Q.The density of a population in a habitat per unit area is measured in different units. Write the unit of measurement against the following:
a. Bacteria
b. Banyan
c. Deer
d. Fish
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Start your 14-day free trial to unlock the full solution →Population density is measured in different units depending on the organism — for bacteria it is number per unit volume, for banyan it is per unit area using a special measure, for deer it is number per unit area, and for fish it is number per unit volume of water.
When ecologists talk about population density, they are asking: how many individuals of a species live in a given space? But the word "individual" itself can be tricky. A single banyan tree, for instance, is one individual, but it covers a huge area with its aerial roots. A bacterium, on the other hand, is microscopic and lives in a drop of water. So the unit of measurement changes depending on what you are counting and where it lives.
The NCERT textbook gives us a clear framework for this. Let us take each organism one by one.
a. Bacteria — These are tiny and live in liquid or semi-solid media like soil or water. You cannot count them per square metre of land in the same way you count deer. Instead, their density is measured as number per unit volume — for example, the number of bacteria per millilitre of water or per gram of soil. The unit is simply "per volume" (like per mL or per cm³).
b. Banyan — Here is a special case. A single banyan tree can spread over a large area through its prop roots, so counting "number of trees per hectare" would be misleading. The NCERT points out that for such large, spreading plants, population density is often measured as per cent cover or biomass — that is, the area covered by the tree's canopy as a percentage of the total habitat area. So the unit is "percentage of area covered" or simply "per unit area" in a relative sense.
The textbook specifically uses the banyan as an example to show that "number per unit area" is not always the best measure — sometimes you need to use cover or biomass instead. …
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