light is essential for photosynthesis practical experiment

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Experiment to Prove Light is Essential for Photosynthesis (With Pictures )

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Experiment to Prove Light is Essential for Photosynthesis!

Experiment:

To show experimentally that light is essential for photosynthesis.

Apparatus and materials required:

A healthy potted plant, a petri dish, a beaker containing water, forceps, a water bath, a piece of wire gauze, a tripod, a burner, a box of matches, alcohol a strip of black paper, iodine solution and clips.

Photosynthesis is a biochemical process by which green plants s5mthesize simple sugar in the presence of sunlight using carbon dioxide from the atmosphere and water from the soil. This simple sugar (glucose) is later converted to starch.

6CO 2 + 12H 2 O ChlorophyII / Sunlight C 6 H 12 O 6 + 6H 2 O + 6O 2

The most important factor for photosynthesis is light. The rate of photosynthesis depends on the quantity and quality of light. The chlorophyll molecule in green leaves absorb light, get excited and emit electrons. The emitted electrons are used in the production of adenosine triphosphate (ATP). Finally the solar energy is converted into chemical energy and stored in the glucose produced.

The rate of photosynthesis is the maximum in the presence of red and blue lights, while in green light the rate is minimum because green light is reflected by the chlorophyll molecules.

Procedure :

1. Take the potted plant and keep it in a dark place for 2-3 days so that the leaves get destarched.

2. Cover a part of one of its leaves with the strip of black paper. Make sure that you cover both the sides of the leaf.

3. Now place this plant in sunlight for 3—4 hours.

4. Pluck the selected covered leaf and remove the black paper covering it.

5. Place this leaf in the beaker containing water and boil it for about 10 minutes.

6. Take out the leaf and now boil it in alcohol, using the water bath, for 10 minutes. This removes the chlorophyll.

7. Take out the leaf and wash it under running water.

8. Place this leaf in the Petri dish and put a few drops of iodine solution on it. Now observe the change in colour.

Observations :

The leaf turns blue-black except in the covered region. As this covered region did not receive light, photosynthesis did not occur. Hence no starch was formed there. The uncovered region received light and starch was formed there due to photosynthesis.

Light is essential for photosynthesis.

Precautions :

1. Before starting the experiment, the leaf must be distracted.

2. The leaf must be covered with black paper properly to prevent the entry of light.

3. Boiling the leaf in alcohol should be done in the water bath.

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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 the light dependent reaction in photosynthesis.

It is fairly easy to show that plants produce oxygen and starch in photosynthesis . At age 14–16 students may have collected the gas given off by pond weed (for example Elodea ) and tested leaves for starch.

It is not quite so easy to demonstrate the other reactions in photosynthesis. For the reduction of carbon dioxide to carbohydrate there must be a source of electrons . In the cell, NADP is the electron acceptor which is reduced in the light-dependent reactions, and which provides electrons and hydrogen for the light-independent reactions.

In this investigation, DCPIP (2,6-dichlorophenol-indophenol), a blue dye, acts as an electron acceptor and becomes colourless when reduced, allowing any reducing agent produced by the chloroplasts to be detected.

Lesson organisation

This investigation depends on working quickly and keeping everything cool. Your students will need to understand all the instructions in advance to be sure that they know what they are doing.

Apparatus and Chemicals

Per student or group of students:.

Centrifuge – with RCF between 1500 and 1800g

Centrifuge tubes

Fresh green spinach, lettuce or cabbage, 3 leaves (discard the midribs)

Cold pestle and mortar (or blender or food mixer) which has been kept in a freezer compartment for 15–30 minutes (if left too long the extract will freeze)

Muslin or fine nylon mesh

Filter funnel

Ice-water-salt bath

Glass rod or Pasteur pipette

Measuring cylinder, 20 cm 3

Beaker, 100 cm 3

Pipettes, 5 cm 3 and 1 cm 3

Bench lamp with 100 W bulb

Test tubes, 5

Boiling tube

Pipette for 5 cm 3

Pipette for 0.5 cm 3

Pipette filler

Waterproof pen to label tubes

Colorimeter and tubes or light sensor and data logger

0.05 M phosphate buffer solution, pH 7.0: Store in a refrigerator at 0–4 °C ( Note 1 ).

Isolation medium (sucrose and KCl in phosphate buffer): Store in a refrigerator at 0–4 °C ( Note 2 ).

Potassium chloride (Low Hazard) ( Note 3 ).

