5.1 autotrophic nutrition UEC Senior 1 Biology

1. 5.1 Autotrophic
nutrition
Ong Yee Sing
2017

2. Quiz
• Autotrophs are capable of producing the following complex
compounds from very simple substances.
A. carbohydrates
B. proteins
C. lipids
D. all the above

3. 5.1.1 Biochemistry of
photosynthesis

4. Objectives
• Memorized the chemical reaction of photosynthesis
• Understanding the components involve in the photosynthesis
• Differentiate different types of photosynthetic pigments
• Understand the overview of photosynthesis

5. Introduction to photosynthesis
• During photosynthesis, carbon dioxide and water are converted into
glucose and oxygen.
• The reaction requires light/solar energy, which is absorbed by a green
substance called chlorophyll.
• The overall equation of photosynthesis is
• Where does the oxygen originated from?

6. Photosynthesis reactions with oxygen isotops
• Using tracer techniques, O2 formed in photosynthesis comes from the
dissociation of water.

7. What actually happens in photosynthesis

8. Quiz
• The waste by-product of photosynthesis is:
A. Oxygen
B. Carbon dioxide
C. Glucose

9. Photosynthesis reaction
• Photosynthesis reactions occurs in
two stages:
• The light reaction (light-dependent)
• The dark reaction (light-independent)
• During light reaction, chlorophyll
absorbs solar energy to convert into
chemical energy.
• During dark reaction, carbon dioxide
is fixed into simple sugar using
energy supplied by the light
reaction.
Dark
reaction

10. Components involved in photosynthesis
• In green plants, photosynthesis
takes place in the chloroplast.
• Chloroplast is a bi-membraned
organelle that contain large
compartment called stroma.
• Membranous thylakoids can be
found within the stroma.
• Space within thylakoids are
called thylakoid space.
• Stacked thylakoid are called
grana.
• Photosynthetic pigments can
be found in the chloroplast.

11. 5.1.1.1
Photosynthetic
pigments

12. Photosynthetic pigments
• Pigments are essential co-factor for photosynthetic
reaction to occur.
• Pigments are chemical compounds which reflect
only certain wavelengths of visible light but at the
same time, absorb certain wavelengths.
• Since each pigment reacts with only a narrow range
of the spectrum, there is usually a need to produce
several kinds of pigments, each of a different color,
to capture more of the sun's energy.
• This also protects the plants from damage caused by
excessive sunlight.
• Photosynthetic pigments are generally found on the
thylakoid membrane.

13. Types of pigments
Plant chloroplasts generally contains:
• Chlorophyll a
• Chlorophyll b
• Carotene
• Xanthophyll
• Chlorophylls are the main pigments for
photosynthesis.
• Carotene and xanthophyll are accessory
pigments which absorbs the wavelength
that chlorophyll cannot absorb. The chemical structure of chlorophyll X*:-CH3 in
chlorophyll a, - CHO in chlorophyll b
caratenoid

14. Absorption spectra of the pigments
• The colour of the
pigment is the
range of light
that the pigment
does not absorb.
(phycobiliprotein)
(phycobiliprotein)

15. Colour of the pigments
• Chlorophyll absorbs red and blue-violet light.
• Chlorophyll a is blue-green in colour.
• Chlorophyll b is yellow-green in colour.
• Carotene and xanthophyll mainly absorb blue-
violet light.
• Carotene is orange in colour.
• Xanthophyll is yellow-orange in colour. Paper chromotography of
spinach leaf pigments

16. Quiz
• Which of the following is only minimally absorbed by chlorophylls a
and b?
A) violet light
B) green light
C) blue light
D) red light

17. Conclusion
• The complete chemical reaction for photosynthesis:
• Photosynthesis occurs in the chloroplast of plant cells.
• During light reaction, chlorophyll absorbs solar energy to convert into
chemical energy.
• During dark reaction, carbon dioxide is fixed into simple sugar using energy
supplied by the light reaction.
• Chlorophylls are the main pigments for photosynthesis.
• Carotene and xanthophyll are accessory pigments which absorbs the
wavelength that chlorophyll cannot absorb.

