1
Think about…
21.1 Basic concepts of photosynthesis
21.2 Requirements for photosynthesis
21.3 Site of photosynthesis
21.4 The process of photosynthesis
21.5 The fate of photosynthetic products
21.6 Factors affecting the rate of
photosynthesis
Recall ‘Think about…’
2
Summary concept map
A greenhouse (溫室) is a transparent
building made for growing plants under
controlled conditions.
3
The conditions promote photosynthesis
to enhance plant growth.
4
Crops like green peppers and tomatoes
are not suitable to grow in Hong Kong.
5
With greenhouses, farmers can grow
them all year round.
6
1
What conditions of a greenhouse
promote photosynthesis
7
2
How do plants make food by
photosynthesis
8
3
What is the significance of
photosynthesis to the ecosystem
9
21.1 Basic concepts of
photosynthesis
What is
photosynthesis?
10
21.1
Basic concepts of photosynthesis
What is photosynthesis?
• the process by which organic substances
are made from simple inorganic
substances using light energy
• an anabolic process
light energy
chemical energy
plants / algae
11
21.1
Basic concepts of photosynthesis
What is photosynthesis?
• occurs in chloroplasts
• overall equation:
CO2
light absorbed
glucose
water
by chlorophyll
O2
by-product
12
21.1
Basic concepts of photosynthesis
What is photosynthesis?
• plants make their own food by
photosynthesis
light
photosynthesis
CO2
minerals
water
inorganic nutrients
13
21.1
Basic concepts of photosynthesis
What is photosynthesis?
photosynthesis
organic nutrients
carbohydrates
lipids
proteins
plant materials
14
21.1
Basic concepts of photosynthesis
What is the
significance of
photosynthesis?
15
21.1
Basic concepts of photosynthesis
1 Maintaining energy flow
in ecosystem
light energy
photosynthesis
chemical energy in green plants
feeding
chemical energy in
consumers
16
21.1
Basic concepts of photosynthesis
2 Providing the basic food source
• most organisms depend on plants
directly or indirectly for food
human
plant
cow
producer
17
21.1
Basic concepts of photosynthesis
3 Maintaining oxygen and carbon
dioxide balance
respiration
consume O2
burning of fuels
release CO2
18
21.1
Basic concepts of photosynthesis
3 Maintaining oxygen and carbon
dioxide balance
• oxygen consumed is
replaced by that
released by plants
during photosynthesis
• plants take in
carbon dioxide for
photosynthesis
19
21.1
Basic concepts of photosynthesis
1 Photosynthesis is the process by
which organic substances are
made from simple inorganic
substances using light energy.
20
21.1
1
Basic concepts of photosynthesis
In plants, glucose is made from
carbon dioxide and water during
photosynthesis. Oxygen is
released as a by-product.
21
21.1
2
Basic concepts of photosynthesis
Photosynthesis occurs in the
chloroplasts . Chlorophyll there
absorbs light energy to drive the
photosynthetic reactions.
22
21.1
Basic concepts of photosynthesis
3 During photosynthesis, light energy
from the sun is captured by plants,
and converted to chemical energy
stored in the organic substances
produced. Photosynthesis maintains
the energy flow in the ecosystem.
23
21.1
Basic concepts of photosynthesis
3 It provides the basic food source
for most organisms.
It maintains the balance of
atmospheric oxygen and carbon
dioxide.
24
21.2 Requirements for
photosynthesis
How do we know if
photosynthesis has
occurred?
25
21.2
Requirements for photosynthesis
Has photosynthesis
occurred?
glucose formed in
photosynthesis
starch
• test for the presence of starch to find
out if photosynthesis has occurred
26
21.2
Requirements for photosynthesis
Has photosynthesis
occurred?
• starch formed before affects the results
 destarching (脫澱粉)
keep in darkness
for 24 hrs
27
21.2
Requirements for photosynthesis
21.1
Video
Detection of starch produced from
photosynthesis (the iodine test)
1 Boil a leaf in water for
a minute.
leaf
boiling
water
28
21.2
Requirements for photosynthesis
21.1
Detection of starch produced from
photosynthesis (the iodine test)
2 Turn off the Bunsen burner.
Transfer the leaf to a boiling
tube half filled with absolute
alcohol. Put the tube into a
beaker of hot water.
alcohol
hot water
29
21.2
Requirements for photosynthesis
21.1
Detection of starch produced from
photosynthesis (the iodine test)
3 When the leaf has lost its
green colour, i.e. decolourized,
transfer it from the tube to hot
water.
hot water
30
21.2
Requirements for photosynthesis
21.1
Detection of starch produced from
photosynthesis (the iodine test)
4 Spread the leaf on a white
tile. Add a few drops of
iodine solution onto its
surface. Observe any colour
change in the leaf.
iodine
decolourized leaf white tile
31
21.2
Requirements for photosynthesis
21.1
Results and discussion
The iodine solution turns blue-black all over
the leaf. This result indicates that starch is
present in the whole leaf.
