Characteristics of rain forests, The temperature in a tropical rain forest varies little. It rarely rises above 95 °F (35 °C) or drops below 64 °F (18 °C). In many regions, the average temperature in the hottest month is only 2 to 5 Fahrenheit degrees (1 to 3 Celsius degrees) higher than the average temperature in the coldest month. Most rain forests receive more than 80 inches (203 centimeters) of rain annually. Some areas may receive more than 250 inches (635 centimeters) of rain each year. Thundershowers can occur more than 200 days a year.
Rain forest soils vary greatly from place to place. In many areas, the soil is acidic and infertile because years of heavy rains have washed out most of the nutrients (nourishing substances). Most rain forest nutrients are part of living plants. Small amounts of nutrients occur in a thin layer of topsoil that contains decaying vegetation.
Rain forest trees have developed several ways of capturing nutrients. For example, they obtain nourishment from rainwater that collects in their leaves or along their trunks and branches. They also withdraw nutrients from their old leaves before they shed them. The roots of most rain forest trees grow close to the surface and quickly absorb soil nutrients before they wash away. Special fungi called mycorrhizae grow in or on many of the roots and help them absorb minerals from the soil.
Rain forests grow in four major layers: (1) the canopy, or top layer; (2) the sub-canopy, a layer of trees just below the canopy; (3) the understory, a shady lower area; and (4) the floor. The tallest trees, known as emergents, grow more than 165 feet (50 meters) tall. The crowns (tops) of these trees dominate the canopy. Emergents receive the greatest amount of sunlight, but they must endure high temperatures and strong winds. The crowns of other trees in the canopy usually form a nearly continuous covering of leaves 65 to 165 feet (20 to 50 meters) above the ground. Some tall trees have large growths called buttresses that extend from the base of the trunk and help support the tree.
More than 70 percent of rain forest animal and plant species reside in the canopy and sub-canopy. Many tree branches have a dense covering of epiphytes, plants that grow on other plants and obtain nourishment from the air and rain. Vines called lianas often climb on or around the trunks and branches of trees.
The shady understory shelters small palms, young trees, and herbaceous (nonwoody) plants that can grow in dim light. Many popular house plants, such as philodendrons, dieffenbachia, and ferns, are developed from species that live in this area. Some scientists believe only 1 percent of the sunlight available to emergent trees reaches the understory.
A thin layer of fallen leaves, seeds, fruits, and branches covers the forest floor. This layer quickly decomposes and is constantly replaced.
The layers of a rain forest continually change. Large old trees die and fall to the ground, leaving a gap in the canopy. Direct sunlight penetrates through to the understory and stimulates the growth of seedlings, saplings, and small trees below. The small trees slowly stretch upward into the canopy. As they branch and expand their crowns, they fill the gaps in the canopy. A mature rain forest consists of a mixture of closed canopies, gaps, and patches of growing trees where the canopy is being rebuilt. The regeneration of many rain forest trees depends on gaps developing regularly in the canopy.
Plants and animals. About 45 percent of the world's plant species occur in tropical rain forests. Scientists have counted over 250 species of trees in small areas of Asian and South American rain forests. A similar plot of land in a northern temperate forest would have only about 10 to 15 tree species. In addition to trees, rain forests support a great variety of bamboos, herbs, and shrubs. Climbing vines, ferns, mosses, and orchids grow directly on the trunks and branches of large trees.
Because of continual moisture and warmth, tropical rain forests stay green all year. Most rain forest trees continually lose old leaves and grow new ones. Only a few species lose all of their leaves for a brief period.
Fish, amphibians, reptiles, birds, and mammals abound in the rain forest and its rivers. However, insects rank as the most plentiful rain forest animals. An individual tree in a South American rain forest may support more than 40 species of ants. Scientists have counted about 1,200 species of beetles living in only 19 tree crowns from Panama.
Plants and animals in the rain forest depend on one another for survival. Many animal groups, especially insects and birds, pollinate the flowers of rain forest trees. Such animals receive food from the flowers' nectar. In return, they pollinate the next flowers they visit. Some trees rely on only one species of insect for pollination. Many rain forest trees also depend on animals to disperse their seeds. In the Amazon rain forest, fish disperse the seeds of some trees.
Frequently Asked Questions About the Rainforest, What is a Rainforest? or Definition of Rainforest. Rainforest is a woodland of tall trees growing in a region of year-round warmth and abundant rainfall. Almost all rain forests lie at or near the equator. They form an evergreen belt of lush vegetation that encircles the planet. German botanist Andreas F. W. Schimper first coined the term rain forest-in German, Regenwald-in 1898.
Tropical rain forests occupy only 6 to 7 percent of the earth's surface. However, they support more than half of the world's plant and animal species (kinds). More kinds of frogs and other amphibians, birds, insects, mammals, and reptiles live in rain forests than in any other area. Scientists believe millions more rain forest species remain undiscovered.
