integrated sc m1 photosynthesis experiments

Module 1 Module 1 Unit 2 Unit 2 Lesson 5 Lesson 5 BEGINBEGIN

OBJECTIVESOBJECTIVES

Photosynthesis A photo-chemical process


Photosynthesis experiments


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INTRODUCTIONINTRODUCTION

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INTRODUCTION

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You’ve learned that plants need chlorophyll to trap light energy for photosynthesis. Do plant leaves that are this colour have

chlorophyll? Can these leaves carry out photosynthesis? How could we find out?

In this lesson, you’ll carry out various tests that will help you answer those, and other, questions and also explore the ways in which tests that confirm the reactants and products of photosynthesis are done.

You can access various subtopics by clicking on the Menu on the left of the slide.

Carefully read the objectives for this lesson.






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OBJECTIVES

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When you complete this slide presentation, you will be able to:perform tests to confirm the products of photosynthesis.perform tests to show some conditions necessary for photosynthesis to occur.accurately observe, record and report on the tests performed.manipulate equipment to conduct experiments.access and use information from the internet.






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Photosynthesis: A Photochemical Process – Activity

The next slides present questions on photosynthesis.

On each question slide, type your response in the box provided.

Read the feedback provided.

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Photosynthesis: A Photochemical Process – Question 1

What do you remember about photosynthesis? Tell a partner what is under each coloured oval and type yourresponses in the box below. Click on each coloured oval to check your response.

Question 2

E. E.

D.D.

A.

B.

C.

B.

A.

C.






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Photosynthesis: A Photochemical Process – Question 2

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Why is photosynthesis a photochemical process?

Photosynthesis is a photochemical process because light is required for some of the reactions to occur. Click the next button for additional feedback.CHECKCHECK






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Photosynthesis: A Photochemical Process – Feedback to Question 2

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Why photosynthesis is a photochemical process?Photosynthesis is a photochemical process because light is required for some of the reactions to occur. The word ‘photo’ means ‘light’ so that part of the word refers to the fact that the light-dependent phase is initiated by the absorption of light by chlorophyll. NOTE: Although the word ‘photon’ is a measure of light, that is not the word incorporated into photosynthesis.(Remember also -- The ‘synthesis’ means to ‘make’/’manufacture’, so that part refers to the manufacturing reactions of the light-independent phase, from which organic molecules are synthesized or made.)

Question 3






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Photosynthesis experiments – Materials for and Products of Photosynthesis – Question 1

If we wanted to prove that photosynthesis occurred in green plants, what tests would we need to do?

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Feedback to Question 1: You already know that the following are needed : light energy H2O, CO2 and chlorophyll. The products are: oxygen gas and glucose - changed to, and stored in leaves as, starch. So, to prove if photosynthesis took place, we can test to observe if light, chlorophyll and carbon dioxide are really needed, or test for one or more products, e.g., oxygen or food that was manufactured during the reactions.CHECKCHECK






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XXXXPhotosynthesis experiments – Materials for and Products of Photosynthesis – Question 2

A common test done, to show that photosynthesis has occurred, is the starch test. Why do we test for starch, not glucose? Discuss it in your group, then tell your teacher.

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Feedback: Glucose, a product of photosynthesis, is soluble and so can affect the osmotic balance in cells in which it is produced. So, it is converted to insoluble starch almost immediately. The insoluble starch granules can be stored in the leaves without affecting the osmotic balance of the cells. So, we can test for this product. See the next slide for more information.CHECKCHECK






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XXXXPhotosynthesis experiments – Materials for and Products of Photosynthesis – Feedback to Question 2

More Feedback to Question 2Glucose, a product of photosynthesis, is soluble and so can affect the osmotic balance in cells in which it is produced. So, it is converted to insoluble starch almost immediately.

The insoluble starch granules can be stored in the leaves without affecting the osmotic balance of the cells. So, we can test for this product.

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6 CO2 + 6 H2O C6H12O6 + 6 O2

starch

Sunlight

Chlorophyll






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XXXXPhotosynthesis experiments – Materials for and Products of Photosynthesis – Question 3

When doing osmosis, you learned that starch reacts with Iodine solution. So how do you think we could use that knowledge to test green leaves for starch?

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To see how we use iodine to test green leaves for starch, watch the video/ read the information at> http://brilliantbiologystudent.weebly.com/testing-a-leaf-for-the-presence-of-starch.html

Iodine in potassium iodide solution is an

indicator that turns blue-black in the presence of

starch.

