Biological World

  Scientific Name :Pontederia crassipes (formerly Eichhornia crassipes) Family:  Pontederiaceae

 

  Physalis minima  Family: Solanaceae

Make two qualitative and two quantitative data sheets on forest cover from the supplied table of the next page . [ Quantitative data sheet ( Quantitative characters : Habit and Colour of Flower - 3 ; Qualitative data sheet ( Qualitative characters : Frequency and Density -5 ; ] [ গুণগত তথ্য তালিকা ( গুণগত বৈশিষ্ট্যাবলি, গাছের প্রকৃতি ও ফুলের রং ) - 3 , পরিমাণগত তথ্য তালিকা ( পরিমাণগত বৈশিষ্ট্যাবলি : উদ্ভিদ প্রজাতির সংঘটন ও ঘনত্ব ) -5 )

 

  Flip flop movement : The flip-flop movement in cell membranes refers to the translocation of phospholipids between the inner and outer leaflets of the lipid bilayer. This process is essential for maintaining the structure and functionality of the cell membrane. Factors Affecting Flip-Flop Movement (a) Lipid Structure and Geometry : 1. The rate of flip-flop movement is influenced by the structure and geometry of the lipid molecules. 2. Cylindrical lipids (e.g., phosphatidylcholine) can undergo faster flip-flop compared to cone-shaped lipids (e.g., phosphatidylethanolamine). (b) Membrane Proteins : 1. The presence of membrane proteins can facilitate or inhibit the flip-flop movement of lipids. 2. Certain proteins, called flippases and scramblases, can actively transport lipids from one leaflet to the other. (c) Lipid Saturation : 1. Unsaturated lipids with cis double bonds tend to undergo slower flip-flop compared to saturated lipids due to their rigid structur...

   Structure of cell membrane based on fluid mosaic model The cell membrane, also known as the plasma membrane, is a crucial structure that surrounds and encloses the contents of a cell. It acts as a selective barrier, regulating the movement of molecules in and out of the cell, and plays a vital role in various cellular processes. The fluid mosaic model, proposed by Singer and Nicolson in 1972, provides a comprehensive explanation for the structure and dynamics of the cell membrane. The fluid mosaic model is a scientific explanation for the structure and function of cell membranes, describing the plasma membrane as a dynamic and flexible arrangement of various molecules. Here are the key components and features of the fluid mosaic model: Basic Structure and Components of Cell membrane The model identifies the cell membrane as a phospholipid bilayer, which is two molecules thick. Phospholipids are amphipathic molecules with a hydrophilic (water-attracting) head and a hyd...

The Vibrant and Versatile Rhododendron Rhododendrons are a beloved group of flowering shrubs and trees known for their spectacular clusters of showy blooms in a vast array of colors. These ornamental plants belong to the genus Rhododendron, which comprises over 1,000 species found across Asia, Europe, and North America.  Native Habitats and Growth Habits While rhododendron species can be found around the world, their native habitats are concentrated in alpine regions of Asia, such as the Himalayas, as well as areas with milder maritime climates like the Pacific Northwest. They exhibit a diverse range of growth habits from compact shrubs to towering trees reaching up to 100 feet tall. Many species are evergreen, retaining their leathery leaves year-round. Floral Extravagance  The true glory of rhododendrons lies in their magnificent flower trusses. In spring and early summer, they burst into bloom with clusters of funnel-shaped flowers in shades spanning reds, pinks, purples, w...

 

 

M.J. Schleiden, a German botanist in 1838 stated that "All plants are formed of one or more cells" . Theodre Schwann, a German Zoologist in 1839 stated that "All animals are fomed of cells, have nuclei and were enclosed by thin cell membrane instead of thick cell wall as found in plant cells " . Schwann described the cell as membrane bound, nucleus containing structure.  They have published some basic properties of cells, which collectively appreciated as Cell Theory.  Basic Postulates of Cell Theory: The various points of cell theory are : 1.Each cell is made of a small mass of protoplasm having a nucleus and bounded by a cell membrane with or without cell wall.  2. All cells are basically alike in structure & metabolism. 3.Organisms are composed of cells and their products.  4. The functions of an organisms are due to activities and interactions of its cells . Drawbacks of Cell Theory: Important drawbacks to cell theory are given below : 1. Viruses are also ci...