A Level Biology: PAG Extension Questions and Answers | Latest Version | 2024/2025 | Graded A+

A Level Biology: PAG Extension Questions and Answers | Latest Version | 2024/2025 | Graded A+ **3.1 If farmers plant hedges around their fields, what impact might this have on species diversity around their land?** Planting hedges would likely increase species diversity by providing more habitats and niches, thereby supporting a variety of species and more complex food webs. **3.2 Besides your interrupted belt transect, what additional information should you collect at the survey site?** Date, time, weather conditions on the day and during the current or preceding growing season, evidence of animal impact such as grazing, signs of human impact, and a sketch map showing key features and the transect line. **3.2 What evidence did you find indicating the presence of animal species in this habitat?** Evidence could include grazed vegetation, live animal sightings (especially insects), droppings (e.g., rabbit), carcasses, footprints, fur caught on spiky plants or barbed wire fences, burrows, or tracks. **7.1 What was the purpose of the lit Bunsen burner during your work?** To create an up-draught that prevents aerial contamination of the workspace. **7.1 Why was a filter paper disc soaked in distilled water used in area D?** It served as a negative control to ensure that any observed effects were not due to the water itself. **7.2 What other methods could determine bacterial density in a culture? Why might these methods differ from dilution plating?** Microscopy such as a haemocytometer could be used, but it may overestimate due to including dead cells. Turbidity or % transmission with a colorimeter can estimate density but might overestimate due to viability variations. **5.1 Describe the relationship between temperature and beetroot cell pigment leakage.** Increasing temperature increases pigment release in a non-linear manner. Students can provide data and units to support their findings. **5.1 Explain the results and graph shape using membrane structure theory.** Higher temperatures increase membrane fluidity, causing phospholipids to disaggregate and proteins to denature, creating larger gaps for pigment leakage via diffusion. **5.1 How does ethanol affect membrane permeability?** Ethanol disrupts membranes by bonding with phospholipid heads, displacing them and denaturing proteins, which increases permeability. Cholesterol solubility in ethanol further enhances permeability. **5.1 What are four limitations of the beetroot pigment leakage procedure?** Limitations include uneven pigment distribution, variable beetroot ages, incomplete washing of surface pigment, and variations in cylinder preparation and drying times. **5.2 Why does red light transmission increase