viruses are classified below the cellular level of biological organization

>RNA cannot undergo replication and have to be synthesised only from DNA. Enzymes are basically proteins that function as biological catalysts. Enzymes carry on their catalytic action by lowering the activation energy required for a reaction to proceed. Sometimes an enzyme may have non-pr..

fig. 14.4 - Levels of Structure in Proteins If the helical polypeptide molecule is folded on itself assuming a complex but specific structure such as spherical or rod like, then it is called tertiary structure. e.g., globulins of blood. Some proteins have two or more polypeptides, each wi..

Growth at the cellular level involves four stages Cell expansion: an increase in the size of the cell due to formation of new protoplasm. Cell division: the cells increase in number due to mitotic cell division Cell differentiation: the cells became specialized to per form speci..

At the molecular level all the different types of cells in living organisms are composed of certain chemical substances. The structure and function of the cell and its components are dependent on the molecular structure, arrangement and properties of these chemical constit..

- The bio-chemical processes involved in respiration which break down the substrate to release energy take place in the tissues within the cells of an organism. Thus, this is called the cellular respiration. Gaseous exchange in earthworm takes place through its skin. The skin..

. Water functions as a universal solvent in which almost all polar and ionic substances can dissolve. It provides a matrix for macromolecules to assume their biologically active conformations. It has a significant role in maintaining a steady state in cells. Minerals form only about 1 to ..

At the cellular level, growth of multi cellular organisms is governed by two main activities Reproduction of individual cells of body by mitotic cell divisions Growth of cells by synthesizing new protoplasm. The interphase stage of the cell cycle is different..

Summary - Growth is an irreversible increase in size and weight of an organism. The cells of the body do not grow uniformly but differentially. The main types of growth are auxetic, multiplicative and accretionary. The human growth curve is sigmoid and is controlled by hormones. Regenerat..

Self Duplication and Survival - Living organisms do not survive indefinitely. Every organism dies after attaining a certain age or due to predation, disease, accident or other factors. The reduction in the number of individuals of a population as a result of death, is restored b..

fig. 13.8 - Classification of Lipids Lipids are also organic compounds containing carbon, hydrogen and oxygen. However, hydrogen and oxygen occur in a ratio much higher than in water. Lipids form about 3.5% of the total chemical composition of a cell. Lipids are generally insoluble in..