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Practical Biology

A collection of experiments that demonstrate biological concepts and processes.

Observing earthworm locomotion

Practical Work for Learning

Published experiments

Investigating factors affecting the rate of photosynthesis, class practical.

In this experiment the rate of photosynthesis is measured by counting the number of bubbles rising from the cut end of a piece of Elodea or Cabomba .

Lesson organisation

The work could be carried out individually or in groups of up to 3 students (counter, timekeeper and scribe).

Apparatus and Chemicals

Students may choose to use:.

Thermometer, –10 °C –110°C

Coloured filters or light bulbs

Push-button counter

Potassium hydrogencarbonate powder or solution (Hazcard 95C describes this as low hazard)

For each group of students:

Student sheets, 1 per student

Beaker, 600 cm 3 , 1

Metre ruler, 1

Elodea ( Note 1 ) or other oxygenating pond plant ( Note 2 )

Electric lamp

Clamp stand with boss and clamp

Health & Safety and Technical notes

Normal laboratory safety procedures should be followed. There is a slight risk of infection from pond water, so take sensible hygiene precautions, cover cuts and wash hands thoroughly after the work is complete.

Read our standard health & safety guidance

1 Elodea can be stored in a fish tank on a windowsill, in the laboratory or prep room. However it is probably a good idea to replace it every so often with a fresh supply from an aquarist centre or a pond. (It’s worth finding out if any colleague has a pond.) On the day of the experiment, cut 10 cm lengths of Elodea , put a paper-clip on one end to weigh them down and place in a boiling tube of water in a boiling tube rack, near a high intensity lamp, such as a halogen lamp or a fluorescent striplight. Check the Elodea to see if it is bubbling. Sometimes cutting 2–3 mm off the end of the Elodea will induce bubbling from the cut end or change the size of the bubbles being produced.

2 Cabomba (available from pet shops or suppliers of aquaria – used as an oxygenator in tropical fish tanks) can be used as an alternative to Elodea , and some people find it produces more bubbles. It does, though tend to break apart very easily, and fish may eat it very quickly.

3 If possible, provide cardboard to allow students to shield their experiment from other lights in the room.

Ethical issues

Look out for small aquatic invertebrates attached to the pond weed used, and remove them to a pond or aquarium.

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How To Set Up and Demonstrate Light Intensity and Photosynthesis for GCSE

In this video, Denise Ralph will show you how to demonstrate photosynthesis using pondweed. This practical is an essential part of the GCSE Biology curriculum, focusing on understanding the vital process of photosynthesis in plants.

This experiment is ideal for teaching the following key learning objectives:

• Carbon Dioxide Requirement: Explore how the addition of a bicarbonate solution provides the necessary carbon dioxide for the photosynthetic process.
• Light as an Essential Factor: Understand the role of light, mimicked by a lamp in this experiment, in driving photosynthesis.
• Oxygen Production: Observe the release of oxygen bubbles from the cut end of the pond weed as a direct result of the photosynthetic activity.

You will need:

• Fresh pond weed (elodea or similar) – 2-3 cm cut
• Bicarbonate of soda solution (3 spatula full in 50 ml water)
• Retort stand with a clamp
• Lamp (light source)
• Measure three spatulas full of bicarbonate of soda and dissolve it in 50 ml of water. Stir until it’s well-mixed.
• Set up the retort stand with a clamp on a stable surface.
• Take the fresh pond weed and cut it to a length of about 2-3 cm. Place the cut end of the pond weed in the test tube, making sure the cut part is facing upward.
• Pour the prepared bicarbonate of soda solution into the test tube until the pond weed is fully submerged. This bicarbonate solution provides carbon dioxide necessary for photosynthesis.
• Firmly fix the test tube into the clamp on the retort stand. Ensure that the pond weed is fully immersed in the bicarbonate solution.
• Position the lamp in such a way that it shines directly on the pond weed in the test tube. The light source is essential for the process of photosynthesis.
• Switch on the lamp to initiate the photosynthesis process.
• Watch for the appearance of bubbles coming from the cut end of the pond weed. These bubbles are oxygen produced during photosynthesis. You can also use a stirring rod to gently stir the solution, which can help in the release of any trapped oxygen.
• Record the observations, noting the time it takes for bubbles to appear and any other changes you observe.

