CBSE Class 12 Biology Exemplar NCERT Solutions: Chapter 13 - Organisms and Populations

Solution: Ecology is broadly defined as the study of the relationships between living organisms and their physical and biological environments. This field is often divided into two main branches: autecology and synecology.

Autecology specifically focuses on the ecological aspects of a single species or an individual organism, examining its interactions with its environment. This includes understanding its adaptations, requirements, and how it fits into its specific habitat.

Synecology, on the other hand, deals with the study of groups of organisms, such as populations, communities, or ecosystems, and their interactions with each other and their environment.

Therefore, the relation of an individual to its environment is precisely what autecology studies.

Answer: (b) relation of an individual to its environment

Solution: In ecology, different communities often exist adjacent to each other. However, the boundary between two distinct natural communities is rarely a sharp, well-defined line. Instead, there is typically a transitional zone where the characteristics of both communities gradually merge.

This transitional area, which contains species from both adjacent communities and may also host unique species adapted to the intermediate conditions, is known as an ecotone. It represents a zone of overlap and interaction.

Options (a), (b), and (d) do not accurately describe this specific ecological concept. A polluted area is a condition, the bottom of a lake is a habitat (benthic zone), and a developing community refers to ecological succession, none of which define the transition zone between communities.

Answer: (c) a zone of transition between two communities

Solution: The biosphere, also referred to as the ecosphere, is the global ecological system integrating all living beings and their relationships, including their interaction with the elements of the lithosphere (land), hydrosphere (water), and atmosphere (air).

It encompasses all life forms found on Earth, from the deepest oceans to the highest mountains and the atmosphere. Crucially, it includes the interactions between these living organisms and their physical surroundings. Therefore, it is not just a single component of an ecosystem, nor is it limited to plants in the soil or life beyond Earth.

Answer: (d) composed of all living organisms present on earth which interact with the physical environment

Solution: An ecological niche is a fundamental concept in ecology that describes the unique role and position a species occupies within its ecosystem. It is more than just the physical space (habitat) it inhabits; it encompasses all the interactions the species has with the biotic and abiotic factors of its environment.

This includes its specific habitat, its food sources, its predators, its reproductive strategies, and its functional role in the community, such as its contribution to nutrient cycling or energy flow. Essentially, it defines how a species lives, interacts, and survives within its environment.

While an ecological niche is an 'ecologically adapted zone' (b), the most precise definition among the options is the one that includes both the physical position and the functional role within the community.

Answer: (c) the physical position and functional role of a species within the community

Solution: Allen's rule is an ecogeographical principle that describes an aspect of mammalian adaptation to climate. It states that endotherms (warm-blooded animals) from colder climates usually have shorter appendages (such as limbs, ears, and tails) than equivalent animals from warmer climates.

The reason for this adaptation is related to heat conservation. Shorter appendages have a smaller surface area-to-volume ratio, which helps to minimize heat loss to the colder environment. Conversely, animals in warmer climates often have longer appendages to facilitate heat dissipation.

Therefore, mammals from colder climates are characterized by shorter ears and shorter limbs to reduce heat loss.

Answer: (d) shorter ears and shorter limbs

Solution: Salinity is a critical abiotic factor that characterizes aquatic environments, particularly marine ecosystems. It refers to the total concentration of dissolved salts in water, typically measured in parts per thousand (ppt).

The salinity of different water bodies varies significantly. For instance, freshwater bodies generally have very low salinity, often less than 5 ppt. In contrast, the open ocean has a relatively stable and higher salinity. The average salinity of sea water is approximately 30 to 35 parts per thousand.

Some specific environments, like lagoons or salt lakes, can have much higher salinities, exceeding 100 ppt, but the standard measure for the sea falls within the 30-35 ppt range.

Answer: (d) 30-35