Photosynthesis

This is a transmission electron micrograph of a chloroplast.

Identify the components labelled A and B and describe how they are adapted for their function.

Identify one similarity and one difference between the structures of chloroplasts and the structures of mitochondria.

A student used thin layer chromatography (TLC) to separate the photosynthetic pigments in a chloroplast extract.

This is the result of the TLC.

Origin Solvent

Calculate the R_f for the most soluble pigment.

Give your answer to 2 significant figures.

The student noticed that the spots were very faint and thought that there might be other pigments present in the mixture that were too faint to be seen.

Describe how the student could increase the intensity of the spots using the same chloroplast extract.

Describe how the student could use the same equipment but increase the accuracy of the calculated R_f value.

The student was not able to identify any of the pigments using R_f values from a data book.

Suggest an explanation for this.

Describe how the student could use TLC to identify the pigments present in the mixture without calculating R_f values.

Which option is not a component of a chloroplast?

A Cristae

B DNA

C Ribosome

D Thylakoid

Your answer

Which of the statements about the relationship between photosynthesis and aerobic respiration in plants is/are correct?

1 During the day, photosynthesis produces all the ATP that cells in the leaves require. 2 Carbon dioxide produced in respiration can be used as a carbon source in photosynthesis. 3 Oxygen produced in photosynthesis can be used in aerobic respiration.

A 1, 2 and 3 are correct

B Only 1 and 2 are correct

C Only 2 and 3 are correct

D Only 1 is correct

Your answer

The image is a transmission electron micrograph (TEM) of a chloroplast.

Complete the table using the letters from the TEM which identifies the structure or function. Each letter may be used once, more than once or not at all.

Complete the sentences using the most appropriate terms.

Carbon fixation occurs in the Calvin cycle when CO₂ combines with the five-carbon

molecule........ This forms an unstable six-carbon

molecule that immediately breaks down into two molecules of........

These are reduced to triose phosphate using........ and

........ that are formed in the light-dependent stage of

photosynthesis. Triose phosphate is used to form hexose phosphates which can be

converted to........ for transport elsewhere in the plant.

The Hill reaction is a model system used to study the light-dependent stage of photosynthesis. It uses a blue dye, DCPIP, which is colourless when reduced.

A student was provided with the following method:

• Cut three small spinach leaves into small pieces and place in a mortar containing 20 cm³ of 0.5 mol dm^–3 sucrose solution.

• Homogenise by grinding vigorously.

• Filter the mixture and pour the filtrate into a centrifuge tube.

• Centrifuge at high speed for 5 minutes.

• Gently pour the supernatant (liquid part) into a clean tube labelled A.

• Resuspend the pellet (sediment) in 20 cm³ of pH 7.0 buffer.

• Add 5 cm³ of resuspended pellet to each of tubes labelled B – D.

• Boil tube B for 5 minutes and then cool.

• Add 10 cm³ DCPIP solution to each of tubes A – E.

• Transfer tube C to a dark cupboard.

• Observe colour of the tubes after 5 minutes.

The table shows the results of the experiment.

State the name of the final electron acceptor in the light-dependent stage of photosynthesis.

DCPIP is reduced in the Hill reaction.

Suggest and explain the function of DCPIP in the Hill reaction.

Using the results shown in the table, explain what can be concluded from each tube, or pair of tubes, about the light-dependent stage of photosynthesis.

Tubes C & D........

The student knew that it was important to use sucrose solution when homogenising the leaves.

Explain why it was important that the pellet was suspended in buffer solution and why it did not contain sucrose.

Suggest and explain two improvements that would increase the validity of the method.

Terrariums are popular for growing houseplants.

A terrarium is a glass container containing soil and small plants.

Once established, a terrarium can be sealed and the plants will be able to grow for months or even years despite not being in contact with the outside atmosphere.

The terrarium maintains moist conditions for the plants.

Suggest one other reason why the plants in a sealed terrarium continue to grow.

Cacti are popular house plants.

Suggest why cacti do not grow well in a terrarium.

A student investigated photosynthetic pigments in spinach leaves using thin layer chromatography (TLC).

Fig. 17.1 shows the student’s plate at the end of the investigation.

The table shows colours and R_f values for several photosynthetic pigments.

Calculate the R_f value for spot 3 and use this to identify the pigment that spot 3 represents.

Predict the colour of spot 4.

The solvent used for the separation was non-polar.

Identify the spot corresponding to the least polar pigment. Give a reason for your choice.

The student used the following method for the investigation:

Step 1: Extraction of pigments

• Take 0.5 g of fresh spinach and add 1 g of sand.

• Grind the mixture until it becomes a fine, light green powder.

• Transfer the powder to a test tube and add 2 cm³ of propanone.