All health and safety measures are the responsibility of the teacher doing the demonstration. A thorough risk assessment should be carried out and guidance procedures followed. It is suggested that you practice before demonstration in front of a class.

Important safety precautions and tips:

• Use a transparent test tube to easily observe the bubbles.
• Ensure that the lamp is at an appropriate distance to provide sufficient light for photosynthesis.
• Repeat the experiment with variations, such as changing the distance of the lamp or using different concentrations of bicarbonate solution, to explore the effects on the rate of photosynthesis.

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Rates of Photosynthesis

Related Topics: GCSE/IGCSE Biology Biology Required Practicals GCSE/IGCSE Physics GCSE/IGCSE Chemistry GCSE/IGCSE Maths

GCSE Biology Required Practical - Photosynthesis Experiment

Investigate the effect of light intensity on the rate of photosynthesis.

• Pondweeds (Algal balls or similar) must be set up and placed at varying distances from a light source to investigate the effect of light intensity on the rate of photosynthesis.
• The rate must be measured and compared to the distance away from the light source.

Rates Of Photosynthesis How to measure the rate of photosynthesis of pondweed?

00:00 Preparing the sample 02:34 Changing light intensity 04:21 Counting bubbles 05:11 Analysing data 05:23 Alternative method - volume of collected gas

Required Practical: Photosynthesis

• How to investigate the effect of light intensity of the rate of photosynthesis in a pondweed.
• Explain how the results of this are affected by the inverse-square law. (Higher Tier)

Check out the sample question and solution on Sample Assessment Material (page 33) , paper 1BI0/1BH and 1BIO/1BF.

A scientist investigates the effect of light intensity on photosynthesis. He sets up the equipment shown in figure 1. He places the lamp 10cm from the test tube and records the numbre of bubbles produced in five minutes. He repeats the procedure with the lamp at a distance of 20cm and 30cm away from the test tube. The scientist wants to repeat his investigation at each distance. State three variables that should be kept constant to improve the results.

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Demonstrating Oxygen Evolution during Photosynthesis using Pondweed

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Watching gas bubble up from a pondweed as it photosynthesises can be a great demonstration or student practical. When placed closer to a light source, the rate of bubbling will speed up, and as the pondweed is taken further away, the bubbles will slow down again – an instant and visual indicator of the importance of light intensity in photosynthesis. Our video demonstrates how best to use this protocol with your students in the lab, which species of pondweed can be used, how to care for pondweeds and a short explanation on the physiology that allows pondweed to bubble.

The bubbles produced by pondweed can be counted and the rate of bubbling can serve as an indication of the rate of photosynthesis, or the gas can be collected in a pipette or microsyringe and the amount measured. Students can investigate the effects of either light intensity or the wavelength (colour) of light on photosynthesis.

This resource includes student sheets with 4 different investigations, technical notes and full teachers’ notes. We have also provided a PowerPoint presentation and notes on pondweed physiology.

Previously, Cabomba caroliniana was recommended as a species for this protocol but this is no longer available in the UK, due to the invasive plant directive. You may find that some exam specifications and text books still mention this species but you can use any of those mentioned in this video or any other species that you find work for you.

In addition, you may wish to consider alternative practicals to look at photosynthesis, such as the ‘algal balls’ practical.

Note: When buying from pet stores in particular, the staff may not be able to identify the type of pondweed they are selling but we hope that you will be able to use the video and images in the guide to pondweeds to help.

See what has been said about the resource

"Straight forward advice to help staff and students select suitable pondweed and equipment to carry out this practical requirement in accordance with curriculum."

What's included?

• SAPS - Bubbling pondweed - Why does pondweed bubble
• SAPS - Bubbling pondweed - Technical Notes
• SAPS - Bubbling pondweed - Teaching Notes
• SAPS - Bubbling pondweed - Student Sheet
• SAPS - Bubbling pondweed - Pondweed species
• Photosynthesis
• Respiration
• Essential practicals

Related content

Teaching resources.