18. Quiz
• The oxygen given off by photosynthesis comes from ___________.
A) CO2
B) CH2O
C) H2O
D) the atmosphere

19. 5.1.1.2
Light reaction

20. Objectives
• Understand the role of chlorophyll and light in the light-dependent
reaction
• Understand the movement and role of electrons in the light-
dependent reaction
• Know the reactants and products of the light-dependent reaction

21. Light-dependent reaction
• Also known as the Hill reaction, named
after chemist Robin Hill
• The light-dependent reactions use light
energy to make the energy storage
molecule adenosine triphosphate (ATP)
and the reduced electron carrier
dihydronicotinamide-adenine
dinucleotide phosphate (NADPH).
• In plants, the light reactions take place in
the thylakoid membranes of the
chloroplasts.
Right: ATP
Bottom: NADPH
还原型辅酶

22. Quiz
• The main purpose of the light-dependent reactions of photosynthesis
is to
A. split water to make oxygen.
B. produce NADH.
C. produce carbohydrates.
D. convert sunlight energy into ATP and NADPH.

23. The overview of Light-dependent reaction
photosynthetic
pigments such
as chlorophyll

24. Step 1: Light Absorption
• Like heme, chlorophyll a contains a cyclic
region with magnesium ion binds at the centre.
• The energy from the light excites an electron
from its ground energy level to an excited
energy level.
• The electron now
contain more energy
and can move
around from one
chlorophyll to
another.
• Chlorophyll that lost
an electron becomes
positively charged.

25. Step 1.5: Replace the electron
• The positively-charged chlorophyll
has to be neutralized for further
reaction to occur.
• The replacement electrons are
donated from water molecule.
• Water molecules are photolysed
光解 to form an O2, a proton (H+)
and an electron (e-).
chlorophyll++e-  chlorophyll0

26. Step 2: The electron ends up with NADP+
• The exited electron are passed from one chlorophyll to the next (from
a medium of high energy to a medium of low energy) around the
energy transport chain until
• all the extra energy is lost as heat
• or it is passed into the reaction centre and is transferred to other enzymes
until it is accepted by NADP+ to reduce it to NADPH.
氧化型辅酶
NADP+ + H+ + 2e− → NADPH (Reduction)
NADP+ + H+ + 2e− ← NADPH (Oxidation)
还原型辅酶
Oxidation 氧化
Gain of oxygen, loss of hydrogen, or loss of electron
Reduction 还原
Loss of oxygen, gain of hydrogen, or gain of electron
电子传递链
/呼吸链

27. Step 2.5: The movement of electrons also
lead to ATP synthesis
• The movement of electron also provide energy for other enzymes to
pump proton into the thylakoid lumen.
• Combined with protons form from the dissociation of water, the
thylakoid membrane has more proton compare to the stroma.
光合磷酸化作用
• This chemical gradient is used
to fuel ATP synthesis from ADP
in the process of
photophosphorylation.

28. Conclusion
• Electron of the chlorophyll are exited with light energy and are
transport down the energy transport chain.
• Water is photolyzed form an O2, a proton (H+) and an electron (e-).
• NADP+ is reduced to NADPH.
• ATP is produced in the process of photophosphorylation.

30. Quiz
• What is the first step in photosynthesis?
A. formation of ATP
B. Ionization of water
C. Attachment of carbon dioxide to five carbon sugar
D. Excitement of an electron of chlorophyll a by a photon of light

31. Quiz
• The light-dependent reactions take place in the
A. chloroplast membrane.
B. stroma.
C. thylakoid membrane.
D. antenna assembly.

32. 5.1.1.3
Dark reaction

33. Dark reaction 暗反应
• Also known as Calvin cycle, after Melvin
Calvin and his associates, who proved
that the fixation of CO2 is carried out in
the dark reaction on unicellular alga
Chlorella with the use of the radioactive
isotope of carbon, 14C, and paper
chromatography method.
• The dark reaction occurs in the stroma
(matrix) of the chloroplast.
• The dark reaction used 3 molecules of
ATP and NADPH produced during the
light reaction to reduce CO2 to glucose.
• Dark reaction will not occur under the
condition of continuous absence of
light because light is required for the
production of ATP and NADPH in the
light reaction.
• As dark reaction involves a lot of
enzyme, it is affected by factors such as
temperature, concentration of CO2 etc.

