UPSC STATIC QUIZ – Environment : 26 March 2024

Solution: a)

• Estuaries and their surrounding wetlands are bodies of water usually found where rivers meet the sea.
• Estuaries are home to unique plant and animal communities that have adapted to brackish water—a mixture of fresh water draining from the land and salty seawater.
• An ecotone is a transition area between two biomes. It is where two communities meet and integrate.
• It has some of the characteristics of each bordering biological community and often contains species not found in the overlapping communities.
• For e.g. the mangrove forests represent an ecotone between marine and terrestrial ecosystem. Other examples are grassland (between forest and desert.)

Estuaries are subject both to marine influences—such as tides, waves, and the influx of saline water—and to riverine influences—such as flows of fresh water and sediment.

The inflows of both sea water and fresh water provide high levels of nutrients both in the water column and in sediment, making estuaries among the most productive natural habitats in the world.

The banks of many estuaries are amongst the most heavily populated areas of the world

Solution: b)

Statement 3 is incorrect.

Dissolved oxygen:

• In aquatic ecosystems oxygen is dissolved in water, where its concentration varies constantly depending on factors that influence the input and output of oxygen in water.
• In fresh water the average concentration of dissolved oxygen is 0.0010 per cent (also expressed as 10 parts per million or 10 ppm) by weight, which is 150 times lower than the concentration of oxygen in an equivalent volume of air.
• Oxygen enters the aquatic ecosystem through the air water interface and by the photosynthetic activities of aquatic plants.
• Therefore, the quantity of dissolved oxygen present in an ecosystem depends on the rate at which the aforesaid two processes occur.
• Dissolved oxygen escapes the water body through airwater interface and through respiration of organisms (fish, decomposers, zooplanktons, etc).
• The amount of dissolved oxygen retained in water is also influenced by temperature. Oxygen is less soluble in warm water. Warm water also enhances decomposer activity. Therefore, increasing the temperature of a waterbody increases the rate at which oxygen is depleted from water. 
• When the dissolved oxygen level falls below 3-5 ppm, many aquatic organisms are likely to die.

Solution: b)

Statement 3 is incorrect.

In an aquatic ecosystem, grazing food chain is the major conduit for energy flow. As against this, in a terrestrial ecosystem, a much larger fraction of energy flows through the detritus food chain than through the grazing food chain.

When energy is passed in an ecosystem from one trophic level to the next, only ten percent of the energy will be passed. Around 90% of energy will be lost.

Solution: b)

Statement 2 is incorrect.

The mechanisms used by most mammals to regulate their body temperature are similar to the ones that we humans use. We maintain a constant body temperature of 370C. In summer, when outside temperature is more than our body temperature, we sweat profusely.

The resulting evaporative cooling, similar to what happens with a desert cooler in operation, brings down the body temperature. In winter when the temperature is much lower than 370C, we start to

shiver, a kind of exercise which produces heat and raises the body temperature. Plants, on the other hand, do not have such mechanisms to maintain internal temperatures.

Thermoregulation is energetically expensive for many organisms. This is particularly true for small animals like shrews and humming birds. Heat loss or heat gain is a function of surface area. Since small animals have a larger surface area relative to their volume, they tend to lose body heat very fast when it is cold outside; then they have to expend much energy to generate body heat through metabolism. This is the main reason why very small animals are rarely found in polar regions.

• Solution: d)

   

  TYPES OF BIODIVERSITY

   

  Based on the three elements of biodiversity, that is, genes, species and ecosystems, biodiversity is considered to be of three types:

   

  Genetic diversity: It can be understood as the diversity of genes within a particular species. This diversity ensures that some species can survive disruptions.

   

  Species diversity: It refers to the variety of species within a particular geographical region. For example, humans and chimpanzees have about 98.4 percent genes which are the same.

   

  Species diversity is measured by :- species richness, which means the number of different species per unit area in a region.

  species evenness equitably, which refers to the relative abundance of individuals of different species in an area.

   

  Ecosystem or Community diversity: It refers to the diversity of different biological communities or ecosystems like forests, deserts, lakes, corals etc.