DCPIP solution (Low Hazard): (1 x 10 - 4 M approx.) ( Note 4 )

Health & Safety and Technical notes

Although DCPIP presents minimal hazard apart from staining, it is best to avoid skin contact in case prolonged contact with the dye causes sensitisation. Do not handle electric light bulbs with wet hands. All solutions used are low hazard – refer to relevant CLEAPSS Hazcards and Recipe cards for more information.

Read our standard health & safety guidance

1 0.05 M phosphate buffer solution, pH 7.0. Na 2 HPO 4 .12H 2 O, 4.48 g (0.025 M) KH 2 PO 4 , 1.70 g (0.025 M). Make up to 500 cm 3 with distilled water and store in a refrigerator at 0–4 °C. Low hazard – refer to CLEAPSS Hazcard 72.

2 Isolation medium. Sucrose 34.23 g (0.4 M) KCl 0.19 g (0.01 M). Dissolve in phosphate buffer solution (pH 7.0) at room temperature and make up to 250 cm 3 with the buffer solution. Store in a refrigerator at 0–4 °C. Low hazard – refer to CLEAPSS Hazcard 40C.

3 Potassium chloride 0.05 M. Dissolve 0.93 g in phosphate buffer solution at room temperature and make up to 250 cm 3 . Store in a refrigerator at 0–4 °C. Use at room temperature.(Note that Potassium chloride is a cofactor for the Hill reaction.) Refer to CLEAPSS Hazcard 47B and Recipe card 51.

4 DCPIP solution DCPIP 0.007–0.01 g, made up to 100 cm 3 with phosphate buffer. Refer to CLEAPSS Hazcard 32 and Recipe card 46.

Keep solutions and apparatus cold during the extraction procedure, steps 1–8, to preserve enzyme activity. Carry out the extraction as quickly as possible.

Preparation

a Cut three small green spinach, lettuce or cabbage leaves into small pieces with scissors, but discard the tough midribs and leaf stalks. Place in a cold mortar or blender containing 20 cm 3 of cold isolation medium. (Scale up quantities for blender if necessary.)

b Grind vigorously and rapidly (or blend for about 10 seconds).

c Place four layers of muslin or nylon in a funnel and wet with cold isolation medium.

d Filter the mixture through the funnel into the beaker and pour the filtrate into pre-cooled centrifuge tubes supported in an ice-water-salt bath. Gather the edges of the muslin, wring thoroughly into the beaker, and add filtrate to the centrifuge tubes.

e Check that each centrifuge tube contains about the same volume of filtrate.

f Centrifuge the tubes for sufficient time to get a small pellet of chloroplasts. (10 minutes at high speed should be sufficient.)

g Pour off the liquid (supernatant) into a boiling tube being careful not to lose the pellet. Re-suspend the pellet with about 2 cm 3 of isolation medium, using a glass rod. Squirting in and out of a Pasteur pipette five or six times gives a uniform suspension.

h Store this leaf extract in an ice-water-salt bath and use as soon as possible.

Investigation using the chloroplasts

Read all the instructions before you start. Use the DCPIP solution at room temperature.

i Set up 5 labelled tubes as follows.

j When the DCPIP is added to the extract, shake the tube and note the time. Place tubes 1, 2 and 4 about 12–15 cm from a bright light (100 W). Place tube 3 in darkness.

k Time how long it takes to decolourise the DCPIP in each tube. If the extract is so active that it decolourises within seconds of mixing, dilute it 1:5 with isolation medium and try again.

Teaching notes

Traditionally the production of oxygen and starch are used as evidence for photosynthesis. The light-dependent reactions produce a reducing agent. This normally reduces NADP, but in this experiment the electrons are accepted by the blue dye DCPIP. Reduced DCPIP is colourless. The loss of colour in the DCPIP is due to reducing agent produced by light-dependent reactions in the extracted chloroplasts.

Students must develop a clear understanding of the link between the light-dependent and light-independent reactions to be able to interpret the results. Robert Hill originally completed this investigation in 1938; he concluded that water had been split into hydrogen and oxygen. This is now known as the Hill reaction.

You can examine a drop of the sediment extract with a microscope under high power to see chloroplasts. There will be fewer chloroplasts in the supernatant – which decolourises the DCPIP more slowly, reinforcing the idea that the reduction is the result of chloroplast activity.

