13.1.5

Investigating Photosynthesis

Test yourself

Investigating Dehydrogenase Activity in Chloroplasts

During the light-dependent reaction, NADP is reduced to NADPH. A dehydrogenase enzyme catalyses this reaction. This experiment will monitor dehydrogenase activity by using DCPIP, a redox indicator.

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DCPIP

  • In this investigation, a blue dye (DCPIP) is used to monitor the rate of dehydrogenase activity. DCPIP is a redox indicator.
  • This means that it is blue in the oxidised state and colourless in its reduced state.
  • When electrons are released by the chlorophyll, DCPIP will change from blue to colourless.
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1) Extracting chloroplasts

  • Put 50 cm3 of isolation medium into a beaker.
  • Tear eight spinach leaves into small pieces and put the pieces into the isolation medium in the beaker.
    • Do NOT put pieces of the midrib or the leaf stalk into the beaker.
  • Half fill a large beaker with ice and place a small beaker on top of the ice.
  • When carrying out this step, all solutions and apparatus should be kept as cold as possible and the extraction should be carried out as quickly as possible.
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2) Suspending chloroplasts

  • Put 3 layers of muslin over the top of the filter funnel and wet with the isolation medium. Rest the filter funnel in the small beaker on the ice.
  • Pour the spinach and isolation medium into the blender and blend for 15 seconds. Pour the blended mixture back into the beaker.
  • Pour your blended mixture through the muslin in the filter funnel. Carefully squeeze the muslin to assist the filtering process.
  • Label this filtrate which is in the small beaker on ice as ‘chloroplast suspension’.
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4) Set up tubes A and B

  • Label five test tubes A, B, C, X and Y and stand them in the large beaker. Put the lamp about 10 cm away so that all tubes are illuminated. Set up tubes A and B as follows:
    • Tube A - 5 cm3 DCPIP solution + 1 cm3 water + 1 cm3 chloroplast suspension. Immediately wrap the tube in aluminium foil to exclude light.
    • Tube B - 5 cm3 DCPIP solution + 1 cm3 water + 1 cm3 isolation medium.
  • Tubes A and B are control experiments. Leave both tubes until the end of your investigation.
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5) Set up tube C

  • Set up tube C as follows:
    • Tube C - 6 cm3 water + 1 cm3 chloroplast suspension.
  • Tube C is for you to use as a standard to help you to determine when any colour change is complete.
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6) Set up tube X

  • Set up tube X as follows:
    • Tube X - 5 cm3 DCPIP solution + 1 cm3 water in the tube.
  • Add 1 cm3 chloroplast suspension to tube X, quickly mix the contents and start the timer.
  • Record in seconds how long it takes for the contents of tube X to change colour from blue-green to green. Use tube C to help you determine when the colour change is complete.
    • Repeat this step four more times.
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7) Set up tube Y

  • Set up tube Y as follows:
    • Tube Y - 5 cm3 DCPIP solution + 1 cm3 ammonium hydroxide.
  • Add 1 cm3 chloroplast suspension to tube Y, quickly mix the contents and start the timer.
  • Record in seconds how long it takes for the contents of tube Y to change colour from blue-green to green. Use tube C to help you determine when the colour change is complete.
    • Repeat this step four more times.
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8) Record the results

  • Record your data in a suitable table.
  • At the end of your investigation, record the colour of the mixtures in tubes A and B.

The Hill Reaction

The Hill reaction was named after Robert Hill, who designed this experiment to understand more about the process of photosynthesis. It investigates the light-dependent reaction in photosynthesis.

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The Hill Reaction

  • The Hill reaction follows these generalised steps:
    • Extract chloroplasts from a plant.
    • Suspend chloroplasts in solution.
    • Add DCPIP (an electron acceptor in place of NADP), which is used to observe whether redox reactions are taking place, to the treatment solutions and a control solution.
    • Expose chloroplast solutions to light and record any colour changes of DCPIP.
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DCPIP

  • DCPIP is an electron acceptor which acts as a substitute for NADP in this reaction.
  • DCPIP is blue when oxidised, and colourless when reduced.
  • If DCPIP turns from blue to colourless, this means it is accepting electrons and a redox reaction is taking place.
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Possible reactions to investigate

  • The Hill reaction can be used to investigate the effect of different variables on photosynthesis.
  • Solutions can be heated to different temperatures to investigate how temperature affects rate of photosynthesis.
  • Solutions can be exposed to light or dark to see how light intensity affects rate of photosynthesis.
  • Solutions can be made up to different pH levels to investigate effect of pH on rate of photosynthesis.
  • The speed at which DCPIP changes from blue to colourless is inversely related to rate of photosynthesis.
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Important findings

  • Hill found that when isolated chloroplasts were exposed to light, the added DCPIP turned from blue to colourless, but not when the chloroplasts were kept in the dark.
  • This was an important finding because it showed that photosynthesis depends at least partly on light, and that redox reactions were happening.
  • The reaction also showed that light was needed for oxygen to be produced, and that production of oxygen happens in a different step to fixation of carbon dioxide.