The rain forest provides people with many benefits. Its plants produce timber, foods, medicines, and such industrial products as dyes, fibers, gums, oils, and resins. Rain forests help regulate the earth's climate and maintain clean air. The forests' lush, green beauty and rich wildlife offer a special source of enjoyment.
In addition, rain forests provide homes to millions of people. Such groups as the Yanomami of South America, the Dayaks of Southeast Asia, and the Pygmies of central Africa have lived in rain forests for centuries. They make their living by hunting, fishing, collecting forest products, and farming. Traditional forest peoples have acquired much knowledge about the rain forest's plants and animals.
In spite of these benefits, people cut down thousands of square miles or square kilometers of rain forest each year. This destruction eliminates thousands of species of animals. A number of governments and conservation organizations are working to preserve the rain forests.
When people build cities or cut down forests to obtain wood or to clear land for farming, they destroy the habitats that animals need to survive. The habitats of animals in tropical forests are particularly threatened today. People are rapidly cutting down these forests to obtain such valuable hardwoods as mahogany and teak. They are also clearing the land to plant crops. However, soils in such areas are not especially fertile, and farms there produce crops for only a few years. To continue farming in such areas, people have to keep cutting down more of the forests to create new farmland. By the early 1990's, about two-fifths of the world's tropical forests had already been destroyed.
Many scientists and other people are especially concerned about the destruction of tropical forests. They point out that these forests have more biodiversity-that is, a greater variety of plant and animal species-than any other place. One square mile (2.6 square kilometers) of forest in South America may have more species of birds and insects than many countries do. In fact, biologists discovered a single tree in a tropical forest in Peru that supported 43 species of ants. That is as many species of ants as live in the entire United Kingdom.
Even though many types of plant and animal life can be found in one place in the tropics, the total range of many tropical species is extremely small. As a result, when a large area of forest is cleared, all the members of some species are killed.
Pollution. Various types of pollution can also destroy animals and their habitats. Agricultural chemicals and industrial wastes sometimes drain into ponds and streams and kill the plants and animals there. Air pollution produced by factories that burn such fossil fuels as coal and oil has seriously damaged forests and wildlife. Acid rain-rainfall with a high concentration of sulfuric and nitric acids due to air pollution-kills fish and other animals.
An increase in carbon dioxide in the atmosphere presents a long-term threat to animals and habitats. Many factories-as well as automobiles and power plants-release carbon dioxide into the air. Forest trees and plants help absorb this gas, but as more of them are cut down, carbon dioxide levels rise. Many scientists believe that higher amounts of carbon dioxide in the atmosphere speed up global warming caused by the phenomenon known as the greenhouse effect. A major global warmup could produce significant changes in Earth's climate. Such changes could destroy many kinds of plants and animals.
Territoriality is a form of animal behavior in which an individual animal or a group defends an area against other members of the same species or against members of other species. The defended area is called a territory. An individual usually wins encounters with intruders while on its own territory, but it usually loses encounters when intruding onto another territory. A territory contains resources that the animal needs to survive and reproduce. These resources may include shelter, food, and water; places where mates can be found; and places where animals can escape from their enemies.
Definition of Territoriality is common in vertebrates (animals with a backbone), including fish, amphibians, reptiles, birds, and mammals. It is less common among insects and other invertebrates (animals without a backbone).
The size of a territory varies, depending on the effort required to defend the area and the resources available. Animals may establish small territories in the immediate vicinity of nesting sites or in areas of abundant food. They may claim large territories when resources are widely scattered. The period a territory is held may vary from less than a day to many years or a lifetime.
Animals may defend a territory by being openly aggressive, such as by chasing and fighting intruders. They also may defend the territory through signals of potential aggression. For example, a wolf marks out its territory by urinating on bushes, rocks, and other objects. The scent of urine warns intruders of the wolf's presence and the risk of an encounter. The more aggressive forms of defense generally are used when the intruder is especially persistent.
Each of the more than 260,000 species of plants differs from every other species in one or more ways. However, plants also have many features in common. Based on these similarities, scientists are able to classify distinct plants into groups. The study of plants is called botany, and scientists who study plants are known as botanists.
This section describes the chief kinds of plants found in the plant kingdom. It is divided into five basic groups: (1) seed plants, (2) ferns, (3) lycopsids, (4) horsetails, and (5) bryophytes. A table showing a more detailed system of plant classification that is used by many botanists appears at the end of the article.
Seed plants consist of a wide variety of plants that bear seeds to reproduce. Most botanists divide the seed plants into two main groups of plants-angiosperms and gymnosperms.
Angiosperms are flowering plants. They make up the vast majority of the more than 260,000 kinds of plants. They produce seeds that are enclosed in a protective seed case. The word angiosperm comes from two Greek words meaning enclosed and seed. All plants that produce flowers and fruits are angiosperms. They include most of our common plants, such as brightly colored garden plants, many kinds of wildflowers, and most trees, shrubs, and herbs. Most of the plants that produce the fruits, grains, and vegetables that people eat also are angiosperms.
