1 2 Think about… 21.1Basic concepts of photosynthesis 21.2Requirements for photosynthesis 21.3Site of photosynthesis 21.4The process of photosynthesis

1

2

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…’

Summary concept map

3controlled conditions.

A greenhouse (溫室 ) is a transparent building made for growing plants under

4

The conditions promote photosynthesis to enhance plant growth.

5

Crops like green peppers and tomatoes are not suitable to grow in Hong Kong.

6

With greenhouses, farmers can grow them all year round.

7

What conditions of a greenhousepromote photosynthesis1

8

How do plants make food by photosynthesis2

9

What is the significance ofphotosynthesis to the ecosystem3

10


What is photosynthesis?

11

What is photosynthesis?21.1 Basic concepts of photosynthesis

• an anabolic process

light energy chemical energy

plants / algae

• the process by which organic substances are made from simple inorganic substances using light energy

12

by-product

light absorbed

by chlorophyll


• overall equation:

CO2 water glucose O2

• occurs in chloroplasts

13


light

inorganic nutrientswater minerals

CO2

photosynthesis

• plants make their own food by photosynthesis

14


carbohydrates

lipids

proteins

organic nutrients

plant materials

photosynthesis

15

What is the significance of

photosynthesis?


16


1 Maintaining energy flow in ecosystem

green plants

consumers

photosynthesis

light energy

chemical energy in

chemical energy in

feeding

17


2 Providing the basic food source

• most organisms depend on plants directly or indirectly for food

plant cow

human

producer

18


3 Maintaining oxygen and carbon dioxide balance

respiration burning of fuels

consume O2 release CO2

19


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

20

1 Photosynthesis is the process by which substances are made from simple inorganic substances using energy.

organic

light


21

In plants, is made from carbon dioxide and water during photosynthesis. is released as a by-product.

glucose

Oxygen

1


22

. there absorbs light energy to drive the photosynthetic reactions.

2 Photosynthesis occurs in the

chloroplasts Chlorophyll


23

the in the ecosystem.

3 During photosynthesis, light energy from the sun is captured by plants, and converted to energy stored in the organic substances produced. Photosynthesis maintains

chemical

energy flow


24

It provides the basic for most organisms.

It maintains the balance of atmospheric and carbon dioxide.

food source

oxygen

3


25


How do we know if photosynthesis has

occurred?

26


• test for the presence of starch to find out if photosynthesis has occurred

glucose formed in photosynthesis

starch

quick conversion

Has photosynthesis occurred?

27


• starch formed before affects the results destarching (脫澱粉 )


keep in darkness for 24 hrs

28


1 Boil a leaf in water for a minute.

21.1

Detection of starch produced from photosynthesis (the iodine test)

Video

leafboiling water

29


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.

21.1


alcoholhot water

30


3 When the leaf has lost its green colour, i.e. decolourized, transfer it from the tube to hot water.

21.1


hot water

31


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.

21.1


iodine

white tiledecolourized leaf

32


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.

33


• oxygen is a by-product of photosynthesis

• test for oxygen using a glowing splint


test tube

if oxygen is present,glowing splint relights

34


1 Put a few Hydrilla plants in a beaker of dilute sodium hydrogencarbonate solution.

21.2

Detection of oxygen produced from photosynthesis

Hydrilla

dilute sodium hydrogencarbonate solution

35


2 Put an inverted filter funnel on three stoppers to cover the plants. Put a test tube completely filled with dilute sodium hydrogencarbonate solution on top of the funnel.

filter funnel

stopper

21.2


36


3 Leave the set-up in bright light for at least one day.

21.2


37


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.

21.2


38



The glowing splint relights. This result shows that the gas released from Hydrilla is oxygen.

21.2

39


• two set-ups in the investigation

- experimental set-up: the factor being tested is present

Requirements for photosynthesis

- control set-up: the factor is absent

40


• impossible to remove chlorophyll from a leaf without killing it use plants with variegated

leaves (斑葉 )

Requirements for photosynthesis1 Chlorophyll

41



Coleus

green part(chlorophyll present)

1 Chlorophyll

42



Coleus

green part(chlorophyll present)

non-green part(chlorophyll absent)

1 Chlorophyll

43


1 Destarch a variegated plant by putting it the dark for at least 24 hours. Pick a leaf and test it for starch.

21.3

Investigation of the need for chlorophyll in photosynthesis

Video

variegated leaf

dark environment

Simulation

44


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.

21.3

Investigation of the need for chlorophyll in photosynthesis

45



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.

