SL Paper 3
When feed for animals is stored, moisture levels need to be kept low to prevent the growth of fungi. Feed was exposed to 15 % moisture and placed into a respirometer. O2 consumption was monitored using the respirometer over a period of six days.
[Source: © International Baccalaureate Organization 2019]
Outline how O2 consumption is measured using a respirometer.
Suggest one conclusion that can be drawn from the results shown in the graph.
Other than humidity, suggest a variable that would need to be controlled in this experiment.
Outline the role of fungi in nutrient cycling.
A study was carried out on the activity of catalase in bacteria living in extreme environments. Catalase decomposes hydrogen peroxide (H2O2). The data were obtained for a strain of bacteria called Vibrio rumoiensis which exhibits high catalase activity.
Describe the relationship between increasing H2O2 concentration and catalase activity.
Identify two factors that would need to be controlled in generating these data.
Evaluate the claim that, based on the data, the optimum H2O2 concentration for catalase is 70 mM.
Students exposed the water plant Cabomba caroliniana to different light intensities. The bubbles of oxygen gas released by the plant were counted each minute.
Compare and contrast the experimental results for the effect of light intensity on the rate of photosynthesis of a green plant with the expected trend line.
C. caroliniana can grow well in water at 27°C. This experiment was carried out at 25°C.
Describe the effect of carrying out the same experiment at 15°C.
This experiment measured the quantity of oxygen gas released by the water plant. State one other way of measuring the rate of photosynthesis.
Thin-layer chromatography was carried out on red and brown algae to discover what photosynthetic pigments they contained. The results were compared with the known pigments found in spinach leaves.
Identify pigment labelled P.
State a suitable solvent for extracting photosynthetic pigments from plant tissue.
Explain how the pigments in the chromatogram of spinach are identified.