CHECKCHECK






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Photosynthesis experimentsQuestion 4

In your SIM, Click to do Worksheet 5.1. Do the starch test as in the video, but test discs from sample leaves instead of the entire leaf.Write up what you did and observed. This website below might help you when you begin to write up your Lab Report > http://www.elateafrica.org/elate/biology/nutrition/studentactivities.htmlMake sure to include labelled diagrams!

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When doing the starch test on green leaves, why is the green leaf boiled in alcohol?

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Feedback: To decolourise it or remove the green pigment, chlorophyll, so that later, any colour-change with Iodine will be clearly seen.Heat also destroys (denatures) the protein in the cell membranes thus making it easier for the Iodine solution to enter the cell and come in contact with stored starch grains. CHECKCHECK






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After being boiled in alcohol, why does the leaf have to be placed in hot water?

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Feedback: The leaf will be brittle, so that prevents it from breaking while it is being placed on the tile. It also makes it more permeable to the Iodine.

CHECKCHECK






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Your teacher may allow time now to write up your test, or else you should do so later.

Continue with the next slides; observe the demonstration and do the various tests indicated in subsequent slides and also in the Worksheet in your SIM.

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Photosynthesis experiments – More Products of photosynthesis

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2. Could we use the gas bubble formation to get an idea of the rate of photosynthesis? How? Tell your teacher.

1. Observe the demonstration. Look for gas bubbles coming out of the leaves, as in this photo, and also rising up through the water.

Check the video experiment at > http://www.youtube.com/watch?v=yg8vqsBOFMwMORE FEEDBACKMORE FEEDBACK






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Photosynthesis experiments – More Products of photosynthesis

3. Next, do the Part A activity on Worksheet 5.2 in your SIM

4. To Think About: How can we be sure that the gas given off is oxygen?

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Watch your teacher collect some gas in the test tube, and insert a glowing wooden splint into the gas in the test tube. Observe what happens to the glowing splint. NOTE: If the glowing splint re-lights and bursts into a flame, that it is a confirmatory test for oxygen gas!

FEEDBACK TO QUESTION FEEDBACK TO QUESTION






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Photosynthesis experiments Is light really needed?

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1. Get test materials and one of the leaves that had been covered on both sides as shown.

2. In the box below, state why we covered a part of the leaf with black paper or foil.

Covered with black paper

You must be in ‘Slide Show’ view to type / delete text.

To exclude light from some areas while leaving other areas of the same leaf exposed to light, so that we can then test both areas to compare where there is starch.FEEDBACK FEEDBACK






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Photosynthesis experiments - Is light really needed?

3. Write a hypothesis on which to base excluding light from parts of a green leaf, then testing the entire leaf for starch.

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Feedback to Item 3: If light is excluded from a green leaf, then it will not be able to carry out the photochemical reactions of photosynthesis, so no glucose will be made and no starch will be present when the leaf is tested.

4. Test leaf discs from covered and uncovered areas of green leaves to determine where starch is present.

Feedback to Item 4: Your results should be that only the leaf discs from the uncovered , green leaf parts should give a positive starch test result.FEEDBACKFEEDBACK

FEEDBACK FEEDBACK






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Photosynthesis experiments Is light really needed?

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Previously green areasstained blue-black

Covered area coloured by Iodine

5. If you had tested the entire leaf (as it was originally covered) for starch, instead of discs punched from it:a) In your notebook, draw the entire leaf to

show starch test results. b) Explain the result/s.

FEEDBACK TO ITEM 5FEEDBACK TO ITEM 5






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XXXXPhotosynthesis experiments Feedback to Question 5 cont’d

5. (b) Explanation of the results: Only the parts of the leaf that were left uncovered and therefore exposed to light, would give a positive starch test result, by showing the blue-black colour when Iodine in potassium iodide solution is added during the test for starch. The covered parts of the leaf were not able to trap the light energy and so would not produce glucose so there would be none to be converted and stored as starch. Thus no blue-black colour would be produced in the test for starch.

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XXXXPhotosynthesis experiments Is CO2 really needed?

1. Is CO2 really needed for photosynthesis? To see how the experiment is set up, watch the animation from the site below.

http://www.youtube.com/watch?v=lji6Zx3_E30

2. Examine the demonstration plants your teacher had set up previously and compare with Figure 5.2 in your SIM. Then, test discs from leaves exposed to CO2 and some from leaves deprived of CO2. Compare and discuss your results.

3. Do Part B simulation of Worksheet 5.2.

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Photosynthesis experiments - Limiting factors4. Read and look at the graphs at > http://tinyurl.com/7s7knw75. From the graphs , what is meant by ‘limiting factors’ for

photosynthesis?