21.3

46


• put a leaf of a destarched plant in a condition without carbon dioxide

• put another leaf in normal atmosphere

Requirements for photosynthesis2 Carbon dioxide

• use potassium hydroxide to remove carbon dioxide

47


1 Destarch a plant by putting it in the dark for at least 24 hours. Pick a leaf and test it for starch.

21.4

Investigation of the need for carbon dioxide in photosynthesis

Simulation

48


2 Set up the apparatus as shown.

conical flask

split cork or cotton wool

potassium hydroxide pellet

potted plant

leaf A

leaf B

21.4


49


3 Expose the whole plant to bright light for about 5 hours.

4 Test leaves A and B for starch.

21.4


50



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.

21.4

51


• needed in many other reactions in plants

Requirements for photosynthesis3 Water

difficult to do the investigation

52


• prevented from reaching part of a leaf by masking it with black paper

Requirements for photosynthesis4 Light

53


Connie’s plant turned yellow. Her brother told her to pull back the curtains.

21.5

Design an investigation of the need for light in photosynthesis

Simulation

54


After a week, the plant turned green again and grew healthily.

21.5


55


Connie wondered if light is needed in photosynthesis. Suppose you were Connie, design and perform an investigation to find out the answer.

21.5


56

1 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 the experiment.

Destarching


during

57

2 Chlorophyll, , water and are required for photosynthesis to occur.

carbon dioxidelight


58

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

59

leaf blade


Adaptive features of a leaf

- broad and flat

provides a large surface area for absorbing sunlight

60

leaf blade



- thin gases and light can reach

the photosynthetic cells easily

61



network of veins

62


Adaptive features of a leafmidrib - contains a vascular bundle

made up of xylem and phloem

63


Adaptive features of a leafmidrib - branches into a network

of veins

64


Adaptive features of a leaf provides efficient transport

of materials: water into and food away from the leaf

midrib

65


Adaptive features of a leafmidrib supports and maintains

the shape of the leaf

66



upper epidermis

lower epidermis

- covered by a thin layer of waxy cuticle

67


Adaptive features of a leaf reduces water loss from the

leaf, so that water is kept inside for photosynthesis and keeping the cells turgid

upper epidermis

lower epidermis

68


Adaptive features of a leaf- contains numerous stomata,

each surrounded by a pair of guard cells

upper epidermis

lower epidermis

69


Adaptive features of a leaf guard cells open the stoma

when the conditions are favourable for photosynthesis

upper epidermis

lower epidermis

70


Adaptive features of a leaf guard cells close the stoma

when the conditions are less favourable

upper epidermis

lower epidermis

71


Adaptive features of a leaf this allows the passage of

gases and water vapour into and out of the leaf

upper epidermis

lower epidermis

72

palisade mesophyll



- consists of tightly packed cells that contain many chloroplasts

73



- located on the upper side of the leaf

palisade mesophyll

74



allows effective absorption of sunlight

palisade mesophyll

75

spongy mesophyll



- consists of loosely packed cells with many air spaces

76



allows gases to diffuse freely inside the leaf

spongy mesophyll

77

Adaptive features of a leaf to photosynthesis:

• provides a large surface area for absorbing

1a Leaf blade is broad and . flat


sunlight

78

and light can reach the photosynthetic cells easily

1b Leaf blade is thin.

gases



79

• allows effective absorption of sunlight

2a Palisade mesophyll consists of tightly packed cells that contain many chloroplasts


.


80

• allows effective absorption of sunlight

2b Palisade mesophyll is located on the upper


side of the leaf.


81

• allows to diffuse freely inside the leaf

3 Spongy mesophyll consists of loosely packed cells withair spaces


gases

.


82

• reduces water loss from the leaf

4a Upper and lower epidermis is covered by a thin layer of waxy cuticle


.


83

• so that water is kept inside for photosynthesis and keeping the cells


turgid


4a Upper and lower epidermis is covered by a thin layer of waxy cuticle .

84

4b Upper and lower epidermis contains numerous , each surrounded by a pair of .

stomata


• allow the passage of gases and water vapour into and out of the leaf

guard cells


85

5 contains a vascular bundle made up of xylem and phloem. It also branches into a network of .

Midrib


• provides efficient transport of materials

veins


86of the leaf shape


• supports and maintains the


5 contains a vascular bundle made up of xylem and phloem. It also branches into a network of .

Midrib

veins

87


1 Examine the external structures of a dicotyledonous leaf and draw a labelled diagram.

21.6

Examination of the structure of leaves

88

2 Examine the photomicrograph or the prepared slide of the transverse section of a dicotyledonous leaf under a microscope.