The sizes of angiosperms vary greatly. The smallest flowering plant, the duckweed, is only about 1/50 inch (0.5 millimeter) long. It floats on the surface of ponds. The largest angiosperms are eucalyptus trees. They grow more than 300 feet (91 meters) tall.
Some botanists divide the angiosperms into two smaller groups. Plants in one group, called monocotyledons or monocots, grow from seeds that contain one seed leaf called a cotyledon. Plants in the other group, called dicotyledons or dicots, have two cotyledons in their seeds.
Gymnosperms include a wide variety of trees and shrubs that produce naked or uncovered seeds. Most gymnosperms bear their seeds in cones. The word gymnosperm comes from two Greek words meaning naked and seed. Gymnosperms do not produce flowers. This group is made up of such plants as conifers, cycads, ginkgoes, and gnetophytes. .
Conifers are the best known of the gymnosperms. They include such trees as cedars, cypresses, firs, pines, redwoods, and spruces. Most conifers have needlelike or scalelike leaves. Their seeds grow on the upper side of the scales that make up their cones. The cones of some conifers, such as junipers, look like berries. Most conifers are evergreens-that is, they shed old leaves and grow new leaves continuously and so stay green throughout the year. Wood from conifers is widely used in construction and papermaking. Conifers also provide animals with food and shelter.
Cycads and ginkgoes have lived on Earth for millions of years. Large numbers of these plants once grew over wide regions of land. Most cycads look much like palm trees. They have a branchless trunk topped by a crown of long leaves. But unlike palm trees, they bear their seeds in large cones. Only one kind of ginkgo survives today. It is an ornamental tree with flat, fan-shaped leaves. It bears seeds at the ends of short stalks along its branches.
Gnetophytes are the gymnosperms most closely related to angiosperms. They have many features that resemble those of flowering plants. For example, Gnetum has broad, oval-shaped leaves and special water-transport tubes, much like those of angiosperms. The cones of all gnetophytes are flowerlike in many details.
Ferns grow chiefly in moist, wooded regions. They vary widely in size and form. Some aquatic ferns have leaves only about 1 inch (2.5 centimeters) long. But in the tropics, tree ferns may grow more than 65 feet (20 meters) high.
Fern leaves, called fronds, usually are made up of many tiny leaflets and may be quite large. On most types of ferns, the fronds are the only parts that grow above the ground. They grow from underground stems that may run horizontally under the surface of the ground. When the fronds first appear, they are tightly coiled. The fronds unwind as they grow.
During prehistoric times, great numbers of large ferns covered Earth. These ferns, along with giant club mosses and horsetails, accounted for much of the plant life that later formed coal. See FERN.
Lycopsids include club mosses, quillworts, and selaginellas. These plants have leaves with a single, central vein. Lycopsids were among the first plants to grow on land.
Club mosses have tiny needlelike or scalelike leaves that usually grow in a spiral pattern. They are not true mosses. Club mosses are found from tropical to temperate regions. They often form a "carpet" on the forest floor.
Quillworts are found chiefly in moist soils around lakes and streams. They have short stems and long, grasslike leaves. The leaves usually grow to about 14 inches (36 centimeters) long. Ancient plants related to quillworts were large trees that grew up to 120 feet (37 meters) tall. These plants lived about 290 million years ago.
There are about 700 kinds of selaginellas. These plants are usually found in tropical and subtropical regions. They often grow in damp places on the forest floor. Selaginellas have small thin leaves. Their stems may either grow upright or along the ground. These plants first appeared on earth over 300 million years ago.
Horsetails are a group of small plants that have hollow, jointed stems. Horsetails grow about 2 to 3 feet (60 to 90 centimeters) tall. The plants have green stems and tiny, black leaves. The stems capture the sunlight used by the plant to make food in photosynthesis. In some horsetails, the branches grow in whorls (circles) around the main stem of the plant, and the plant resembles a horse's tail. Tiny amounts of minerals are concentrated in the stems of horsetails, including gold and silica. Silica makes the stems very coarse, like sandpaper. Some kinds of horsetails are called scouring rush because people once used these plants to scour their pots and pans.
Bryophytes are a group made up of liverworts, mosses, and hornworts. These plants live in almost all parts of the world, from the Arctic to tropical forests. They grow in such moist, shady places as forests and ravines. Bryophytes are the only types of plants that lack vascular tissue-that is, tissue that carries water and food throughout the plant.
Most liverworts, mosses, and hornworts measure less than 8 inches (20 centimeters) tall. None of these plants have true roots. Instead, they have hairy rootlike growths called rhizoids that anchor the plants to the soil and absorb water and minerals.