• Stir for about 1 minute then allow to stand for another minute.

• Transfer the dark green upper layer with a pipette to a clean test tube and seal with film when not in use.

Step 2: TLC analysis

• Hold the TLC plate carefully by the edges and avoid damaging the surface of the plate.

• Draw a pencil line across the width of the TLC plate 1 cm from the bottom edge.

• Spot the extract on the pencil line using a pipette, one drop at a time, allowing the spot to dry before adding the next drop.

• Place chromatography solvent in a jar so that it is no more than 0.5 cm deep.

• Lower the TLC plate into the jar and lean the top against the side of the jar. Make sure the plate does not touch the sides of the jar anywhere else.

• Place a cap on the jar and allow the solvent to soak up the plate.

• When the solvent has reached a few mm from the top of the plate, remove the plate from the jar and mark the position of the solvent front with a pencil.

Explain why the method included the following precautions:

Hold the TLC plate carefully by the edges and avoid damaging the surface of the plate.

Make sure the plate does not touch the sides of the jar anywhere else.

Suggest an advantage of working as quickly as possible in Step 1.

Algae are single-celled photosynthetic organisms.

An investigation was carried out into the effect of CO₂ concentration on the concentrations of ribulose bisphosphate (RuBP) and glycerate 3-phosphate (GP) present in algae.

Algae were grown in a solution containing a high concentration of CO₂. The concentration of CO₂ was then reduced.

RuBP and GP concentration were measured for 2 minutes before and 3 minutes after the reduction in CO₂ concentration.

The results are shown in Fig. 17.2.

concentration

time (min)

Fig. 17.2

Describe and explain the effect of reducing the CO₂ concentration on the concentration of RuBP and GP in the algae.

Chromista are photosynthetic protoctists that live in water.

Chromista are different from other photosynthetic organisms because they contain the pigment chlorophyll c.

Chlorophyll c is not found in plants.

Outline the importance of photosynthetic pigments in photosynthesis.

The wavelengths of light absorbed by chlorophyll c are different from those wavelengths absorbed by chlorophyll a and chlorophyll b.

Suggest why Chromista need pigments that are different from those of other photosynthetic organisms.

Fig. 17.1 is a diagram of the chloroplast found in a Chromista cell.

Outline the structural differences between the Chromista chloroplast in Fig. 17.1 and the chloroplasts found in flowering plants.

Fig. 17.2 is a diagram of part of the plasma membrane of a Chromista cell.

State and explain how one property of region A in Fig. 17.2 contributes to the stability of the plasma membrane.

There are differences between the plasma membrane and membranes within cells.

Outline the role of membranes within cells.

A scientist used a respirometer to investigate the rate of respiration and photosynthesis of maize in different light intensities.

• The scientist placed ten maize seedlings in a respirometer and kept it in the dark for three hours.

• The respirometer contained soda-lime to remove any CO₂ produced by the seedlings.

• The scientist placed ten maize seedlings in a separate respirometer without soda-lime and placed it in different light intensities for three hours at a time.

The diameter of the capillary tubing was 0.1 mm.

The volume of a cylinder can be calculated using the following formula:

Calculate the rate of oxygen uptake by the seedlings in the dark. Give your answer to two significant figures. Show your working.

Answer =........ mm³ h^–1

1700 lux is a typical light intensity on a cloudy day in the UK. Calculate the percentage increase in gas production between 1700 and 2000 lux. Show your working.

Suggest why soda-lime was not placed in the respirometer with the seedlings grown in the light.

The scientist made the following claim:

These results suggest that, in maize seedlings, the rate of photosynthesis only exceeds the rate of respiration when the light intensity is above 1510 lux.

Use the data in Table 22.1 to explain why the scientist made this claim.

Fig. 1.1 shows the structure of the amino acid leucine.

On Fig. 1.1, draw a circle around the R group of leucine.

Students used thin layer chromatography to separate leucine from other amino acids. The chromatogram they produced is shown in Fig. 1.2.

What can you conclude about the chemical properties of leucine and amino acid X?

Amino acid Z was in the mixture analysed by the students. It is not shown on the chromatogram in Fig. 1.2. Amino acid Z has an R_f value that is 0.20 lower than that of amino acid Y.

Place a dot on the chromatogram in Fig. 1.2 to show the distance moved by amino acid Z.

Show your working.

Thin layer chromatography can also be used to separate photosynthetic pigments.

State a material that can be used as the stationary phase in thin layer chromatography.

State the precise location of photosynthetic pigments in a chloroplast.

When sequencing DNA, fragments of DNA are separated by electrophoresis.

Describe three differences between the process of thin layer chromatography and the form of electrophoresis used to sequence DNA.