Photosynthesis as an energy transfer process

Ribulose 1,5-bisphosphate carboxylase/oxygenase (rubisco) is a key enzyme in the light independent stage (Calvin cycle) of photosynthesis. It carries out carbon fixation by joining carbon dioxide with RuBP. In some cases, a sugar phosphate occupies rubisco's active site, which leaves the enzyme inactive. Rubisco can be reactivated when another enzyme, rubisco activase, is present.

Feb/March 2018

Section B. Answer a single question.

Feb/March 2018

Red algae consist of multicellular protoctists that carry out photosynthesis and contain phycoerythrin. Phycoerythrin is a photosynthetic pigment.

Feb/March 2021

Describe the role of the internal membranes of the chloroplast in photosynthesis.

Feb/March 2023

The light-dependent stage of photosynthesis takes place in chloroplasts. During this stage, electrons are released from chlorophyll $a$ molecules and passed on to electron acceptors. If a redox indicator such as DCPIP is added to a suspension of illuminated chloroplasts, electrons are transferred to DCPIP, causing its colour to change from blue to colourless. A student investigated how the wavelength of light (colour of light) affected the rate of photosynthesis.

Feb/March 2024

Fig. 4.1 shows a photomicrograph of a transverse section of a C4 plant leaf.

May/June 2010

Section B. Attempt one question.

May/June 2010

Answer just one question.

May/June 2010

Section B - Select and answer one question.

May/June 2010

Section B. Respond to one question.

May/June 2011

Answer any one question.

May/June 2011

Answer only one question.

May/June 2011

Fig. 1.1 presents a transverse section of a dicotyledonous leaf.

May/June 2013

Explain how the leaf physiology of a C4 plant, such as maize, is adapted so that carbon fixation remains efficient at high temperatures.

May/June 2013

Describe the main structure of a chloroplast.

May/June 2013

Fig. 1.1 presents a transverse section of a dicotyledonous leaf.

May/June 2013

Section B. Answer only one question.

May/June 2013

Fig. 1.1 shows an electron micrograph of a chloroplast taken from a maize leaf cell.

May/June 2014

Fig. 1.1 shows a transverse section through part of a dicotyledonous leaf from the tea plant Camellia sinensis.

May/June 2015

Fig. 1.1 presents an electron micrograph of a chloroplast.

May/June 2015

Fig. 1.1 presents a section through part of a dicotyledonous leaf from the tea plant Camellia sinensis.

May/June 2015

Fig. 2.1 illustrates how temperature affects the rate of photosynthesis in a plant at low light intensity and at high light intensity.

May/June 2016

Corals live in shallow seawater. They are formed from colonies of tiny animals called polyps. These polyps contain photosynthetic protoctists, called algae, inside their cells, which benefits both the coral polyps and the algae. The algae living inside the polyps’ cells can also survive independently as free-living algae.

May/June 2017

Chloroplasts are one class of organelle within the plastid group. Although the different plastid types differ in structure and function, one plastid type can convert into another when environmental or developmental signals act. Example 1: plants kept in the dark contain plastids called etioplasts, and these do not have chlorophyll. When such plants receive light, the etioplasts rapidly become chloroplasts. Example 2: in the outer tissues of tomato fruits, chloroplasts turn into plastids called chromoplasts as the fruits ripen. The thylakoid membranes break down and chlorophyll synthesis stops. Chromoplasts make and store the red lycopene and orange β-carotene pigments.

May/June 2017

Corals are found in shallow seawater. They are made up of colonies of tiny animals known as polyps. Inside the cells of these polyps are photosynthetic protoctists called algae, and this arrangement benefits both the coral polyps and the algae. The algae that live inside the cells of the polyps are also able to survive independently as free-living algae.

May/June 2017

Fig. 7.1 shows the sequence for non-cyclic photophosphorylation in the chloroplast of a leaf mesophyll cell.

May/June 2018

Fig. 7.1 presents part of a section through the leaf of a C4 plant such as maize. The letters A, B and C indicate three cell types present in the leaf.

May/June 2018

Fig. 7.1 shows a transmission electron micrograph of a section of a chloroplast from a maize leaf cell.

May/June 2018

Describe how chloroplast structure is linked to its functions.

May/June 2019

Describe the function of chloroplast pigments in absorbing light.

