Wellsway school science dept.
Curriculum 2011 – AQA Additional Science
-1-
Biology workbook
Wellsway school science dept.
Curriculum 2011 – AQA Additional Science
Biology workbook
WORKBOOK 3 - PHOTOSYNTHESIS
Green plants and algae use light energy to make their own food. They obtain the raw
materials they need to make this food from the air and the soil. The conditions plants
are grown in can be changed to promote growth.
Candidates should use their skills, knowledge and understanding to:
■ interpret data showing how factors affect the rate of photosynthesis
■ evaluate the benefits of artificially manipulating the environment in which plants are
grown.
Subject content - Photosynthesis
a) Photosynthesis is summarised by the equation:
light energy
carbon dioxide + water glucose + oxygen
b) During photosynthesis:
■ light energy is absorbed by a green substance called chlorophyll, which is found in
chloroplasts in some plant cells and algae
■ this energy is used by converting carbon dioxide (from the air) and water (from the
soil) into sugar (glucose)
■ oxygen is released as a by-product.
c) The rate of photosynthesis may be limited by:
■ shortage of light
■ low temperature
■ shortage of carbon dioxide.
d) Light, temperature and the availability of carbon dioxide interact and in practice any
one of them may be the factor that limits photosynthesis.
e) The glucose produced in photosynthesis may be converted into insoluble starch for
storage. Plant cells use some of the glucose produced during photosynthesis for
respiration.
f) Some glucose in plants and algae is used:
■ to produce fat or oil for storage
■ to produce cellulose, which strengthens the cell wall
■ to produce proteins.
g) To produce proteins, plants also use nitrate ions that are absorbed from the soil.
1
Discuss with your teacher or in small groups how plants feed.
Watch the video or PowerPoint on photosynthesis.
Decide whether each of these statements is TRUE or FALSE. Check your answers,
then correct any which are false:
a. plants get all their food from the soil
F
b. plants get water and mineral ions (e.g. nitrates) from the soil
T
c. plants make all the substances they need by photosynthesis
F
d. plants use heat energy from the sun to power photosynthesis
F
e. some plant cells use a green pigment called chlorophyll to absorb light energy
T
f. chlorophyll is found inside mitochondria in leaf cells
F
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Wellsway school science dept.
Curriculum 2011 – AQA Additional Science
Biology workbook
g. plants can make food using light energy to combine carbon dioxide and water
T
h. plants produce the waste gas hydrogen from photosynthesis
F
i.
the waste gas from photosynthesis is essential for aerobic respiration
j.
plants can make sugars, starch, cellulose and fats from photosynthesis
T
T
2
Write down the word equation for photosynthesis (and the balanced chemical
equation below it if you know it!):
Carbon dioxide + water (chlorophyll, light energy)
6CO2
3
+ 6H2O
glucose + oxygen
C6H12O6 +
6O2
(This section may be completed after section 4 if preferred.)
Watch the teacher demonstration of photosynthesis in pondweed.
Read your textbook or support material on limiting factors for photosynthesis.
Explain the term limiting factor:
Any factor which can affect the rate of photosynthesis, by
speeding it up or slowing it down.
What are the 3 main limiting factors for photosynthesis?
Explain HOW and WHY each one limits photosynthesis:
(i) Temperature. Photosynthesis increases with temperature because the
enzymes which control PHS work more quickly, so more sugar is made.
However, at very high temperatures these enzymes are DENATURED
(destroyed), so PHS slows down & eventually stops.
(ii) Light intensity. The higher the light intensity, the faster the plant
photosynthesises. Light supplies LIGHT ENERGY to the plant, which is
absorbed by chlorophyll molecules in the leaf, and used to make sugars
from carbon dioxide and water. Once the light intensity reaches a certain
level, the chlorophyll can’t absorb it any faster, so the rate of PHS levels
off at a maximum.
(iii) Carbon Dioxide. CO2 is needed to make sugars, so the higher the
concentration of CO2 , the faster sugar can be made. Once the CO2
concentration reaches a certain level, the plant can’t absorb it any faster,
so the rate of PHS levels off at a maximum.
4
ICT INVESTIGATION: LIMITING FACTORS FOR PHOTOSYNTHESIS
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Wellsway school science dept.
Curriculum 2011 – AQA Additional Science
Biology workbook
You are asked to use software and an Excel spreadsheet and graph wizard. They are
quite easy to use, but ask for guidance, or use the support sheets provided if you
need to.
•
In pairs, using the “Focus” science investigations software to carry out
simulations of photosynthesis experiments.
Pathway to software: subjects / science / science investigations / photosynthesis
• Investigate separately the effects of the independent variables light,
temperature and carbon dioxide on the rate of photosynthesis in pondweed, i.e.
you are carrying out 3 different investigations. Remember that you must only
change ONE factor at a time for fair testing, e.g. if you vary temperature, keep
light & carbon dioxide constant at a maximum. There is no need to repeat
experiments, as they produce reliable results.