32
21.2
Requirements for photosynthesis
Has photosynthesis
occurred?
• oxygen is a by-product of photosynthesis
• test for oxygen using a glowing splint
test tube
if oxygen is
present,
glowing splint
relights
33
21.2
Requirements for photosynthesis
21.2
Detection of oxygen produced from
photosynthesis
1 Put a few Hydrilla plants in a
beaker of dilute sodium
hydrogencarbonate solution.
dilute sodium hydrogencarbonate solution
Hydrilla
34
21.2
Requirements for photosynthesis
21.2
Detection of oxygen produced from
photosynthesis
filter
2 Put an inverted filter funnel
funnel
on three stoppers to cover the
plants. Put a test tube
completely filled with dilute
sodium hydrogencarbonate
solution on top of the funnel.
stopper
35
21.2
Requirements for photosynthesis
21.2
Detection of oxygen produced from
photosynthesis
3 Leave the set-up in bright
light for at least one day.
36
21.2
Requirements for photosynthesis
21.2
Detection of oxygen produced from
photosynthesis
4 Remove the test tube
carefully so that the gas
cannot escape. Put a glowing
splint over the mouth of the
test tube to test for oxygen.
37
21.2
Requirements for photosynthesis
21.2
Results and discussion
The glowing splint relights. This result shows
that the gas released from Hydrilla is oxygen.
38
21.2
Requirements for photosynthesis
Requirements for
photosynthesis
• two set-ups in the investigation
- experimental set-up: the factor
being tested is present
- control set-up: the factor is absent
39
21.2
Requirements for photosynthesis
Requirements for
photosynthesis
1 Chlorophyll
• impossible to remove chlorophyll
from a leaf without killing it
 use plants with
variegated leaves (斑葉)
40
21.2
Requirements for photosynthesis
Requirements for
photosynthesis
1 Chlorophyll
green part
(chlorophyll
present)
Coleus
41
21.2
Requirements for photosynthesis
Requirements for
photosynthesis
1 Chlorophyll
green part
(chlorophyll
present)
non-green part
(chlorophyll
absent)
Coleus
42
21.2
Requirements for photosynthesis
21.3
Video
Simulation
Investigation of the need for chlorophyll
in photosynthesis
variegated leaf
1 Destarch a variegated plant
by putting it the dark for at
least 24 hours. Pick a leaf
and test it for starch.
dark environment
43
21.2
Requirements for photosynthesis
21.3
Investigation of the need for chlorophyll
in photosynthesis
2 Expose the whole plant to bright light for
about 5 hours.
3 Pick a leaf. Draw a sketch of it to show the
colour pattern.
4 Test the leaf for starch. Draw another sketch
of it to show the result of the iodine test.
44
21.2
Requirements for photosynthesis
21.3
Results and discussion
Starch is present only in the green parts which
contains chlorophyll. There is no or little starch
in the non-green parts where chlorophyll
is absent. These results show that chlorophyll
is required for photosynthesis. In this practical,
the non-green parts of the leaf serve as
the control.
45
21.2
Requirements for photosynthesis
Requirements for
photosynthesis
2 Carbon dioxide
• put a leaf of a destarched plant in a
condition without carbon dioxide
• put another leaf in normal atmosphere
• use potassium hydroxide to remove
carbon dioxide
46
21.2
Requirements for photosynthesis
21.4
Simulation
Investigation of the need for carbon
dioxide in photosynthesis
1 Destarch a plant by putting it in the dark
for at least 24 hours. Pick a leaf and test it
for starch.
47
21.2
Requirements for photosynthesis
21.4
Investigation of the need for carbon
dioxide in photosynthesis
2 Set up the apparatus as shown. split cork or
cotton wool
conical
flask
potassium
hydroxide
leaf A
pellet
potted
plant
leaf B
48
21.2
Requirements for photosynthesis
21.4
Investigation of the need for carbon
dioxide in photosynthesis
3 Expose the whole plant to bright light for
about 5 hours.
