the first four billion years of Earth’s history. Attempts to understand life’s origins are difficult, as there are very few clues left in the fossil record from those early times.

The hypotheses and models of the origin of life that have been developed are based on contemporary understanding of how life works at the molecular and cellular levels and on assumptions about the conditions on Earth three billion to four billion years ago.

One assumption made about the origins of life involves the composition of the atmosphere shortly after the earth was formed. According to this assumption, the earth’s atmosphere at this time contained very little free oxygen. It was an atmosphere perhaps made primarily of methane, ammonia, carbon dioxide, nitrogen, carbon monoxide, and water vapor.

Ferns (Pterophyta)

As a result of prehistoric events such as the Permian-Triassic extinction event and the Cretaceous-Tertiary mass extinction event,many plant families and some ancestors of extant plant were extinct before the beginning of recorded history.

The general trend of earth’s plant diversification involves four major plant groups that rose to dominance from about the Middle Silurian period to present time. The first major group providing land vegetation comprised the seedless vascular plants, represented by the phyla Rhyniophyta, Zosterophyllophyta, and Trimerophytophyta. The second major group appearing in the late Devonian period was made up of the ferns (Pterophyta).

The third group, the seed plants (sometimes called the Coal Age plants), appeared at least 380 million years ago (mya). This third group includes the gymnosperms (Gymnospermophyta), which dominated land flora for most of the Mesozoic era until 100 mya.

Exorgenic reaction

Exergonic reactions are spontaneous chemical reactions in which the products are at a lower energy level than the reactants; these reactions release energy. Endergonic reactions are nonspontaneous chemical reactions in which the products are at a higher energy level than the reactants; these reactions consume energy.

The primary source of energy for life on the earth is the sun,which is the energy source for photosynthesis: the biological process that transforms radiant energy into chemical energy. Chemical energy is stored in biological molecules, which can then be used as the fuel to provide an organism’s energy needs.

Such biological molecules include sugars (or carbohydrates), proteins, and lipids (or fats). In the reactions of metabolism, many types of molecules are synthesized (anabolism), and many are broken down (catabolism). Changes in energy content occur in all these reactions.

Extranuclear inheritance is a non-Mendelian form of heredity that involves genetic information located in cytoplasmic organelles, such as mitochondria and chloroplasts, rather than on the chromosomes found in the cell nucleus.

Extranuclear genes, also known as cytoplasmic genes, are located in mitochondria and chloroplasts of a cell rather than in the cell’s nucleus on the chromosomes. Both egg and sperm contribute equally to the inheritance of nuclear genes, but extranuclear genes are more likely to be transmitted through the maternal line because the egg is rich in the cytoplasmic organelles where these genes are located, whereas the sperm contributes only its nucleus to the fertilized egg.

Therefore, extranuclear genes do not follow genetic pioneer Gregor Mendel’s statistical laws of segregation and recombination. Cytoplasmic genes are of interest in understanding evolution, genetic diseases, and the relationship between genetics and embryology.

Farmland

Land used as farmland typically has good agricultural soil and is able to produce food and fiber in an efficient way.

Land suitable for agriculture is not evenly distributed throughout the world; it tends to be concentrated in limited areas. In order to be considered good farmland, land must be located at the proper elevation and slope.

Because the soil supplies the mineral nutrients required for plant growth, it must also have the appropriate fertility, texture, and pH. Approximately 64 percent of the world’s land has the proper topography, and about 46 percent has satisfactory soil fertility to grow crops.

Ferns

Ferns are among the most recognizable members of the phylum Pterophyta, which are primitive, nonflowering, vascular plants that primarily reproduce by spores and occur in many variations, complicating classification.

Approximately twelve thousand extant species of fern are classified in the phylum Pterophyta. These seedless plants display a diversity of physical and reproductive characteristics that separate them taxonomically. They have leaves containing branching veins known as megaphylls. Fossils from the Devonian period, about 395 million years ago, include some structures resembling Pterophyta.

These plants are believed to have been the source for gymnosperms. Most early fernlike plants that evolved in a variety of forms during the next period, the Carboniferous (approximately 345 million to 280million years ago), which is often referred to as the age of the ferns, became extinct afterward.

Fertilizers

Fertilizers are materials used to modify the chemical composition of soil in order to enhance plant growth. They represent an important use of natural resources because agricultural systems depend upon an ability to retain soil fertility.