• A Leaf in Time - A Popular Introduction to Photosynthesis
• Photosynthesis - A Survival Guide for Teachers
• Stomatal opening and closing in Commelina communis
• Investigating Photosynthesis with the SAPS / NCBE Photosynthesis Kit

Photosynthesis Experiments

Measuring the rate of photosynthesis.

The rate that pond weed produces bubbles indicates the rate of photosynthesis. The bubbles released are oxygen, a waste product of photosynthesis.

Investigating Photosynthesis Rates

Light intensity is not the only factor that can affect the rate of photosynthesis. Other factors that you might want to investigate are:

Temperature

Carbon dioxide concentration.

1 Cell Biology

1.1 What's in Cells?

1.1.1 Types of Cells

1.1.2 Properties of Prokaryotes

1.1.3 Standard Form

1.1.4 Standard Form - Calculations

1.1.5 Addition in Standard Form - Calculations

1.1.6 Subtraction in Standard Form - Calculations

1.1.7 Multiplication in Standard Form - Calculations

1.1.8 Division in Standard Form - Calculations

1.1.9 Animal Cells

1.1.10 Plant Cells

1.1.11 Differences Between Animal & Plant Cells

1.1.12 Bacterial Cells

1.1.13 Types of Cells HyperLearning

1.1.14 Cell Specialisation in Animals

1.1.15 Sperm Cells

1.1.16 Nerve Cells

1.1.17 Muscle Cells

1.1.18 Cell Specialisation in Plants

1.1.19 Microscopy

1.1.20 Developments in Microscopy

1.1.21 Microscope Practical

1.1.22 Microscopy - Calculations

1.1.23 Culturing Microorganisms

1.1.24 Contamination

1.1.25 Avoiding Contamination

1.1.26 Calculating Bacteria

1.1.27 Calculating Bacteria - Calculations

1.1.28 End of Topic Test - What's in Cells?

1.1.29 Exam-Style Questions - Cell Structure & Microscopy

1.2 Cell Division

1.2.1 Chromosomes

1.2.2 The Cell Cycle

1.2.3 Mitosis

1.2.4 Exam-Style Questions - Mitosis & Cell Cycle

1.2.5 Stem Cells

1.2.6 Use of Stem Cells

1.2.7 Disadvantages of Stem Cells

1.3 Transport in Cells

1.3.1 Diffusion

1.3.2 Factors Affecting Diffusion

1.3.3 Surface Area : Volume

1.3.4 Surface Area : Volume - Calculations

1.3.5 Exchange Surfaces

1.3.6 Examples of Exchange Surfaces

1.3.7 Osmosis

1.3.8 Osmosis Practical

1.3.9 Active Transport

1.3.10 Transport in Cells

1.3.11 End of Topic Test - Cell Division & Transport

1.3.12 Grade 9 - Cell Transport

2 Organisation

2.1 Principles of Organisation

2.1.1 Cells & Tissues

2.1.2 Organs

2.1.3 Organ Systems

2.1.4 Organisms

2.2 Enzymes

2.2.1 Enzymes

2.2.2 Enzymes HyperFlashcards

2.2.3 Rate of Reaction

2.2.4 Calculating Rate of Reaction

2.2.5 Rate of Reaction - Calculations

2.2.6 Digestion

2.2.8 Examples of Digestive Enzymes - Amylase

2.2.9 Examples of Digestive Enzymes - Protease

2.2.10 Examples of Digestive Enzymes - Lipase

2.2.11 Testing for Biological Molecules

2.2.12 End of Topic Test - Organisation & Enzymes

2.2.13 Grade 9 - Enzymes

2.2.14 Exam-Style Questions - Enzymes

2.3 Circulatory System

2.3.1 Types of Blood Vessel

2.3.2 Blood Vessels - Arteries

2.3.3 Blood Vessels - Capillaries

2.3.4 Blood Vessels - Veins

2.3.5 The Heart - Structure

2.3.6 The Heart - Function

2.3.7 Important Blood Vessels

2.3.8 Double Circulatory System