Peat moss, a substance made up of thick growths of Sphagnum and other mosses, is often used in gardening. Gardeners mix peat moss into the soil to keep the soil loose and to help it hold moisture.
Roots of plants are an important part affecting the growth and life of the plant. Root including vegetative organs of plants, in addition to the stem and leaves .
There are three functions that are important to the plant roots are:
- First; roots as an anchor that helps plants stand firmly on the ground. The roots of the plant stuck to the ground and strengthen the plants from strong winds so it did not collapse. On plant root systems to grow vertically into the ground but there is also a growing horizontally spread onto the surface of the ground.
- Root function is as a means of absorption or uptake of nutrients from the soil. Plants absorb water needs, including using a spread roots in the soil. The roots of primary, secondary and tertiary plants scattered through small roots called root hairs. At the root ends of the hood there is a root that helps the absorption.
- The third function is as a food reserve perverts. In the plant roots are parenchymal cells and tissues as a place to store the results of photosynthesis in the form of carbohydrates. Plants that have food reserves in the roots like cassava, potatoes, carrots, potatoes and many other similar crops.
First roots develop from seed is the main root. It produces many branches called secondary roots. Secondary roots produce their own branches. There are two main types of root systems, taproot or fibrous. In a taproot system, the primary root grows straight down and called the taproot.
Taproot still larger than the secondary roots throughout the plant life. In some plants, including beets and carrots, taproot being fat (bloated). Grass is an example of a plant with a fibrous root system in such a system, the primary roots do not stay more than the others. Many thin secondary roots growing in all directions. A fibrous root system can be very broad. For example, the roots of wheat plants may have a combined length of approximately 380 miles (612 kilometers).
Some plants have modified roots that perform specific functions. Roots that grow from the roots or branches primer called adventitious roots. They include supporting the roots of corn and some other crops. Prop roots grow into the soil from the bottom of the stem and helps hold plants upwind. Some species of orchids and other plants that live in the branches of a tree issuing aerial roots, which are attached to the branches. Aerial roots absorb water and minerals from the surface of the tree and from the air. Parasite is one of the few plants with roots that penetrate the tree body. The roots, called sinkers, absorb food, water, and minerals directly from the tree .
Definition of Dominance is a form of behavior among individual animals that shows their ability to win aggressive encounters with other animals. These animals may be members of the same species or of different species. Dominance determines which individuals have first choice of resources that are needed to survive and reproduce and that are in limited supply. These resources include food, water, a resting place, or mates. Animals that lose the aggressive encounters or give in to dominant individuals without a fight are called subordinates. Subordinates that are denied use of scarce resources may be among the first to die or to leave an area.
In a group, a particular individual may be dominant to some members and subordinate to others. This results in a dominance hierarchy--that is, a ranking of individuals by their dominance in relation to each other. In many cases, an individual is subordinate to all those ranked above it and dominant to those below it. This type of ranking is called linear dominance hierarchy. However, dominance hierarchies may be more complicated. For example, in circular dominance hierarchy, individual A may be dominant to individual B and B dominant to individual C, but C is dominant to A. Individuals can improve their position in the group's dominance hierarchy as they gain experience or maturity, or as their reproductive condition changes.
Encounters that establish dominance only occasionally include actual fighting. In most cases, these encounters involve only signals that indicate an individual's willingness or ability to win a potential fight. An individual's large size or threatening natural weapons, such as the horns of mountain sheep or the powerful jaws of a wolf, might cause subordinates to give up without a fight.
Dominance differs from territoriality, a form of animal behavior in which an individual or group claims a certain area as its own. A dominant individual usually can win wherever it is.
Plants, animals, and other organisms that live together in the same area-such as a forest or a pond-form a community. Within a community, the members of one species make up a population. The size of each population stays fairly stable unless some change alters conditions in the community. Biologists refer to the relative stability of each population within a community as the balance of nature.
Maintaining the balance
All living things are closely related to their environment. Any change in one part of nature-for example, a natural increase or decrease in a population of any species of animal or plant-causes reactions in several other parts. In most cases, these reactions work to restore the balance of nature.
Ecosystems. An ecosystem consists of the biological and physical environments of an area. The biological environment is made up of all living things in the community. The physical environment includes air, soil, water, and weather. All these biological and physical factors interact within an ecosystem. They compose a network of complex relationships that control population growth.
Each organism is related to a variety of the biological and physical factors of its ecosystem. For example, rabbits need air and water from the physical environment to breathe and drink. They also need biological features, such as plants, for food and cover (shelter). On the other hand, rabbits are eaten by foxes and other predators (flesh-eating animals). In addition, several kinds of parasites live in and on rabbits.
