Ecosystems and Biodiversity Questions and Answers

Answer: C

This is the edge effect.

Where two communities meet, such as a forest and a grassland, there is a transition zone called an ecotone. It contains species from both communities and some found only in the ecotone itself, so the variety and often the density of species is greater there than in either community. This tendency is the edge effect.

Ordination is a statistical method for arranging communities along gradients, a continuum is a gradual change in community composition along a gradient, and an ecotype is a locally adapted population of a species.

Answer: B

The inhibition of one species by toxic substances released by another is allelopathy.

Allelopathic plants release chemicals from their roots, leaves or decaying litter that suppress the germination or growth of neighbouring plants. Black walnut, which releases juglone, and Parthenium are well-known examples.

Chelation is the binding of metal ions by organic molecules. Microcosms and mesocosms are small and medium-sized experimental ecosystems used in research, not interactions between species.

Answer: A

Kaziranga National Park is known for the one horn rhino.

Kaziranga, on the floodplains of the Brahmaputra in Assam, holds about two-thirds of the world's greater one-horned rhinoceroses, the largest population anywhere. It is a UNESCO World Heritage Site, inscribed in 1985.

The park also has tigers, wild water buffalo and elephants, but its fame rests on the rhino. Crocodiles and bison (gaur) are not what it is known for.

Answer: D

The Redfield ratio concerns Carbon, nitrogen, phosphorus.

Alfred Redfield found that marine phytoplankton, and the dissolved nutrients in deep sea water, contain carbon, nitrogen and phosphorus in a nearly constant atomic ratio of about 106 : 16 : 1. The ratio is used to judge which nutrient limits growth in the ocean.

Hydrogen and oxygen, potassium and iron, and sulphur are not part of the ratio; iron does limit growth in some waters, but it is not one of Redfield's three elements.

Answer: C

This is called Functional diversity.

Functional diversity is the variety of roles organisms play in an ecosystem: how they behave, how they obtain food and how they use resources such as light, water and nutrients. Two communities with the same number of species can differ widely in functional diversity.

Species diversity counts the number and relative abundance of species, ecosystem diversity is the variety of habitats and ecosystems in a region, and genetic diversity is the variation in genes within a species.

Answer: A

The final stable community is the Climax.

Ecological succession is a sequence of communities replacing each other until one is reached that is in equilibrium with the climate and soil and changes little over time: the climax community.

A sere is the whole series of stages of a succession, not its end. Pioneers are the first organisms to colonise bare ground, and carnivores are a trophic group found in many communities, not a stage.

Answer: B

The one that is not a functional unit is Stratification.

An ecosystem is described by its structure (species composition, biomass, and the vertical layering of plants and animals called stratification) and by its functions: productivity, energy flow, decomposition and nutrient cycling.

Stratification is a structural feature, the arrangement of the community into layers such as canopy, understorey and ground, so it is the odd one out. Productivity, energy flow and decomposition are all processes, the functional aspects.

Answer: D

Denitrification is a process of Reduction.

Under low-oxygen conditions, bacteria such as Pseudomonas use nitrate in place of oxygen as the electron acceptor for respiration, reducing it step by step:

\[ \begin{aligned} &\mathrm{NO_{3}^{-} \rightarrow NO_{2}^{-} \rightarrow NO} \\ &\rightarrow \mathrm{N_{2}O \rightarrow N_{2}} \end{aligned} \]

Nitrogen goes from oxidation state +5 to 0 and returns to the atmosphere. The opposite process, nitrification of ammonium to nitrate, is the oxidation. Hydration (adding water) and carbonation (reaction with carbonic acid) are weathering reactions, unrelated to the nitrogen cycle.

Answer: C

The Ramsar site is Chilka lake.

Chilika Lake in Odisha, Asia's largest brackish-water lagoon, was designated in 1981 as one of India's first two Ramsar wetlands of international importance, together with Keoladeo National Park. It is a major wintering ground for migratory birds and home to the Irrawaddy dolphin.

Koyna, Ujani and Jayakwadi are large reservoirs in Maharashtra, created by dams on the Koyna, Bhima and Godavari rivers. Jayakwadi is a bird sanctuary, but none of the three had been listed under the Ramsar Convention.

Answer: D

Dissolved oxygen shows a decrease from top to bottom.

Oxygen enters water at the surface, by diffusion from the air and from photosynthesis by algae in the sunlit upper layer. Deeper down, light is too weak for photosynthesis while bacteria decomposing settled organic matter keep using oxygen up. In a thermally stratified lake the bottom layer (hypolimnion) is also cut off from the surface, so it can become nearly anoxic in summer.

'Less on the top and more at bottom' and 'an increase from top to bottom' describe the same reversed profile, which is why neither can be right. A uniform level is found only briefly, when a lake mixes completely at turnover.