MCQ
Bell-shaped age pyramid indicates that
- ANumber of pre-reproductive and reproductive individual is almost equal
- BPost-reproductive individuals are comparatively fewer
- CThe population size remains stable
- ✓All of the above
A bell-shaped polygon indicates a moderate proportion of young to old. As the rate of growth becomes slow and stable, the pre-reproductively and reproductive age group become more or less equal in size and post-reproductive group remaining as the smallest. In stable population 'r' is zero.
And bell-shaped curve only possible when $r=0$ means growth of population is zero
Age pyramid Graphic representation of different age groups found in a population with pre-reproductive group at the base. Reproductive ones in the middle and post-reproductive group at the top is called age pyramid.
Age pyramid have three kinds
$(i)$ Triangular Age Pyramid The number of pre-reproductive is very large. Number of reproductive individual is moderate and post-reproductive are fewer. Population size is growing
$(ii)$ Bell-shaped Age Pyramid The number of prereproductive and reproductive individuals is almost equal. Post-reproductive individuals are comparatively fewer. Population size is stable
$(iii)$ Urn-shaped Age Pyramid Proportion of reproductive age group is higher than the individuals in pre-reproductive age group. Number of postreproductive individuals is also sizable. It is declining population with negative growth
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$(i)$ Neurospora, which is used in biochemical and genetic work is a member of this class.
$(ii)$ They are mostly multicellular, e.g., Yeast, or rarely unicellular, e.g., Penicillium.
$(iii)$ They are saprophytic, decomposers, parasitic or coprophilous.
$(iv)$ Some examples are Aspergillus, Claviceps and Neurospora.