NCHS_Bio_P3ans

SEC 4 BIOLOGY PRELIMINARY EXAMINATION 2020 PAPER 3 Qn Answer Marker’s comments 1(a)(i) - Neat table [1] with column headings at appropriate positions [1] - Correct Trend [1] Yeast mixture Number of bubbles released in 2 minutes A SS results 0 bubbles (accepted range 0-3) B SS results: 36 bubbles 1(a)(ii) There is a smaller number of bubbles released from B than A (or based on students’ answers in 1ai) [1]. A high temperature of water at 70oC, denatured the enzymes in yeast [1]. Less aerobic respiration to release carbon dioxide bubbles [1]. 1(a)(iii) Attach a syringe at the end of the delivery tube to measure the volume of gas released. 1(a)(iv) Any 2 of below: - Volume of mixture in the syringe was read at eye-level to reduce parallax error - No mixing of syringes to prevent contamination - To remove air bubbles in the syringe by moving the liquid up and down/ draw mixture slowly

1(b) Size of drawing more than 2/3 of space (> 6.0 cm), with sharp, continuous lines [1] Accurate drawing (3 layers drawn; transverse section with seeds radiating from center) [1] Correct labelling of at least two parts e.g. flesh / seed / skin/ placenta [1] Magnification line measures longest width of drawing and is drawn outside of drawing [1] 2(a)(ii) Magnification calculated with working shown (length of drawing / length of actual) [1] Final value to 1 d.p with an ‘x’ in front [1] Students need to be reminded that magnification has to be written in ONE DECIMAL PLACE, with an ‘x’ in front.