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Improper functioning of immune system can cause comfort, disease or even death. These disorders may involve: Figure 1 1. Hypersensitivity or Allergy: Allergy means inappropriate and excessive response to common antigens. Substances causing allergic reaction are called allergens. The common allergens are dust, pollens, mould, spores, fabrics, feathers, fur, plants, bacteria, foods, heat, cold, sunlight. Parthenium flower is a common allergen in India. Allergy mostly affects the skin and the mucous membrane. Hay fever affects the mucous membranes of the nose, eyes and upper respiratory tracts. In asthma, the lower portions of the respiratory system are severely affected. In eczema , the skin becomes red, followed by the appearance of minute blisters. During allergic reaction there is increased release of histamine from mast cells. It causes marked dilation of all the peripheral blood vessels and the capillaries become highly permeable so that large amounts o

Water absorbing structure of the plant is root hair zone . Root hair is tubular prolongation of epiblema cells . Root hairs are unicellular, short lived and arranged in an acropetal manner. Root hairs are found in zone of cell maturation. During transplantation the root hairs are removed, that is why, the plant remains wilted in the new habitat . The cell wall of the hair is made up of two layers. The outside wall is of pectin which dissolves in water, so that root hair surface becomes slimy and sticky. The inner wall is made up of cellulose. They are about 10 micro m. There OP is higher ( 3-8 atm ) as compared to soil solution ( less than 1 atm ) . Many forest trees, shrubs and some conifers have scantly root hairs so they make association with the fungi, called mycorrhiza . Orchid roots have a specific type of tissue for absorbing environmental moisture; this tissue is called velaman tissue. Movement of water from root hair cell to xylem may occour by two possible pa

Traditionally plant kingdom has been divided into two sub-kingdoms named as PHANEROGAMAE and CRYPTOGAMAE. (a) CRYPTOGAMAE (phaneros-visible, gamos-marriage): All flowering plants which bear seeds are included in this group. They are also known as spermatophytes (sperma-seed, phyton- plant), since they produce seeds. These seed bearing plants are further divided into divisons gymnospermae and angiospermae. Gymnosperms have naked ovules or seeds. The angiosperms (covered seed) include all the flowering plants which produce seed and have ovules in ovary or fruit . (b) PHANEROGAMAE (kryptos-concealed, gamos-marriage): All non flowering plants such a algae, fungi, lichen, moses and ferns are included in this sub-kingdom. The cryptogams are further classified into three divisions- THALLOPHYTA, BRYOPHTA and PTERIDOPHYTA. A. Early attempts for classification Aristole and other Greek philosophers divided living organisms into two groups: plants and

  (1) Two Kingdom Classification: It was given by Linnaeus . Traditionally all the organisms of the world were divided into two kingdoms - the animal kingdom ( Animalia ) and the plant kingdom ( Plantae ). The major creation of classification was the presence or absence of cell wall. Other Criteria’s were locomotion, modes of nutrition to external stimuli etc. Short comings of two-kingdom system of classification: Two-kingdom system of classification presented too many inconsistencies. This system did not distinguish between the eukaryotes and prokaryotes , unicelled and multicelled organisms and photosynthetic and non-photosynthetic organisms. There are few organisms like Chlamydomonas , Euglena and the slime moulds which have been claimed by both zoologists and botanists (organisms which share characteristics of both animals and plants). Since there are certain organisms that do not fall naturally into either plant or animal kingdom, it was proposed that a new kingdom