21.6



89

21.6


3 Identify the internal structures of the leaf and draw a high power diagram.


90

Adaptive features of a chloroplast


• bound by a double membrane

• filled with a jelly-like fluid called stroma (基質 )

outer membraneinner membrane

stroma

3D model

91



• stroma contains enzymes• stroma holds temporary stores of

photosynthetic products

starch grains

92



• chlorophyll is located in the thylakoid membrane

thylakoidgranum (基粒 )

93



• about 50 grana, each consisting of about 50 thylakoids provide a large area to pack

more chlorphyll


94



• grana are interconnected

allows efficient transport of photosynthetic products


95


1 Examine the photomicrograph or live cell image of a chloroplast.

21.7

Examination of the structure of chloroplasts

96


21.7

Examination of the structure of chloroplasts

2 Identify various structures of the chloroplast and draw a high power diagram.

97

• holds which are temporary stores of photosynthetic products

• contains that catalyse photosynthetic reactions

1 Stroma is a jelly-like fluid. enzymes


starch grains

Adaptive features of a chloroplast to photosynthesis:

98

• provide a large to pack chlorophyll

2a Thylakoids are membranous sacs with space inside. They are large in numbers and arranged in stacks called .grana


surface area


99

2b Grana are interconnected by the extensions from thylakoids.• allows efficient of

photosynthetic products within the chloroplast

transport



100


Let’s recall the overall equation

of photosynthesis.

101


• includes two main stages:

carbon fixation (碳固定 )

photochemical reactions (光化學反應 )

light absorbed

by chlorophyllCO2 water glucose O2

102

• occur in thylakoids

• require light

• also called light reactions


Photochemical reactions

• involve three main processes:

generation of ATP

light absorption

photolysis of water

103

• chlorophyll absorbs light energy

• some electrons in chlorophyll are raised to higher levels


Photochemical reactions1 Light absorption

excited electrons

104

• excited electrons pass along the electron transport chain (電子傳遞鏈 )



electron carriers of decreasing energy levels

105




e

energy

energy

energy

106




energy is released gradually

107

energy released by electrons


Photochemical reactions2 Generation of ATP

adenosine

ADP (腺苷二磷酸 )

P P Pphosphate

group

adenosineP P P

ATP (腺苷三磷酸 )

108

• photophosphorylation (光磷酸化 )



light energy

chemical energy

absorbed by chlorophyll

stored in ATP

2 Generation of ATP

109


Photochemical reactions3 Photolysis of water

H2Ooxygen

hydrogen

energy released by electrons

110

reducing agent in carbon fixation

• oxygen is released as a gas to the atmosphere


Photochemical reactions3 Photolysis of water

• hydrogen is accepted by NADPNADP + H NADPH

111


Photochemical reactionsSummary

ATP

oxygen

NADPH

by-product

used to drive carbon fixation

112

• occurs in stroma

• does not require light

• also called dark reactions and Calvin cycle (卡爾文循環 )


Carbon fixation

discover: Melvin Calvin

113

• three steps:


Carbon fixation

1 Carbon dioxide fixation & formation of 3-C compound

CO2

5-C compound

3-C compound2 x

114

• three steps:


Carbon fixation

2 Reduction of 3-C compound and formation of glucose

ATP

triose phosphate (3-C)

3-C compound

NADPHADP + P

NADP

115

• three steps:


Carbon fixation

2 Reduction of 3-C compound and formation of glucose

2 x triose phosphate (3-C)

glucose (6-C)

116

• three steps:


Carbon fixation

3 Regeneration of carbon dioxide acceptor

triose phosphate (3-C)

5-C compound

ATPADP + P

117


light absorbed by chlorophyll

6 CO2 6 H2O C6H12O6 O2


chloroplastthylakoid

118

NADPH


light

H2O

ATP

O2


6 CO2 6 H2O C6H12O6 O2

119


Calvin cycle

stroma

NADPHlight

H2O

ATP

O2


6 CO2 6 H2O C6H12O6 O2

120


CO2

glucose

ADP + P

NADPHlight

H2O

ATP

O2

NADP


6 CO2 6 H2O C6H12O6 O2

121

releasing gradually.

Chlorophyll absorbs and some electrons in the chlorophyll are excited. These excited electrons then pass along the ,

light energy

electron transport chain


1 Photochemical reactions:

energy

122

Energy released by the electrons is used to form from a phosphate group and ADP. Light energy is converted into

ATP

chemicalenergy in ATP.



123

Water molecules are split into hydrogen and oxygen using energy released by the electrons ( of water). Oxygen is released as a gas. Hydrogen is accepted by NADP to form .

photolysis

NADPH



124

is accepted by a 5-C compound to form two molecules of a 3-C compound.

Under the action of enzymes, carbon dioxide


2 Calvin cycle:

125

. It is then used to synthesize .

Using energy from ATP and hydrogen from NADPH, the 3-C compound is reduced to triosephosphate

glucose


2 Calvin cycle:

126

Some triose phosphate molecules are used to regenerate the original 5-C carbon dioxide , so that the Calvin cycle can repeat. The regeneration uses energy from .

acceptor


ATP

2 Calvin cycle:

127

produced from photochemical reactions to operate.