34. Step 1: Carbon fixation
• CO2 combines with a pentose sugar,
ribulose bisphosphate (RuBP)
to form an extremely unstable 6C
compound.
• The short-lived intermediate rapidly
dissociates into two 3C molecules,
phosphoglyceric acid (PGA).
二磷酸核酮糖
磷酸甘油酸

35. Step 2: Reduction of PGA
• Phosphoglyceric acid (PGA)
is reduced using ATPs and
NADPHs.
• PGA accepts a proton from
NADPH to form
phosphoglyceraldehyde
(PGAL, or G3P). 磷酸甘油醛

36. Step 3: Regeneration of RuBP
• Ribulose bisphosphate (RuBP)
needs to be regenerated.
• Small portion of
phosphoglyceraldehyde (PGAL) is
converted into the 6C glucose.
• Most 3C PGAL is converted back to
the 5C RuBP.
• For every five PGAL, 3 ATP is
required and 3 RuBP is produced.

37. Overall equation of the dark reaction
• For every three carbon fixed into a G3P (PGAL),
• 9 ATP is used (6 for G3P, 3 for recovery of RuBP);
• 6 NADPH is used (for G3P).

38. Quiz
• For every 1 carbon fixed by the plant, how many ATP is required for
production of G3P? How many ATP is required for the whole dark
cycle?
A. 1, 1
B. 1, 2
C. 2, 2
D. 2, 1

39. Comparison between light and dark reaction
Subject Light Reaction Dark Reaction
Condition Light is required
Water is required, CO2 is not
required.
Light is not required (but can
be carried out in the presence
of light)
Water is not required, CO2 is
required.
Site of reaction In the grana of chloroplast In the stroma of chloroplast
Main reactants H2O, ADP, Pi , NADP+ ATP, NADPH, CO2
Main products O2, ATP, NADPH 3C sugar, PGAL
Source of energy Light energy ATP
Factors affecting the
reaction rate
Light quality and light
intensity
Temperature, concentration
of CO2 and O2

40. Conclusion
• The dark reaction occurs in the stroma of the chloroplast.
• The dark reaction used 3 molecules of ATP and NADPH to reduce CO2
to glucose.
• The sum of reactions in the Calvin cycle is the following:
• As dark reaction is affected by environmental factors such as
temperature, concentration of CO2 etc.
3 CO2 + 6 NADPH + 6 H+ + 9 ATP → glyceraldehyde-3-phosphate (G3P)
+ 6 NADP+ + 9 ADP + 3 H2O + 8 Pi

44. 5.1.2
Photorespiration

45. Objectives
• Understand the process of photorespiration
• Understand the disadvantages of undergoing photorespiration
• Understanding the characteristics of C3, C4 and CAM plants
• Understand the evolutionary significance of C4 and CAM plants

46. Photorespiration
• Photorespiration occurs when ribulose bisphosphate (RuBP) binds with
oxygen instead of carbon dioxide.
O2 + RuBP  phosphoglyceric acid (PGA) + phosphoglycolic acid
• Photorespiration occurs when there is excessive oxygen and when the
temperature is high and the plant close their stomata to reduce water loss.
• Unlike respiration (a process which energy is released from glucose),
photorespiration does not produce energy.
呼吸作用
光呼吸
磷酸乙醇酸

47. Disadvantages of photorespiration
• Decrease the production of phosphoglyceric acid (PGA)
• Consume ATP produced in the light reaction
• Lost a carbon atom in the form of carbon dioxide
• Reduce the efficiency of photosynthesis
enzyme

49. Quiz
• Which of the following statements about photosynthesis is true?
A. the light-dependent reactions can occur only in the light, the light-
independent reactions only in the dark
B. photorespiration is more efficient at producing glucose than is
photosynthesis
C. the light-dependent reactions produce the energy-rich compounds
that are used to run the light-independent reactions
D. all of the above are true

50. 5.1.3
C3 and C4 plants
And CAM plants

51. C3 plants
• The C3 plants use the C3 pathway –
the first intermediate product
formed after CO2 fixation is the 3C
phosphoglyceric acid (PGA).
• Example of C3 plants includes swamp
rice crop, soya bean, wheat, trees
and cotton.
• C3 plants are high photorespiration
plants (the rate of photorespiration
in the C3 plants is high).

