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


  One of the most distinguished botanists not only of India but of the entire world
• Panchanan Maheshwari was born in November 1904 in Jaipur (Rajasthan)
• Panchanan Maheshwari moved to Allahabad for higher education where he obtained his D.Sc.
• During his college days, Panchanan Maheshwari was inspired by Dr W. Dudgeon, an American missionary teacher, to develop interest in Botany and especially morphology
• Panchanan Maheshwari worked on embryological aspects and popularised the use of embryological characters in taxonomy
• Panchanan Maheshwari established the Department of Botany, University of Delhi as an important centre of research in embryology and tissue culture
• Panchanan Maheshwari emphasised the need for initiation of work on artificial culture of immature embryos
• Panchanan Maheshwari's work on test tube fertilisation and intra-ovarian pollination won worldwide acclaim
• Panchanan Maheshwari was honoured with fellowship of Royal Society of London (FRS), Indian National Science Academy and several other institutions of excellence
• Panchanan Maheshwari 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
• A look at the diversity of structures of the inflorescences, flowers and floral parts, shows an amazing range of adaptations to ensure formation of the end products of sexual reproduction, the fruits and seeds
• Flowers are objects of aesthetic, ornamental, social, religious and cultural value
• Flowers have always been used as symbols for conveying important human feelings such as love, affection, happiness, grief, mourning, etc.
• Floriculture refers to the cultivation of flowering and ornamental plants for commercial purposes
• Much before the actual flower is seen on a plant, the decision that the plant is going to flower has taken place
• Several hormonal and structural changes are initiated which lead to the differentiation and further development of the floral primordium
• Inflorescences are formed which bear the floral buds and then the flowers
• In the flower the male and female reproductive structures, the androecium and the gynoecium differentiate and develop
• The androecium consists of a whorl of stamens representing the male reproductive organ and the gynoecium represents the female reproductive organ
• Stamen


  The long and slender stalk called the filament, and the terminal generally bilobed structure called the anther
• The proximal end of the filament is attached to the thalamus or the petal of the flower
• The number and length of stamens are variable in flowers of different species
• A typical angiosperm anther is bilobed with each lobe having two theca, i.e., they are dithecous
• The anther is a four-sided (tetragonal) structure consisting of four microsporangia located at the corners, two in each lobe
• Microsporangium


  The pollen sacs where pollen grains develop
• Microsporangium wall layers


  • Epidermis, endothecium, middle layers and the tapetum
• Tapetum


  The innermost wall layer that nourishes the developing pollen grains
• Microsporogenesis


  The process of formation of microspores from a pollen mother cell (PMC) through meiosis
• Microspore tetrad


  The cluster of four cells formed after meiosis of the pollen mother cell
• Pollen grain


  The male gametophyte