Explain how the structure of the gas exchange system of an insect ensures that there is a large surface area for gas exchange.

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Corey Harris
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i Explain how the structure of the gas exchange system of an insect ensures that there is a large surface area for gas exchange.

1 1 Gas exchange takes place by diffusion. surfacearea differenceinconcentration diffusion lengthof diffusionpath a The diagram shows part of an insect tracheal system. i Explain how the structure of the gas exchange system of an insect ensures that there is a large surface area for gas exchange. ii Describe one way in which the transport of oxygen to the muscles of an insect is different to transport of oxygen to the muscles of a fish. iii Breathing movements can bring air into the tracheoles. What causes the diffusion of oxygen molecules into the muscle fibre? This resource sheet may have been changed from the original 1

2 b Air enters the tracheal system via the spiracles on the insect body surface. Valves allow these spiracles to open and close. i Use the information in the graph to suggest what causes the spiracles to open. ii Explain the advantage of these spiracle movements to insects that live on land. 2 Plant scientists measured the potassium ion concentration in sections taken through closed and open stomata on the leaves of a bean plant. a The scientists found an increase in the concentration of potassium ions in the guard cells when the stomata were open. Suggest where these potassium ions come from. b The increase in potassium ion concentration will affect the water potential of the guard cells. Explain how this causes the stomata to open. (3 marks) This resource sheet may have been changed from the original 2

c When stomata are open, the increase in potassium ion concentration involves active transport. The scientists treated the guard cells with a respiratory poison and the stomata started to close.

3 c When stomata are open, the increase in potassium ion concentration involves active transport. The scientists treated the guard cells with a respiratory poison and the stomata started to close. Suggest why. (3 marks) 3 A student used a spirometer to measure her tidal volume and breathing rate. The diagram below shows a spirometer. The top of the chamber of air is attached to a position sensor, which records movement of the chamber and displays the results on a computer screen. To measure her tidal volume and breathing rate the student breathed in and out through the mouthpiece while wearing a nose clip. a i Describe what happened to the chamber of air during inspiration. ii Chamber T contains a chemical that absorbs carbon dioxide. Suggest why it is important that carbon dioxide is absorbed in chamber T. iii The student wore a nose clip when using the spirometer to measure her tidal volume. Suggest a reason why. This resource sheet may have been changed from the original 3

ii Use the diagram to calculate her breathing rate in breaths per minute. Show your working.

4 b The diagram below shows the trace obtained by the student using the spirometer. i Use the diagram to calculate the tidal volume for this student. Show your working. ii Use the diagram to calculate her breathing rate in breaths per minute. Show your working. c Explain how the student could use her answers to part b to calculate her pulmonary ventilation rate. This resource sheet may have been changed from the original 4

5 4 Miner s lung is a disease caused by breathing in dust in coal mines. The dust causes the alveolar epithelium to become thicker. People with miner s lung have a lower concentration of oxygen in their blood than healthy people. a i Describe the path by which oxygen goes from an alveolus to the blood. ii Explain why people with miner s lung have a lower concentration of oxygen in their blood. b In healthy lungs, a gradient is maintained between the concentration of oxygen in the alveoli and the concentration of oxygen in the lung capillaries. i Describe how ventilation helps to maintain this difference in oxygen concentration. ii Give one other way that helps to maintain the difference in oxygen concentration. c Scientists investigated the number of cases of miner s lung reported in Britain between 1992 and Coal mining in Britain had been dramatically reduced by Some scientists concluded that the rise in reported cases of miner s lung after 1992 shows that the disease takes a long time to develop. Evaluate this conclusion. AQA June 2010 This resource sheet may have been changed from the original 5

iii Explain why it is an advantage for a polypeptide to be digested by an endopeptidase before an exopeptidase.

6 5 The diagram shows the action of a peptidase enzyme on a polypeptide. a i Give the evidence from the diagram that the enzyme is an endopeptidase. ii Describe the reaction catalysed by the enzyme. iii Explain why it is an advantage for a polypeptide to be digested by an endopeptidase before an exopeptidase. b The graph shows the effect of ph on the activity of the endopeptidase. Suggest the region of the human gut in which this peptidase would be active. Explain your answer. (3 marks) This resource sheet may have been changed from the original 6

c Peptidases are usually secreted in an inactive form and activated to the active form once in the gut lumen. i Explain the advantage of peptidases being secreted in an inactive form.

The diagram below shows the apparatus he used. Visking tubing is a semipermeable membrane that allows small molecules to pass through. In this experiment it models the lining of the gut.

7 c Peptidases are usually secreted in an inactive form and activated to the active form once in the gut lumen. i Explain the advantage of peptidases being secreted in an inactive form. ii Amylase is not secreted in an inactive form. Explain why this is not a disadvantage. 6 A student set up an experiment to model digestion of starch in the gut. The diagram below shows the apparatus he used. Visking tubing is a semipermeable membrane that allows small molecules to pass through. In this experiment it models the lining of the gut. a Before putting the amylase and starch mixture into the Visking tubing, the student tested a sample of the mixture with iodine solution and did a Benedict s test on a second sample. Colour of amylase and starch mixture after testing with iodine Blue-black Colour of amylase and starch mixture after Benedict s test Blue This resource sheet may have been changed from the original 7

8 Suggest why he carried out these tests. b After he had put the amylase and starch mixture into the Visking tubing he rinsed the outside of the tubing under the tap. Explain why. c The boiling tube containing the distilled water and Visking tubing sac were placed in a water bath at 37 C. Suggest why the boiling tube was placed in the water bath at 37 C. Every 5 minutes, samples of the distilled water surrounding the Visking sac were tested using iodine solution and a Benedict s test was also done on separate samples. The table below shows the student s results. Time/min Colour of solution after testing with iodine Colour of solution after Benedict s test 5 Yellow Blue 10 Yellow Blue 15 Yellow Blue 20 Yellow Green d i Explain the student s results at 5 minutes and at 20 minutes. This resource sheet may have been changed from the original 8

9 After 20 minutes the student removed the Visking tubing sac and emptied the contents into a beaker. The solution was tested with iodine and Benedict s test. Colour of solution from inside Visking tubing after testing with iodine Yellow Colour of solution from inside Visking tubing after Benedict s test Brick red ii Explain the difference in colour of the Benedict s test on the sample from the water surrounding the Visking tubing and colour of the Benedict s test on the solution inside the Visking tubing after 20 minutes. This resource sheet may have been changed from the original 9

3.3.2 Gas Exchange SPECIFICATION

alevelbiology.co.uk 3.3.2 Gas Exchange SPECIFICATION Adaptations of gas exchange surfaces, shown by gas exchange: Across the body surface of a single-celled organism In the tracheal system of an insect