A-level Biology Paper 1 2021 with correct answers 100% 2025

A-level Biology Paper 1 2021 with correct answers 100% 2025 Suggest and explain a procedure the scientists could've used to stop each reaction - Correct Answer - boil - denatures the enzyme Explain the change in ATP concentration with increasing inorganic phosphate concentration - Correct Answer Increasing Pi concentration means more E-S complexes can be formed At 40dm-3 active sites are all occupied Suggest how the environmental conditions have resulted in the adaptions of systems using Model A rather than B - Correct Answer - water has a lower oxygen partial pressure - this reduces diffusion distance Use figure 3 to justify this conclusion - fish exchange system is more efficient than gas - Correct Answer - in fish, blood has more oxygen than water leaving - in humans, blood leaving has less oxygen than air leaving Describe how one amino acid is added to a polypeptide that's being formed at a ribosome during translation - Correct Answer - tRNA brings specific amino acid over to bind to the ribosome - anticodon on tRNA binds to codon on mRNA - amino acids join together through a condensation reaction forming peptide bonds between them Use information in table 2 to suggest why this amino acid replacement changes the properties of crystallin - Correct Answer - tertiary structure changes - hydrogen bonds form instead of ionic Describe how a sample of chloroplasts could be isolated from leaves. - Correct Answer - break open cells/tissue and filter - in cold, same water potential, pH controlled solution - centrifuge/spin and remove nuclei/cell debris - centrifuge at high(er) speed so that chloroplasts settle out Give one feature of chloroplast that allow protein to be synthesised and describe one difference between this feature and similar features in the rest of the cell - Correct Answer DNA - not associated with his tones Name the 3 phases shown and describe the role of the spindle fibres and the behaviour of chromosomes during each of these phases - Correct Answer - prophase, metaphase, anaphase - in prophase, chromosomes condense - in metaphase, centromere attaches to spindle fibres - in anaphase, centromeres divide - in any, spindle fibres shorten Use this information to explain why the treatment with an ADC often causes side effects - Correct Answer - binds to healthy cells - causes damage to healthy cells Suggest and explain two further investigations that should be done before this ADC is tested on human breast cancer patients - Correct Answer - test on other mammals to see side effects - test on healthy humans to see side effects Suggest one reason why a data logger was used and explain why it was important in the investigation - Correct Answer To increase resolution as the length was too small Use this information and Table 6 to show how each population is better adapted for its natural environment when compared with the other population - Correct Answer - Population 1 grew longer roots in warm temperatures and population 2 grew longer roots in cool temperatures - SDs don't overlap so difference in mean not due to chance - 1 is better adapted to warm conditions as it has more saturated FA so more energy available - 2 is better adapted to cool conditions as. it hasw more unsaturated FA so more lipase activity Contrast the structure of the 2 cells visible in the electron micrographs shown in figure 14 - Correct Answer - magnification figures shows A is bigger than B - A has a nucleus whereas B has free DNA