The relationship among rabbits, plants, and foxes can be shown by an example of an ecosystem that includes these three organisms. Assume that during a certain year, the temperature and rainfall within this ecosystem are ideal for plant growth. As a result, rabbits have a more plentiful supply of food than usual. The female rabbits are well-fed and healthy, and most of them produce large litters. The young rabbits have enough food, and nearly all of them survive. In time, the area becomes overpopulated with rabbits, and they continually compete with one another for food and cover. The losers become weak and unprotected, and they may fall victim to disease and parasites. They also become easy targets for foxes, and so the rabbit population decreases.
More rabbits means more food for foxes. The foxes respond in much the same way as the rabbits did to an increased food supply-their population grows. But more foxes means that even more rabbits are hunted, and so the number of rabbits shrinks even further. The rabbit population will continue to decrease until it again comes into balance with the ecosystem's ability to support it-an ability known as the ecosystem's carrying capacity. Similar controls govern plant populations. On a small scale, such actions and reactions go on every day.
Competition plays a major role in controlling population growth. An ecosystem has limited amounts of the food and cover necessary for each population. Therefore, individual members of the same population must compete for those necessities. But competition is much less intense between different populations. For example, deer and rabbits are herbivores (plant-eating animals), but they usually eat different kinds of plants.
Competition for food. If a population becomes too large for the available supply of food, many of the weaker members will starve. Others may migrate into another ecosystem, but they may not survive. Still others, weakened by hunger, may die from disease and parasites, or they may be killed by predators.
Competition for cover. Competition for cover. Cover is a requirement for most populations. Only a certain number of rabbits can live in a given brier patch, and only so many foxes can occupy the available den sites. If the rabbit population becomes too large for the brier patch, competition will force some individuals to live in poorer cover. There, they will be more likely to be attacked by predators or by disease and parasites.
Predators can help maintain the quality of their prey population if the two species have lived for a long time in the same ecosystem. Under such conditions, the prey species learns to deal with the predators. Therefore, predators normally kill only the weakest and least desirable members of the prey population. The prey population thus stays in a healthy state.
Disease and parasites can reduce or even wipe out a population. But most pathogens (diseases and parasites) have been present throughout history. Most host (infected) species have become adapted to living with their pathogens. Disease and parasites serve as important population controls primarily in the presence of other factors, such as competition for food or cover.
Behavior helps govern the size of some animal populations. Three behavioral factors may be important: (1) territoriality, (2) dominance hierarchy, and (3) stress.
Territoriality occurs among animals that require a certain minimum amount of space, regardless of the available food and cover. Among such species, one animal or a group of animals establishes a territory. No other members of the species are allowed in this area, and breeding is usually restricted to the animals with territories. Such behavior ensures that the strongest members of the population-the animals with territories-survive and produce offspring.
Dominance hierarchies, often called "pecking orders," occur among many types of social animals. Within populations of such animals, the stronger individuals dominate the weaker ones. These dominant animals get the best food, cover, and breeding places. Weaker individuals are forced into areas with poorer food and cover, and some do not survive. The offspring of dominant parents also have the best chance to survive. The traits of the strongest individuals thus are passed on to the next generation of the species.
Stress occurs among crowded populations of animals. Stressed animals become aggressive and irritable, and they often fight with one another. Some individuals do not breed, and those that do breed produce small litters. Many females do not take care of their young. Diseases and parasites spread rapidly among crowded animals, further reducing their number.
Upsetting the balance
Natural factors and human factors may alter the relationships within an ecosystem. Earthquakes, floods, and fires started by lightning are natural factors that may upset nature's balance. Human factors that may do so include logging and livestock grazing. As a result of these and other factors, entire populations may be wiped out or may grow suddenly at an astounding rate.
A historical example illustrates a change in balance. During the early 1900's, a stable population of about 4,000 mule deer lived on the Kaibab Plateau in northwestern Arizona. Beginning in 1907, human hunters began killing the deer's natural predators-coyotes, mountain lions, and wolves. As a result, the population of deer on the plateau increased to about 100,000 by 1924. But there was not enough food for so many deer, and thousands of deer starved. Balance did not return to the ecosystem of the Kaibab Plateau until 1939.
In another case, a chain of events known as the ripple effect began when fishing crews apparently overharvested fish populations in the northern Pacific Ocean. As a result, seals and sea lions, which eat fish, declined. In 1998, biologists reported that killer whales, which normally prey on seals and sea lions, had begun to prey on sea otters. The killer whales sharply reduced some sea otter populations. Next, sea urchins, a major food of the otters, increased. The sea urchins consumed huge amounts of a type of algae known as kelp. They reduced the ocean's kelp beds, which provide habitat for many other species. Beginning with fewer fish, an entire marine ecosystem-seals and sea lions, killer whales, sea otters, sea urchins, and kelp beds-was upset. No one knows when balance will return.
The primary function of chloroplasts is photosynthesis, the light-driven fixation of carbon dioxide into organic compounds. The products of the photochemical reactions that occur within thylakoid membranes provide the material with which the plant cells grow and on which all forms of life on the surface of Earth depend.
