How plants have adapted or become acclimated to shade.
How plants have adapted or become acclimated to shade. Plants which grow in shady conditions have altered structurally and biochemically in order to cope with the low levels of light and harvest it efficiently. Low level light is rich in far-red light and plants have also adapted to make use of this. Shade plants have also had to make adjustments to cope with sudden high levels of light, for example during sunflecks. Whilst some plants show physiological adaptation, many changes are the result of genetic evolution. * Leaves are thinner with a shallow layer of palisade mesophyll cells and a patchy spongy mesophyll with air spaces (fig 1.). This uses less energy and resources to construct. Many shade plants (such as ferns) do not produce flowers for the same reason. * Shade leaves have more chlorophyll in the antenna systems to feed more energy to the reaction centres. There is also an increase in the number of reaction centres. * Shade light contains more light in the far-red range. The reaction centre of photosystem II (PSII) absorbs more light from the far-red range than photosystem I (PSI); hence there is a greater proportion of PSII to PSI. This is achieved by the presence of wide grana with larger numbers of stacked thylakoids (figure 2.). This enables the photosystems to be excited equally in far-red light. * Plants which grow in shade are often exposed to periods
Cerealor Sugar Case Studies.
Title: Cerealor Sugar Case Studies - Rice Date: 21.11.01 Botany Rice is a semiaquatic, annual grass of the family Graminae, genus Oryza. It has a panicle inflorescence with one floret per spikelet (Marshall & Wadsworth., 1993). Furthermore, it has a perfect flower (both male and female), which consists of two interlocking hulls, six anthers and a single ovary. Most importantly, rice is naturally self-pollinating (Marshall & Wadsworth., 1993). Rice growers in some countries such as USA use pure line cultivars whereas most of them in China use hybridisation. Taxonomy Cultivated rice is referring to either Oryza sativa L. or Oryza glaberrima Steud (Marshall & Wadsworth., 1993). However, O. sativa is the predominant species and O. glaberrima is grown only in Africa on a limited scale (Marshall & Wadsworth., 1993). Oryza sativa is a tremendously variable species whish has worldwide distribution. Kato et al. (1928) classified these varieties into indica, the tropical race and japonica types, the temperate race. However, Morinaga (1954) proposed another group called javanicas. Several authors have ranked javanicas at the same taxonomic level as indicas and japonicas. (Singh et al, 2000) Domestication The date and geographical location of the first cultivated rice (Oryza sativa L.) is unclear. Nonetheless, domestication of
The combination of constant warmth and abundant moisture of the tropical regions demonstrates a successful environment for many plants and animals.
Sex and the tropics The tropical forests have their origins almost 200 million years ago, during the early days of dinosaurs. The continents were huddled together in a giant super-continent called Pangea. Gradually the Pangea started breaking off giving rise to separate continents. Through the process of division and development of the territories the ecosystem also took its course of progression. Thus the forest monkeys that evolved in the old and new worlds, while coming from the same ancient stock and living similar lives are now anatomically quite distinct. Similarly, lemurs survived only on Madagascar, partly because the island had no large predators. We also examine the evidence that Cactoblastis, cactus moth, has been rather successful in Australia, yet caused so many problems in North America. To capitalise the response we must note that Australia has no native cactus species, and so far the moth has not attacked any other type of plant. In areas where there are other native species of Opuntia, the exotic moth is destructive and unfavourable. Classes of organisms introduced to regions beyond their original ranges are known to achieve much greater population densities in comparison with their origins. The pending explanation explores the fact of no predators occupying the newly attained territory. Although the motion carries then the introduction of predators and