May/June 2020

The structures and compounds taking part in the light-dependent stage of photosynthesis are shown, labelled A to J. A - thylakoid membrane B - starch grain C - chlorophyll $a$ D - chlorophyll $b$ E - water F - NADP G - electron H - proton I - ATP J - chloroplast envelope

May/June 2020

Photosynthesis is the process in which complex organic molecules are synthesised. Respiration is the process in which complex organic molecules are broken down.

May/June 2021

In eukaryotes, plant cells and photosynthetic protoctist cells contain chloroplasts.

May/June 2022

Stomata play a role in both transpiration and photosynthesis in plants. Fig. 9.1 shows an open stoma, its guard cells and the epidermal cells around it.

May/June 2022

Photosynthesis is an energy transfer process that leads to carbohydrate being made. It has two phases: the light-dependent stage and the light-independent stage. Cyclic photophosphorylation and non-cyclic photophosphorylation are key routes in photosynthesis that take place during the light-dependent stage.

May/June 2022

Fig. 1.1 presents a transmission electron micrograph of a section of a chloroplast.

May/June 2023

In plants such as rice, $Oryza\ sativa$, rubisco shows a low activity rate, and this reduces the rate of photosynthesis. The cereal crop sorghum, $Sorghum\ bicolor$, shows a high activity rate of rubisco. A genetically modified (GM) type of rice was made. Sections of the quaternary structure of rubisco in rice were changed so that they matched the rubisco in sorghum. The activity rate of rubisco in non-GM rice and GM rice was measured at different atmospheric carbon dioxide ($CO_2$) concentrations. The results are shown in Fig. 8.1.

May/June 2023

Fig. 8.1 shows a chloroplast diagram. Complete Table 8.1 using the letters K-N. A letter may be used once, more than once, or not used at all.

May/June 2023

Photosynthesis is the process of energy transfer in chloroplasts. Fig. 5.1 illustrates several biochemical events taking place in a chloroplast during the light-dependent stage of photosynthesis. Photosystems I and II (PSI and PSII) together with some associated proteins in the thylakoid membrane are shown.

May/June 2024

Scientists have devised a method of making food by means of artificial photosynthesis. - Solar panels change sunlight energy into electrical energy. - That electricity drives an electrolysis reaction between carbon dioxide gas and water, producing the organic product acetate. - The single-celled alga Chlamydomonas, which is a protoctist, is able to use acetate for growth and reproduction in the dark, rather than photosynthesising in the light. - The algae can then be processed to produce a food product. Fig. 4.1 presents an outline of the artificial photosynthesis process.

May/June 2025

A chloroplast consists of several different structures, and each one has a distinct role. The chloroplast structures listed are: stroma, lamellae, thylakoid membrane, ribosome, thylakoid space, starch grain, DNA, outer membrane.

May/June 2025

Fig. 9.1 shows a diagram of non-cyclic photophosphorylation.

May/June 2025

This question is about photosynthesis and the factors that influence its rate in flowering plants.

Oct/Nov 2010

In flowering plants, the light-dependent reactions are performed by photosynthetic pigments that are classified into two groups: primary pigments and accessory pigments.

Oct/Nov 2010

The rate at which photosynthesis takes place at different wavelengths of light can be plotted on a graph known as an action spectrum (Fig. 8.1).

Oct/Nov 2010

Section B - Answer only one question.

Oct/Nov 2011

Section B. Attempt one question.

Oct/Nov 2011

Respond to one question.

Oct/Nov 2011

Section B. Answer any one question.

Oct/Nov 2012

Describe the organisation and position of chloroplast pigments and discuss how they influence absorption spectra.

Oct/Nov 2012

An investigation was done to find out how light of different colours affects photosynthesis. Fifteen leaf discs from one plant were taken. Five sealed test-tubes were prepared, each with three leaf discs in hydrogencarbonate indicator solution. Hydrogencarbonate indicator solution changes colour at different $\text{pH}$ values. At the beginning of the investigation the indicator solution in all five test-tubes was orange-red. Four of the test-tubes were exposed to light of a particular colour. The test-tubes were exposed for the same time period. The fifth test-tube was wrapped in black paper and acted as a control. The outcomes are shown in Table 7.1. As the $\text{pH}$ rises, the indicator turns purple and as the $\text{pH}$ falls, the indicator becomes yellow.

Oct/Nov 2013

The light-dependent phase of photosynthesis occurs on the thylakoid membranes of the chloroplast. Fig. 7.1 illustrates some of the components involved in the light-dependent phase.