Sample results

Using a bench centrifuge

The experimental procedure was followed. A standard lab centrifuge was used to spin down the chloroplasts (Clifton NE 010GT/I) at 2650 RPM, 95 X g for 10 minutes.

The experiment was started within 5 minutes of preparing the chloroplasts. The reaction was followed using an EEL colorimeter with a red filter – readings taken every minute.

Tube 3 (incubated in the dark) gave a reading of 5.4 absorption units after 20 minutes. Tube 2 (DCPIP with no leaf extract) was 6.2 absorption units.

Using a micro-centrifuge

The experiment was repeated using a micro-centrifuge.

Tube 3 (incubated in the dark) gave a reading of 4.9 absorption units after 10 minutes.

Tube 2 (DCPIP with no leaf extract) was 6.4 absorption Units.

The relative activity of the pellet was higher than when the bench centrifuge was used. The micro-centrifuge tubes were only 1.5 cm 3 capacity – not ideal for this practical. A higher speed bench centrifuge would be better.

In order to check for loss of chloroplast activity, the experiment was repeated using the same chloroplast suspension 1 and 2 hours after preparation. Chloroplast suspension was kept in a salt-ice bath. There was no loss of activity when the extract was kept in ice for up to 2 hours.

Student questions

1 Describe and explain the changes observed in the five tubes. Compare the results and make some concluding comments about what they show.

2 The rate of photosynthesis in intact leaves can be limited by several factors including light, temperature and carbon dioxide. Which of these factors will have little effect on the reducing capacity of the leaf extract?

3 Describe how you might extend this practical to investigate the effect of light intensity on the light-dependent reactions of photosynthesis.

1 Colour change and inferences that can made from the results: Tube 1 (leaf extract + DCPIP) colour changes until it is the same colour as tube 4 (leaf extract + distilled water). Tube 2 (isolation medium + DCPIP) no colour change. This shows that the DCPIP does not decolourise when exposed to light. Tube 3 (leaf extract + DCPIP in the dark) no colour change. It can therefore be inferred that the loss of colour in tube 1 is due to the effect of light on the extract. Tube 4 (leaf extract + distilled water) no colour change. This shows that the extract does not change colour in the light. It acts as a colour standard for the extract without DCPIP. Tube 5 (supernatant + DCPIP) no colour change if the supernatant is clear; if it is slightly green there may be some decolouring. The results should indicate that the light-dependent reactions of photosynthesis are restricted to the chloroplasts that have been extracted.

2 Carbon dioxide will have no effect, because it is not involved in the light-dependent reactions.

3 Students should describe a procedure in which light intensity is varied but temperature is controlled.

Health and safety checked, September 2008

Related experiment

Investigating photosynthesis using immobilised algae

To show experimentally that light is necessary for photosynthesis - Lab Work

To show experimentally that light is necessary for photosynthesis - science practicals.

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Light is Essential for Photosynthesis: Virtual Lab Observation

What is Photosynthesis ? 

All living organisms ultimately depend on energy derived from the sun. Photosynthesis is a biological process in plants and other organisms such as cyanobacteria. This process involves the conversion of solar energy into chemical energy. The chemical energy is utilised in cellular respiration to generate ATP which is used for metabolic activities. This process is anabolic and endergonic, synthesising carbohydrates with the help of carbon dioxide, water, sunlight and light-harvesting pigments. This process involves the transfer of energy in solar radiation and through metabolic pathways converted into utilisable chemical energy.

Photosynthesis’s significance is as follows: Globally, 90% of the photosynthetic activity is carried out by algae in oceans and fresh waters.  Atmospheric oxygen is contributed mainly by this process, food for living organisms is produced directly or indirectly by this process. Photosynthesis also provides vast energy reserves to humankind in the form of fuel-rich substances- coal, oil, peat, wood, and dung.

Diagram of Photosynthesis Process

Light reaction

Dark reaction

Photosynthesis occurs in two phases:

• Light reaction: It is a photochemical phase that takes place in the light. This process occurs in the grana of chloroplasts, i.e. in the thylakoid membranes. These membranes contain some integral membrane proteins which catalyse the light-dependent reactions. During this process, NAD+ is reduced to NADPH, ATP is generated, and water molecules are split into hydrogen and oxygen. In this process, oxygen is liberated through stomatal pores.
• Dark reaction: A biochemical phase occurs in the presence or absence of light. This metabolic pathway occurs in the stroma of the chloroplast . During this process, products of the light reactions, i.e. ATP and NADPH, are utilised in the fixation of carbon dioxide molecules to a glucose molecule. 

