2018 GCE O Level Bio Suggested Answer

2018 GCE O Level Biology Suggested Answer Paper 1 1 2 3 4 5 6 7 8 9 10 A A B B C D C A B A 11 12 13 14 15 16 17 18 19 20 C B C D A B C C B D 21 22 23 24 25 26 27 28 29 30 B D A D C C D B B A 31 32 33 34 35 36 37 38 39 40 C D A C D A C B D D Paper 2 (Section A) 1 (a) (i) State Chromosome 1 6 (ii) State Stage 3: Metaphase Stage 4: Anaphase 1 1 (b) (i) State Plant 2 1 (ii) State Plant 1: AA Plant 3: aa 1 1 2 (a) (i) State any 3 functions 1. Liver converts excess glucose to glycogen when stimulated by insulin 2. Produce bile 3. Stores iron 4. Deaminates excess amino acids 5. Detoxification of harmful substances into harmless substances 3 10

6. Liver converts stored glycogen to glucose when stimulated by glucagon (ii) State letter C 1 (iii) State Name: Bile Describe Function: Emulsifies large fat droplets into smaller fat droplets to increase surface area to volume ratio for faster rate digestion by lipase. 1 1 (b) (i) State 40 ◦C 1 (ii) Suggest The enzyme, rennin, had denatured and therefore lost its 3D active site so it could not bind to milk and cause it to clot. Therefore it did not form lumps. 1 (c) Suggest When it forms lumps, the flow of milk through the alimentary canal is slower and this increases the time for complete digestion and maximum absorption of nutrients for the developing young cow. 1 1 3 (a) (i) State 3 minutes 1 5 (ii) Describe relationship As temperature increases, the time taken for human blood to clot decreases. The graph shows that as temperature increases from 15 ◦C to 35 ◦C, the time taken for human blood to clot decreases from 24 minutes to 2.5 minutes. 1 1

(b) State 2 functions 1. Seals the wound to prevent excessive bleeding/ excessive loss of blood. 2. It prevents foreign particles (bacteria and virus) from entering the bloodstream and causing an infection. 1 1 4 (a) Describe adaptation 1. The wall of the alveolus is one cell thick. This provides a shorter diffusion distance for gases ensuring a faster rate of diffusion. 2. A thin film of moisture covers the inner surface of the alveolus and allows oxygen to dissolve in it for efficient diffusion of oxygen across alveolar wall. 3. The wall of the alveolus is supplied with a blood capillary that helps maintain the concentration gradient of gases for efficient diffusion with the continuous flow of blood. 1 1 1 11 (b) Suggest effect Carbon dioxide will not be fully removed from tissues and excreted from the lungs during exhalation. Explain effect Carbonic anhydrase, an enzyme present in the red blood cell, catalyses a reversible reaction in the formation of carbonic acid from carbon dioxide and water. Carbonic acid then dissociates into hydrogen ions and bicarbonate ions, transported in blood to the lungs. Hence, low levels of carbonic anhydrases indicates that less carbon dioxide can be brought to lungs to be excreted. 1 1 1 (c) (i) Describe The pressure in the alveoli decreases from 0 to -1.0 in 1s and then increases from -1.0 to 0 in another 1s during inhalation. 1 1

(ii) Describe The diaphragm muscles contracts and diaphragm flattens. External intercoastal muscles contract while internal intercoastal muscles relax. Ribs move upwards and outwards. Sternum moves up and forward. The volume of the thoracic cavity increases, the lung expands and volume increases. 1 1 1 5 (a) (i) 173.5 1 6 (ii) Calculate 180-175.5= 4.5 4.5/180 x 100= 2.5% 1 (iii) State Urea 1 (b) Describe role Structure A filters small molecules such as glucose, amino acids, urea and water from the blood through its partially permeable basement membrane into the Bowman’s capsule through the process of ultrafiltration. Some of these small molecules such as glucose, amino acids and water are selectively reabsorbed into B. The remaining substances such as urea and excess water that are not reabsorbed into B then determine the volume and concentration of urine. 1 1 1 6 (a) Describe function A contains the xylem and phloem. The xylem in the vein transports water and mineral salts from the soil to the leaves while the phloem transports sucrose and amino acids from the leaves to all parts of the plant. 1 1 6 (b) (i) State sucrose 1 (ii) State The phloem 1

(iii) Calculate 65/2.5=26 2 7 (a) Explain Process P, respiration, and process S, combustion, release carbon dioxide into the environment ensuring that there is a continuous supply of carbon dioxide for plants to carry out photosynthesis. Process Q, photosynthesis, absorbs carbon dioxide from the environment to synthesise carbohydrates which non-photosynthetic organisms can use to stay alive. In this way, processes P, Q and S play an important role in the carbon cycle by ensuring the carbon dioxide concentration in the atmosphere remain relatively constant. 1 1 1 6 (b) Describe role Decomposers such as bacteria and fungi break down dead organic matter and release carbon dioxide into the environment. 1 1 1 Paper 2 (Section B) 8 (a) (i) Axes with units Scale Plots Smooth curve 1 1 1 1 11 (ii) Calculate 100-15=85 1 (iii) Describe relationship As wavelength of light increases from 420nm to 500nm, the sensitivity of the retina increases from 5au to 100au. As wavelength of light increases beyond 500nm to 600nm, the sensitivity of the retina decreases from 100au to 5au. 1 1 (iv) 76 1

(b) Describe As light intensity increases, the circular muscles of the iris contract and the radial muscles of iris relax. The pupil becomes smaller or constricts To reduce the amount of light entering the eye. 1 1 1 9 (a) Compare Any 3: Osmosis is the net movement of water molecules only while diffusion and active transport involves the net movement of other molecules and ions. Osmosis and diffusion involves movement down a water or concentration gradient while active transport is against the concentration gradient. Osmosis and active transport requires a partially permeable membrane while diffusion does not. Active transport requires energy while diffusion and osmosis does not. 1 1 1 1 (b) (i) Explain Cell B The sugar solution has a higher water potential than the cell sap of cell B. Hence, water from the sugar solution entered the vacuole via osmosis causing the cell to expand and the vacuole to increase in size. Cell C The sugar solution has a lower water potential than the cell sap of cell C. Hence, water moves from the vacuole into the sugar solution via osmosis causing the cell to shrink and vacuole to decrease in size. 1 1 (ii) State B 1

(iii) Explain how its maintained The root hair cells have many mitochondria to release energy for the roots to take up ions via active transport. Importance The high ion concentration in the root hair cell helps to create the water potential gradient necessary for water to enter the root hair cell via osmosis. 1 1 1 Either 10 (a) Describe process Photosynthesis is the process by which light energy absorbed by chlorophyll is transformed into chemical energy. The chemical energy is used to synthesise carbohydrates from the raw materials water and carbon dioxide. Oxygen is realeased during the process. Chemical/word equation 1 1 1 1 1 1 10 (b) Explain Photosynthesis is an enzyme controlled reaction in the chloroplast and thus, temperature will affect the rate of photosynthesis. On a warm day, the temperature is higher and therefore enzymes and substrates have more kinetic energy so more collisions occur and more enzyme substrate complexes are formed. Thus, rate of photosynthesis is faste