Turn over 27 9 Plants and animals are adapted for gas exchange. (a) (i) Which row of the table describes gas exchange in the root of a plant? (1) A B C D Net movement of carbon dioxide Net movement of oxygen in only out only out only in only in and out in and out neither in nor out neither in nor out (ii) Which is the gas exchange surface in the stem of a woody plant? (1) A lenticel B pit C plasmodesmata D stomata 28 (b) Spiracles are small openings in the exoskeletons of insects that allow air to enter the respiratory system. Water can evaporate out of the spiracles when they are open. The insect can close the spiracles to reduce water loss. In an investigation, the water loss from insects in air with different humidities was measured. The insects were kept in air with 80% humidity and then moved into air with a lower humidity. Water loss was then measured. The investigation was repeated in air high in carbon dioxide to keep the spiracles open. The table shows the results of this investigation. Percentage humidity (%) Water loss from insects / mg hr–1 Insects in air Insects in air high in carbon dioxide 0 0.10 0.90 20 0.13 0.68 40 0.15 0.50 60 0.13 0.35 80 0.07 0.07 (i) State how the water loss could have been measured in this investigation. (1) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (ii) Calculate the percentage increase in water loss from the insects kept in air at 0% humidity compared with those kept at 80% humidity. Give your answer to two decimal places. (1) Answer .............................................................. % Turn over 29 (iii) Explain why the insects were kept in air with 80% humidity at the start of this investigation. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (iv) Explain the results of this investigation. (3) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 30 (c) The gas exchange surfaces of fish are the gills. The diagram shows part of the structure of a gill. direction of flow of water gill filaments lamellae Fish can be divided into two groups: species of fish that are active and species of fish that are inactive. The table shows some information about some species of fish and their gills. Species of fish Mass of fish / g Total number of gill filaments Number of lamellae on each side of filament per mm Surface area of gills / cm2 per g of fish Diffusion distance between water and blood / µm Active species Trachurus 26 1665 39 7.8 2.2 Lucioperca 70 1811 15 18.0 no data Salmo 394 1606 19 2.0 6.4 Katsuwonus 3258 6066 32 13.5 0.6 Thunnus 26600 6480 24 8.9 no data Inactive species Callionymus 39 478 16 2.1 no data Ictalurus 239 no data 10 1.2 no data Opsanus 251 660 11 1.9 5.0 Tinca 268 1764 22 1.8 2.5 Turn over 31 (i) Lamellae are present on both sides of the gill filaments. The mean length of a gill filament is 25 mm. Calculate the total number of lamellae on the gill filaments of Thunnus. Express your answer in standard form. (1) Answer .............................................................. 32 *(ii) Analyse the data to explain the relationships between the activity of these fish and the structure of their gills. 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(Total for Question 9 = 16 marks) TOTAL FOR PAPER = 90 MARKS