2.3.9 Gas Exchange

2.3.10 Gas exchange - Calculations

2.3.11 Alveoli

2.3.12 Blood Components

2.3.13 Platelets

2.3.14 Red Blood Cells

2.3.15 White Blood Cells

2.3.16 End of Topic Test - Circulatory System

2.4 Non-Communicable Diseases

2.4.1 Health Issues

2.4.2 Disease Interactions

2.4.3 Sampling

2.4.4 Sampling - Calculations

2.4.5 Risk Factors

2.4.6 Examples of Risk Factors

2.4.7 Risk Factor Graphs

2.4.8 Coronary Heart Disease

2.4.9 Heart Valve Disease

2.4.10 Heart Failure

2.4.11 Treating Heart Disease

2.4.12 Cancer

2.4.13 Cancer Risk Factors

2.4.14 End of Topic Test - Non-Communicable Diseases

2.4.15 Exam-Style Questions - Coronary Heart Disease

2.5 Plant Tissues, Organs & Systems

2.5.1 Plant Tissues

2.5.2 Leaves

2.5.3 Transpiration

2.5.4 Rate of Transpiration

2.5.5 Measuring Transpiration

2.5.6 Translocation

2.5.7 Transpiration Tissues

2.5.8 Stomata

2.5.9 Premium Knowledge - Transpiration

2.5.10 End of Topic Test - Plants

2.5.11 Exam-Style Questions - Plant Tissues

3 Infection & Response

3.1 Communicable Disease

3.1.1 Spreading Disease

3.1.2 Viruses

3.1.3 Other Pathogens

3.1.4 Human Defence Systems

3.1.5 Human Defence Systems 2

3.1.6 Grade 9 - Immune System

3.1.7 Antibiotics

3.1.8 Drug Development

3.1.9 Drug Testing

3.1.10 Drug Testing / Efficacy - Calculations

3.1.11 End of Topic Test - Communicable Diseases

3.1.12 Exam-Style Questions - Microorganisms & Disease

3.2 Monoclonal Antibodies

3.2.1 Producing & Using Monoclonal Antibodies

3.2.2 Grade 9 - Monoclonal Antibodies

3.3 Plant Diseases

3.3.1 Diseases & Defence

3.3.2 Identifying Disease

3.3.3 End of Topic Test - Antibodies & Plant Disease

4 Bioenergetics

4.1 Photosynthesis

4.1.1 Photosynthesis

4.1.2 Photosynthesis 2

4.1.3 Photosynthesis - Calculations

4.1.4 Photosynthesis Experiments

4.1.5 Grade 9 - Photosynthesis Experiment

4.1.6 Exam-Style Questions - Rate of Photosynthesis

4.2 Respiration

4.2.1 Respiration

4.2.2 Respiration - Calculations

4.2.3 Exercise

4.2.4 Respiration HyperLearning

4.2.5 End of Topic Test - Photosynthesis and Respiration

4.2.6 Exam-Style Questions - Anaerobic Respiration

5 Homeostasis & Response

5.1 Homeostasis

5.1.1 Homeostasis

5.1.2 Homeostasis & Negative Feedback

5.1.3 Exam-Style Questions - Exercise & Homeostasis

5.2 The Human Nervous System

5.2.1 The Nervous System

5.2.2 The Nervous System HyperFlashcards

5.2.3 Synapses

5.2.4 Reflexes

5.2.5 Exam-Style Questions - Nervous System

5.2.6 The Brain

5.2.7 Eye Anatomy

5.2.8 Eye Function

5.2.9 Control of Body Temperature

5.2.10 Warming Up & Cooling Down

5.2.11 Body Temperature HyperLearning

5.2.12 End of Topic Test - Human Nervous System

5.3 Hormonal Coordination in Humans

5.3.1 Endocrine System

5.3.2 Thyroxine & Adrenaline

5.3.3 Blood Glucose

5.3.4 Diabetes

5.3.5 Control of Water Balance

5.3.6 Urine

5.3.7 Dialysis

5.3.8 Transplants

5.3.9 Puberty

5.3.10 Menstruation

5.3.11 Contraception

5.3.12 Contraception 2

5.3.13 Hormones for Infertility

5.3.14 End of Topic Test - Homeostasis & Hormones

5.3.15 Grade 9 - Hormonal Coordination

5.3.16 Exam-Style Questions - Hormones & Contraception

