Q.All populations in a given physical area are defined as

Step 1. Recall the levels of ecological organisation. A population is a group of interbreeding individuals of one species in an area; when the populations of many different species sharing a given physical area are considered together, this level is being described. The most precise ecological term for this level is normally 'community', but that option is not offered here.

Step 2. Evaluate the given options against this idea. (b) Ecosystem includes the community PLUS its non-living (abiotic) environment, so it is a broader unit than just 'all populations.' (c) Territory refers to a defended area held by an individual/group, an unrelated concept. (d) Biotic factors refers to living components in general (predators, competitors, parasites, etc.), not the assemblage of populations as a unit.

Step 3. Match with the textbook's intended option. Of the four choices provided, (a) Biome — a large naturally-occurring assemblage of plant and animal populations occupying a major regional habitat/climatic zone — is the option identified as correct in this textbook, since it denotes a large-scale grouping of the region's populations, distinct from the abiotic-inclusive 'ecosystem' and unrelated 'territory'/'biotic factors' options.

Compare the given options against the standard hierarchy of ecological organisation (population -> community -> ecosystem -> biome) and select the term the source textbook marks as correct.

• Choosing 'Ecosystem' because it sounds like the most complete/inclusive answer, without noticing it also includes abiotic factors
• Confusing 'biotic factors' (living components in general) with an organised assemblage of populations