Soil is a dynamic, chemically reactive medium, and agricultural soils must provide structural support for plants, contain a sufficient supply of plant nutrients, and exhibit an adequate capacity to hold and exchange minerals.

Topsoil, the 6-inch layer of soil covering the earth’s landmasses, is the root zone for the majority of the world’s food and fiber crops. As plants grow and develop, they remove the essential mineral nutrients from the soil. Because crop production normally requires the removal of plants or plant parts, nutrients are continuously being removed from the soil.

Flagella and Cilia

Flagella and cilia are hairlike structures,made primarily of protein, found on the surfaces of cells and used for movement by microorganisms and some specialized cells, such as the gametes of certain plants with motile sperm. Because flagella and cilia are so similar, many scientists use the term “undulipodia” for both in reference to eukaryotic organisms.

Although the term “flagellum” is used in reference to both prokaryotes (archaea and bacteria) and eukaryotes (fungi, protists, plants, and animals), the structure and mechanism of action of this structure in prokaryotes are quite different from the structure and mechanism of action in eukaryotes.

Eukaryotic flagella and cilia, however, are structurally and functionally identical. The differences between them are in their number, length, and position. Flagella are less numerous, longer, and usually polar, while cilia are more numerous and shorter, covering much of the cell’s surface.

Flowers are the modified shoots bearing modified leaves that serve as the sexual reproductive organs of angiosperms. This strategy for reproduction has been so successful that angiosperms now dominate the plant world, and accordingly there are many variations on the basic structure of a flower.

Flowers are organs of sexual reproduction produced by the angiosperms (phylum Anthophyta), the largest phylum of photosynthetic organisms, with roughly 250,000 species. This large number represents a great diversity of flower types, but all flowers have some common structural elements.

Flower Parts

Flowers are modified shoots bearing modified leaves. In the typical flower, the modified leaves can be grouped into four sets based on appearance and function: sepals, petals, stamens, and pistils. The sepals and petals are lowermost on the shoot toward the sides of the flower. The stamens and pistils are at the tip of the shoot at the inside.

Yellow hibiscus flower

The flower is the most distinctive feature of the phylum Anthophyta, commonly referred to as angiosperms or flowering plants, and is responsible in making them the most dominant, diverse, and widespread of all groups of plants.

There are already about 250,000 species of flowering plants that have been discovered and named. The basis for their diversity comes from their incredible reproductive success in a wide variety of habitats.

The success of this group is also reflected by the diversity of their flowers that show astonishing displays of different forms, sizes, shapes, and colors—all of these to lure pollinators and effect sexual reproduction.

Flowering regulation

All flowering is regulated by the integration of environmental cues into an internal sequence of processes. These processes regulate the ability of plant organs to produce and respond to an array of signals. The numerous regulatory switches permit precise control over the time of flowering.

Control over the time of flowering is essential for the survival of flowering plants (angiosperms). Insect pollinators may be present only at certain times; unless an insect-pollinated plant is flowering at that time, pollination and the production of the next generation cannot occur.

Embryo and seed development may be successful only under certain climatic conditions. The ability to respond to environmental cues is an essential factor in the regulation of flowering.

Fluorescent Staining of Cytoskeletal Elements

Fluorescent antibody staining is a precise technique for marking elements of the cytoskeleton so they become visible under a microscope. The technique has revealed much about the location and functions of the cytoskeleton within a cell. It also offers some of the most visually appealing of the microscopic images available to biologists.

Cells require an internal system of fibers in order to maintain and change their shape. Perhaps the most straightforward function of the cytoskeleton is to provide cell support, a scaffolding that gives each cell a distinctive three-dimensional shape.

Without such support every cell would be shaped like a fried egg. The fibers found in the cytoskeleton serve other functions as well: for example, as rails along which substances shuttle from one part of the cell to another.

The food chain concept allows ecologists to interconnect the organisms living in an ecosystem and to trace mathematically the flow of energy from plants through animals to decomposers.

The food chain concept provides the basic framework for production biology and has major implications for agriculture, wildlife biology, and calculating the maximum amount of life that can be supported on the earth. As early as 1789, naturalists such as Gilbert White described the many sequences of animals eating plants and themselves being eaten by other animals.

However, the use of the term “food chain” dates from 1927, when Charles Elton described the implications of the food chain and food web concept in a clear manner. His solid exposition advanced the study of two important biological concepts: the complex organization and interrelatedness of nature, and energy flow through ecosystems.