5.4 Plant Hormones

5.4.1 Plant Hormones

5.4.2 Plant Hormones 2

5.4.3 End of Topic Test - Hormones

6 Inheritance, Variation & Evolution

6.1 Reproduction

6.1.1 Reproduction

6.1.2 Reproduction 2

6.1.3 Genome

6.1.5 Protein Synthesis

6.1.6 Genetic Inheritance

6.1.7 Genetic Crosses

6.1.8 Inherited Disorders

6.1.9 Inherited Disorders 2

6.1.10 Genetic Crosses - Calculations

6.1.11 Genome Screening & Sex Determination

6.1.12 End of Topic Test - Reproduction

6.1.13 Exam-Style Questions - DNA & Genetics

6.2 Variation & Evolution

6.2.1 Variation & Evolution

6.2.2 Selective Breeding

6.2.3 Selective Breeding 2

6.2.4 Genetic Engineering

6.2.5 Uses of Genetic Modification

6.2.6 Cloning

6.2.7 Cloning 2

6.2.8 End of Topic Test - Variation & Evolution

6.2.9 Exam-Style Questions - Selective Breeding

6.3 Genetics & Evolution

6.3.1 Natural Selection

6.3.2 Speciation

6.3.3 Evidence for Evolution

6.3.4 Genetics & Extinction

6.3.5 Grade 9 - Evolution

6.4 Classification

6.4.1 Classification of Living Organisms

6.4.2 Classification of Living Organisms 2

6.4.3 End of Topic - Genetics & Classification

7.1 Adaptations & Interdependence

7.1.1 Communities

7.1.2 Communities 2

7.2 Organisation of Ecosystems

7.2.1 Population Dynamics

7.2.2 Environmental Change

7.2.3 Assessing Ecosystems

7.2.4 Assessing Ecosystems - Calculations

7.2.5 The Cycling of Materials

7.2.6 Decay

7.2.7 Decay Practical

7.2.8 End of Topic Test - Organisation of Ecosystems

7.2.9 Grade 9 - Ecosystems

7.2.10 Exam-Style Questions - Decomposition

7.3 Biodiversity

7.3.1 Human Interactions with Ecosystems

7.3.2 Human Interactions with Ecosystems 2

7.3.3 Greenhouse Gases

7.3.4 Greenhouse Gases 2

7.3.5 Hardest Questions - Humans & the Environment

7.3.6 End of Topic Test - Adaptations & Biodiversity

7.4 Trophic Levels

7.4.1 Trophic Levels

7.4.2 Trophic Levels 2

7.4.3 Transfer efficiency - Calculations

7.4.4 Premium Knowledge - Trophic Levels & Food Chains

7.4.5 Exam-Style Questions - Food Chains

7.5 Food Production

7.5.1 Food Production

7.5.2 Farming & Fishing

7.5.3 Food Production - Calculations

7.5.4 End of Topic Test - Food & Trophic Levels

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Photosynthesis - Calculations

Grade 9 - Photosynthesis Experiment

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Photosynthesis practical - bubbling pondweed

Subject: Biology

Age range: 14-16

Resource type: Lesson (complete)

Last updated

29 February 2024

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In this practical experiment, the rate of photosynthesis is measured by counting the number of bubbles rising from the cut end of a piece of Cabomba pondweed.

Cabomba caroliniana is no longer available to purchase in the UK. Please see the SAPS website for guidance on achieving good results with other species of pondweed.

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Measuring the Rate of Photosynthesis - Biology Practical

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Investigating the Rate of Photosynthesis ( AQA A Level Biology )

Revision note.