Photosynthesis begins when light is absorbed by the green pigment chlorophyll, which occurs only in photosynthetic thylakoid membranes. The absorbed light energy is transferred to a reaction center called Photosystem II (PSII), where electrons are removed from water to release molecular oxygen. The electrons are carried through an electron transport chain in thylakoid membranes to Photosystem I (PSI) to eventually produce reduced compounds (for example, NADPH) that drive carbon fixation reactions. The flow of electrons through this linked set of carriers also transfers protons (H+) from the stroma to the thylakoid lumen, which generates a concentration gradient. These protons can only flow back to the stroma through protein channels within the thylakoid membrane. At the stromal end of the membrane channels is adenosine triphosphate (ATP) synthase, which uses the flow of H+ to drive the synthesis of H+ ATP. ATP is used as the primary energy source for biosynthetic reactions within the cell. The ATP and NADPH created are then used to produce sugars from carbon dioxide.
The most abundant enzyme in the biosphere, ribulose 1,5-bisphosphate carboxylase/oxygenase (rubisco, for short), catalyzes the reaction of carbon dioxide with ribulose 1,5-bisphosphate, a 5-carbon compound, to make glyceraldehyde 3-phosphate and 3-phosphoglycerate. These two 3-carbon compounds enter the reductive pentose-phosphate cycle (also called the Calvin-Benson cycle) and eventually are converted to a 6-carbon sugar, glucose 6-phosphate, the ultimate product. Glucose 6-phosphate is the precursor of many of the storage products in the plant cell, such as starch, sucrose, and lipids, and is also the starting point for biosynthesis of most of the cellular material. All fatty acids and most amino acids used by the cell are also synthesized in the chloroplast.
Rubisco is a large enzyme—containing eight large (molecular weight 52,000) and eight small (molecular weight 14,000) subunits—that is also very sluggish, catalyzing a reaction only three times per second even when saturated with carbon dioxide. The usual concentration of carbon dioxide in the watery cell interior is sufficient for only one-half this rate. Perhaps these are the reasons why plants developed mechanisms to achieve a high concentration of the enzyme in the stroma to catalyze this reaction that is essential to maintenance of life. Approximately two million molecules of rubisco are present in each chloroplast.
The chloroplast is a membrane-bound organelle within a cell that conducts photosynthesis. From the molecular perspective, the chloroplast is very large and contains millions of protein molecules along with vast sheets of membranes. If we imagine an average-sized enzyme molecule to be the size of an automobile, a chloroplast in a plant leaf cell would be about 6 kilometers on its long axis and about 2 kilometers on its short axis. The approximately cube-shaped plant cell, 15 to 20 kilometers per side, would contain fifty to one hundred of these compartments.
The chloroplast is enclosed by two membranes, designated the outer and inner membranes of the chloroplast envelope. About one-half the volume within the chloroplast is occupied by stacks of fifty to one hundred flattened sacs called thylakoids, from the Greek word meaning "like an empty pouch." The thylakoid membrane surrounds the lumen or interior space and is the major membrane of the chloroplast. Groups of thylakoids adhere into stacks called grana. The remaining soluble phase of the chloroplast, outside thylakoids, is the stroma.
A chloroplast processing enzyme functions as the general stromal processing peptidase
A highly specific stromal processing activity is thought to cleave a large diversity of precursors targeted to the chloroplast, removing an N-terminal transit peptide. The identity of this key component of the import machinery has not been unequivocally established.
We have previously characterized a chloroplast processing enzyme (CPE) that cleaves the precursor of the light-harvesting chlorophyll ayb binding protein of photosystem II (LHCPII). Here we report the overexpression of active CPE in Escherichia coli. Examination of the recombinant enzyme in vitro revealed that it cleaves not only preLHCPII, but also the precursors for an array of proteins essential for different reactions and destined for different compartments of the organelle. CPE also processes its own precursor in trans. Neither the recombinant CPE nor the native CPE of chloroplasts process a preLHCPII mutant with an altered cleavage site demonstrating that both forms of the enzyme are sensitive to the same structural modification of the substrate. The transit peptide of the precursor of ferredoxin is released by a single cleavage event and found intact after processing by recombinant CPE and a chloroplast extract as well. These results provide the first direct demonstration that CPE is the general stromal processing peptidase that acts as an endopeptidase. Significantly, recombinant CPE cleaves in the absence of other chloroplast proteins, and this activity depends on metal cations, such as zinc.
STEFAN RICHTER AND GAYLE K. LAMPPA
Definition of Seed is the specialized part of a plant that produces a new plant. It contains an embryo (partly developed plant) that consists of an immature root and stem. A seed also has a supply of stored food and a protective covering.
Seeds are produced by approximately 250,000 kinds of plants. Flowering plants make up the largest group of seed-producing plants. These plants, which botanists call angiosperms, include the vast majority of trees, shrubs, and soft-stemmed plants. Seeds are also produced by about 800 kinds of trees and shrubs called gymnosperms. Most gymnosperms develop cones.
