• Cell biology

    THE CELL AND CELL THEORY

    Landmarks in the study of a cell Soon after Anton Van Leeuwenhoek invented the microscope, Robert Hooke in 1665 observed a piece of cork under the microscope and found it to be made of small compartments which he called “cells” (Latin cell = small room). In 1672, Leeuwenhoek observed bacteria, sperms and red blood corpuscles, all of which were cells. Much later, in 1831, Robert Brown, an Englishman observed that all cells had a centrally positioned body which he termed the nucleus. The cell theory In 1838 M.J. Schleiden and Theodore Schwann formulated the “cell theory.” Which maintains that: all organisms are composed of cells. cell is the structural and…

  • Biochemistry

    COMPONENTS OF THE CELL

    The major components of the cell are (1) cell membrane, (2) cytoplasm, and (3) nucleus. Cell membrane (Plasma membrane) Each cell has a limiting boundary, the cell membrane, plasma membrane or plasmalemma. It is a living membrane, outermost in animal cells but internal to cell wall in plant cells. It is flexible and can fold in (as in food vacuoles of Amoeba) or fold out (as in the formation of pseudopodia of Amoeba) The plasma membrane is made of proteins and lipids and several models were of Life proposed regarding the arrangement of proteins and lipids. The fluid mosaic model proposed by Singer and Nicholson (1972) is widely accepted. According to…

  • Biochemistry

    CELLULAR RESPIRATION

    Cellular respiration is the set of the metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate (ATP) and then release waste products. The reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy in the process as weak so-called “high-energy” bonds are replaced by stronger bonds in the products. Respiration is one of the key ways a cell gains useful energy to fuel cellular activity. Cellular respiration is considered an exothermic redox reaction. The overall reaction is broken into many smaller ones when it occurs in the body, most of which are redox…

  • Cell biology

    TRANSPORT ACROSS CELL MEMBRANE

    Two types of transport process occur across the membrane. Non-mediated transport Mediated transport Non-mediated transport occurs through the simple diffusion process and the driving force for the transport of a substance through a medium depends on its chemical potential gradient. Whereas mediated transport requires specific carrier proteins. Thus, the substance diffuses in the direction that eliminates its concentration gradient; at a rate proportional to the magnitude of this gradient and also depends on its solubility in the membrane’s non-polar core. Mediated transport is classified into two categories depending on the thermodynamics of the system: Passive-mediated transport or facilitated diffusion: In this type of process a specific molecule flows from high…

  • Botony

    TRANSPIRATION

    Although large quantities of water are absorbed by the plant from the soil only a small amount of it is utilized. The excess of water is lost from the aerial parts of plants in the form of water vapours. This is called as transpiration. Transpiration is of three types 1. Stomatal transpiration Most of the transpiration takes place through stomata. Stomata are usually confined in more numbers on the lower sides of the leaves. In monocots. Eg. Grasses they are equally distributed on both sides. While in aquatic plants with floating leaves they are present on the upper surface. 2. Cuticular transpiration The cuticle is impervious to water, even though,…

  • Botony

    ROOT SYSTEM

    The root system is the descending (growing downwards) portion of the plant axis. When a seed germinates, radicle is the first organ to come out. It elongates to form primary or the tap root. It gives off lateral branches (secondary and tertiary roots) and thus forms the root system. It branches through large and deep areas in the soil and anchors the plant very firmly. It also plays another vital role in absorbing water and mineral salts from the soil and transporting them upwards. CHARACTERISTICS OF ROOTS Non-green due to absence of chlorophyll Not divided into nodes and internodesA Absence of leaves and buds Positively geotropic (grow towards gravity) Positively…