• Record all your results in 3 tables using an Excel spreadsheet:
3 on one
page
• Produce 3 line graphs of these results using the Excel chart wizard: 3 on one
page
• Check your tables and graphs with your teacher, and then print out a copy of
each per person.
• File your tables and graphs with this booklet.
Analysis of Results:
For each of the 3 independent variables below:
a. DESCRIBE the effects of varying it on the rate of photosynthesis in pondweed;
b. EXPLAIN the effects of varying it on the rate of photosynthesis in pondweed;
(i)
Temperature (°C)
(consider 0-20°C; 20°C;
20-40°C)
Graph should be “bell” shaped.
Photosynthesis increases with temperature because the
enzymes which control PHS work more quickly, so more sugar
is made. However, at very high temperatures these enzymes
are DENATURED (destroyed), so PHS slows down & eventually
stops.
(ii)
Light distance (cm)
Graph should increase linearly (straight diagonal line), then
reach a plateau (it doesn’t level off on Focus software)
The higher the light intensity, the faster the plant
photosynthesises. Light supplies LIGHT ENERGY to the plant,
which is absorbed by chlorophyll molecules in the leaf, and used
to make sugars from carbon dioxide and water. Once the light
intensity reaches a certain level, the chlorophyll can’t absorb it
any faster, so the rate of PHS levels off at a maximum.
(iii)
Carbon Dioxide concentration
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Wellsway school science dept.
Curriculum 2011 – AQA Additional Science
Biology workbook
Graph should increase linearly (straight diagonal line), then
reach a plateau.
CO2 is needed to make sugars, so the higher the concentration
of CO2 , the faster sugar can be made. Once the CO2
concentration reaches a certain level, the plant can’t absorb it
any faster, so the rate of PHS levels off at a maximum.
Evaluation:
LIST the advantages of using this software simulation compared with carrying out a
real investigation in the laboratory.
•
•
•
•
Much quicker.
No fiddly apparatus to set up.
Works every time – very reliable results.
Can produce a good graph of results from Excel
spreadsheet.
• Very easy to repeat investigation several times.
LIST the disadvantages of using this software simulation compared with carrying out a
real investigation in the laboratory.
• Does not provide practical experience in setting up the
apparatus and carrying out the investigation.
• Less realistic – PHS investigations never work this well!
• Light distance and intensity are not linked by the Inverse
square law (see below).
• The light experiment does not level off when it should.
If you have finished…(and you are good at Maths!)
Look again at the light distance and intensity scale. The inverse square law states that
if the light distance is doubled, the intensity decreases by the square of the distance.
e.g.
LIGHT DISTANCE (cm)
RELATIVE DISTANCE
INVERSE SQUARE
LIGHT INTENSITY (%)
5
1
1/1
100
10
2
1/4
25
15
3
1/9
11
20
4
1/16
6
25
5
1/25
4
Do the light distance and intensity show this relationship? How can you tell? If they do
not, clearly the software programmers have overlooked an important scientific
principle! This is a big drawback of the software if they have!
Inverse square law is NOT shown on this software, which is a
pity, because it invalidates the simulation from a quantitative
point of view (i.e. the results cannot be used to accurately
compare rate of PHS with light distance).
5
INVESTIGATING STARCH PRODUCTION IN LEAVES
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Wellsway school science dept.
Curriculum 2011 – AQA Additional Science
Biology workbook
Using the worksheet provided, work in small groups to investigate the effect of light
and chlorophyll on starch production in leaves.
A leaf stencil is one where parts of a leaf are covered with foil, so no light can reach
them.
A variegated leaf is one where parts of the leaf lack chlorophyll, so are yellow, not
green.
Please note carefully the safety hazards in this investigation:
•
•
•
•
1. Boiling water - risk of scalding, especially if beaker tips over
2. Bunsen flames - risk of burning
3. Ethanol
- highly flammable, TURN OFF BUNSEN before getting ethanol
4. Iodine
- stains hands, clothes, benches, etc.
Explain the reason for the following steps in the method:
1. Putting the leaf in boiling water.
Kills the leaf & makes it permeable to iodine solution.
2. Putting the leaf in boiling ethanol.
Removes chlorophyll & makes the starch test easier to see.
3. Returning the leaf to hot water.
Softens the leaf so it can be easily laid flat on the tile.
4. Covering the leaf in iodine solution.
Shows up where starch is present (blue-black) or absent
(orange-brown).
Results:
Make a neat drawing to show the colours of each leaf after staining with iodine
solution:
1. PLAIN GREEN LEAF
Blue-black all over.
2. LEAF STENCIL
Blue-black only
where light fell
on the leaf.
3. VARIEGATED LEAF
Blue-black only
where chlorophyll
was present
(the green parts).
Conclusion:
Explain the results for each leaf in terms of conditions needed for photosynthesis and
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Wellsway school science dept.
Curriculum 2011 – AQA Additional Science
Biology workbook
starch production.
1. Plain Leaf.
The leaf had light energy AND chlorophyll, so could make starch
by PHS.