The seeds of different kinds of plants vary greatly in size. The double coconut tree produces the largest seed, which weighs up to 50 pounds (23 kilograms). On the other hand, orchid seeds are so tiny that 800,000 of them weigh no more than an ounce (28 grams). The size of a seed has no relationship to the size of the plant that develops from it. For example, the giant redwood tree grows from a seed only 1/16 inch (1.6 millimeters) long.
The number of seeds produced by an individual plant varies according to the size of the seeds. A coconut tree has only a few large seeds, but an orchid or pigweed plant produces millions of tiny ones.
Definition of Adaptation is a characteristic of an organism that makes it better able to survive and reproduce in its environment. No two organisms of the same species are exactly alike. Every trait, such as size, color, and personality, shows some variation. Additionally, in nature, organisms produce more offspring than can survive. The offspring most likely to survive and reproduce are those with adaptations best suited to the environment. Offspring with variations less suited to the environment do not compete as successfully for food, water, and other necessities. This process of competition, by which those best adapted are most likely to survive and reproduce is called natural selection.
Some forms of life are adapted to living in many different environments. For example, people live in all kinds of climates, ranging from the tropics to the Arctic. Thus, human beings are generalized-that is, the human body has adaptations that enable people to live in widely different environments. But such organisms as mosquitoes and bamboo plants are more specialized. Because of their physical makeup, they can live only in a rather warm, wet climate.
Living things often die when they cannot adapt to a changing environment. Many kinds of plants and animals that once lived on the earth have become extinct. For example, millions of years ago, dinosaurs roamed the earth. But the environment in which they lived changed. The dinosaurs failed to adapt, and they died out.
The word adaptation also refers to the ability of living things to adjust to varying conditions in their environment. If people move to the mountains, their bodies adapt to the lower oxygen supply at high altitudes by making more oxygen-carrying red blood cells. A dog adapts to warm weather by shedding its hair. Adaptations that occur over a relatively short time, particularly because of changes in climate, are often called acclimatizations.
The definition and understanding of the roots of plants are part of plants that are below ground level and is a very important for plants because it functions not only as a buffer and a founding upright stems but also for absorption of water and nutrients.
In the cultivation of forest treatments silviculture should be based on the properties of the roots, because the studies related to the rooting is not an easy thing to do.
The properties of the roots of the trees varies from type to type, from individual to individual in the same type, and even on different roots in the same individual. Root growth extends laterally commonly associated with growing conditions, while the direction of root growth is influenced by the genetic traits.
The point of view of silviculture , the dynamics of the roots is very important due to the absorption of water and nutrients depends on the ability of roots to grow. In the process of germination, root principal emerged and elongated rapidly, as supply of energy and nutrients in the seeds.
Furthermore, the growth rate decreased root and depending on soil conditions. Root development is closely related to soil fertility, the more fertile the soil, the better development of roots.
Definition of environmental pollution is the inclusion of the organism, energy substances, and or other components into the environment or change the order of the environment by human activities or natural processes so that environmental quality decreases to a certain level cause the environment to be less or cease to function as intended. Pollution may arise as a result of human activities or due to natural (eg volcanic eruption, toxic gases).
Environmental science usually discuss pollution caused by human activities, which can be prevented and controlled. Due to human activities, environmental pollution inevitable. Environmental pollution can not be avoided. What you can do is to reduce pollution, pollution control, and increasing public awareness and concern for the environment so as not to contaminate lingkngan. Substances or materials that could cause pollution called pollutants. The terms of a substance called a pollutant if its existence could cause harm to a living creature. For example, the carbon dioxide content of 0.033% in air beneficial for the plant, but if it is higher than 0.033% can give damaging effects.
A substance can be called a pollutant if:
- Excess of the normal.
- Being on time is not right.
- Being in the wrong place.
- Damaging for a while, but when it reacts with another substance does not damage the environment.
- Damaging in a long time. For example, Pb does not damage when low concentrations. However, in the long term, Pb can accumulate in the body to damaging levels.
Definition of Legume is any of the plants that belong to the pea family. They make up the second largest family of flowering plants. The composite family is the largest. Botanists recognize between 14,000 and 17,000 species (kinds) of legumes. The group gets its name from the legumes (seed pods) that the plants bear.
Many legumes are of great economic importance throughout the world. Such legumes as peas, beans, and peanuts are valuable foods. Alfalfa, clover, and vetch are important forage and pasture plants. Other legumes yield medicines, dyes, oils, and timber.
Legumes grow in most parts of the world. They vary widely and may be trees, shrubs, or herbs. Many are climbing plants. The flowers of one large subfamily of legumes look like butterflies. Botanists call this group Papilionoideae, from the Latin word for butterfly. The common sweet pea belongs to this group. The flowers of other legumes may be small and regular. The flowers of still others may be irregular, with spreading petals.
