In a field experiment, autotrophs are provided a ¹⁴C-labelled carbon compound for photosynthesis. Radioactivity (¹⁴C) levels were then monitored at regular intervals in all the trophic levels. In which ecosystem is the radioactivity likely to be detected fastest at the primary carnivore level?

• Open ocean

• Desert

• Deciduous forest

• Grassland

112.

A population is growing logistically with a growth rate (r) of 0.15/week, in an environment with a carrying capacity of 400. What is the maximum growth rate (No. of individuals/ week) that this population can achieve?

• 15

• 30

• 22.5

• 60

Important chemical reactions involved in nutrient cycling in ecosystems are given below:

a. NO${}_2^{-} \to {\mathrm{NO}}_3^{-}$

b. N₂ → NH₃

c. NH${}_4^{+} \to {\mathrm{NO}}_2^{-}$

d. NO${}_3^{-}$ → N₂

The organisms associated with these chemical reactions are

• a - Nitrosomonas; b - Pseudomonas; c - Nostoc; d - Nitrobacter

• a - Pseudomonas; b - Nitrobacter; c - Nostoc; d - Nitrosomonas

• a - Nitrobacter; b - Nostoc; c - Nitrosomonas; d - Pseudomonas

• a - Nostoc; b - Nitrosomonas; c - Nitrobacter; d - Pseudomonas

Which of the following statements about the birth rates (b₁, b₂) and death rates (d₁, d₂) of species 1 and 2 indicated in the figure is NOT true?

• Birth rates of species 1 are density-independent.

• Death rates of both species are density-dependent.

• Birth rates of species 2 are density-dependent.

• Density-dependent effects on death rates are similar for both the species.

A red coloured tubular flower without any odour is most likely to be pollinated by

• beetles

• bees

• butterflies

• birds

Which gas does NOT contribute to global warming through its greenhouse effect?

• Nitrous oxide

• Methane

• Carbon dioxide

• Nitric oxide

In the following equations

(a) dN/ dt = rN

(b) Nt = N₀e^rt

(c) dN/ dt = rN $\left(\frac{\mathit{K}\mathit{ }\mathit{-}\mathit{ }\mathit{N}}{\mathit{K}}\right)$

(d) dN/ dt = rN × N/K

exponential population growth is described by

• a and b

• a only

• c only

• b and d

The birth rates (b) and death rates (d) of two species 1 and 2 in relation to population density (N) are shown in the graph. Which of the following is NOT true about the density-dependent effects on birth rates and death rates?

• Birth rates are density-dependent in species 1 and density-independent in species 2.

• Death rates are density-dependent in both the species.

• The density-dependent effect on the birth rate is stronger in species 1 than in species 2.

• The density-dependent effects on death rates are similar in both the species.

In a lake subjected to progressive eutrophication, temporal changes in the magnitude of selected parameters (A, B, C, D) are shown in the graph

The parameters A, B, C, D are

• A - Green algal biomass; B - Cyanobacterial biomass; C - dissolved oxygen concentration; D - Biological Oxygen Demand

• A - Biological Oxygen Demand; B - Cyanobacterial biomass; C - Dissolved oxygen concentration; D - Green algal biomass

• A - Biological oxygen demand; B - Green algal biomass; C - Cyanobacterial biomass; D - Dissolved oxygen concentration

• A - Cyanobacterial biomass; B - Biological oxygen demand; C - Green algal biomass; D - Dissolved oxygen concentration

The approximate P: B (Net Primary Production: Biomass) ratios in four different ecosystems A, B, C, D) are:

A - 0.29; B - 0.042; C - 16.48; D - 8.2

The four ecosystems are

• A - Ocean; B - Lake; C - Grassland; D - Tropical forest

• A - Grassland; B - Tropical forest; C - Ocean; D - Lake

• A - Tropical forest; B - Ocean; C - Grassland; D - Lake

• A - Grassland; B - Ocean; C - Lake; D - Tropical forest