Yogy's biology

01 Reproduction in Lower and Higher Plants - part 07 - Pollen - Pistil Interaction and Double Fertilization Pollen - Pistil Interaction :  It is the interaction of pollen grains with sporophytic tissue (stigma).  It  begins with pollination  and  ends with fertilization.  All the events from the deposition of pollen grain on stigma to the  entry of pollen tube in the ovule (synergid)  are referred as  pollen - pistil interaction.  Pollination does not guarantee the transfer of right type of pollen, often wrong type also land on stigma.  The pistil has the ability to recognise and accept the  right or compatible pollen  of the same species. Thus wrong type of pollen is discarded by pistil.  Compatibility and incompatibility of the pollen-pistil is determined by  special proteins.  This process involves pollen recognition followed by promotion or inhibition of pollen.  The stigmatic surface of flower refuse other wrong type or incompatible pollen grains.  A physiologial mechanism operate

01 Reproduction in Lower and Higher Plants - part 04 - Structure of Anatropous ovule and Megasporogenesis Structure of Anatropous ovule :  Each ovule develops inside the ovary and is attached to the  placenta  by a small stalk called  funiculus .  The place of attachment of funiculus with the main body of ovule, is called  hilum .  In angiosperms, the most common type of ovule is  anatropous  in which micropyle is directed downwards and is present adjacent to the funiculus (funicle).  The ovule consists of central parenchymatous tissue, the  nucellus  which is surrounded usually by two protective coverings called  integuments viz.  Outer and an inner integument. A narrow opening at the apex of the ovule is called  micropyle .  Chalaza  is the base of ovule directly opposite to micropyle.  Embryo sac  (female gametophyte) is oval multicellular structure embedded in the nucellus. Megasporogenesis :  It is the process of formation of  haploid megaspores  from diploid megaspore mother cell

01 Reproduction in Lower and Higher Plants - part 03 - Microsporogenesis Microsporogenesis :  Each microspore mother cell divides meiotically to form  tetrad  of haploid microspores (pollen grains).  Structure of microspore :  Typical pollen grain is a  non-motile, haploid, unicellular body with single nucleus. It is surrounded by a two layered wall called  sporoderm .  The outer layer  exine  is thick and made up of complex, non-biodegradable, substance called sporopollenin.  It may be smooth or with a sculptured pattern (characteristic of the species). It is resistant to chemicals. At some places exine is very thin showing thin areas known as  germ-pores.  These are meant for the growth of emerging pollen tube during germination of pollen grain.  The inner wall layer,  intine  consists of  cellulose and pectin. Always Remember : ·  Pollen viability  (viability is the functional ablity of pollen grain to germinate to develop male gametophyte) depends upon environmental conditions of t

01 Reproduction in Lower and Higher Plants - part 02 - Sexual Reproduction, T. S. of Anther Sexual Reproduction : It involves  fusion of two compatible gametes or sex cells.  All organisms reach to the maturity in their life before they can reproduce sexually.  In plants, the end of juvenile or vegetative phase marks the begining of the  reproductive phase  and can be seen easily in the  higher plants  at the time of flowering.  The flower  is specialized reproductive structure of a plant in which sexual reproduction takes place.  The function of flower is to produce  haploid gametes  and to ensure that fertilization will take place.  Typical flower consists of  four different whorls  viz. -  Calyx Corolla  Androecium and  Gynoecium.   Sexual reproduction involves two major events viz. -  Meiosis and fusion of gametes to form diploid zygote and  Production of genetically dissimilar offsprings.   Variations  are useful from the point of view of the survival and the evolution of species,

01 Reproduction in Lower and Higher Plants - part 01 - Asexual Reproduction  Reproduction : It  is the production of young ones like parents.  Essential process as it leads to  continuation of species as well as to maintain the continuity of life.  Each organism has its own particular method of reproduction.  All these methods generally fall into two categories :  Asexual reproduction  Sexual reproduction. 1. Asexual Reproduction :  Asexual reproduction  does not involve fusion  of two compatible gametes or sex cells.  It is the process resulting in the production of  genetically identical progeny from a single organism and inherits the genes of the parent.  Such morphologically and genetically identical individuals are called  clones.  Organisms choose to reproduce asexually by different modes or ways:  A. Fragmentation :  Multicellular organisms can break into fragments due to one or the other reasons.  e.g.  Spirogyra.  These  fragments  grow into new individuals. B. Budding :  It i

                          Index 1} Reproduction in lower & higher plants. 2} Reproduction in lower & higher animals. 3} Inheritance & Variation. 4} Molecular basis of inheritance. 5} Origin of evaluation of life. 6} Plant water relation. 7} plant growth & mineral nutrition. 8} Respiration & Circulation. 9} Control & co- ordination. 10}Human health & diseases. 11}Enhancement of food production. 12}Biotechnology. 13}Organisms & population. 14} Ecosystem & Energy flow. 15} Biodiversity, conservation & environmental issues.