Jump to other topics

1Cell Structure

1.1Cell Structure

1.1.1Studying Cells - Microscopes

1.1.2Introduction to Eukaryotic & Prokaryotic Cells

1.1.3Ultrastructure of Eukaryotic Cells

1.1.4Ultrastructure of Eukaryotic Cells 2

1.1.5Ultrastructure of Eukaryotic Cells 3

1.1.6Prokaryotic Cells

1.1.7Viruses

1.1.8End of Topic Test - Cell Structure

1.1.9Exam-Style Question - Microscopes

1.1.10A-A* (AO2/3) - Cell Structure

2Biological Molecules

2.1Testing for Biological Modules

2.1.1Tests for Sugars & Starch

2.1.2Tests for Lipids & Proteins

2.2Carbohydrates & Lipids

2.2.1Monomers & Polymers

2.2.2Carbohydrates

2.2.3Examples of Carbohydrates

2.2.4Triglycerides & Phospholipids

2.2.5Types of Fatty Acids

2.2.6Exam-Style Question - Carbohydrates

2.2.7End of Topic Test - Carbohydrates & Lipids

2.3Proteins

2.3.1Amino Acids & Overview of Protein Structure

2.3.2Primary & Secondary Structure

2.3.3Tertiary & Quaternary Structure

2.3.4Globular & Fibrous Proteins

2.3.5Haemoglobin

2.3.6Collagen

2.3.7End of Topic Test - Proteins

2.4Water

2.4.1Water Structure & Function

2.4.2End of Topic Test - Water

3Enzymes

3.1Enzymes

3.1.1Enzyme Action

3.1.2Factors Affecting Enzyme Activity

3.1.3Factors Affecting Enzyme Activity 2

3.1.4A-A* (AO2/3) - Enzymes

4Cell Membranes & Transport

4.1Biological Membranes

4.1.1Fluid Mosaic Model

4.1.2Cell Signalling

4.1.3End of Topic Test - Biological Membranes

4.1.4Exam-Style Question - Membranes

4.2Movement Into & Out of Cells

4.2.1Passive Movement Across the Membrane

4.2.2Active Movement Across the Membrane

4.2.3Osmosis

4.2.4Osmosis & Plant Cells

4.2.5Surface Area to Volume Ratio

4.2.6Adaptions to Surface Area to Volume Ratio

4.2.7Calculations - Volume

4.2.8Calculations - Surface Area

5The Mitotic Cell Cycle

5.1Replication & Division of Nuclei

5.1.1Chromosomes

5.1.2The Cell Cycle

5.1.3Mitosis

5.1.4Role of Mitosis

5.1.5Stem Cells

5.1.6Mitosis & Cancer

5.1.7End of Topic Test - Replication & Division

5.1.8A-A* (AO2/3) - Cell Cycle & Transport

6Nucleic Acids & Protein Synthesis

6.1Nucleic Acids

6.1.1Introduction to DNA & RNA

6.1.2Nucleotides

6.1.3Polynucleotides

6.1.4ADP & ATP

6.1.5DNA

6.1.6DNA Replication

6.1.7RNA

6.1.8End of Topic Test - Nucleic Acids & ATP

6.2Protein Synthesis

6.2.1The Genetic Code

6.2.2Polypeptide Synthesis

6.2.3RNA Processing in Eukaryotes

6.2.4Mutations

6.2.5Exam-Style Question - Protein Synthesis

6.2.6A-A* (AO2/3) - Coronavirus Translation

7Transport in Plants

7.1Transport in Plants

7.1.1Plant Vessels

7.1.2Xylem

7.1.3Investigating Transpiration

7.1.4Adaptations to Water Availability

7.1.5Phloem

7.1.6End of Topic Test - Transport in Animals & Plants

7.1.7A-A* (AO2/3) - Transport in Animals & Plants

8Transport in Mammals

8.1Circulatory System

8.1.1Double Circulation

8.1.2Blood Vessels

8.1.3Important Blood Vessels

8.1.4Blood Cells

8.1.5Tissue Fluid

8.2Transport of Oxygen & Carbon Dioxide

8.2.1Haemoglobin

8.2.2Oxygen Dissociation

8.3The Heart

8.3.1Structure of the Heart

8.3.2The Cardiac Cycle

8.3.3Coordination of Heart Action

9Gas Exchange

9.1Gas Exchange System

9.1.1Mammalian Gas Exchange

9.1.2Smoking

10Infectious Diseases

10.1Infectious Diseases

10.1.1Transmission of Disease

10.1.2Tuberculosis

10.1.3HIV

10.1.4Malaria

10.1.5Cholera

10.1.6Measles

10.2Antibiotics

10.2.1Antibiotics

11Immunity

11.1The Immune System

11.1.1Phagocytes

11.1.2Antigens

11.1.3Lymphocytes

11.1.4Primary & Secondary Response

11.2Antibodies & Vaccination

11.2.1Antibodies

11.2.2Monoclonal Antibodies

11.2.3Immunity

11.2.4Vaccines

11.2.5Exam-Style Question - Immune System

11.2.6A-A* (AO2/3) - Disease & Immune System

12Energy & Respiration (A2 Only)