Forest and rangeland

Forest and range policies are laws protecting forests and rangelands. Such policies usually seek to sustain and protect biodiversity while setting guidelines for the sustainable use of natural resources.

Many national governments have established forest and range policies. Rangeland, land that supplies forage for grazing and browsing animals, covers almost one-half of the ice-free land on earth. More than three billion cattle, sheep, goats, camels, buffalo, and other domestic animals graze on rangelands.

These animals are important in converting forages into milk and meat, which provide nourishment for people around the world. Forests cover almost 30 percent of the earth and provide humans with lumber, fuel woods, food products, latex rubber, and valuable chemicals that constitute prescription and nonprescription drugs.

Forest management

Forest management includes reforestation programs as well as techniques to manage logging practices, provide grazing lands, support mining operations, maintain infrastructure networks, or slow the destruction of rain forests.

Forests provide lumber for buildings, wood fuel for cooking and heating, and raw materials for making paper, latex rubber, resin, dyes, and essential oils. Forests are also home to millions of plants and animal species and are vital in regulating climate, purifying the air, and controlling water run-off.

A 1993 global assessment by the United Nations Food and Agriculture Organization (FAO) found that three-fourths of the forests in the world still have some tree cover, but less than one-half of these have intact forest ecosystems. Deforestation is occurring at an alarming rate, and management practices are being sought to try to halt this destruction.

Forests

Forests are complex ecosystems in which trees are the dominant type of plant. There are three main forest biomes: tropical, temperate, and boreal.

Both humans and animals depend on forests for food, shelter, and other resources. Forests once covered much of the world and are still found from the equator to the Arctic regions.

A forest may vary in size from only a few acres to thousands of square miles, but generally any natural area in which trees are the dominant type of plant can be considered a forest.

Fossil Plant

Fossil plants are remnants, impressions, or traces of plants from past geologic ages preserved in the earth’s crust.

The rise of land-dwelling animals paralleled the rise of plants, which have always been the basis for animal life. Fossil plants are a valuable source of information regarding such phenomena as changes in climate, ancient geography, and the evolution of life itself.

Thallophytes

The earliest fossil plants are represented by a phylum called the thallophytes. The geological record of the thallophytes is incomplete. Of seven large groups, only a few are represented by fossils.

Fruit crops

Fruits are mature, or ripened, ovaries of angiosperms, their contents, and any accompanying accessory structures. From a botanical point of view, common foods such as grains, nuts, dried beans, squash, eggplant, and tomatoes are fruits, but in common usage the term is usually restricted to fleshy fruits that are commonly grown commercially as crops and are eaten, primarily raw, for their fleshy and juicy pulp.

Fertilization of ovules and the initiation of seed development lead to hormone production that triggers fruit development. Consequently, fruits usually contain seeds, but seeds can form without fertilization (parthenogenesis), and fruits can develop without seeds (parthenocarpy).

Many fruits that are cooked or eaten as part of a main course are usually classed as vegetables. This dichotomy is reflected in the origins of the two words: fruit, from the Latin fruor, “to enjoy,” and vegetable, from the Latin vegetare, “to enliven.”

Fruits

Fruits are the seed-containing reproductive organs, including nuts and grains, produced by angiosperms (flowering plants).

When most people think of a fruit, what typically comes to mind is a juicy, edible object, such as an apple, orange, or banana. To botanists, however, fruit includes many plant-derived structures, such as grains, nuts, and many vegetables.

In essence, a fruit is an enlarge dovary, often with some accessory tissue, that develops after a flower has been pollinated. After pollination, seed development begins, and soon the peripheral parts of the flower fall away, leaving the immature fruit. The fruit subsequently enlarges and then ripens to maturity. It is then often edible.

Fungi

The kingdom of non photosynthetic eukaryotic organisms, fungi are heterotrophic organisms, feeding on other materials rather than making their own food. They live on dead organisms by secreting digestive enzymes and absorbing the breakdown products.

Although these organisms are stationary like plants and thus traditionally studied in botany courses, the heterotropic fungi are fundamentally different from plants, which are autotrophic organisms.

Although some unicellular forms of fungi exist, most fungi are characterized by a mycelial growth form; that is, they generally are made up of a mass of hyphae (tubular filaments). All fungi live in their food and have an absorptive mode of nutrition by which they secrete digestive enzymes and absorb the breakdown products. They are therefore heterotrophs.