Biology & Environmental Systems and Societies

Apparatus & Techniques: Investigating the Rate of Photosynthesis

• Investigations to determine the effects of light intensity, carbon dioxide concentration and temperature on the rate of photosynthesis can be carried out using aquatic plants , such as Elodea or Cabomba (types of pondweed )
• Light intensity – change the distance ( d ) of a light source from the plant (light intensity is proportional to 1/ d 2 )
• Carbon dioxide concentration – add different quantities of sodium hydrogencarbonate (NaHCO 3 ) to the water surrounding the plant, this dissolves to produce CO 2
• Temperature (of the solution surrounding the plant) – place the boiling tube containing the submerged plant in water baths of different temperatures
• For example, when investigating the effect of light intensity on the rate of photosynthesis, a glass tank should be placed in between the lamp and the boiling tube containing the pondweed to absorb heat from the lamp – this prevents the solution surrounding the plant from changing temperature
• Distilled water
• Aquatic plant, algae or algal beads
• Sodium hydrogen carbonate solution
• Thermometer
• Test tube plug
• This will ensure oxygen gas given off by the plant during the investigation form bubbles and do not dissolve in the water
• This will ensure that the plant contains all the enzymes required for photosynthesis and that any changes of rate are due to the independent variable
• Ensure the pondweed is submerged in sodium hydrogen carbonate solution (1%) – this ensures the pondweed has a controlled supply of carbon dioxide (a reactant in photosynthesis)
• Cut the stem of the pondweed cleanly just before placing into the boiling tube
• Measure the volume of gas collected in the gas-syringe in a set period of time (eg. 5 minutes)
• Change the independent variable (ie. change the light intensity, carbon dioxide concentration or temperature depending on which limiting factor you are investigating) and repeat step 5
• Record the results in a table and plot a graph of volume of oxygen produced per minute against the distance from the lamp (if investigating light intensity), carbon dioxide concentration, or temperature

The effect of light intensity on an aquatic plant is measured by the volume of oxygen produced

Results - Light Intensity

• The closer the lamp, the higher the light intensity (intensity ∝ 1/ d 2 )
• Therefore, the volume of oxygen produced should increase as the light intensity is increased
• This is when the light stops being the limiting factor and the temperature or concentration of carbon dioxide is limiting the rate of photosynthesis
• The effect of these variables could then be measured by increasing the temperature of water (by using a water bath) or increasing the concentration of sodium hydrogen carbonate respectively
• Rate of photosynthesis = volume of oxygen produced ÷ time elapsed

Limitations

• Immobilised algae beads are beads of jelly with a known surface area and volume that contain algae, therefore it is easier to ensure a standard quantity
• Immobilised algae beads are easy and cheap to grow, they are also easy to keep alive for several weeks and can be reused in different experiments
• The method is the same for algae beads though it is important to ensure sufficient light coverage for all beads

Light intensity – the distance of the light source from the plant (intensity ∝ 1/ d 2 )

Temperature - changing the temperature of the water bath the test tube sits in

Carbon dioxide - the amount of NaHCO 3 dissolved in the water the pondweed is in

Also remember that the variables not being tested (the control variables) must be kept constant.

Required Practical: Affecting the Rate of Dehydrogenase Activity

• The light-dependent reactions of photosynthesis take place in the thylakoid membrane and involve the release of high-energy electrons from chlorophyll a molecules
• These electrons are picked up by the electron acceptor NADP in a reaction catalysed by dehydrogenase
• However, if a redox indicator (such as DCPIP or methylene blue ) is present, the indicator takes up the electrons instead of NADP
• DCPIP: oxidised ( blue ) → accepts electrons → reduced ( colourless )
• Methylene blue: oxidised ( blue ) → accepts electrons → reduced ( colourless )
• The colour of the reduced solution may appear green because chlorophyll produces a green colour
• When light is at a higher intensity, or at more preferable light wavelengths, the rate of photoactivation of electrons is faster, therefore the rate of reduction of the indicator is faster

Light activates electrons from chlorophyll molecules during the light-dependent reaction. Redox indicators accept the excited electrons from the photosystem, becoming reduced and therefore changing colour.