In a typical photosynthesis process, 18 molecules of ATPs are required to synthesise a glucose molecule from 6 molecules of carbon dioxide.

What are the requirements of Photosynthesis?

The mechanism of photosynthesis occurs in two phases: Light reaction and Dark reaction.

Requirements for Light reaction: 

• Light: The optimum wavelengths in the visible light region are – the blue range (425 – 450nm) and the red range (600 – 700nm).
• Photosystem I and II: These are protein complexes composed of a reaction centre and light-harvesting complex both are involved in trapping light and generating electrons.
• The water-splitting protein complex is associated with the splitting of water molecules.
• Set of integral protein complexes- Photosystem I and II, cytochrome b6f complex and ATP synthase, which are involved in generating ATP and NADPH

The entire process of light reaction occurs in the thylakoid membrane of chloroplasts.

Requirements for Dark reaction: 

• The key enzyme involved in the dark reaction is RuBisCO (Ribulose 1-5 bisphosphate carboxylase oxygenase). Other enzymes are also required for phosphorylation, reduction, isomerisation and transfer of functional groups.

What are the factors affecting Photosynthesis ?

Factors which are mainly affecting the rate of photosynthesis are as follows.

• Light intensity: As light intensity increases, the rate of light-dependent reactions also increases. The more the photons fall on the leaf, the more chlorophyll pigments are ionised, and more ATP and NADPH are generated. As the light intensity increases, the rate of photosynthesis remains constant, which is due to limitations by some other factors.
• Carbon dioxide: The concentration of carbon dioxide is directly proportional to the rate of photosynthesis. However, the rate of photosynthesis remains constant when the rate of carbon dioxide fixation is reached maximum levels.
• The light-independent reaction (Dark reaction) is dependent on the temperature. When the photosynthetic enzymes are at optimum temperature, the overall rate of photosynthesis also increases. When the temperature rises above the optimum values, the photosynthesis rate decreases due to enzymes’ denaturation.

The rate of photosynthesis is also regulated by limiting factors. According to the law of limiting factors, the rate of photosynthesis will be limited by the factor in the shortest supply (limiting factor). For example,  due to variations of light intensity in the day, light is the limiting factor of photosynthesis, even though there is a higher concentration of carbon dioxide.  

W hy is light essential for Photosynthesis?

Photosynthesis is the process in which solar energy is converted into chemical energy. Using the energy of photons, energy-rich molecules, i.e. carbohydrates, are synthesised from carbon dioxide and water. The photons in the sunlight are absorbed by chlorophyll pigments which results in the excitation of electrons in the photosystem I and II, these excited electrons are passed into an electron transport chain which subsequently results in the generation of ATPs and NADPH. For photosynthesis to occur, the light should be composed of optimum wavelengths, i.e. visible light region – blue range (425 – 450nm) and red range (600 – 700nm).

The importance of light in photosynthesis is experimentally proven with the help of a destarched plant. In this experiment, the leaf was covered with a black strip, and the leaf part did not have access to sunlight. Photosynthesis did not occur in the leaf part, which is further confirmed by the iodine test. 

Light is Essential for Photosynthesis Experiment

Experiment Title – Light is essential for photosynthesis

Experiment Description – Photosynthesis is the process whereby plants synthesise carbohydrates using CO 2 , water, sunlight and chlorophyll. Learn how light is an essential requirement for photosynthesis.

Aim of Experiment – To show that light is essential for photosynthesis

Material Required – Destarched potted plant, thick black paper strips, paper clips, alcohol, iodine Solution, beaker (250 ml), burner, tripod stand, wire gauze, boiling tube, forceps and Petri dish.

Procedure – 

• Take a destarched plant. Using strips of thick black paper and paper clips, cover a part of an intact leaf of the plant. You may cover several leaves of the same plant with black paper strips and clips. Place the set-up in bright sunlight for about two hours.
• Take about 150 ml of water in a beaker and boil it.
• Pluck the experimental leaves from the potted plant and remove the black paper strips from them. Keep these leaves in boiling water for some time till the leaves become soft. Stop heating the water. Remove the beaker from the tripod stand. Allow it to cool to about 60°C.
• Transfer the leaves to a boiling tube containing alcohol.
• Place the boiling tube (containing experimental leaves in alcohol) in the beaker containing hot water at about 60°C. Keep the boiling tube in the beaker till the leaves become colourless.
• Take some iodine solution in a petri dish.
• Wash the leaves in water and dip them in iodine solution in the petri dish.
• After about five minutes, remove the leaves from the iodine solution, wash them with water and observe the colours of the exposed part and unexposed (covered with black paper) part of the leaves.