53. C4 plants
• The C3 plants use the C4 pathway – the first
intermediate product formed after CO2 fixation
is a 4C compound oxaloacetic acid (OAA).
• Many C4 plants are tropical-originated such as
maize, sugar cane and sorghum.
• C4 plants are low photorespiration plants and
such the economic value of C4 plants is higher
than that of C3 plants since the yield of crop is
higher in C4 plants compare to that of C3.
• The light-dependent reactions and the Calvin
cycle are physically separated in the C4 plants
• The light reactions occurs in the mesophyll cells and
the dark reaction occurs in the bundle-sheath cells.
• Carbon fixation still occurs in the mesophyll cell,
where OAA is produced.
• CO2 is shuttled to the bundle-sheath cells as malate.
• Decaboxylation occurs to release CO2 in the bundle-
sheath cells in large quantity to maintain a high
concentration of CO2 to out-compete O2 in the
binding of rubisco.
维管束鞘细胞
叶肉细胞

54. 高粱
小米

55. Quiz
The immediate products of C3 and C4 photosynthesis are, respectfully:
A. ribulose 1,5-bisphosphate; malic acid
B. malate; carbon dioxide
C. 3-phosphoglycerate; oxaloacetic acid
D. glyceraldehyde 3-phosphate; phospho-enol-pyruvate (PEP)
E. malic acid; glucose

56. CAM plants
• This name comes from Crassulaceae family.
• CAM plants are adapted to dry environments and
deserts, such as cacti, orchids and pineapples.
• The crassulacean acid metabolism (CAM) pathway
to minimize photorespiration by temporal
separation the light and dark reaction.
• At night, CAM plants open their stomata, allowing CO2 to
diffuse into the leaves and fixe into OAA, then converted
to malate or other type of organic acid.
• The organic acid is stored inside vacuoles until the next
day.
• In the daylight, the CAM plants close their stomata and
no atmospheric oxygen can enter the cells.
• The organic acids are transported out of the vacuole
enters the Calvin cycle.
• This maintains a high concentration CO2 around the
rubisco.
景天科

57. Comparison of C3, C4 and CAM plants
Type
Separation of
initial CO2 fixation
and Calvin cycle
Stomata
open
Best adapted to
C3 No separation Day
Cool, wet
environments
C4
Between
mesophyll and
bundle-sheath
cells (in space)
Day
Hot, sunny
environments
CAM
Between night and
day (in time)
Night
Very hot, dry
environments

58. Quiz
• Which of the following organisms have the greatest problem with
photorespiration?
A. C4 plants
B. heterotrophs
C. C3 plants
D. CAM plants
E. purple sulfur bacteria

59. Conclusion
• Photorespiration is a wasteful pathway that occurs when the Calvin
cycle enzyme rubisco acts on oxygen rather than carbon dioxide.
• C3 plants form PGA and have no special features to combat
photorespiration.
• C4 plants form OAA and minimize photorespiration by separating
initial C02 fixation and the Calvin cycle in space, performing these
steps in different cell types.
• Crassulacean acid metabolism (CAM) plants minimize
photorespiration and save water by temporal separating these steps.

61. 5.1.4 Factors
affecting photosynthesis

62. Objectives
• Understanding the factors that affecting photosynthesis
• Able to infer from graphs representing those factors

63. Factors affecting photosynthesis
• Photosynthesis is affected by environment factors such as light,
carbon dioxide, oxygen, temperature and water.
• Among these factors, light, carbon dioxide and temperature are
limiting factors to one another.
• Limiting factors limits the speed of the photosynthesis.

