Sustainability and Change · Paper 2 — Free Biology HL Practice Questions

A research team investigated the use of microalgae (Chlorella vulgaris) as a renewable biofuel feedstock. The algae were grown in open raceway ponds ($500\,\text{m}^2$ each) under natural sunlight over a 30-day growth period. Data collected: - Initial algal biomass: $0.25\,\text{g\,L}^{-1}$ (dry mass) - Final algal biomass: $1.80\,\text{g\,L}^{-1}$ (dry mass) - Pond volume: $100{,}000\,\text{L}$ - Lipid content of dried algae: $32\%$ by mass - Energy content of algal lipids: $37.8\,\text{MJ\,kg}^{-1}$ - Energy required for harvesting and lipid extraction: $8.2\,\text{MJ}$ per kg of dry algae processed - $\text{CO}_2$ absorbed during growth: $1.83\,\text{kg CO}_2$ per kg dry algae - $\text{CO}_2$ emitted during biodiesel combustion: $2.68\,\text{kg CO}_2$ per kg biodiesel - $\text{CO}_2$ emitted from processing energy: $0.94\,\text{kg CO}_2$ per kg dry algae Useful relationships: $$\text{Net energy} = \text{Energy output} - \text{Energy input}$$ $$\text{Mass} = \text{concentration} \times \text{volume}$$

The island nation of Palau has committed to protecting $80\%$ of its marine territory as a 'no-take' marine reserve. A team of ecologists is evaluating the sustainability of this conservation strategy by comparing fish communities inside the reserve with those in adjacent fishing zones. Data from a 2023 survey: - Simpson's diversity index ($D$) inside the reserve: $0.92$ - Simpson's diversity index ($D$) in the fishing zone: $0.68$ - Total fish biomass inside the reserve: $4500\,\text{kg km}^{-2}$ - Total fish biomass in the fishing zone: $2100\,\text{kg km}^{-2}$ - Annual fish catch in the fishing zone: $380\,\text{kg km}^{-2}\,\text{year}^{-1}$ - Estimated annual fish recruitment in the fishing zone: $420\,\text{kg km}^{-2}\,\text{year}^{-1}$ - Reserve area: $250\,\text{km}^2$; fishing zone area: $800\,\text{km}^2$