• Isolation medium
• Pestel and mortar
• Aluminium Foil

Method - Measuring light as a limiting factor

• This produces a concentrated leaf extract that contains a suspension of intact and functional chloroplasts
• The medium must have the same water potential as the leaf cells so the chloroplasts don’t shrivel or burst and contain a buffer to keep the pH constant
• The medium should also be ice-cold (to avoid damaging the chloroplasts and to maintain membrane structure)
• The room should be at an adequate temperate for photosynthesis and maintained throughout, as should carbon dioxide concentration
• If different intensities of light are used, they must all be of the same wavelength (same colour of light) - light intensity is altered by changing the distance between the lamp and the test tube
• If different wavelengths of light are used, they must all be of the same light intensity - the lamp should be the same distance in all experiments
• DCPIP of methylene blue indicator is added to each tube, as well as a small volume of the leaf extract
• A control that is not exposed to light (wrapped in aluminium foil) should also be set up to ensure the affect on colour is due to the light
• This is a measure of the rate of photosynthesis
• A graph should be plotted of absorbance against time for each distance from the light
• This is because the lowered light intensity will slow the rate of photoionisation of the chlorophyll pigment, so the overall rate of the light dependent reaction will be slower
• This means that less electrons are released by the chlorophyll, hence the DCPIP accepts less electrons. This means that it will take longer to turn from blue to colourless
• A higher rate of decrease, shown by a steep gradient on the graph, indicates that the dehydrogenase is highly active.
• This experiment is not measuring the rate of dehydrogenase activity directly (through measuring the rate of substrate use or product made) but is instead predicting what the rate would be by measuring the rate of electron transfer from the photosystems
• It is therefore important to control the amount of leaf used to produce the chloroplast sample and also how much time is spent crushing the leaf to release the chloroplast
• It is also a good idea to measure a specific wavelength absorption by each sample on the colorimeter before and after the experiment so you can get a more accurate change in oxidised DCPIP concentration
• Results should also be repeated and the mean value calculated
• The time taken to go colourless is subjective to each person observing and therefore one person should be assigned the task of deciding when this is

In chemistry the acronym ‘OILRIG’ is used to remember if something is being oxidised or reduced. Oxidation Is Loss (of electrons) and Reduction Is Gain (of electrons). Therefore the oxidised state is when it hasn’t accepted electrons and the reduced state has accepted electrons.

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Author: Alistair

Alistair graduated from Oxford University with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems & Societies. Alistair has continued to pursue his interests in ecology and environmental science, recently gaining an MSc in Wildlife Biology & Conservation with Edinburgh Napier University.

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Warming Is Getting Worse. So They Just Tested a Way to Deflect the Sun.

A spraying machine designed for cloud brightening on the flight deck of the Hornet, a decommissioned aircraft carrier that is now a museum in Alameda, Calif. Credit...

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By Christopher Flavelle

Photographs by Ian C. Bates

Christopher Flavelle reported from a decommissioned aircraft carrier in Alameda, Calif. He spoke with scientists, environmentalists and government officials.

• April 2, 2024

A little before 9 a.m. on Tuesday, an engineer named Matthew Gallelli crouched on the deck of a decommissioned aircraft carrier in San Francisco Bay, pulled on a pair of ear protectors, and flipped a switch.

A few seconds later, a device resembling a snow maker began to rumble, then produced a great and deafening hiss. A fine mist of tiny aerosol particles shot from its mouth, traveling hundreds of feet through the air.

It was the first outdoor test in the United States of technology designed to brighten clouds and bounce some of the sun’s rays back into space, a way of temporarily cooling a planet that is now dangerously overheating. The scientists wanted to see whether the machine that took years to create could consistently spray the right size salt aerosols through the open air, outside of a lab.

If it works, the next stage would be to aim at the heavens and try to change the composition of clouds above the Earth’s oceans.

As humans continue to burn fossil fuels and pump increasing amounts of carbon dioxide into the atmosphere, the goal of holding global warming to a relatively safe level, 1.5 degrees Celsius compared with preindustrial times, is slipping away. That has pushed the idea of deliberately intervening in climate systems closer to reality.

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