This slide explain the photosynthesis process in plants.

1. Photosynthesis:
Life from Light and Air

2. PHOTO//SYNTHESIS

3. • Photosynthesis is the process by autotrophic
organisms that use light energy, carbon dioxide
and water to make sugar and oxygen gas
PHOTOSYNTHESIS

4. PHOTOSYNTHESIS
6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2
(Carbon
dioxide)
(water) (glucose) (oxygen)

5. •Organisms that use light energy from the sun to
produce food—autotrophs (auto = self)
Ex: plants and some microorganisms (some bacteria
and protists)

6. •Organisms that CANNOT use the sun’s energy to make
food—heterotrophs
Ex: animals and most microorganisms

7. Photosynthesis:
•Photosynthesis is the process by which the energy of
sunlight is converted into the energy of glucose

12. • Chloroplasts
– double membrane
– stroma
• fluid-filled interior
– thylakoid sacs
– grana stacks
• Thylakoid membrane contains
– chlorophyll molecules
– electron transport chain
– ATP synthase
• H+ gradient built up within
thylakoid sac
Plant structureH+H+
H+
H+
H+
H+
H+H+
H+
H+
H+
outer membrane inner membrane
thylakoid
granum
stroma
thylakoid
chloroplast
ATP

13. Chloroplast
• Organelle where photosynthesis takes place.
Granum
Thylakoid
Stroma
Outer Membrane
Inner Membrane

14. Thylakoid
Thylakoid Membrane
Thylakoid Space
Granum

15. Why is Photosynthesis important?
Makes organic molecules (glucose) out
of inorganic materials (carbon dioxide
and water).
It begins all food chains/webs. Thus all
life is supported by this process.
It also makes oxygen gas!!

16. Photosynthesis-starts ecological food webs!

17. PHOTOSYNTHESIS
• Absorbing Light Energy to
make chemical energy:
glucose!
– Pigments: Absorb
different colors of white
light (ROY G BIV)
• Main pigment: Chlorophyll
a
• Accessory pigments:
Chlorophyll b and
Carotenoids
• These pigments absorb all
wavelengths (light) BUT
green!

18. – Chlorophyll a
– Chlorophyll b
– Carotenoids
– Xanthophyll
Chloroplasts contain several pigments

19. Why do we see green?
– Green color from white light reflected NOT absorbed
– Chloroplast: organelle responsible for
photosynthesis
• Chlorophyll: located within Chloroplast
– Green pigment

20. Light: absorption spectra
• Photosynthesis gets energy by absorbing wavelengths of
light
– chlorophyll a
• absorbs best in red & blue wavelengths & least in green
– accessory pigments with different structures absorb light of
different wavelengths
• chlorophyll b, carotenoids, xanthophylls
Why are
plants green?

22. violet blue green yellow orange red

23. Chlorophyll Molecules
• Located in the thylakoid membranes.
• Chlorophyll have Mg+ in the center.
• Chlorophyll pigments harvest energy (photons) by
absorbing certain wavelengths (blue-420 nm and
red-660 nm are most important).
• Plants are green because the green wavelength is
reflected, not absorbed.

24. Plants
Leaves are green
because they
contain
the pigment:
chlorophyll
Leaves have a
large surface area
to absorb as much
light as possible

25. What happens during photosynthesis?
• Plants capture light energy and use that
energy to make glucose
• Sunlight provides the energy needed by
chlorophyll to change molecules of carbon
dioxide and water into glucose
• Oxygen is also released in this reaction

26. Photosynthesis

27. Photosynthesis: An
Overview
• The net overall equation for photosynthesis is:
• Photosynthesis occurs in 2 “stages”:
1. The Light Reactions (or Light-Dependent
Reactions)
2. The Calvin Cycle (or Light-Independent Reactions)
27
6 CO2 + 6 H2O C6H12O6 + 6 O2
light

28. Photosynthesis
• Light reactions
– light-dependent reactions
– energy conversion reactions
• convert solar energy to chemical energy
• ATP & NADPH
• Calvin cycle
– light-independent reactions
– sugar building reactions
• uses chemical energy (ATP & NADPH) to reduce
CO2 & synthesize C6H12O6

29. Light Reactions
O2
H2O
Energy Building
Reactions
ATP
 produces ATP
 produces NADPH
 releases O2 as a
waste product
sunlight
H2O ATP O2
light
energy
 +
+ + NADPH
NADPH

30. H+ H+
ATP Synthase
H+ H+ H+ H+
H+ H+
high H+
concentration
H+
ADP + P ATP
PS II PS I
E
T
C
low H+
concentration
H+
Thylakoid
Space
Thylakoid
SUN (Proton Pumping)