4 Test leaves A and B for starch.
49
21.2
Requirements for photosynthesis
21.4
Results and discussion
Starch is present in leaf A but absent in leaf B.
As leaf B is exposed to air without carbon
dioxide, the results show that carbon dioxide is
required for photosynthesis. In this practical,
leaf B serves as the control.
50
21.2
Requirements for photosynthesis
Requirements for
photosynthesis
3 Water
• needed in many other reactions in plants
 difficult to do the investigation
51
21.2
Requirements for photosynthesis
Requirements for
photosynthesis
4 Light
• prevented from reaching part of a leaf
by masking it with black paper
52
21.2
Requirements for photosynthesis
21.5
Simulation
Design an investigation of the need for
light in photosynthesis
Connie’s plant turned yellow. Her brother
told her to pull back the curtains.
53
21.2
Requirements for photosynthesis
21.5
Design an investigation of the need for
light in photosynthesis
After a week, the plant turned green again and
grew healthily.
54
21.2
Requirements for photosynthesis
21.5
Design an investigation of the need for
light in photosynthesis
Connie wondered if light is needed in
photosynthesis. Suppose you were Connie,
design and perform an investigation to find
out the answer.
55
21.2
1
Requirements for photosynthesis
Destarching is the removal of
starch from the leaves of a plant by
putting it in the dark for a period of
time. This is to make sure that the
starch detected at the end of the
experiment was made during the
experiment.
56
21.2
Requirements for photosynthesis
2 Chlorophyll, carbon dioxide
,
water and light are required for
photosynthesis to occur.
57
21.3 Site of photosynthesis
• all green parts of a plant contain
chloroplasts
 can carry out photosynthesis
• leaves contain the most chloroplasts
 leaves are the main site of
photosynthesis
• both leaves and chloroplasts have
structural adaptations
58
21.3
Site of photosynthesis
Adaptive features of a leaf
leaf blade
- broad
and flat
 provides a large surface
area for absorbing sunlight
59
21.3
Site of photosynthesis
Adaptive features of a leaf
leaf blade
- thin
 gases and light can reach
the photosynthetic cells
easily
60
21.3
Site of photosynthesis
Adaptive features of a leaf
network
of veins
61
21.3
Site of photosynthesis
Adaptive features of a leaf
midrib
- contains a vascular bundle
made up of xylem and
phloem
62
21.3
Site of photosynthesis
Adaptive features of a leaf
midrib
- branches into a network
of veins
63
21.3
Site of photosynthesis
Adaptive features of a leaf
midrib
 provides efficient transport
of materials: water into
and food away from
the leaf
64
21.3
Site of photosynthesis
Adaptive features of a leaf
midrib
 supports and maintains
the shape of the leaf
65
21.3
Site of photosynthesis
Adaptive features of a leaf
upper
epidermis
- covered by a thin layer of
waxy cuticle
lower
epidermis
66
21.3
Site of photosynthesis
Adaptive features of a leaf
upper
epidermis
lower
epidermis
 reduces water loss from the
leaf, so that water is kept
inside for photosynthesis
and keeping the cells turgid
67
21.3
Site of photosynthesis
Adaptive features of a leaf
upper
epidermis
- contains numerous stomata,
each surrounded by a pair of
guard cells
lower
epidermis
68
21.3
Site of photosynthesis
Adaptive features of a leaf
upper
epidermis
 guard cells open the stoma
when the conditions are
favourable for photosynthesis
lower
epidermis
69
21.3
Site of photosynthesis
Adaptive features of a leaf
upper
epidermis
 guard cells close the stoma
when the conditions are less
favourable
lower
epidermis
70
21.3
Site of photosynthesis
Adaptive features of a leaf
upper
epidermis
 this allows the passage of
gases and water vapour into
and out of the leaf
lower
epidermis
71
21.3
Site of photosynthesis
Adaptive features of a leaf
palisade
mesophyll
- consists of tightly packed cells that
contain many chloroplasts
72
21.3
Site of photosynthesis
Adaptive features of a leaf
palisade
mesophyll
- located on the upper side of the leaf
73
21.3
Site of photosynthesis
Adaptive features of a leaf
palisade
mesophyll
 allows effective absorption of sunlight
74
21.3
Site of photosynthesis
Adaptive features of a leaf
spongy
mesophyll
- consists of loosely packed cells with
many air spaces
75
21.3
Site of photosynthesis
Adaptive features of a leaf
spongy
mesophyll
 allows gases to diffuse freely inside
the leaf
76
21.3
Site of photosynthesis
Adaptive features of a leaf to
photosynthesis:
1a Leaf blade is broad and flat .