Oct/Nov 2013

Fig. 8.1 illustrates several reactions occurring within a palisade mesophyll cell.

Oct/Nov 2014

Fig. 8.1 illustrates some reactions occurring within a palisade mesophyll cell.

Oct/Nov 2014

Fig. 7.1 presents the absorption spectra for chlorophyll a and chlorophyll b, together with the matching action spectrum.

Oct/Nov 2015

Maize, sorghum and sugarcane are examples of C4 grass crops. These are commonly found in tropical regions. Oats and wheat, which are usually grown in temperate regions, are C3 plants. Most plants belong to the C3 group. They are described as ‘C3’ because the first product of photosynthesis is a three carbon compound.

Oct/Nov 2016

Grass crops like maize, sorghum and sugarcane are C4 plants. These are typical grass crops of tropical areas. Oats and wheat, which are commonly cultivated in temperate regions, are C3 plants. The majority of plants are C3 plants. They are called ‘C3’ because the first product of photosynthesis is a three carbon compound.

Oct/Nov 2016

Most plants are C3 plants, and they are called that because the first photosynthetic product they make is a three-carbon compound. The enzyme ribulose bisphosphate carboxylase/oxygenase (rubisco) catalyses the fixation of carbon dioxide in the Calvin cycle and is used by both C3 and C4 plants. Each molecule consists of eight large polypeptides and eight small polypeptides. Fig. 2.1 shows the molecule from the side.

Oct/Nov 2016

The light-dependent phase of photosynthesis in a suspension of isolated chloroplasts can be studied through the Hill reaction. Dichlorophenolindophenol (DCPIP) can be used to track the change. DCPIP is a blue dye that turns colourless when it is reduced by taking in hydrogen and electrons. Oxidised DCPIP (blue)  reduced DCPIP (colourless).

Oct/Nov 2017

Section B. Answer one question.

Oct/Nov 2017

The light-dependent phase of photosynthesis in a suspension of isolated chloroplasts can be examined with the Hill reaction. Dichlorophenolindophenol (DCPIP) may be used to track the process. DCPIP is a blue dye that becomes colourless when it is reduced by taking in hydrogen and electrons. Oxidised DCPIP (blue) \rightarrow reduced DCPIP (colourless).

Oct/Nov 2017

The Hill reaction can be used to investigate the light-dependent stage of photosynthesis in a suspension of isolated chloroplasts. DCPIP may be used to monitor the reaction. DCPIP is a blue dye that becomes colourless when it is reduced by gaining hydrogen and electrons. Oxidised DCPIP (blue) changes to reduced DCPIP (colourless).

Oct/Nov 2017

Explain how rice is adapted for growth when its roots are submerged in water.

Oct/Nov 2017

Fig. 7.1 shows a transmission electron micrograph of a chloroplast. A chloroplast contains many compounds and structures that take part in photosynthesis.

Oct/Nov 2018

Fig. 7.1 shows a simplified diagram of the Calvin cycle.

Oct/Nov 2018

Figure 7.1 shows a transmission electron micrograph of a chloroplast. A number of compounds and structures needed for photosynthesis are found inside a chloroplast.

Oct/Nov 2018

Fig. 5.1 presents the seaweed Laminaria hyperborea. It is a photosynthetic protoctist that lives in coastal waters near Norway. This seaweed is cultivated commercially so that the glucose polysaccharide alginate can be extracted. Alginate is incorporated into some food products. Rising atmospheric carbon dioxide has led to greater carbon dioxide levels in the ocean. As a result, ocean pH has fallen, causing ocean acidification. Scientists are investigating seaweeds such as L. hyperborea because photosynthesis in these organisms removes large amounts of carbon dioxide. In theory, this could raise ocean pH and help to reverse ocean acidification.

Oct/Nov 2019

Mining can cause heavy metal ions to be released, which pollutes lakes and rivers. When the concentration of heavy metal ions, including cadmium $(\text{Cd}^{2+})$ and copper $(\text{Cu}^{2+})$, is high, photosynthesis in plants slows down.

Oct/Nov 2019

Fig. 1.1 shows a transverse section of a maize leaf, Zea mays. Maize is a C4 plant.

Oct/Nov 2020

Fig. 1.1 displays a transmission electron micrograph of a chloroplast.

Oct/Nov 2020

Fig. 1.1 shows a transverse section of a maize leaf, $\textit{Zea mays}$. Maize is a C4 plant.

