Respiration in Organisms

All organisms need energy, which they get from food by respiration. In cellular respiration, food is broken down inside cells to release energy. In aerobic respiration, glucose is broken down using oxygen: glucose -> carbon dioxide + water + energy. Some organisms, such as yeast, respire without oxygen in anaerobic respiration, giving glucose -> alcohol + carbon dioxide + energy, which is why yeast is used in making bread and wine. During heavy exercise our muscle cells also respire anaerobically and form lactic acid, causing muscle cramps. Breathing means taking in oxygen-rich air (inhalation) and giving out air rich in carbon dioxide (exhalation). An adult at rest breathes about 15 to 18 times a minute. During inhalation, the ribs move up and outwards and the diaphragm moves down, enlarging the chest cavity so air enters the lungs. Other animals breathe differently: cockroaches through spiracles and tracheae, earthworms through their moist skin, and fish through gills. Plants exchange gases through stomata in leaves, while roots take air from the spaces between soil particles.

Detailed Worksheet: Respiration in Organisms Section A - Definitions (10 marks) 1. What is cellular respiration? Why is it necessary? (2 marks) 2. Distinguish between aerobic and anaerobic respiration. (2 marks) 3. Define inhalation and exhalation. (2 marks) 4. What is breathing rate? What is its normal value for an adult at rest? (2 marks) 5. What are spiracles and tracheae? In which animal are they found? (2 marks) Section B - Calculations and Applications (15 marks) 6. Write word equations for (i) aerobic respiration (ii) anaerobic respiration in yeast (iii) anaerobic respiration in muscles. (3 marks) 7. Name the respiratory organ of (i) earthworm (ii) fish (iii) cockroach (iv) frog on land (v) human (vi) whale. (3 marks) 8. Why do we get muscle cramps after heavy exercise? How do a hot water bath or massage give relief? (3 marks) 9. Why do we breathe faster after running? Why does a person yawn when sleepy or tired? (3 marks) 10. Explain why (i) plants die when the soil is overwatered (ii) we sneeze when we inhale dust (iii) it is advisable not to sleep in a closed room with a burning coal stove. (3 marks) Section C - Diagrams (10 marks) 11. Draw a labelled diagram of the human respiratory system showing the nostrils, nasal cavity, windpipe, lungs, ribs and diaphragm. (4 marks) 12. Draw diagrams showing the position of the ribs and diaphragm during inhalation and exhalation. (3 marks) 13. Draw a labelled model of the lungs made with a bottle, balloons, a Y-tube and a rubber sheet, and explain what happens when the sheet is pulled down. (3 marks) Section D - Analysis and Higher-order Thinking (15 marks) 14. Boojho blew air into a test tube of lime water through a straw, and also pumped ordinary air through another tube of lime water using a syringe. (i) Which tube turned milky first? (ii) Why? (iii) What does this show about exhaled air? (iv) Write the gas that causes the change. (5 marks) 15. Deep-sea divers and mountaineers carry oxygen cylinders. (i) Why do divers need them? (ii) Why do mountaineers need them at high altitudes? (iii) Why do fish not need cylinders underwater? (iv) How do whales and dolphins breathe? (5 marks) 16. Yeast is mixed with flour and sugar to make bread rise. (i) What kind of respiration does yeast perform? (ii) Which gas makes the dough rise? (iii) Write the word equation. (iv) Why does the alcohol not remain in baked bread? (5 marks) Instructions: Time allowed 2 hours. Attempt all sections. Write word equations with arrows and label all diagrams.