1. Name the two products and one waste product of the light-dependent reaction.
Answer
Products: reduced NADP (NADPH) and ATP
Waste product: Oxygen
2. Name the type of reaction when ATP is converted to ADP.
Answer
Hydrolysis.
3. What is the term given to the maintenance of a proton gradient across the thylakoid membrane and the subsequent movement of those protons back across the membrane down their concentration gradient ?
Answer
Chemiosmotic theory or chemiosmosis.
4. Name the two ways in which triose phosphate can be used during the light-independent stage of photosynthesis.
Answer
Regeneration of RuBP and conversion into organic substances (glucose).
5. Scientists wanted to investigate the effect that changes to environmental conditions had on the rate of photosynthesis. They provided a plant with radioactive carbon in the form of carbon dioxide, as shown in the figure below.
The scientists were able to record the concentrations of RuBP and GP produced over time. After 3 minutes the scientists changed one environmental factor in order to study the effect this had on the production of specific substances. All other conditions were kept the same.
Experiment 1: Light, dark after 3 minutes
Experiment 2: CO2, removed after 3 minutes
Details of the experiments and the results are shown in the table below.
Radioactive carbon dioxide was used in this investigation. Explain why.
Answer
Radioactivity can be traced. Carbon dioxide is used in the light-independent reaction.
6. Explain the results of Experiment 1.
Answer
Between hour 1 and 2, the concentrations of RuBP and GP increase, then plateau. They remain constant because the amount being used equals the amount being produced. RuBP then decreases when light is removed, while GP increases. This is because, without light, no ATP or NADPH is produced. As a result, TP cannot be formed, and RuBP cannot be regenerated. GP is not reduced into triose phosphate, so its concentration increases.
7. Explain the results of Experiment 2.
Answer
Between hours 1 and 2, the concentration of RuBP/GP increases and then plateaus. It remains constant because the amount being used is equal to the amount being produced. RuBP then increases when carbon dioxide is removed, while GP decreases. This is because, without carbon dioxide, RuBP cannot be carboxylated, converted to GP, or combined with carbon dioxide. As a result, GP cannot be formed. RuBP builds up since it is being regenerated but not consumed.
8. A student investigated the effect of light intensity on the rate of photosynthesis. In order to measure the rate he used dichlorophenolindophenol (DCPIP). DCPIP is dark blue when oxidised, but when reduced it is colourless. A suspension of chloroplasts was prepared and used to set up six tubes. The table below lists the contents of each tube.
The table below shows the conditions for each tube.
All tubes were placed in their positions for 6 minutes. The student used a colorimeter to measure the absorbance of light through each mixture as an indicator of the rate of photosynthesis. This was measured at the start and then after 6 minutes. The table below shows the results.
Explain the purpose of test tubes 1, 2 and 3.
Answer
These were used as controls and standards. Tube 1 to show the absorbance in the absence of DCPIP. Tube 2 to show that DCPIP cannot become reduced without chloroplasts and therefore light dependent-reaction occurring. Tube 3 to show that DCPIP cannot become reduced solely with chloroplasts, and it requires light in order to get reduced.
9. The student processed the data so that he could compare rates of photosynthesis. Complete the table below.
Answer
10. Describe and explain the results above.
Answer
As the distance from the lamp (or light) decreases, the intensity increases, and the percentage of absorbance decreases at a faster rate. This indicates that the light-dependent reaction is occurring more rapidly. DCPIP is reduced more quickly, causing the solution to become lighter and therefore absorb less light.
11. Describe the steps the student should have taken before he used the colorimeter.
Answer
The student should calibrate the colorimeter using a chloroplast suspension in buffer solution so that the absorbance is set to 0.
12. The midrib of the leaf was removed from the leaf before blending. Suggest why.
Answer
Midrib has xylem and phloem, and no chloroplasts.