Biology Set-1

Q1. In a grassland ecosystem the gross primary productivity is $GPP=800\ \text{g C m}^{-2}\ \text{yr}^{-1}$ and autotrophic respiration is $R_a=350\ \text{g C m}^{-2}\ \text{yr}^{-1}$. Using $NPP=GPP-R_a$, what is the net primary productivity $NPP$ in $\text{g C m}^{-2}\ \text{yr}^{-1}$?

Q2. An ecosystem has $NPP=1000\ \text{kJ m}^{-2}\ \text{yr}^{-1}$. Herbivores consume $C=25\%$ of NPP; their assimilation efficiency is $A=50\%$ and production efficiency is $P=20\%$. Using $P_h = NPP \times C \times A \times P$, and if one herbivore needs $5\ \text{kJ yr}^{-1}$ for annual biomass production, how many herbivores can be produced per m$^2$ per year?

Q3. In a lake, annual primary productivity of phytoplankton is $P_p=365\ \text{g C m}^{-2}\ \text{yr}^{-1}$ and standing biomass $B_p=2\ \text{g C m}^{-2}$. Zooplankton standing biomass is $B_z=50\ \text{g C m}^{-2}$ with annual secondary productivity $P_z=50\ \text{g C m}^{-2}\ \text{yr}^{-1}$. Using turnover time $t=\dfrac{B}{P}$, which of the following is the correct calculation and ecological implication for the biomass pyramid?

Q4. Assertion (A): Soon after clear‑cutting a forest the concentration of nitrate in soil solution commonly shows a short‑term increase, whereas soil organic nitrogen declines over years to decades.
Reason (R): Removal of vegetation exposes the soil to intensified raindrop impact and surface runoff that preferentially removes the organic‑rich topsoil horizon, causing long‑term loss of soil organic nitrogen.

Q5. A soil has an organic carbon pool $C_0=2000\ \text{g C m}^{-2}$. The decomposition constant at $10^\circ\text{C}$ is $k_{10}=0.2\ \text{yr}^{-1}$. For decomposition the temperature sensitivity is given by $k_{T+\Delta T}=k_T\times Q_{10}^{\Delta T/10}$ and $Q_{10}=2$. If mean temperature rises by $\Delta T=10^\circ\text{C}$ and there are no carbon inputs during the year, what is the annual CO$_2$ flux from decomposition (in $\text{g C m}^{-2}\ \text{yr}^{-1}$) and the remaining soil organic carbon after one year?

Q6. In a grassland ecosystem, gross primary productivity (GPP) is $1800\ \text{g C m}^{-2}\ \text{yr}^{-1}$ and autotrophic respiration ($R$) is $600\ \text{g C m}^{-2}\ \text{yr}^{-1}$. The net primary productivity (NPP) of this ecosystem is:

Q7. In an ecosystem the annual net primary production (NPP) is $5000\ \text{kJ m}^{-2}\ \text{yr}^{-1}$. Herbivores ingest 15% of NPP. If assimilation efficiency of herbivores is 70% and production efficiency (fraction of assimilated energy converted to growth/reproduction) is 25%, the annual secondary production by herbivores is closest to:

Q8. Litter decomposition follows $M(t)=M_{0}e^{-kt}$. If $40\%$ of the initial litter mass is lost after one year, the decomposition constant $k$ (in yr$^{-1}$) and the half‑life $t_{1/2}$ (in years) are approximately:

Q9. Assertion (A): Persistent hydrophobic pollutants such as DDT often biomagnify, leading to much higher concentrations in apex predators than in primary producers or water. Reason (R): These pollutants are resistant to degradation, are lipophilic and accumulate in fatty tissues; they are transferred and concentrated at each trophic transfer. Choose the correct option:

Q10. In a simplified aquatic food chain measured standing biomass (g C m$^{-2}$) and annual productivity (g C m$^{-2}$ yr$^{-1}$) are: primary producers (phytoplankton) — biomass $10$, productivity $1200$; primary consumers (zooplankton) — biomass $300$, productivity $240$; secondary consumers (small fish) — biomass $100$, productivity $60$. Which interpretation is correct?