1. What is the only stage of respiration that takes place in both aerobic and anaerobic respiration, and where does it take place ?
Answer
Glycolysis, in the cytoplasm.
2. A student investigated the respiration of yeast as shown in the figure below. Suggest why oil was used in this investigation.
Answer
The oil prevents oxygen from entering the space with the yeast, so the yeast respires anaerobically.
3. The table below shows the colour of the carbonate indicator at different pHs. Explain the change in the colour of the carbonate indicator when gas removed by the syringe is passed through it.
Answer
The gas that passed through the solution was carbon dioxide. It caused the indicator to turn yellow due to increased acidity.
4. This investigation would not produce the same result if the yeast was replaced with animal cell/tissue. Explain why.
Answer
Animals do not produce carbon dioxide when respiring anaerobically.
5. Students investigated respiration in woodlice. The flasks contained the following: W – Potassium hydroxide, X – Limewater, Y – Woodlice and Z – Limewater. Potassium hydroxide can absorb carbon dioxide. They set up the equipment as shown in the figure below. Explain why it was necessary to have potassium hydroxide in flask W.
Answer
The potassium hydroxide in flask W removed carbon dioxide from the air being drawn in, so any carbon dioxide entering flask Z was solely due to the respiration of the woodlice.
6. Explain why the student included flask X.
Answer
Flask X showed that the carbon dioxide had been removed from the air passing through, as demonstrated by the limewater not turning cloudy.
7. Suggest what you would expect the appearance of the limewater in flasks X and Z to be after 30 minutes.
Answer
X = Limewater remains clear because potassium hydroxide absorbed carbon dioxide before air entered flask X.
Z = Limewater has gone cloudy due to carbon dioxide being released in respiration.
8. A scientist was investigating the effect of different environmental conditions on the photosynthesis and respiration of oak leaves. She set up the investigation as shown in the figure below. The solution at the bottom of each test tube was carbonate indicator solution. Each test tube was equidistant from a light source. Explain the reason for setting up tube 4.
Answer
Tube 4 was used as a control to show that the changes in the other tubes were due to the living leaf carrying out photosynthesis or respiration.
9. Explain the results in tube 1, 2 and 3.
Answer
Tube 1: Plants can't photosynthesise. They respire and release CO2 which causes acidic conditions/indicator to turn yellow
Tube 2: Rate of respiration is greater than rate of photosynthesis. So more CO2 released than used causing acidic conditions.
Tube 3: Rate of photosynthesis is greater than respiration CO2 being removed from tube causing indicator to turn purple.
10. Name the conditions that the scientist should ensure were kept constant.
Answer
Temperature, light intensity, type of leaf, size of leaf and tube.