3 The Calvin cycle requires andNADPH

and formed in the Calvin cycle are used in photochemical reactions.

ADP


ATP

NADP

128


• primary product: triose phosphate

• triose phosphate and other intermediates can be converted to other biomolecules

129


1 Carbohydratestriose phosphate

glucose - main energy source

starch - for storage

sucrose - transported by phloem

cellulose - major component of cell walls

130


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

131


2 Lipids

• form cell membranes

intermediates of photosynthesis

glycerol fatty acids

lipids

• as food reserve

132


3 Proteins

• for growth and repair

intermediates of photosynthesis

inorganic ions amino acids

• components of cell membranes

• for synthesis of enzymes

133

1 Triose phosphate is converted to carbohydrates like glucose, sucrose, and .starch


cellulose

Fate of photosynthetic products:

134

then converted to which is transported to other parts of the plant.

In dicotyledonous plants, glucose is soon converted to . It is


sucrose

Fate of photosynthetic products:

2starch

135

and fatty acids which form

, and which form proteins.

The intermediates of photosynthesis are converted to glycerol


lipids amino acids

3Fate of photosynthetic products:

136


Let’s study the effects of light intensity and carbon dioxide concentration on the rate of

photosynthesis.

137


Light intensity• use Hydrilla to study the effect

• the rate of oxygen bubbles being given off indicates the rate of photosynthesis

138

1 Set up the apparatus as shown.

21.8

Investigation of the effects of light intensity on the rate of photosynthesis

Simulation

rubber tubing

clip

pipette

dilute sodium hydrogencarbonate solution

thermometer

Hydrilla


139

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.

21.8



140

2 Suck up the solution from the boiling tube. Close the clip completely and record the starting position of the meniscus in the pipette.

21.8


3 After 5 minutes, record the final position of the meniscus in the pipette. Calculate the rate of photosynthesis. Record two more readings.


141

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.

21.8



142


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.

21.8


143


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.

21.8


144


Light intensity

• the rate increases rapidly with light intensity as more energy is supplied

rate

of

phot

osyn

thes

is

light intensity

145


Light intensity

• the increase levels off when light intensity reaches a saturation point

rate

of

phot

osyn

thes

is

light intensity

saturation point (飽和點 )

146


Light intensity

• the rate is now limited by other factors such as temperature

rate

of

phot

osyn

thes

is

light intensity


147


Light intensityra

te o

f ph

otos

ynth

esis

light intensity


optimum light intensity

148

• the rate increases with CO2 concentration as more substrates are supplied to Calvin cycle


Carbon dioxide concentrationra

te o

f ph

otos

ynth

esis

light intensity

low CO2 concentration

149

• if the CO2 concentration is increased, the rate levels off at a higher rate


Carbon dioxide concentrationra

te o

f ph

otos

ynth

esis

light intensity

low CO2 concentration

high CO2 concentration

150

Design an investigation of the effect of carbon dioxide concentration on the rate of photosynthesisPractical 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.

21.9


151


Regulating the rate of photosynthesis• by monitoring the light intensity and

CO2 concentration in greenhouses increase productivity (生產力 ) improve quality

of crops

152

up to a certain point and then becomes because the rate is limited by other factors.

1 The rate of photosynthesis increases with light intensity. As the factor increases, the rateincreases

constant


153

with carbon dioxide concentration. It will finally level off because of other .

2 The rate of photosynthesisincreases


limiting factors

154

What conditions of a greenhouse 1promote photosynthesis?The increased light intensity, carbon dioxide concentration and temperature promote photosynthesis.

155

How do plants make food by2photosynthesis?During photosynthesis, light energy captured by chlorophyll is used to drive the reduction of carbon dioxide to form carbohydrates.

156

What is the significance of 3photosynthesis 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.

157

occurs in two stages

light energy

Photosynthesis

captures and converts

photochemical reactions

Calvin cycle

158

converted to

stored in

absorbed by

present in

mostly in

light energy

chlorophyll chemical energy

chloroplasts organic compounds

leaves

159

providingmaintaining

important in

Photosynthesis

energy flow in ecosystem

basic food source

balance of atmospheric oxygen and carbon dioxide

maintaining

160

produce

produces

involve

photochemical reactions

photolysis of water

oxygen NADPH

ATP

161

Calvin cycle

involves

reduction of carbon dioxide

NADPH

ATP used in

glucose

produces

Documents

1 2 Think about… 21.1Basic concepts of photosynthesis 21.2Requirements for photosynthesis 21.3Site of photosynthesis 21.4The process of photosynthesis