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A “limiting factor is any factor beyond which the rate of photosynthesis can not be increased, until the factor is dealt with”. These are factors such as light intensity, CO2 concentration and temperature that can limit/control the increase in the rate of photosynthesis.

Go to section 5) in your SIM.

For example, the first graph (Below) shows that as light intensity increases, photosynthesis rate also increases until it reaches a point where the rate remains constant and is no longer increased or affected by any further increase in light intensity.

FEEDBACK TO ITEM 5FEEDBACK TO ITEM 5






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XXXXPhotosynthesis experiments -Does food-making also occur in variegated leaves?

You’ve learned that all leaves contain chlorophyll pigments. But, some also have other pigments, such as anthocyanins and carotinoids, which make them look red and purple, or orange, respectively. These other pigments mask or hide chlorophyll and can also help to absorb light.

24http://www.palmpedia.net/wiki/File:IMG_1843.JPG

So, can these leaves carry out photosynthesis? Tell your teacher what you think!

Check section 5) in your SIM.






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XXXXSUMMARY

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Photosynthesis takes place in two stages: Light-dependent or photochemical reactions - in which plants

use light energy they absorb by means of chlorophyll to split the water molecules, which had been absorbed by roots and transported to the leaves, into hydrogen and oxygen.

Light independent or ‘dark’ stage – in which plants use the hydrogen they obtained in the light dependent stage and combine it with carbon dioxide, which entered the leaves via stomata, to form simple sugars such as glucose. Oxygen is given off through stomata.

Glucose can be quickly converted to insoluble starch and stored in leaf cells, or glucose can be used in respiration to release energy which the plant cells require for various processes. Some glucose can be trans-located via phloem tissue to storage areas.

Photosynthesis experiments can be done (a) to show the materials needed for photosynthesis (e.g. light, CO2, chlorophyll) or (b) to confirm the products of photosynthesis (e.g. starch and O2).






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QUIZ AND REVIEW

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Get ready to test yourself! There are four Multiple Choice (4 M.C.) items

that you are required to do. For each item, click on the letter of the correct

response, click the ‘Feedback’ to check your answer, then click ‘NEXT QUESTION’ to continue.

There is also a set of Review Questions. Click the ‘BEGIN QUIZ’ to start doing this quiz.






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M.C. Question 1

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When doing a starch test on a green leaf, which technique removes the chlorophyll from a leaf?

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B. Leaving the plant in the dark for one day.

D. Boiling the plant in hot water for five minutes.

C. Dipping the leaf in hot water.

A. Boiling the leaf in alcohol.

FEEDBACKFEEDBACKFEEDBACKFEEDBACK






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Feedback to M. C. Question 1

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When doing a starch test on a green leaf, which technique removes the chlorophyll from a leaf? The answer is A.

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A. Boiling the leaf in alcohol is the correct answer.

B. Would cause the plant to be destarched.C. Only softens a brittle leaf after it has been

boiled in alcohol to de-colourise it. D. Boiling the plant in hot water for 5 minutes

would kill all of its cells!

NEXT QUESTIONNEXT QUESTION






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M.C. Question 2

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Carbon dioxide enters the leaf through the ……… .

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B. chloroplasts

A. cuticle

C mesophyll cells


D. stomata






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The answer is D.Carbon dioxide enters the leaf through the stomata.

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D. Stomata are the tiny pores/openings on leaves, through which gases such as CO2 (and O2) can diffuse into (and out of ) the leaf.A. The cuticle is the waxy layer covering leaf epidermal surfaces.B. Chloroplasts are the sites of the photosynthesis reactions.C. Mesophyll cells form the middle layer of leaves.







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M. C. Question 3

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The organic food molecule produced directly by photosynthesis is ……… .

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B. lipids

A. oxygen

C. starch

D. glucose







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Feedback to M.C. Question 3

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The answer is D.The organic food molecule produced directly by photosynthesis is glucose.

NOTE: Organic compounds always contain carbon while most inorganic compounds do not contain carbon. Also, almost all organic compounds contain C-H bonds.

Glucose is the first organic food molecule produced in photosynthesis. A.Oxygen is an inorganic molecule and is not food.B. & C. Glucose is quickly linked to other glucose molecules to form starch & cellulose molecules and later even proteins and lipids (fats).







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M. C. Question 4

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In an experiment to test a green leaf for starch, the leaf is initially placed in boiling water, as shown. Why is this done?

