[Mission 2022] QUIZ – 2022: INSIGHTS STATIC QUIZ, 22 December 2021 – Environment – INSIGHTSIAS

Solution: b)

Detrivores (e.g., earthworm) break down detritus into smaller particles. This process is called fragmentation.

• By the process of leaching, water soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.
• Bacterial and fungal enzymes degrade detritus into simpler inorganic substances. This process is called as catabolism. It is important to note that all the above steps in decomposition operate simultaneously on the detritus.
• Humification and mineralization occur during decomposition in the soil. Humification leads to accumulation of a dark colored amorphous substance called humus that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate. Being colloidal in nature it serves as a reservoir of nutrients. The humus is further degraded by some microbes and release of inorganic nutrients occurs by the process known as mineralization.

Solution: c)

ECOLOGICAL SUCCESSION

• An important characteristic of all communities is that their composition and structure constantly change in response to the changing environmental conditions. This change is orderly and sequential, parallel with the changes in the physical environment. These changes lead finally to a community that is in near equilibrium with the environment and that is called a climax community. The gradual and fairly predictable change in the species composition of a given area is called ecological succession. During succession some species colonies an area and their population become more numerous whereas populations of other species decline and even disappear.
• The entire sequence of communities that successively change in a given area are called sere(s). The individual transitional communities are termed seral stages or seral communities.
• Succession is hence a process that starts in an area where no living organisms are there – these could be areas where no living organisms ever existed, say bare rock; or in areas that somehow, lost all the living organisms that existed there. The former is called primary succession, while the latter is termed secondary succession.
• Secondary succession begins in areas where natural biotic communities have been destroyed such as in abandoned farm lands, burned or cut forests, lands that have been flooded. Since some soil or sediment is present, succession is faster than primary succession.

Solution: d)

Ecotone

• Ecotone is a zone of junction between two or more diverse ecosystems. For e.g. the mangrove forests represent an ecotone between marine and terrestrial ecosystem. Other examples are – grassland, estuary and river bank.

Characteristics of Ecotone

• It may be very narrow or quite wide.
• It has the conditions intermediate to the adjacent ecosystems. Hence it is a zone of tension.
• A well-developed ecotone contains some organisms which are entirely different from that of the adjoining communities.
• Sometimes the number of species and the population density of some of the species is much greater in this zone than either community. This is called edge effect.
• The organisms which occur primarily or most abundantly in this zone are known as edge species. In the terrestrial ecosystems edge effect is especially applicable to birds.
• For example, the density of birds is greater in the mixed habitat of the ecotone between the forest and the desert.

Solution: d)

• In order for biomagnification to occur, the pollutant must be: long-lived, mobile, soluble in fats, biologically active. If a pollutant is short-lived, it will be broken down before it can become dangerous. If it is not mobile, it will stay in one place and is unlikely to be taken up by organisms. If the pollutant is soluble in water, it will be excreted by the organism. Pollutants that dissolve in fats, however, may be retained for a long time.
• If a pollutant is not active biologically, it may biomagnify, but we really don’t worry about it much, since it probably won’t cause any problems Examples: DDT

Solution: a)

The organisms (both flora and fauna) in the aquatic ecosystem are unevenly distributed but can be classified on the basis of their life form or location into five groups

1. i) Neuston:

• These are unattached organisms which live at the air water interface such as floating plants, etc.

1. ii) Periphyton:

• These are organisms which remain attached to stems and leaves of rooted plants or substances emerging above the bottom mud such as sessile algae and their associated group of animals.

iii) Plankton:

• This group includes both microscopic plants like algae (phytoplankton) and animals like crustaceans and protozoans (zooplankton) found in all aquatic ecosystems, except certain swift moving waters.

1. iv) Nekton:

• This group contains animals which are swimmers.
• The nektons are relatively large and powerful as they have to overcome the water currents.
• The animal’s range in size from the swimming insects (about 2 mm long) to the largest animals, the blue whale.

1. v) Benthos:

• The benthic organisms are those found living in the bottom of the water mass.
• Practically every aquatic ecosystem contains well developed benthos.