Sexual reproduction

• Biology in essence is the story of life on earth
• While individual organisms die without fail, species continue to live through millions of years unless threatened by natural or anthropogenic extinction
• Reproduction


  A vital process without which species cannot survive for long
• Sexual mode of reproduction


  Enables creation of new variants, so that survival advantage is enhanced
• This unit explains the details of reproductive processes in flowering plants and humans as easy to relate representative examples
• A related perspective on human reproductive health and how reproductive ill health can be avoided is also presented to complete our understanding of biology of reproduction
• Chapter 1: Sexual Reproduction in Flowering Plants
• Chapter 2: Human Reproduction
• Chapter 3: Reproductive Health
• Panchanan Maheshwari (1904-1966) was a distinguished botanist from India
• He moved to Allahabad for higher education where he obtained his D.Sc.
• He was inspired by Dr W. Dudgeon, an American missionary teacher, to develop interest in Botany and especially morphology
• He worked on embryological aspects and popularised the use of embryological characters in taxonomy
• He established the Department of Botany, University of Delhi as an important centre of research in embryology and tissue culture
• He emphasised the need for initiation of work on artificial culture of immature embryos
• His work on test tube fertilisation and intra-ovarian pollination won worldwide acclaim
• He was honoured with fellowship of Royal Society of London (FRS), Indian National Science Academy and several other institutions of excellence
• He encouraged general education and made a significant contribution to school education by his leadership in bringing out the very first textbooks of Biology for Higher Secondary Schools published by NCERT in 1964
• Flowers do not exist only for us to be used for our own selfishness. All flowering plants show sexual reproduction
• In this chapter, let us understand the morphology, structure and the processes of sexual reproduction in flowering plants (angiosperms)
• Flower


  A fascinating organ of angiosperms
• Flowers

  • Objects of aesthetic, ornamental, social, religious and cultural value
  • Used as symbols for conveying important human feelings such as love, affection, happiness, grief, mourning, etc.
• Flowers of ornamental value commonly cultivated at homes and in gardens


  • List at least five
• Flowers used in social and cultural celebrations in your family

  • Find out the names of five
• Floriculture


  Refers to the cultivation of flowering and ornamental plants
• In the flower the male and female reproductive structures, the androecium and the gynoecium differentiate and develop
• Stamen


  The male reproductive organ consisting of a filament and an anther
• Anther

  • Bilobed structure with each lobe having two theca (dithecous)
  • Consists of four microsporangia located at the corners, two in each lobe
• Microsporogenesis


  Formation of microspores from a pollen mother cell (PMC) through meiosis
• Pollen grain


  Represents the male gametophyte
• Pollen grain

  • Generally spherical, 25-50 micrometers in diameter
  • Has a prominent two-layered wall - the hard outer exine made of sporopollenin and the inner intine made of cellulose and pectin
  • Contains a vegetative cell and a generative cell
• Pollen grains of many species cause severe allergies and bronchial afflictions in some people often leading to chronic respiratory disorders
• Gynoecium


  The female reproductive part of the flower consisting of one or more pistils
• Pistil


  Consists of the stigma, style and ovary
• Ovule


  The megasporangium arising from the placenta inside the ovary
• Locule

  Ovarian cavity
• The placenta is located inside the ovarian cavity
• Pollen grains are rich in nutrients
• Pollen consumption has been claimed to increase the performance of athletes and race horses
• Arising from the placenta are the megasporangia, commonly called ovules