2. Leaf Stencil.
Where the leaf was covered in foil, no light energy could be
absorbed by chlorophyll, so no starch could be made by PHS.
3. Variegated Leaf.
Where there was no chlorophyll (white/yellow parts of the leaf),
no light energy could be absorbed by chlorophyll, so no starch
could be made by PHS.
These results show that BOTH light energy AND chlorophyll are
needed for PHS.
6
Discuss with your teacher the uses of glucose by plant cells.
Read your textbook or support material on the uses of glucose by plant cells.
List the uses of glucose by plant cells.
• Used up in RESPIRATION, to give the plant energy.
• Converted to STARCH and stored for future use (e.g. in
roots).
• Used to make CELLULOSE, for building CELL WALLS.
• Converted to FATS & OILS, for storage in seeds.
• Combined with nitrates to make AMINO ACIDS, which
can be built up into PROTEINS, for GROWTH &
REPAIR.
Well done – you have finished the Photosynthesis workbook!
Useful web links & clips:
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Wellsway school science dept.
Curriculum 2011 – AQA Additional Science
Biology workbook
BBC bitesize
http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/plants/plants1.shtml
The student room
http://www.thestudentroom.co.uk/wiki/Revision:GCSE_Biology__Plant_Biology#Photosynthesis
Purchon
http://www.purchon.com/biology/revision.htm#Digestion
Schoolsnet
http://www.schoolsnet.com/pls/hot_school/sn_revision.page_pls_revision_detail?x=&p_rev_id
=118&p_res_type_id=16
S-Cool
http://www.s-cool.co.uk/gcse/biology/photosynthesis/revise-it/photosynthesis
Revision World
http://www.revisionworld.co.uk/gcse/biology/green-plantsorganisms/photosynthesis/photosynthesis-introduction
Glossary. (Muddled in groups of 5 – sort them out!)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Carbon dioxide
Cellulose
Chlorophyll
Chloroplast
Ethanol
Fats (oils)
Glucose
Iodine solution
Light energy
Light intensity
Limiting factor
Nitrates
Oxygen
Proteins
Starch
Stencil
Temperature
Variegated
Green pigment which absorbs light energy for photosynthesis
Gas needed for photosynthesis; limiting factor
Dissolves chlorophyll and decolourises leaves in starch test
Cell wall polysaccharide; made from many glucose units
Small structures inside leaf cells packed with chlorophyll
Turns blue-black when mixed with starch
Energy-rich storage compounds e.g. sunflower oil
Increasing this increases light energy; limiting factor
Sugar made in plants by photosynthesis; used in respiration
Absorbed by chlorophyll; needed for photosynthesis
Waste gas produced by photosynthesis; used in respiration
Storage polysaccharide; made from many glucose units
Mineral ions absorbed from soil; needed to make proteins
Made from sugars and nitrates; needed for plant growth
Any independent variable which controls rate of photosynthesis
Limiting factor; supplies heat energy for enzymes to work
A leaf containing yellow areas which lack chlorophyll
Leaf partly covered in foil, excluding light from covered areas
Additional notes
Questions.
-8-
3
1
5
2
4
8
6
10
7
9
13
15
12
14
11
17
18
16
Wellsway school science dept.
Curriculum 2011 – AQA Additional Science
(Q3 – soda lime removes carbon dioxide from the air.)
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Biology workbook
Wellsway school science dept.
Curriculum 2011 – AQA Additional Science
- 10 -
Biology workbook
Wellsway school science dept.
Curriculum 2011 – AQA Additional Science
Biology workbook
AQA Past paper question.
4 The diagram shows bushes in a hedge growing near to a house.
The bushes were the same species and the same age.
(a) (i) The student said, “I have noticed that the short bushes grow next to the house.
I think that the more light the bushes get, the faster they will grow.”
Draw lines to match each of the student’s statements to the correct term.
Draw only two lines.
(2 marks)
(ii) Complete the word equation for photosynthesis.
..................................... + water (+ light energy) → ................................ + oxygen
marks)
(b) The student decided to investigate the effect of light intensity on the rate of
photosynthesis.
She used the apparatus shown in the diagram.
She measured the rate of photosynthesis by counting the number of gas bubbles
given off each minute.
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Wellsway school science dept.
Curriculum 2011 – AQA Additional Science
Biology workbook
(i) Suggest how the student varied the intensity of the light received by the pondweed.
..................................................................................................................................
.......................................................................................................................… (1 mark)
(ii) The student’s results are shown on the graph.
Describe the pattern shown on the graph.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
....................................................................................................................... (2 marks)
(iii) This is what the student wrote for her conclusion.
“Increasing the light intensity increases the rate of photosynthesis of the pondweed.”
Why was her conclusion incomplete?
..................................................................................................................................
......................................................................................................................... (1 mark)
(F PAPER – JAN 2008)
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Wellsway school science dept.
Curriculum 2011 – AQA Additional Science
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Biology workbook