Hydroponics

Categories Agriculture disciplines economic botany and plant uses gardening water-related life Literally water culture, hydroponics originally referred to the growth of plants in a liquid medium. It now applies to all systems used to grow plants in nutrient solutions with or without the addition of synthetic soil for mechanical support. Hydroponics has become an important method of crop production with the increase in the number of commercial greenhouse operations. Greenhouses are utilized in...

Types of Systems

The four most commonly used hydroponic systems are sand-culture systems, aggregate systems, nutrient film techniques, and floating systems. While these systems are similar in their use of nutrient solutions, they vary in both the presence and type of supporting medium and in the frequency of nutrient application. In sand culture, coarse sand is used in containers or spread over a greenhouse floor or bed, on top of a recirculating drain system. A drip irrigation system is used to apply nutrient...

Habitat Loss

By far the most significant threat to plant species is habitat loss or destruction. Habitat loss can occur because of resource harvesting for food, medicine, and other products, deforestation, and the conversion of wilderness for agricultural, industrial, or urban uses. Wood consumption and tree clearing for agriculture and development threaten the world's forests, especially the tropical forests, which may disappear by the mid-twenty-first century if sufficient preventive action is not taken....

Nitrogen Fertilizer from Legumes

The importance of legumes as a green fertilizer has been recognized for centuries. As early as the third century b.c.e., the Greek philosopher and scientist Theophrastus recommended that beans should be planted to enrich farm soils. Then, as now, a common agricultural practice was to rotate cereal crops, such as corn or wheat, with legumi nous crops, such as clover or alfalfa (Medicago sativa). The legumes used as green fertilizer not only contribute nitrogen to the soil but also can be...

Fighting Asthma Gastrointestinal Disorders Parasites

The major anti-asthma drugs come from ephed-rine, extracted from the ma huang plant (Ephedra sinaica), and its structural derivatives. Plant-derived drugs that affect the gastrointestinal tract include castor oil, senna, and aloes as laxatives, opiate alkaloids as antidiarrheals, and ipecac from Cephaelis acuminata as an emetic. The most useful plant-derived antiparasitic agent is quinine, derived from the bark of the chincona plant (Chincona succirubra). Quinine has been used to control...

Hardyweinberg Theorem

The Hardy-Weinberg theorem is the principal that, in the absence of external pressures for change, the genetic makeup of an ideal population of randomly mating, sexually reproducing diploid organisms will remain the same, at what is called Hardy-Weinberg equilibrium. Population genetics is the branch of genetics that studies the behavior of genes in populations. The two main subfields of population genetics are theoretical or mathematical population genetics, which uses formal analysis of the...

Isoflavonoids as Phytoestrogens

Isoflavonoids are a type of secondary metabolite and are found almost exclusively in the legume pea family of plants. They are known to function in plant defense. They have been shown to deter herbivores and also to facilitate a plant's defense response to pathogen attack. Interestingly, some isoflavonoids have chemical structures that, in overall size, shape, and polarity, resemble estrogens. The resemblance includes the flatness, or planarity, of the molecules and the positions and...

Simple and Compound Leaves

Simple Leaf And Compound Leaf

To discriminate between simple and compound leaves, one may locate the axillary bud at the base of a leaf petiole in the node region of the stem. This area signifies the basal end of the entire leaf in both simple and compound leaves. A simple leaf has only one blade, or lamina, associated with it. There are no leaflets. In singly compound leaves, the leaf is sudivided into leaflets, which attach to a central rachis axis . The rachis is continuous with the petiole, which attaches to the node...

List Of Illustrations Charts And Tables

Acid Precipitation pH Scale bar Africa, Desertification of African Countries with More than 15 Percent Arable Land, Leading Agricultural Crops of table . . . I-15 African Rain Forests Africa's Agricultural Products Air Pollutant Emissions by Pollutant and Source, 1998 table I-45 Algae, Classification of Algae, Types of Angiosperm, Life Cycle of an Angiosperms and Continental Drift Antibiotic Resistance, The Growth of Ants and Acacias Asian Countries with More than 15 Percent Arable Land,...

Germination

What Walnut Plumule

The seeds from the previous year's crop of summer annuals wait to germinate in spring. Seeds of many species will germinate when soil temperatures reach a threshold constant. Others require daily fluctuations of temperature, waiting until the daily fluctuation becomes sufficiently large. Seeds of most species require a light stimulus to germinate. The light is absorbed by the pigment phytochrome, which is positioned in the cotyledons of the embryo. Phytochrome acts as a shade detec tor. White...

Energy Flow In Plant Cells

Energy Flow Marine

Categories Cellular biology photosynthesis and respiration physiology 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...

Garden Plants Shrubs

Categories Angiosperms economic botany and plant uses gardening Shrubs are perennial, woody plants that have multiple ecological uses and are economically important for a variety of landscape purposes. Like trees, the shrubs consist of both primary and secondary cambium cells that ultimately form wood or bark , but unlike trees, shrubs typically have multiple stems and are somewhat shorter in height. Native and nonnative shrubs have many uses, both in private gardens and as elements in...