Precautions – 

• Use a healthy potted plant.
• Since alcohol is highly inflammable, it should not be heated directly on a flame.
• The plant needs to be completely destarched to obtain satisfactory results.
• Be careful while clipping the leaves to avoid tearing or breaking.

FAQs on Light is Essential for Photosynthesis Experiment

Ans.  A plant in which all traces of starch are removed is called a destarched plant. Since starch is the product of photosynthesis, removing starch in the experimental plant is important to prove that light is essential for photosynthesis.

Ans. Red coloured strips do not absorb all wavelengths of visible radiation, this strip will transmit light to the leaf hence allowing the process of photosynthesis subsequently, the importance of light in photosynthesis is not proven.

Ans. The presence of starch in a sample is detected by performing an iodine test, iodine reacts with starch to form an iodine-starch complex in blue. The presence of blue colour indicates the presence of starch in the sample.

Ans. Boiling the leaf with ethanol dissolves the chlorophyll pigment and removes the green colouration in the leaf, and the leaf turns white. Thus while performing the iodine test, it will be easy to observe the colour change.

Ans. Amylose and amylopectin are constituents of a starch molecule. Amylopectin is a huge branched polymer of glucose, whereas amylose is composed of linear helical chains of glucose units.

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Experiment to show that sunlight is essential for photosynthesis.

Experiment to prove that sunlight is essential for photosynthesis: procedure: step 1: keeping the plant in the darkroom: at first, we need to place a healthy green potted plant in a dark room for 1-2 days. this is done to ensure that the plant consumes all its reserve food and the leaves do not contain any starch. ​ step 2: covering a specific part of a leaf: a part of the leaf is covered on both sides with two uniform pieces of black paper, fixed in position with two paper clips on both sides so that the leaf region below the black paper is not exposed to sunlight. ​ step 3: exposing the plant to sunlight: now the plant is exposed to bright sunlight with the specific part of the leaf staying covered. ​ step 4: decolorizing the leaf: after a few hours the specific leaf with the covering is removed. the black papers are removed and then the leaf is subjected to decolorization using alcohol in boiling water. the decolorization occurs as the chlorophyll is removed from the leaf and hence the leaf loses its pigmentation. ​ step 5: adding iodine solution: to the decolorized leaf, iodine solution is added. ​ observation: after adding the iodine solution the part of the leaf that was covered by black paper remains colorless while the region that was exposed to sunlight will have blue-black color. inference: the food prepared by plants (carbohydrates) through the process of photosynthesis is stored as starch. this starch reacts with the iodine solution to change to a blue-black color. only those portions of the leaf that were exposed to sunlight could photosynthesize and hence, change to a blue-black color when tested with iodine. ​ the region that was closed by black papers on both sides were not able to photosynthesize and hence the color did not appear. this proves the importance of sunlight in the process of photosynthesis as it does not occur in the parts of leaves that are not exposed to sunlight..

Practical: Investigating Photosynthesis ( Edexcel IGCSE Biology )

Revision note.

Biology Lead

Practical: Evolution of Oxygen

• We can demonstrate the evolution of oxygen (from the process of photosynthesis) using water plants such as   Elodea or Cabomba - types of pondweed
• As photosynthesis occurs, oxygen gas produced is released 
• As the plant is in water, the oxygen released can be seen as bubbles leaving the cut end of the pondweed
• Boiling tube
• Bunsen burner (for the oxygen test)
• Heat proof mat
• Take a bundle of shoots of a type of pondweed
• Submerge them in a beaker of water underneath an upturned funnel
• Fill a boiling tube with water and place it over the end of the funnel
• As oxygen is produced, the bubbles of gas will collect in the boiling tube and displace the water

Results and analysis

• Show that the gas collected is oxygen by relighting a glowing splint
• The quantity of bubbles / volume of oxygen can also be measured in order to investigate the rate of photosynthesis over a certain amount of time

Experiment to show the evolution of oxygen from a water plant

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Practical: Investigating Light & Photosynthesis