• provides a large surface area
for absorbing sunlight
77
21.3
Site of photosynthesis
Adaptive features of a leaf to
photosynthesis:
1b Leaf blade is thin.
gases and light can reach the
photosynthetic cells easily
78
21.3
Site of photosynthesis
Adaptive features of a leaf to
photosynthesis:
2a Palisade mesophyll consists of
tightly packed cells that contain
many chloroplasts .
• allows effective absorption of
sunlight
79
21.3
Site of photosynthesis
Adaptive features of a leaf to
photosynthesis:
2b Palisade mesophyll is located on
the upper side of the leaf.
• allows effective absorption of
sunlight
80
21.3
Site of photosynthesis
Adaptive features of a leaf to
photosynthesis:
3
Spongy mesophyll consists of
loosely packed cells with
air spaces .
• allows gases to diffuse freely
inside the leaf
81
21.3
Site of photosynthesis
Adaptive features of a leaf to
photosynthesis:
4a Upper and lower epidermis is
covered by a thin layer of
waxy cuticle .
• reduces water loss from
the leaf
82
21.3
Site of photosynthesis
Adaptive features of a leaf to
photosynthesis:
4a Upper and lower epidermis is
covered by a thin layer of
waxy cuticle .
• so that water is kept inside for
photosynthesis and keeping the
cells turgid
83
21.3
Site of photosynthesis
Adaptive features of a leaf to
photosynthesis:
4b Upper and lower epidermis
contains numerous stomata ,
each surrounded by a pair
of guard cells .
• allow the passage of gases
and water vapour into and out
of the leaf
84
21.3
Site of photosynthesis
Adaptive features of a leaf to
photosynthesis:
5
Midrib contains a vascular
bundle made up of xylem and
phloem. It also branches into a
network of veins .
• provides efficient transport of
materials
85
21.3
Site of photosynthesis
Adaptive features of a leaf to
photosynthesis:
5
Midrib contains a vascular
bundle made up of xylem and
phloem. It also branches into a
network of veins .
• supports and maintains the
shape of the leaf
86
21.3
Site of photosynthesis
21.6
Examination of the structure of leaves
1 Examine the external structures of a
dicotyledonous leaf and draw a labelled
diagram.
87
21.3
Site of photosynthesis
21.6
Examination of the structure of leaves
2 Examine the photomicrograph or the
prepared slide of the transverse section of a
dicotyledonous leaf under a microscope.
88
21.3
Site of photosynthesis
21.6
Examination of the structure of leaves
3 Identify the internal structures of the leaf
and draw a high power diagram.
89
21.3
Site of photosynthesis
Adaptive features of
a chloroplast
3D model
• bound by a double membrane
• filled with a jelly-like fluid called
stroma (基質)
outer membrane
inner membrane
stroma
90
21.3
Site of photosynthesis
Adaptive features of
a chloroplast
• stroma contains enzymes
• stroma holds temporary stores of
photosynthetic products
starch grains
91
21.3
Site of photosynthesis
Adaptive features of
a chloroplast
• chlorophyll is located in the
thylakoid membrane
thylakoid
granum (基粒)
92
21.3
Site of photosynthesis
Adaptive features of
a chloroplast
• about 50 grana, each consisting of about
50 thylakoids
 provide a large area to pack
more chlorphyll
thylakoid
granum (基粒)
93
21.3
Site of photosynthesis
Adaptive features of
a chloroplast
• grana are interconnected
 allows efficient transport of
photosynthetic products
thylakoid
granum (基粒)
94
21.3
Site of photosynthesis
21.7
Examination of the structure of
chloroplasts
1 Examine the photomicrograph or live cell
image of a chloroplast.
95
21.3
Site of photosynthesis
21.7
Examination of the structure of
chloroplasts
2 Identify various structures of the chloroplast
and draw a high power diagram.
