Question 1: A biologist studied the population of rats in a granary. He found the average natality was 280, average mortality was 200, immigration was 40 and emigration was 50. The net increase in population is :

• A. 80
• B. 70
• C. 10
• D. 90

Question 2: (a) How is the interaction between Ophrys and its specific bee pollinator one of the best examples of co-evolution? Explain.
OR
(b) Arrange the given important steps of decomposition in their correct order of occurrence in the breakdown of complex organic matter and explain the fourth step in the process.
Catabolism, Fragmentation, Leaching, Mineralisation, Humification

Question 3: (a) Explain how the interaction between sea anemone and clownfish is one of the best examples of commensalism in nature.
OR
(b) Correctly depict (also indicate the trophic level) and describe the ecological pyramid of biomass in sea with $40$ standing crop of phytoplankton supporting $90$ standing crop of zooplankton which further supports $120$ small fishes.

Question 4: Observe the population growth curve and answer the questions given below:
[Graph with labels $\frac{dN}{dt}=rN$, $\frac{dN}{dt}=rN(\frac{K-N}{K})$, A, B, K]
(a) State the conditions under which growth curve 'A' and growth curve 'B' plotted in the graph are possible.
(b) Mention what does 'K' in the graph represent.

Question 5: (a) Draw a graph for a population whose population density has reached the carrying capacity.
(b) Out of the two population growth curves, which one is considered a more realistic for most populations? Why?
(c) Draw a growth curve where resources are not limiting for the growth of a population and give its equation.

Question 6: (a) (i) Describe the population growth curve applicable in a population of any species in nature that has limited resources at its disposal.
(ii) Give the equation of this growth curve.
(iii) Name the growth curve and depict a graphical plot for this type of population growth.
OR
(b) (i) Explain the Species-Area relationship within a natural forest and also predict the nature of graph when species richness is plotted against the area for a wide variety of taxa.
(ii) Depict the graphical relationship between species richness and area.
(iii) Give the equation of the Species-Area relationship for a wide variety of taxa on a logarithmic scale.

Question 7: Read the following passage and answer the questions that follow: In nature, we rarely find isolated, single individuals of any species; majority of them live in groups in a well-defined geographical area, share or compete for similar resources, potentially interbreed and thus constitute a population. The population has certain attributes whereas, an individual organism does not. A population at a given time is composed of individuals of different ages. The size of the population tells us a lot about its status in the habitat. Whatever ecological processes we wish to investigate in a population, be it the outcome of competition with another species, the impact of the predator or the effect of pesticide application, we always evaluate in terms of any change in the population size. The size, in nature, could be low or go into millions. Population size, technically called population density (N) need not necessarily be measured in numbers only. The size of a population for any species is not a static parameter. It keeps on changing with time depending on various factors including food availability, predation pressure and adverse weather. (a) The Monarch butterfly is highly distasteful to its predator because of a special chemical present in its body. How does the butterfly acquire this chemical? (b) If population density at a time $t+1$ is $800$, Emigration $=100$, Immigration $=200$, Natality $=200$ and Mortality $=150$, calculate the population density at time $t$ and comment upon the type of age pyramid that will be formed in this case. Student to attempt either sub-part (c) or (d): (c) What is the difference in a method of measuring population density in an area if there are $200$ carrot grass plants to only single huge banyan tree? OR (d) Name two methods to measure the population density of tigers.