01}Reproduction in lower & higher plants part 2 sexual reproduction.

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. - 
  1. Calyx
  2. Corolla 
  3. Androecium and 
  4. Gynoecium. 
  • Sexual reproduction involves two major events viz. - 
  1. Meiosis and fusion of gametes to form diploid zygote and 
  2. Production of genetically dissimilar offsprings. 
  • Variations are useful from the point of view of the survival and the evolution of species, over the time.
  • Sexual reproduction is characterised by  - 
  1. fusion of the male and female gametes (fertilization)
  2. Formation of zygote and 
  3. Embryogenesis. 
  • Sequential events that occur in sexual reproduction are grouped into three distinct stages viz,
  1. Pre-fertilization
  2. Fertilization and the 
  3. Post-fertilization.
Always Remember :
  • Diploid sporophyte is the predominant plant body in all angiosperms, where meiosis takes place to produce haploid spores that form gametophyte.  
  • Gametophytes are considerably reduced and develop within the flower. 
  • They produce gametes.
  • The male reproductive whorl of flower is called androecium. 
  • Individual member of androecium, is called stamen. 
  • Stamen consists of -  
  1. Filament
  2. Connective and 
  3. Anther. 


Structure of Anther : 

  • An immature stage of anther is represented by group ofparenchymatous tissue surrounded by single layered epidermis. 
  • Anther is generally dithecous (having two lobes) and tetrasporongiate. 
  • Each monothecous anther contains two pollen sacs. 
  • In dithecous anther four pollen sacs are present. Therefore, it is tetrasporongiate. 
  • The heterogenesity (differenciation) arises when some hypodermal cells get transformed into archesporial cells.



T. S. of Anther : 

  • The archesporial cell divides into an inner sporogenous cell and outer primary parietal cell. 
  • Sporogenous cell forms sporogenous tissue. 
  • Each cell of sporogenous tissue is capable of giving rise to a microspore tetrad. 
  • Parietal cell undergoes divisions to form anther wall layers. 
  • The wall of mature anther consists of four layers. 
  1. Epidermis
  2. Endothecium
  3. Middle layer
  4. Tapetum
  • Epidermis is the outermost protective layer made up of tabular (flattened) cells. 
  • Endothecium is sub-epidermal layer made up of radially elongated cells with fibrous thickenings. 
  • Inner to endothecium is middle layer made up of thin walled cells (1-2 layered), which may disintegrate in mature anther. 
  • Tapetum is the inner most nutritive layer of anther wall. It immediately encloses the sporogenous tissue (microspore mother cells)

Comments

Post a Comment

Popular posts from this blog

6. Biomolecules - part 01 - Carbohydrates

Image
  6. Biomolecules - part 01 - Carbohydrates Introduction : Our planet is having a wide diversity of living organisms that are classified as - unicellular  (consisting of a single cell; including bacteria and yeast) or  multicellular  having many cells (e.g. plants and animals).  living organisms have cell as the basic structural and functional unit.  The cells have protoplasm containing numerous chemical molecules, the biomolecules. Biochemistry  : Biochemistry is  biological chemistry  that provides us the idea of the chemistry of living organisms and molecular basis for changes taking place in plants, animals and microbial cells.  It develops the foundation or understanding  all biological processes  and communication within and between cells as well as chemical basis of inheritance and diseases in animals and plants. Chemical analysis of all living organisms indicates presence of the most common elements like  carbon, h...
Read more

6. Biomolecules - part 02 - Lipids

Image
  6. Biomolecules - part 02 - Lipids B. Lipids : These are group of substances with greasy consistency with  long hydrocarbon chain containing carbon, hydrogen and oxygen. In lipids, hydrogen to oxygen ratio is  greater than 2:1  (in carbohydrates it is always 2:1). Lipid is a broader term used for fatty acids and their derivatives.  They are soluble in organic solvents (non-polar solvents).  Fatty acids are organic acids which are composed of hydrocarbon chain  ending in carboxyl group (-COOH).  They can be  saturated fatty acids  with no double bonds between the carbon atoms of the hydrocarbon chain.  Palmitic and stearic acids  found in all animal and plant fats are examples of saturated fatty acids. Unsaturated Fatty Acids  are with one or more double bonds between the carbon atoms of the hydrocarbon chain.  Oleic acid  found in nearly all fats and  linoleic acid  found in many seed oils are example...
Read more

6. Biomolecules - part 05 - Enzymes

Image
  6. Biomolecules - part 05 - Enzymes Enzymes : Thousands of different chemical reactions take place automatically at a given time in a tiny living cell. The reactions take place at the body temperature.  If these enzymes were not present in the cell, either the reactions would not occur or if they occur they would occur at a  very very slow rate . Know the scientists : German chemist  Edward Buchner  discovered enzymes by accident.  Buchner discovered that living cells were not necessary but that  yeast  extract could bring about fermentation.  He then coined the term Enzyme (Gk. En = in, zyma = yeast i.e. in yeast). This term is now commonly used for all biocatalysts. Each enzyme catalyzes a small number of reactions, specifically perhaps only one. Substrate :  The substance upon which an enzyme acts is termed as the substrate.  Endo-enzymes :  The enzymes which act within the cell in which they are synthesizedare known as en...
Read more