12.1Energy

12.1.1Energy & ATP

12.1.2Respiratory Substrates & Quotient

12.1.3Respirometers

12.2Respiration

12.2.1Introduction to Respiration

12.2.2Anaerobic Respiration

12.2.3Aerobic Respiration

12.2.4Chemiosmosis & Coenzymes

12.2.5Mitochondria

12.2.6Respiration Experiments

12.2.7End of Topic Test - Respiration

12.2.8A-A* (AO3/4) - Respiration

13Photosynthesis (A2 Only)

13.1Photosynthesis

13.1.1Introduction to Photosynthesis

13.1.2Light-Dependent Reactions

13.1.3Light-Independent Reactions

13.1.4Limiting Factors

13.1.5Investigating Photosynthesis

13.1.6End of Topic Test - Photosynthesis

13.1.7A-A* (AO3/4) - Photosynthesis

14Homeostasis (A2 Only)

14.1Homeostasis

14.1.1Homeostasis

14.1.2Negative Feedback

14.2The Kidney

14.2.1Kidneys & Osmoregulation

14.3Cell Signalling

14.3.1Messengers & cAMP

14.4Blood Glucose Concentration

14.4.1Blood Glucose Concentration

14.4.2Controlling Blood Glucose

14.4.3Urinalysis

14.5Homeostasis in Plants

14.5.1Stomata & Guard Cells

15Control & Coordination (A2 Only)

15.1Control & Coordination in Mammals

15.1.1Neurones

15.1.2Receptors

15.1.3Taste

15.1.4Reflexes

15.1.5Action Potentials

15.1.6Saltatory Conduction

15.1.7Synapses

15.1.8Cholinergic Synnapses

15.1.9Neuromuscular Junction

15.1.10Skeletal Muscle

15.1.11Sliding Filament Theory Contraction

15.1.12Sliding Filament Theory Contraction 2

15.1.13Menstruation

15.1.14Contraceptive Pill

15.2Control & Co-Ordination in Plants

15.2.1Venus Flytrap

15.2.2Auixns

15.2.3Gibberellins

16Inherited Change (A2 Only)

16.1Passage of Information to Offspring

16.1.1Meiosis

16.1.2Gametogenesis

16.1.3Meiosis & Genetic Diversity

16.2Genes & Phenotype

16.2.1Key Terms in Genetics

16.2.2Inheritance

16.2.3Linkage

16.2.4Multiple Alleles

16.2.5Chi-Squared Test

16.2.6Mutations

16.2.7Specific Mutations

16.2.8End of Topic Test - Genetics

16.2.9A-A* (AO2/3) - Genetics

16.3Gene Control

16.3.1lac Operon

16.3.2Transcription Factors

16.3.3Gibberellins & DELLA Proteins

17Selection & Evolution (A2 Only)

17.1Variation

17.1.1Phenotypic Variation

17.1.2Continuous & Discontinuous Variation

17.1.3t-Tests

17.2Natural & Artificial Selection

17.2.1Natural Selection & Evolution

17.2.2Types of Selection

17.2.3Types of Selection Summary

17.2.4Genetic Drift & Founder Effect

17.2.5Populations

17.2.6Hardy-Weinberg Principle

17.2.7Artificial Selection

17.3Evolution

17.3.1Evolution by Natural Selection

17.3.2Evidence for Evolution

17.3.3Speciation

17.3.4Extinction

18Classification & Conservation (A2 Only)

18.1Biodiversity

18.1.1Key Terms

18.1.2Biodiversity

18.1.3Sampling Methods

18.1.4Correlation

18.1.5Spearman’s Rank

18.1.6Measuring Biodiversity

18.2Classification

18.2.13-Domain Classification System

18.2.2Linnaean Classification System

18.3Conservation

18.3.1Importance of Biodiversity

18.3.2Conservation

18.3.3Zoos, Seedbanks, & Other Conservation Methods

18.3.4Assisted Reproduction & Contraception

18.3.5Non-Governmental Organisations

19Genetic Technology (A2 Only)

19.1Manipulating Genomes

19.1.1Recombinant DNA & Genetic Engineering

19.1.2Restriction Endonucleases

19.1.3Gel Electrophoresis

19.1.4DNA Probes & Microarrays

19.1.5End of Topic Test - Manipulating Genomes

19.1.6A-A* (AO2/3) - Manipulating Genomes

19.2Genetic Technology Applied to Medicine

19.2.1Bioinformatics

19.2.2Applications of Recombinant DNA

19.2.3Genetic Screening

19.2.4Gene Therapy

19.2.5Ethics

19.2.6DNA Profiling & Forensics

19.3Genetically Modified Organisms in Agriculture

19.3.1GM Crops & Livestock

19.3.2Ethics

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Limiting Factors

End of Topic Test - Photosynthesis