64. Light: light quality
• Light quality refers to the
wavelength of light
available for the plants.
• Blue-violet light and red
light are the most
effective wavelengths in
photosynthesis as
chlorophyll absorbs light
of these spectrum.
• Photosynthesis is least
effective under yellow-
green light.
(Edited by Chris Paine)

65. Light: light quality
• The action spectrum of
photosynthesis is wider
than the absorption
spectrum of chlorophyll.
• The action spectrum also
accounts for the
absorption of light by
accessory pigments such
as carotenoids, which
indirectly supply energy
for the chlorophyll in the
electron transport chain.
(Edited by Chris Paine)

66. Light: Light intensity
• Light intensity refers to the amount
of light, at a given wavelength,
available to the plant.
• When light is the limiting factor,
the rate of photosynthesis is
directly proportional to the
intensity of light.
• However, there is a saturation
point where an increase in light
intensity will not cause an increase
in the rate of photosynthesis. At
this time the rate of photosynthesis
of plant is said to have reached a
saturation /plateau.
• Other factors such as
temperature, CO2 concentration,
enzymes or chloroplasts working
at maximum efficiency is limiting
photosynthesis instead.
• The saturation point is different
for different plant.
RateofPhotosynthesis
Light intensity
When light intensity is increased
the rate of photosynthesis
increases therefore it is the
limiting factor at low levels.
At high levels of light intensity further increases have
no effect on the rate of photosynthesis. Therefore
light intensity is not the limiting factor.

67. When carbon dioxide
concentration is increased the
rate of photosynthesis increases
therefore it is the limiting factor at
low concentrations.
RateofPhotosynthesis
Carbon dioxide concentration
Another factor is limiting photosynthesis
as further increases in carbon dioxide do
not increase the rate of photosynthesis.
Carbon dioxide concentration
• As CO2 is a substrate for
the key enzyme involved in
the Calvin cycle, hence it
effects photosynthesis,
hence its effects is similar
to how enzyme reactions
are limited by substrate
concentration.
• The rate of photosynthesis
will increases with the
concentration of CO2 until
the point of saturation,
where the rate of
photosynthesis is limited
by other factors
(temperature/ light), and
the rate of photosynthesis
will reach a plateau.

68. Carbon dioxide – the most important factor
• Under specific light intensity and temperature, the concentration of CO2 in
the air always becomes an important factor that limits the rate of
photosynthesis of plants.

69. After the optimum
temperature enzymes
denature rapidly
causing a fast
decrease in the rate of
photosynthesis as
temperature increases
further.
As the temperature
approaches the
optimum the enzymes
begin to denature
(active site changes to
become non-functional)
causing the rate of
photosynthesis to
increase more slowly
and eventually peak.
Increases in temperature give
molecules more kinetic energy
causing substrates to collide
with active sites more
frequently, this increases the
rate of photosynthesis
Temperature
RateofPhotosynthesis
Temperature
• Photosynthesis is a
metabolic pathway
hence the relationship
is similar to how
enzyme reactions are
affected by
temperature.
• The rate of reaction
will increase the rate
of photosynthesis
until the optimum
temperature is
reached, then the rate
of photosynthesis
decreases rapidly.

70. Temperature
• High temperature may further decreases
rate of photosynthesis as the plants close
their stomata to avoid further water loss.
• This limits the amount of carbon dioxide
available in the plant for the Calvin cycle.
• Plants growing in different environment (or
habitats) show great differences in the
adaptation to temperature.
Algal and lichen in hot spring.Conifer in the snow. Tropical rain forest.

71. Oxygen
• An increase in the concentration of O2 generally decreases the rate of
photosynthesis in the C3 plants.
• This is because the excessive O2 will compete with CO2 for combining
with the 5C sugar (RuBP), forcing the plant to undergo
photorespiration.

72. Water
• Water is a material of
photosynthesis.
• It is also the medium for all the
chemical reactions occurring
inside the body.
• Hence a change in the quantity
of water (in the guard cells) can
also affect the opening and
closure of stomata.
• This indirectly controls the
entry and exit of CO2.

73. Conclusion
• Limiting factors restrict the maximum photosynthetic rate.
• Three factors can limit the speed of photosynthesis -
light intensity, carbon dioxide concentration and temperature.
• Concentration of oxygen indirectly affecting rate of photosynthesis by
competing with CO2 for RuBP.
• Water indirectly controls the entry and exit of CO2 by affecting the
opening and closure of stomata.