• Although plants synthesise glucose during photosynthesis, their leaves cannot be tested for its presence as the glucose produced is quickly used up, converted into other substances and transported or stored as starch
• Starch is stored in the chloroplasts where photosynthesis occurs so testing a leaf for starch is a reliable indicator of which parts of the leaf are photosynthesising
• Leaf tissue
• Bunsen burner
• Gauze platform
• Safety goggles
• Iodine solution

Investigating the requirement for light in photosynthesis

• Before testing for starch, complete the following procedure:

Method Part 1 - Preparing the leaf to be tested

• This ensures that any starch already present in the leaves will be used up and will not affect the results of the experiment
• Following de-starching, partially cover a leaf of the plant with aluminium foil and place the plant in sunlight for a day
• Remove the covered leaf and test for starch using the method below

Method Part 2 - Testing the leaf for starch

• This kills the tissue and breaks down the cell walls
• This removes the chlorophyll so colour changes from iodine can be seen more clearly
• This is done to soften the leaf tissue after being in ethanol
• Spread the leaf out on a white tile and cover it with iodine solution

Testing a leaf for starch

• In a green leaf, the entire leaf will turn blue-black as photosynthesis is occurring in all areas of the leaf
• When the cells can't photosynthesise they break down the starch to use the glucose for respiration
• This proves that light is necessary for photosynthesis and the production of starch

Photosynthesis cannot occur in sections of the leaf where light cannot reach the chloroplasts

• In the experiment example shown above, after testing for starch the majority of the leaf would appear blue-black, however there would be a strip of orange-brown with a blue-black triangle in the centre
• Care must be taken when carrying out this practical as ethanol is extremely flammable, so at that stage of the experiment, the Bunsen burner should be turned off
• The safest way to heat the ethanol is in an electric water bath rather than using a beaker over a Bunsen burner with an open flame

Applying CORMS evaluation to practical work

• When working with practical investigations, remember to consider your CORMS evaluation

CORMS evaluation

• C - We are changing whether there is light or no light onto the leaf
• O - The leaves will be taken from the same plant or same species, age and size of the plant
• R - We will repeat the investigation several times to ensure our results are reliable
• M1 - We will observe the colour change of the leaf when iodine is applied
• M2 - ...after 1 day
• S - We will control the temperature of the room

Examiner Tip

Remember that when using CORMS you must make sure to use the word same when stating your Organism e.g. same species. Then you have to pick a different factor for your Same part of the answer. There are often two marks available for listing two different control variables for the Same part of the answer. 

Practical: Investigating Carbon Dioxide & Photosynthesis

• The iodine test for starch can be used to investigate the requirement for carbon dioxide in photosynthesis
• Conical flasks
• Potassium hydroxide solution
• Clamp stands
• The potassium hydroxide will absorb carbon dioxide from the surrounding air
• Enclose another leaf with a conical flask containing no potassium hydroxide (control experiment)
• Place the plant in bright light for several hours
• Drop the leaf in boiling water
• Transfer the leaf into hot ethanol in a boiling tube for 5-10 minutes
• Rinse the leaf in cold water

Experiment to test if carbon dioxide is needed for photosynthesis

• The leaf from the conical flask containing potassium hydroxide will remain orange-brown as it could not photosynthesise due to lack of carbon dioxide
• The leaf from the control conical flask not containing potassium hydroxide should turn blue-black as it had all necessary requirements for photosynthesis
• C - We are changing whether there is carbon dioxide or no carbon dioxide
• O - The leaves will be taken from the same plant or same species, age and size of plant
• S - We will control the temperature of the room and the light intensity

Practical: Investigating Chlorophyll and Photosynthesis

• Starch is stored in chloroplasts where photosynthesis occurs so testing a leaf for starch is a reliable indicator of which parts of the leaf are photosynthesising
• This method can also be used to test whether chlorophyll is needed for photosynthesis by using a variegated leaf (one that is partially green and partially white)
• Leaf tissue (leaves must be variegated )
• The white areas of the leaf contain no chlorophyll and when the leaf is tested only the areas that contain chlorophyll stain blue-black
• The areas that had no chlorophyll remain orange-brown as no photosynthesis is occurring here and so no starch is stored
• C - We are changing whether there is chlorophyll or no chlorophyll

Don't forget that CORMS questions in your exams will likely ask about unfamiliar experiments so you need to practice applying CORMS to lots of different practical scenarios. 

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Author: Lára

Expertise: Biology Lead

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.