Photosynthesis as an Energy Transfer Process (CIE A Level Biology)

Chloroplasts contain photosynthetic pigments.

Describe the arrangement of the pigments inside a chloroplast.

Outline the following processes connected to the pigment arrangements described in part a):

Photoactivation

[2]

Photolysis

[2]

In addition to the processes outlined in part b) the light dependent reactions of photosynthesis also involve the processes of oxidation and reduction.

Explain where oxidation and reduction occur during the light dependent reactions.

Pigment molecules are arranged in light-harvesting clusters known as photosystems: photosystem I (PSI) and photosystem II (PSII). These are involved in different photophosphorylation reactions of the light-dependent stage of photosynthesis. 

Fig. 1 shows some of the events of the light independent reactions.

Fig. 1

Identify the process shown in Fig.1.

[1]

Give two reasons for your answer to part (i).

[2]

The element cadmium, sometimes present in polluted soils, is toxic to plants even at low concentrations. Research has shown that cadmium can bind to photosystem II, impacting the process marked A in Fig 1.

Name the process marked A in Fig.1.

[1]

With reference to your answer to part i), outline the impact that cadmium would have on photosynthesis.

Describe the process taking place at the position marked B in Fig.1.

Fig.1 shows a representation of the light independent stages of photosynthesis.

Fig. 1

From Fig.1, identify:

Compound M.

[1]

(ii)

Compound O.

[1]

(iii)

The enzyme that catalyses the reaction between compounds M and O.

[1]

With reference to Fig.1 explain how the products of the light dependent reactions are used in the light independent reactions.

Compound P is a product of the light independent reactions.

Give three other molecules that could be formed from compound P inside plant cells.

[3]

Name the type of reaction that would convert compound P into a polymer.

Explain one reason why compound P is converted into other molecules such as those given in part c) i) rather than being stored as a six-carbon (6C) molecule in the cells.

Fig. 1 is a transmission electron micrograph of a chloroplast.

Fig. 1

Many compounds and structures involved in photosynthesis are located in a chloroplast.

Using the labels A, B or C, complete Table 1 to show the location of four of these compounds or structures.

You may use each of the letters A, B and C once, more than once, or not at all.

Table 1

[3]

Elodea canadensis is an aquatic plant that lives submerged in freshwater.

Equal‐sized plants of E. canadensis were exposed to different wavelengths of light for the same period of time. As each plant photosynthesised, the number of bubbles of oxygen leaving the plant was counted.

For each wavelength, the rate of oxygen production was calculated.

The results are shown in Fig. 2.

Fig. 2

Describe and explain the results shown in Fig. 2

Chlorophyll b, carotene and xanthophyll are known as accessory pigments.

Describe the role of the accessory pigments in photosynthesis.

Fig.1 is an outline diagram of the Calvin cycle.

Fig. 1

With reference to Fig. 1, describe stage A of the Calvin cycle.

Outline the importance of the light-dependent reactions in allowing stage B of the Calvin cycle, as indicated in Fig. 1, to proceed.

Substance C in Fig. 1 represents a variety of complex organic molecules. 

Give three named examples of substance C and the Calvin cycle intermediates from which these examples are produced.

Corals grow in shallow seawater. Corals consist of colonies of small animals called polyps. These polyps have photosynthetic protoctists called algae within their cells, which is advantageous both to the coral polyps and to the algae.

The algae that live within the cells of coral polyps can also live independently as free-living algae.

The algae that live within the cells of coral polyps have five different chloroplast pigments.

Table 1 shows the light wavelengths at which each algal chloroplast pigment shows its two largest peaks of light absorption.

Table 1

Corals can be kept in glass tanks that are usually lit by lamps radiating mainly violet and blue light, with wavelengths in the range of 400 nm to 490 nm.

With reference to Table 1, suggest why lamps radiating mainly violet and blue light are expected to increase the growth of coral polyps more than lamps radiating light of all wavelengths.

Photosynthesis in the algae living within the cells of coral polyps is the same as photosynthesis in plant cells.

Outline the process of cyclic photophosphorylation.

Paper chromatography can be used to separate photosynthetic pigments obtained from chloroplasts.

Fig. 1 shows the chromatography strip with distinct pigment bands.

Fig. 1

The four bands represent four pigments: chlorophyll a, chlorophyll b, xanthophylls and carotenes (but not necessarily in that order). A student suggests bands 3 and 4 most likely represent the two chlorophyll pigments.

Explain why the student is correct. 

Describe how to accurately identify the pigments in the chromatogram shown in part (a).

Fig. 2 shows the chromatograms.

Fig. 2

Palmaria also 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.

Suggest why this might be.

Light of shorter wavelengths penetrates water to greater depths than light of longer wavelengths.

Using information here and from part (c), suggest why red algae such as Palmaria can live at greater depths than many other aquatic algae.

The concentration of carbon dioxide gas in the air of a woodland changes over 24 hours. Carbon dioxide concentrations 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 woodland over time and at different heights. Assume that there is no air movement caused by wind throughout the 24 hours.

A team of researchers investigated the effect of changing the carbon dioxide concentration on the levels of glycerate-3-phosphate (GP) and ribulose bisphosphate (RuBP) in photosynthesising cells.

Table 1 shows the results obtained when the carbon dioxide concentration was reduced.

Table 1

Explain the results for RuBP and GP at 0.003% carbon dioxide concentration.

The researchers carried out a similar experiment but increased the carbon dioxide concentration from 1.0 % to 2.0 %. The relative levels of GP and RuBP remained the same both before and after the experiment.

Explain two reasons why this might be the case.

Fig. 1 shows the absorption spectra for three different photosynthetic pigments.

Fig. 1

Compare the absorption spectra of chlorophyll b and carotenoids shown in Fig.1.

With reference to Fig. 1:

Suggest the colour of carotenoid pigments.

[1]

Explain your answer to part (i).

[1]

It is also possible to represent action spectra on a graph like that shown in Fig. 1.

State how the information represented by an action spectrum is different to that represented by an absorption spectrum.

Sketch a suggested action spectrum onto the graph shown in Fig.1.

A researcher wanted to investigate the wavelengths of light that hit the ground in a woodland area. They measured the wavelengths of direct sunlight and sunlight that had passed through the tree canopy. Fig. 2 shows their results.

Fig. 2

Only a small number of plant species are found on the ground below the trees in woodland areas.

Use Fig. 1 and 2 to suggest why.

Some species of deep ocean-living bacteria carry out the process of chemosynthesis. Chemosynthesis uses energy stored in chemicals such as methane, hydrogen sulfide (H₂S) and carbon dioxide, to produce glucose.

A simplified example of a chemosynthesis reaction is shown below:

6CO₂  + 12H₂S → C₆H₁₂O₆ + 6H₂O + 12S

Use your knowledge of photosynthesis to suggest the role of hydrogen sulfide in chemosynthesis.

A suspension of photosynthetic pigments was isolated from another species of aquatic bacteria. A reagent that is blue when oxidised and colourless when reduced was added to the suspension.

The suspension of pigments in blue reagent was exposed to sunlight and the blue colour disappeared.

Explain this observation.

In the same suspension, the concentration of glycerate-3-phosphate (GP) was also measured. It was found to increase during the addition of the blue reagent. 

Explain this observation.

The bacteria species described in parts (b) and (c) live underwater at a depth of 5 metres. Most of the light that penetrates to this depth falls at wavelengths of between 400-600 nm.

Suggest which photosynthetic pigment(s) is/are likely to be most abundant in these bacterial cells. Explain your answer.