96
21.3
Site of photosynthesis
Adaptive features of a chloroplast to
photosynthesis:
1 Stroma is a jelly-like fluid.
• contains enzymes that catalyse
photosynthetic reactions
• holds starch grains which are
temporary stores of
photosynthetic products
97
21.3
Site of photosynthesis
Adaptive features of a chloroplast to
photosynthesis:
2a Thylakoids are membranous sacs
with space inside. They are large in
numbers and arranged in stacks
called grana .
• provide a large surface area to
pack chlorophyll
98
21.3
Site of photosynthesis
Adaptive features of a chloroplast to
photosynthesis:
2b Grana are interconnected by the
extensions from thylakoids.
• allows efficient transport of
photosynthetic products within
the chloroplast
99
21.4 The process of
photosynthesis
Let’s recall the
overall equation of
photosynthesis.
100
21.4
CO2
The process of photosynthesis
light absorbed
glucose
water
by chlorophyll
O2
• includes two main stages:
photochemical reactions
(光化學反應)
carbon fixation (碳固定)
101
21.4
The process of photosynthesis
Photochemical reactions
• occur in thylakoids
• require light
• also called light reactions
• involve three main processes:
light absorption
generation of ATP
photolysis of water
102
21.4
The process of photosynthesis
Photochemical reactions
1 Light absorption
• chlorophyll absorbs light energy
• some electrons in chlorophyll are raised
to higher levels
 excited electrons
103
21.4
The process of photosynthesis
Photochemical reactions
1 Light absorption
• excited electrons pass along the
electron transport chain (電子傳遞鏈)
electron carriers of
decreasing energy levels
104
21.4
The process of photosynthesis
Photochemical reactions
1 Light absorption
• excited electrons pass along the
electron transport chain (電子傳遞鏈)
e
energy
energy
energy
105
21.4
The process of photosynthesis
Photochemical reactions
1 Light absorption
• excited electrons pass along the
electron transport chain (電子傳遞鏈)
 energy is released gradually
106
21.4
The process of photosynthesis
Photochemical reactions
2 Generation of ATP
adenosine
P
phosphate
group
P
P
ADP (腺苷二磷酸)
energy released
by electrons
adenosine
P
P
ATP (腺苷三磷酸)
P
107
21.4
The process of photosynthesis
Photochemical reactions
2 Generation of ATP
• photophosphorylation (光磷酸化)
light
energy
chemical
energy
absorbed by
chlorophyll
stored in ATP
108
21.4
The process of photosynthesis
Photochemical reactions
3 Photolysis of water
energy released
by electrons
oxygen
H2O
hydrogen
109
21.4
The process of photosynthesis
Photochemical reactions
3 Photolysis of water
• oxygen is released as a gas to
the atmosphere
• hydrogen is accepted by NADP
NADPH
NADP + H
reducing agent
in carbon fixation
110
21.4
The process of photosynthesis
Photochemical reactions
Summary
oxygen
ATP
NADPH
by-product
used to drive
carbon fixation
111
21.4
The process of photosynthesis
Carbon fixation
• occurs in stroma
• does not require light
• also called dark reactions
and Calvin cycle
(卡爾文循環)
discover:
Melvin Calvin
112
21.4
The process of photosynthesis
Carbon fixation
• three steps:
1 Carbon dioxide fixation & formation
of 3-C compound
CO2
5-C
compound
2 x 3-C compound
113
21.4
The process of photosynthesis
Carbon fixation
• three steps:
2 Reduction of 3-C compound and
formation of glucose
3-C compound
ATP
ADP + P
NADPH
triose
NADP
phosphate (3-C)
114
21.4
The process of photosynthesis
Carbon fixation
• three steps:
2 Reduction of 3-C compound and
formation of glucose
triose
2x
phosphate (3-C)
glucose (6-C)
115
21.4
The process of photosynthesis
Carbon fixation
• three steps:
3 Regeneration of carbon dioxide
acceptor
5-C
compound
ADP + P
ATP
triose
phosphate (3-C)
116
21.4
6 CO2
The process of photosynthesis
light
absorbed by
C6H12O6
6 H2O
chlorophyll
O2
Photochemical
reactions
thylakoid
chloroplast
117
21.4
6 CO2
The process of photosynthesis
light
absorbed by
C6H12O6
6 H2O
chlorophyll
H2O
light
O2
ATP
NADPH
O2
118
21.4
6 CO2
The process of photosynthesis
light
absorbed by
C6H12O6
6 H2O
chlorophyll
H2O
light
O2
ATP
NADPH
Calvin
cycle
stroma
O2
119
21.4
6 CO2
The process of photosynthesis
light
absorbed by
C6H12O6
6 H2O
chlorophyll
H2O
CO2
light
O2
ATP
NADPH
NADP
ADP + P
O2
glucose
120
21.4
The process of photosynthesis
1 Photochemical reactions:
Chlorophyll absorbs light energy
and some electrons in the
chlorophyll are excited. These
excited electrons then pass along
the electron transport chain ,
releasing energy gradually.