B. The starch test only works at a high temperatures such as boiling water.

A. To remove chlorophyll from the leaf

C. To speed up starch formation.

D. To kill the cells in the leaf.


http://www.science

quiz.net/jcscience/jcbiology/

pphotosynthesis/

photosyn_mcq.htm

http://www.sciencequiz.net/jcscience/jcbiology/pphotosynthesis/

photosyn_mcq.htm






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The answer is D.In an experiment to test a green leaf for starch, the leaf is initially placed in boiling water. Why is this done? To kill the cells in the leaf.

A. To remove chlorophyll from the leaf, we boil it in alcohol in a water bath.B. The starch test does not require high temperatures (e.g. if you drop iodine on bread or the cut surface of a potato, you’d get the blue-black colour showing starch is present). The use of heat kill cells, making their membranes more permeable to the penetration of the indicator.

C. Starch was already formed from glucose in the cells.







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Review Questions Review Questions

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Plants with variegated leaves, like these in the pictures, were first de-starched, then given all other conditions needed for photosynthesis. Two different leaves were picked from each plant and each was tested for starch. In your notebook, write your responses to these questions.1. What result/s would you get? 2. Explain why.3. How do you de-starch a plant before a photosynthesis test?4. Why is de-starching necessary? http://garden-photos-com.photoshelter.com/gallery-image/

Variegated-Plants-Leaves-Stock-Photos/G0000vnItmZIbleQ/I0000xjcfiNs1en4






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Photosynthesis experiments Feedback to Questions 1 - 4 Feedback to Questions 1 - 4

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1.

1. The photos at left show the kind of result you would get for variegated leaves, i.e. only the original green parts of the leaves would show the blue-black colour when Iodine is added during the test for starch.

2. This is because only the original green parts contained chlorophyll. So it is in those cells that photosynthesis occurred. The glucose made there was converted to insoluble starch and stored in those leaf cells which showed blue-black when tested with iodine.

3. A plant is de-starched by keeping it in a dark cupboard or box, for at least 24 hours and perhaps even up to three days, thus preventing its green leaves and other green parts from getting any sun)light, so it will no longer make glucose. Also, any starch that had been present would most likely be used up in respiration or changed and trans-located elsewhere for use/storage..

4. De-starching a plant or a leaf prior to photosynthesis tests will ensure that all starch has been transported away from the leaves, so that any positive starch test obtained during the test will indicate that photosynthesis had occurred during the test..

FEED

BACK







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Photosynthesis experimentsReview Question 5

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5. The diagrams show Before and After for a starch test for photosynthesis. The top diagram (Before) shows that vaseline was smeared on one half of a green leaf, from a plant that had been fully de-starched then given the necessary conditions for photosynthesis and finally tested for starch. Explain the ‘After’ or results.

Feedback: When vaseline was smeared on the test leaf, the stomata were covered so no air, containing CO2 could enter the leaf. CO2 is essential for simple carbohydrates e.g. glucose, to be made during photosynthesis, so without it, there was no glucose to be converted to starch and stored in leaf cells. Therefore in the half of the leaf from which CO2 entry was prevented, photosynthesis did not occur, so the starch test there was negative. The other half acted as a control and showed a positive starch test.

FEEDBACK TO REVIEW QUESTION 5FEEDBACK TO REVIEW QUESTION 5






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CREDITS

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http://www.und.nodak.edu/dept/jcarmich/101lab/lab8/lab8.html http://click4biology.info/c4b/3/chem3.8.htm m31corp.edublogs.org/files/.../Photosynthesis-Rm-31-Corp-Videos.ppt http://www.fotosearch.com/photos-images/green-leaves.html http://www.elateafrica.org/elate/biology/nutrition/nutritionintro.html http://www.elateafrica.org/elate/biology/nutrition/nutritionintro.html http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/plants/plants2.shtml https://www.google.com.jm/search?

q=starch+test+on+variegated+leaves&rlz=1T4ADBR_enJM313JM317&tbm=isch&tbo=u&source=univ&sa=X&ei=VUjQUuTXKs7NsQTSpYKYBg&ved=0CC8QsAQ&biw=813&bih=398

http://garden-photos-com.photoshelter.com/gallery-image/Variegated-Plants-Leaves-Stock-Photos/G0000vnItmZIbleQ/I0000xjcfiNs1en4

B4YX8F Alamy images http://www.afripics.com/home/products/product.php?ProductID=130095568664 http://www.sciencequiz.net/jcscience/jcbiology/pphotosynthesis/photosyn_mcq.htm http://tinyurl.com/7s7knw7 http://www.uq.edu.au/_School_Science_Lessons/9.147.GIF

integrated sc m1 photosynthesis experiments

Education

products of photosynthesis

photochemical process

photochemical process

photochemical process

word photo means light

question slide

various tests

light energy