Integrated sc M1 Photosynthesis Experiments

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

OBJECTIVESOBJECTIVES
Photosynthesis
A photo-chemical
process
Photosynthesis
A photo-chemical
process
Photosynthesis
experiments
Photosynthesis
experiments
QUIZQUIZ
INTRODUCTIONINTRODUCTION
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INTRODUCTION
2
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.

Photosynthesis
A photo-chemical
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Photosynthesis
A photo-chemical
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Photosynthesis
experiments
Photosynthesis
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OBJECTIVES
3
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.

Photosynthesis
A photo-chemical
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Photosynthesis
A photo-chemical
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Photosynthesis
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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.
4

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A photo-chemical
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A photo-chemical
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Process – Question 1
What do you remember about photosynthesis? Tell a
partner what is under each coloured oval and type your
responses 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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A photo-chemical
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A photo-chemical
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Process – Question 2
6
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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A photo-chemical
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Photosynthesis
A photo-chemical
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Photosynthesis
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Process – Feedback to Question 2
7
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

Photosynthesis
A photo-chemical
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Photosynthesis
A photo-chemical
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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?
8
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

Photosynthesis
A photo-chemical
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Photosynthesis
A photo-chemical
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Photosynthesis
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Photosynthesis
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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.
9
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

Photosynthesis
A photo-chemical
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Photosynthesis
A photo-chemical
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Photosynthesis – Feedback to Question 2
More Feedback to Question 2
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.
10
6 CO2 + 6 H2O C6H12O6 + 6 O2
starch
Sunlight
Chlorophyll

Photosynthesis
A photo-chemical
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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?
11
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-
Iodine in potassium
iodide solution is an
indicator that turns blue-
black in the presence of
starch.
CHECKCHECK

Photosynthesis
A photo-chemical
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Photosynthesis
A photo-chemical
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Photosynthesis experiments
Question 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/stud
Make sure to include labelled diagrams!
12

Photosynthesis
A photo-chemical
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A photo-chemical
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Question 5
When doing the starch test on green leaves, why
is the green leaf boiled in alcohol?
13
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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Question 6
After being boiled in alcohol, why does the leaf
have to be placed in hot water?
14
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.
15

Photosynthesis
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A photo-chemical
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More Products of photosynthesis
16
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

Photosynthesis
A photo-chemical
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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?
17
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 QUESTIONFEEDBACK TO QUESTION

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Is light really needed?
18
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.FEEDBACKFEEDBACK

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A photo-chemical
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Photosynthesis experiments -
3. Write a hypothesis on which to base excluding light
from parts of a green leaf, then testing the entire leaf
for starch.
19
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
FEEDBACKFEEDBACK

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20
Previously
green areas
stained
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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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.
21

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A photo-chemical
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A photo-chemical
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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.
22

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Limiting factors
4. Read and look at the graphs at > http://tinyurl.com/7s7knw7
5. From the graphs , what is meant by ‘limiting factors’ for
photosynthesis?
23
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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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/Fil
e: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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SUMMARY
25
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
26
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
27
When doing a starch test on a green leaf, which
technique removes the chlorophyll from a leaf?
27
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
28
When doing a starch test on a green leaf, which
technique removes the chlorophyll from a leaf?
The answer is A.
28
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
29
Carbon dioxide enters the leaf through the ……… .
29
B. chloroplasts
A. cuticle
C mesophyll cells
D. stomata

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30
The answer is D.
Carbon dioxide enters the leaf through the
stomata.
30
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
31
The organic food molecule produced directly by
photosynthesis is ……… .
31
B. lipids
A. oxygen
C. starch
D. glucose

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Feedback to M.C. Question 3
32
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
33
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.scien
cequiz.net/jcscienc
e/jcbiology/pphot
osynthesis/photosy
n_mcq.htm
http://www.sciencequiz.net/jcscie
nce/jcbiology/pphotosynthesis/p
hotosyn_mcq.htm

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34
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 QuestionsReview Questions
35
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/Va

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Feedback to Questions 1 - 4Feedback to Questions 1 - 4
36
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..
FEEDBACK

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Review Question 5
37
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
38
 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

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