31. Calvin Cycle
sugars
CO2
Sugar
Building
Reactions
ADP
 builds sugars
 uses ATP &
NADPH
 recycles ADP
& NADP
 back to make
more ATP &
NADPH
ATP
NADPH
NADP
CO2 C6H12O6
 +
+ + NADP
ATP + NADPH ADP

32. Putting it all together
CO2 H2O C6H12O6 O2
light
energy 
+ +
+
Sugar
Building
Reactions
Energy
Building
Reactions
Plants make both:
energy
ATP & NADPH
sugars
sunlight
O2
H2O
sugars
CO2
ADP
ATP
NADPH
NADP

33. Photosynthesis summary
• Light reactions
– produced ATP
– produced NADPH
– consumed H2O
– produced O2 as byproduct
• Calvin cycle
– consumed CO2
– produced G3P (sugar)
– regenerated ADP
– regenerated NADP NADP
ADP

34. Different Carbon-Fixing Pathways
• Environments differ, and so do details of
photosynthesis
– C3 plants
– C4 plants
– CAM plants

36. Stomata
• Stomata ()
– Small openings through the waxy cuticle covering
epidermal surfaces of leaves and green stems
– Allow CO2 in and O2 out
– Close on dry days to minimize water loss

37. C3 Plants
• C3 plants
– Plants that use only the Calvin–Benson cycle to fix
carbon
– Forms 3-carbon PGA in mesophyll cells
– Used by most plants, but inefficient in dry
weather when stomata are closed

38. Photorespiration
• When stomata are closed, CO2 needed for
light-independent reactions can’t enter, O2
produced by light-dependent reactions can’t
leave
• Photorespiration At high O2 levels, rubisco
attaches to oxygen instead of carbon
– CO2 is produced rather than fixed

39. C4 Plants
• C4 plants
– Plants that have an additional set of reactions for
sugar production on dry days when stomata are
closed; compensates for inefficiency of rubisco
– Forms 4-carbon oxaloacetate in mesophyll cells,
then bundle-sheath cells make sugar
– Examples: Corn, switchgrass, bamboo

40. C3 and C4 Plant Leaves

41. CAM Plants
• CAM plants (Crassulacean Acid Metabolism)
– Plants with an alternative carbon-fixing pathway
that allows them to conserve water in climates
where days are hot
– Forms 4-carbon oxaloacetate at night, which is
later broken down to CO2 for sugar production
– Example: succulents, cactuses

42. Fig. 7-13a, p. 117
C3

43. Fig. 7-13b, p. 117
C4

44. Fig. 7-13c, p. 117
CAM

45. A CAM Plant
• Jade plant (Crassula argentea)

47. FACTORS AFFECTING THE RATE OF
PHOTOSYNTHESIS:

48. 1) LIGHT
As light intensity increases, the rate
of photosynthesis initially increases,
and thereafter, levels off to a
plateau.

49. • This plateau represents the maximum rate of
photosynthesis ---as seen in the diagram.
• Higher light intensity initially causes more electrons
in the chlorophyll molecules to become excited (gain
energy).
Modern Biology (Holt)

50. • As more and more electrons are excited, the light
reactions occur more rapidly.
• At a certain light intensity, however, all the
available electrons are excited and a further
increase in light intensity will not increase the rate
of photosynthesis.
Modern Biology (Holt)

51. 2) Carbon dioxide
Like increasing light intensity, increasing levels of carbon
dioxide around the plant stimulates photosynthesis
until it reaches a plateau. This graph would resemble
that of light intensity.
Modern Biology (Holt)

52. 3) Temperature
a) Raising the temperature accelerates various
chemical reactions of photosynthesis. As a result,
the rate of photosynthesis increases, over a certain
range.
Modern Biology (Holt)

53. • b) The rate of photosynthesis generally peaks
at a certain temperature, as seen in the
graph.
• c) Above this temperature, the rate
decreases.

54. Why is temperature important?
The light-independent reaction of photosynthesis is
controlled by enzymes. Temperature affects enzyme reactions.
As temperature increases, collision frequency between reactant
particles and between reactant and enzyme increases. This
increases the rate of reaction up to the optimum temperature.
Beyond the optimum temperature however, enzymes begin to
be denatured. Their tertiary structure breaks down, changing
the shape of the active site so that reactant molecules no
longer fit.
up to optimum
temperature
enzyme denatured
at high temperature

55. d) As the temperature increases, the stomates begin to
close, to limit water loss. This will have the effect of
stopping the carbon dioxide from entering the leaf.
This will also decrease the rate of photosynthesis.
(Also: Enzymes do not function well at too high a
temperature.)

56. 4) Water
• A lack of water will also slow the rate of
photosynthesis. Stomata can close from
water loss.
• Plants such as the cactus have adaptations
to prevent water loss in dry, desert
climates.