Oct/Nov 2020

Describe and explain how guard cells bring about stomatal opening.

Oct/Nov 2021

Scientists are looking for new methods to lower the concentration of carbon dioxide ($\text{CO}_2$) in the global atmosphere. There is concern that a rising atmospheric $\text{CO}_2$ concentration could cause changes that reduce biodiversity. Algae are aquatic photosynthetic protoctists. Some researchers genetically altered the unicellular alga, $\textit{Chlorella vulgaris}$, in an attempt to raise the rate of the light independent stage of photosynthesis. $\textit{C. vulgaris}$ was changed so that the gene coding for aldolase was expressed more strongly. Aldolase is an enzyme that increases the concentration of rubisco. Two cultures of $\textit{C. vulgaris}$, one genetically unmodified (unmodified) and one genetically modified, were grown under controlled conditions for 14 days. At regular intervals during the 14 days, samples were removed from the cultures to measure dry mass. The results are shown in Fig. 2.1.

Oct/Nov 2021

Part B Answer one question.

Oct/Nov 2021

Photosynthesis is a significant process for transferring energy.

Oct/Nov 2022

Photosynthesis is an energy-transfer process that occurs in the chloroplasts of plant cells.

Oct/Nov 2022

Photosynthesis is a vital process for transferring energy.

Oct/Nov 2022

Chloroplasts perform photosynthesis. Fig. 1.1 illustrates several structural features of a chloroplast and a number of processes that take place inside it.

Oct/Nov 2023

Outline the main features of non-cyclic photophosphorylation, which takes place in the light-dependent stage of photosynthesis.

Oct/Nov 2023

Photosynthesis takes place in chloroplasts. Fig. 1.1 illustrates several structural features of a chloroplast together with some of the processes occurring inside it.

Oct/Nov 2023

Mimosa pudica leaves are composed of several structures called pinnae. When the leaf is touched, the pinnae fold, causing the leaf to shut. Fig. 4.1 shows an open leaf of M. pudica before it is touched. Fig. 4.2 shows the same leaf after it has closed following touch.

Oct/Nov 2024

Paper chromatography is a method that can be used to separate and identify a range of chloroplast pigments.

Oct/Nov 2024

Mimosa pudica leaves are composed of several parts called pinnae. When the leaf is touched, the pinnae fold inwards and the leaf closes. Fig. 4.1 shows an open leaf of M. pudica before it is touched, whereas Fig. 4.2 shows the same leaf after closing in response to touch.

Oct/Nov 2024

Chloroplasts contain several different photosynthetic pigments in plants. A student separated and identified the chloroplast pigments in a spinach leaf extract by using two slightly different procedures. In Method A, thin layer chromatography (TLC) was used to separate the pigments, with a solvent mixture of ether and cyclohexane in the TLC. In Method B, the student carried out TLC again after treating the spinach leaf extract with a chemical. This chemical replaces a magnesium ion in a pigment with two hydrogen ions. The student used a leaf from the same spinach plant and the same solvent as in Method A. After calculating $R_f$ values and comparing them with reference values, the student identified the pigments. Fig. 3.1 displays the outcomes for Method A and Method B.

Oct/Nov 2025

(a) Fig. 9.1 presents an absorption spectrum for chlorophyll $a$ together with the matching action spectrum for a plant species. (b) Scientists examined how temperature affected the rate of photosynthesis and the rate of respiration in the trailing azalea, Kalmia procumbens, under a high light intensity. Fig. 9.2 displays the outcomes of this investigation.

Oct/Nov 2025

Plants contain a range of photosynthetic pigments inside their chloroplasts. A student separated and identified the chloroplast pigments in a leaf extract from a spinach plant by using two slightly different methods. Method A: a form of chromatography called thin layer chromatography (TLC) was used to separate the pigments; a solvent made from ether and cyclohexane was used in TLC. Method B: the student repeated TLC but first treated the spinach leaf extract with a chemical; this chemical causes a magnesium ion in a pigment to be substituted by two hydrogen ions. The student used a leaf from the same spinach plant, and the same solvent as in method A. The student worked out $R_f$ values and compared them with reference values to identify the pigments. Fig. 3.1 shows the outcomes for method A and method B.

Oct/Nov 2025

Cyclic photophosphorylation and non-cyclic photophosphorylation take place in the light-dependent stage of photosynthesis.

Oct/Nov 2025