Legumes take nitrogen into their roots from the air. Certain bacteria, called rhizobia, live in nodules (knotlike growths) that form along the roots of the plants. These bacteria take nitrogen from the air and change it into forms that can be used by plants. This characteristic makes leguminous plants valuable in agriculture. Farmers often use them as green manure and as cover crops to improve poor soil.
Nitrogen cycle is the circulation of nitrogen among the atmosphere, the soil and water, and the plants and animals of the earth. All living things require nitrogen, but most organisms cannot use the nitrogen gas that makes up about 78 percent of the atmosphere. They need nitrogen that has combined with certain other elements to form organic compounds. But the supply of this fixed nitrogen is limited, so complex methods of recycling nitrogen have developed in nature.
One part of the nitrogen cycle involves circulation of nitrogen between the soil and living things. After plants and animals die, they undergo decomposition by certain bacteria and fungi. These microorganisms produce ammonia from nitrogen compounds in dead organic matter and in body wastes excreted by animals. Plants absorb some of the ammonia and use it to make proteins and other substances essential to life. The rest of the ammonia is changed into nitrates by nitrifying bacteria. First, nitrifying bacteria called nitrite bacteria convert ammonia into nitrites. Then nitrate bacteria change nitrites into nitrates. Plants absorb most of the nitrates and use them in the same way as ammonia. Animals get nitrogen by eating plants or by feeding on animals that eat plants.
In another part of the cycle, a process called nitrogen fixation constantly puts additional nitrogen into biological circulation. In this process, nitrogen-fixing bacteria in the soil or water, or living within plants such as legumes, convert nitrogen from the atmosphere into nitrogen-containing organic substances.
While nitrogen fixation converts nitrogen from the atmosphere into organic compounds, a series of processes called denitrification returns an approximately equal amount of nitrogen to the atmosphere. Denitrifying bacteria convert nitrates and nitrites in soil into nitrogen gas or into gaseous compounds such as nitrous oxide or nitric oxide. However, fixed nitrogen may circulate many times between organisms and the soil before denitrification returns it to the atmosphere.
Some human activities influence the nitrogen cycle. Industry fixes vast quantities of nitrogen to produce fertilizer, much of which is washed off farmland and into waterways, polluting the water. The combustion of certain fuels produces nitrogen compounds that pollute the air. These compounds may also play a part in the warming of the earth's climate
These landscape and stand level examples, illustrating the functions of some important forest composition and structures, indicate why practices such as clearcutting and elimination of old growth forests are not consistent with maintaining fully functioning forests. If the degradation caused by clearcutting and removal of old growth forests were more evident, people might be more willing to adopt ecologically responsible approaches to timber management.
However, because forests operate on such long timeframes, and because, for millennia, forests have been building biological legacies through many generations of trees that have lived and died, human activities that remove composition and structures do not immediately appear to be as damaging as they actually are. However, as timber managers continue to degrade composition and structures of forests, from landscape to stand levels, damage to forest functioning becomes cumulative. Eventually this approach leads to degraded ecosystems, which provide few ecological functions, compared to the fully functioning forests they replaced. Because forest degradation occurs relatively slowly, successive generations of human beings inherit degraded forests which they assume to be natural, “healthy” ecosystems. In other words, we don’t live long enough to see the results of our mistakes.
An ecosystem-based approach attempts to avoid loss of forest functioning by maintaining forest composition and structures from the smallest soil bacteria to the landscape patterns of a large forest watershed. We may not understand the functions of particular forest composition and structures; nevertheless, an ecologically responsible approach protects all composition and structures. When parts of the forest are altered during activities such as ecologically responsible timber management or tourism, provisions for the replacement of forest composition and structures are built into ecologically responsible plans and activities.
As well as providing for the protection and maintenance of forest functioning, an ecosystem-based approach fosters the development of diverse, sustainable human economies. Because an ecosystem-based approach creates the least modification to forest ecosystem composition and structures, it provides for the largest diversity of compatible forest uses. In other words, by maintaining trees on the sites where we practice timber management and by ensuring that ecologically viable old growth stands are found in each landscape, we provide an environment where the broadest spectrum of uses, from adventure tourism to timber extraction, can coexist. Such a range of activities is not possible where conventional timber management systems, such as clearcuts and tree plantations, are employed.
From a timber standpoint, because ecologically responsible timber management produces steady supplies of mature wood, the long-term economic benefits exceed those of conventional timber management practices. Mature wood—long-fibred and strong—is superior for many uses, from structural materials and pulp to furniture and fine cabinets. In comparison, short-fibred, juvenile wood is not as strong and will warp and twist easily. Mature wood is produced when the cambium layer (the single layer of cells between the wood and the bark) divides around dead branches or no branches. Obviously, increasing amounts of mature wood are produced as a tree gets larger and older.
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