121
21.4
The process of photosynthesis
1 Photochemical reactions:
Energy released by the electrons is
used to form ATP from a
phosphate group and ADP. Light
energy is converted into chemical
energy in ATP.
122
21.4
The process of photosynthesis
1 Photochemical reactions:
Water molecules are split into
hydrogen and oxygen using energy
released by the electrons
( photolysis of water). Oxygen is
released as a gas. Hydrogen is
accepted by NADP to form NADPH .
123
21.4
The process of photosynthesis
2 Calvin cycle:
Under the action of enzymes,
carbon dioxide is accepted by a
5-C compound to form two
molecules of a 3-C compound.
124
21.4
The process of photosynthesis
2 Calvin cycle:
Using energy from ATP and
hydrogen from NADPH, the 3-C
compound is reduced to triose
phosphate . It is then used to
synthesize glucose .
125
21.4
The process of photosynthesis
2 Calvin cycle:
Some triose phosphate molecules
are used to regenerate the original
5-C carbon dioxide acceptor , so
that the Calvin cycle can repeat.
The regeneration uses energy
from ATP .
126
21.4
The process of photosynthesis
3 The Calvin cycle requires
ATP and
NADPH produced from
photochemical reactions to operate.
NADP and ADP formed in the
Calvin cycle are used in
photochemical reactions.
127
21.5 The fate of photosynthetic
products
• primary product: triose phosphate
• triose phosphate and other intermediates
can be converted to other biomolecules
128
21.5
The fate of photosynthetic products
1 Carbohydrates
triose phosphate
glucose - main energy source
starch - for storage
sucrose - transported by phloem
cellulose - major component of
cell walls
129
21.5
The fate of photosynthetic products
1 Carbohydrates
• stored in different parts of plants as
energy reserve
• some plants store starch
grains, e.g. potato tubers
• some plants convert
starch into lipids,
e.g. corn
130
21.5
The fate of photosynthetic products
2 Lipids
intermediates of photosynthesis
glycerol
fatty acids
lipids
• form cell membranes
• as food reserve
131
21.5
The fate of photosynthetic products
3 Proteins
intermediates of photosynthesis
inorganic ions
amino acids
• for growth and repair
• for synthesis of enzymes
• components of cell membranes
132
21.5
The fate of photosynthetic products
Fate of photosynthetic products:
1 Triose phosphate is converted to
carbohydrates like glucose,
sucrose, starch and cellulose .
133
21.5
The fate of photosynthetic products
Fate of photosynthetic products:
2 In dicotyledonous plants, glucose is
soon converted to starch . It is
then converted to sucrose which
is transported to other parts of the
plant.
134
21.5
The fate of photosynthetic products
Fate of photosynthetic products:
3 The intermediates of
photosynthesis are converted to
glycerol and fatty acids which form
lipids , and amino acids which
form proteins.
135
21.6 Factors affecting the rate of
photosynthesis
Let’s study the effects of light
intensity and carbon dioxide
concentration on the rate of
photosynthesis.
136
21.6
Factors affecting the rate of photosynthesis
Light intensity
• use Hydrilla to study the effect
• the rate of oxygen bubbles being given
off indicates the rate of photosynthesis
137
21.6
Factors affecting the rate of photosynthesis
21.8
Simulation
Investigation of the effects of light
intensity on the rate of photosynthesis
1 Set up the apparatus as shown.
rubber tubing
dilute sodium
clip
hydrogencarbonate
solution
pipette
thermometer
Hydrilla
138
21.6
Factors affecting the rate of photosynthesis
21.8
Investigation of the effects of light
intensity on the rate of photosynthesis
1 Check the thermometer to ensure a constant
temperature. Turn on the bench lamp at a
distance of 0.1 m from the plant. Allow the
plant to equilibrate for 5 minutes.
139
21.6
Factors affecting the rate of photosynthesis
21.8
Investigation of the effects of light
intensity on the rate of photosynthesis
2 Suck up the solution from the boiling tube.
Close the clip completely and record the
starting position of the meniscus in the pipette.
