The following diagrams are the age pyram | Class 12 Biology Chapter Organisms and Population, Organisms and Population NCERT Solutions

Population is divided into three important age classes: Pre- reproductive, Reproductive and Post- reproductive. An age pyramid is a graphical representation which shows the number and the proportion of the individuals that belongs to various age classes in a population of an individual at the given time. There are three types of age pyramid: Upright broad based pyramid, Bell shaped pyramid and Urn shaped pyramid.

Figure A is the Upright broad base pyramid which represents the expanding population with the high birth rate. It shows high proportion of pre- reproductive age class individuals than the reproductive and post- reproductive age class; which gives pyramid shaped age structure.

Figure B is the Bell- shaped pyramid which represents the stable population which contains moderate proportion of young to old population. Pre- and reproductive age class becomes equal in size and the post- reproductive remains small in size which makes this pyramid bell shaped.

Figure C is the Urn- shaped structure pyramid which shows declining population. It contains low proportion of pre- reproductive age class individuals due to low natality in comparison to reproductive and post- reproductive age class.