Paper chromatography can be used to separate photosynthetic pigments obtained from chloroplasts. The chromatography strip below shows distinct pigment bands.
The teacher explains that the four bands represent four pigments: chlorophyll a, chlorophyll b, xanthophylls and carotenes (but not necessarily in that order). The teacher asks a student to suggest which bands most likely represent the two chlorophyll pigments. The student suggests bands 3 and 4.
The photosynthetic pigments from two aquatic algae, green alga genus Oedogonium and red alga genus Palmaria, were separated by thin layer chromatography. The chromatograms are shown below.
Palmariaalso contain a red pigment known as phycoerythrin. The pigment appears red because it absorbs blue light and reflects red light. The pigment phycoerythrin is absent from the chromatogram above.
A commercial farmer growing peppers keeps her greenhouses at 25 °C and circulates air around the greenhouses. Air has a CO2 concentration of 0.04 % and the ambient light intensity is 3 000 lux.
i)
Use the graph in part a) to state whether the farmer would be more likely to achieve higher pepper yields by raising the carbon dioxide concentration to 0.1 % or by raising the temperature to 35 °C.
There are two types of chlorophyll in chloroplasts, chlorophyll a and chlorophyll b. Researchers created a genetically-modified (GM) vine plant with an allele that caused them to synthesise higher levels of chlorophyll b than wild-type vine plants. They investigated the effect of this new allele on the rate of plant growth.
The researchers grew wild-type and GM vines. They grew some of each in low light intensity and grew others in high light intensity. They extracted chloroplasts from mature plants of both types. Finally, they measured oxygen production at different light intensities by the chloroplasts they had extracted from the plants.
i)
Oxygen production here is used as a measure of the rate of photosynthesis.
State why this is possible.
[1 mark]
ii)
Calculate the percentage improvement in oxygen production caused by the genetic modification for vines grown at high light intensity at an experimental light intensity of 20 mmol photons m-2 min-1. Give your answer to 3 significant figures.
Lab technicians wanted to determine the effects of light intensity and temperature on the rate of photosynthesis in rhododendron plants growing in parks and gardens. They recorded the effect of different temperatures on the net rate of photosynthesis at various light intensities. Their experiment also recorded the rate of respiration at the different temperatures. The graph below shows the results from their experiment.
Explain the increase in the net rate of photosynthesis between points A and B on the graph.
In another experiment a student looked at the effect of light intensity on the rate of photosynthesis in pond weed. They set up the investigation as shown below and altered the light intensity by changing the distance between the lamp and the pondweed.
Identify four variables that need to be controlled in this investigation.
The graph below shows the student’s results from their investigation in part b).
Calculate the percentage decrease in the rate of photosynthesis that takes place when the distance from the lamp is 10 cm compared to when it is 90 cm. Show your working.
Identify, with a reason, one challenge that would be faced by the technicians in a) that would not be faced by the student in part b) when carrying out their experiments.
A variegated plant was grown in a laboratory by a student. One of its leaves is shown below (Fig. 1). The student left the whole plant in the dark for 12 hours to inhibit photosynthesis. After this time they covered part of the leaf with a rectangle of black card (Fig. 2). Following the exposure of the plant to sunlight for a further 3 hours the student removed the black card and then removed the leaf from the plant before testing the whole leaf for starch (Fig. 3).
Suggest why photosynthesis was inhibited for 12 hours.
One mark will be awarded for clarity of communication throughout this question.
a)
Explain how researchers could prepare an initial concentrated solution containing photosynthetic pigments for separation during thin layer chromatography.
In a woodland the concentration of carbon dioxide gas in the air changes during a 24-hour period. It can also vary depending on the height above the ground at which a gas measurement is taken.
Explain the variation in carbon dioxide concentration in a woodland over time and at different heights. Assume that there is no air movement caused by wind throughout the 24-hour period.