3 After 5 minutes, record the final position of
the meniscus in the pipette. Calculate the
rate of photosynthesis. Record two more
readings.
140
21.6
Factors affecting the rate of photosynthesis
21.8
Investigation of the effects of light
intensity on the rate of photosynthesis
4 Repeat steps 1 to 3 with the bench lamp
placed at a distance of 0.2 m, 0.3 m, 0.4 m
and 0.5 m from the plant.
141
21.6
Factors affecting the rate of photosynthesis
21.8
Results and discussion
At low to moderate level of light intensity, the
rate of photosynthesis increases proportionally
with increasing light intensity. This is because
more energy is provided to the plant to carry
out photosynthesis.
142
21.6
Factors affecting the rate of photosynthesis
21.8
Results and discussion
When light intensity has reached a certain
level, the rate of photosynthesis does not
increase with further increase in light intensity.
This is because other factors such as carbon
dioxide concentration become limiting.
143
21.6
Factors affecting the rate of photosynthesis
rate of
photosynthesis
Light intensity
light
intensity
• the rate increases rapidly with light
intensity as more energy is supplied
144
21.6
Factors affecting the rate of photosynthesis
rate of
photosynthesis
Light intensity
saturation point
(飽和點)
light
intensity
• the increase levels off when light
intensity reaches a saturation point
145
21.6
Factors affecting the rate of photosynthesis
rate of
photosynthesis
Light intensity
saturation point
(飽和點)
light
intensity
• the rate is now limited by other
factors such as temperature
146
21.6
Factors affecting the rate of photosynthesis
rate of
photosynthesis
Light intensity
saturation point
(飽和點)
light
intensity
optimum light intensity
147
21.6
Factors affecting the rate of photosynthesis
rate of
photosynthesis
Carbon dioxide concentration
low CO2 concentration
light
intensity
• the rate increases with CO2 concentration
as more substrates are supplied to
Calvin cycle
148
21.6
Factors affecting the rate of photosynthesis
rate of
photosynthesis
Carbon dioxide concentration
high CO2 concentration
low CO2 concentration
light
intensity
• if the CO2 concentration is increased,
the rate levels off at a higher rate
149
21.6
Factors affecting the rate of photosynthesis
21.9
Design an investigation of the effect of
carbon dioxide concentration on the
rate of photosynthesis
Practical 21.4 shows that carbon dioxide is
required for photosynthesis. Revise
Practical 21.8 and try to design an
experiment to investigate the effect of carbon
dioxide concentration on the rate of
photosynthesis.
150
21.6
Factors affecting the rate of photosynthesis
Regulating the rate of
photosynthesis
• by monitoring the light intensity and
CO2 concentration in greenhouses
 increase productivity (生產力)
 improve quality
of crops
151
21.6
Factors affecting the rate of photosynthesis
1 The rate of photosynthesis
increases with light intensity. As the
factor increases, the rate
increases up to a certain point
and then becomes constant
because the rate is limited by other
factors.
152
21.6
Factors affecting the rate of photosynthesis
2 The rate of photosynthesis
increases with carbon dioxide
concentration. It will finally level off
because of other limiting factors .
153
1
What conditions of a greenhouse
promote photosynthesis?
The increased light intensity, carbon
dioxide concentration and temperature
promote photosynthesis.
154
2
How do plants make food by
photosynthesis?
During photosynthesis, light energy
captured by chlorophyll is used to drive
the reduction of carbon dioxide to form
carbohydrates.
155
3
What is the significance of
photosynthesis to the ecosystem?
Photosynthesis maintains the energy
flow in the ecosystem and provides the
basic food source for most organisms. It
also maintains the balance of
atmospheric oxygen and carbon dioxide.
156
Photosynthesis
captures and
converts
light energy
occurs in two
stages
photochemical
reactions
Calvin cycle
157
light energy
absorbed by
chlorophyll
present in
chloroplasts
converted to
chemical energy
stored in
organic compounds
mostly in
leaves
158
Photosynthesis
important in
maintaining
energy flow
in ecosystem
providing
basic food
source
maintaining
balance of atmospheric oxygen
and carbon dioxide
159
photochemical
reactions
involve
photolysis of water
produce
ATP
produces
oxygen
NADPH
160
Calvin cycle
ATP
NADPH
used
in
involves
reduction of
carbon dioxide
produces
glucose
161