2023 SASS Bio Prelims Ans

Prelim Examination 2023/4Exp ANSWERS Paper 1 – MCQ 1 A 11 B 21 B 31 D 2 B 12 B 22 C 32 C 3 A 13 B 23 A 33 B 4 D 14 A 24 D 34 D 5 C 15 C 25 A 35 D 6 D 16 C 26 B 36 B 7 B 17 B 27 C 37 B 8 C 18 B 28 A 38 A 9 A 19 A 29 C 39 C 10 D 20 A 30 C 40 D Paper 2 – Section A (50 marks) Qn. Answer Marks Comments 1a - An individual with anemia have a lower red blood cell count than a healthy individual; 1 R: less blood cells (not specific) Generally well done. 1b - Red blood cells contain haemoglobin that binds reversibly with oxygen - This allows red blood cells to transport oxygen from the lungs to the rest of the body - A lower red blood cell count results in a decrease in oxygen transported to the brain 1 1 1 Poorly done. Many students did not state the function of haemoglobin. Many also did not specify the brain despite the question stating ‘light-headness’.

Prelim Examination 2023/4Exp ANSWERS 1c - Tachycardia / faster heart rate / heart failure / heart cells die / heart to be overworked / heart to be strained - to compensate for its reduced ability of blood to carry oxygen 1 1 R: high blood pressure (condition is not specific to the heart) A: weaker contractions as heart muscle tissue does not receive sufficient oxygen 2ai - A consists of layers of long cylindrical, closely packed cells while B consists of irregularly shaped cells with numerous large intercellular air spaces between them. - A contains more chloroplasts than B. - B contains the transport tissues / xylem and phloem while A does not. - Cells in B are covered with a thin film of moisture while cells in A does not. Any 2 2 R: functional differences (a handful of students did not read the question properly) Poorly done question, while most students can identify the 4 structures, many are not familiar with the structural features. Some students are not making comparisons but rather simply listing structural features. 2aii - C is made up of dead cells while D is made up of living cells. - C has a continuous lumen / no cross walls while D contains cross-walls / sieve plates between cells. - C contains lignin deposits while D does not. Any 2 2 2b 3 1 mark for accurate drawing a pair of guard cells and stoma 1 mark for any three correctly labelled structures 1 mark for drawing criterias (solid lines without shading, appropriate size, neat labels) Poorly done. Many are not clear about structures in guard cells, shaded the nucleus, had label lines cutting across excessively and labelled stomata (plural).

Prelim Examination 2023/4Exp ANSWERS 2c - A moist environment has higher humidity; - which means higher accumulation of water vapour outside the stomata; - This makes the water vapour concentration gradient between the leaf and the atmosphere less steep / more gentle; - This results in a lower rate of transpiration; An