1. Solar energy + carbon dioxide + water → carbohydrate + oxygen
Photosynthesis
Converts solar energy into the potential chemical energy of a carbohydrate in this way:
Solar energy + carbon dioxide + water → carbohydrate + oxygen
Photosynthetic organisms include plants, algae, and certain bacteria.
These organisms are called producers; they synthesize organic molecules from raw materials.

2. Photosynthetic organisms

3. Nearly all life is dependent on solar energy because:
Photosynthetic organisms use solar energy to produce organic nutrients.
Almost all organisms depend either directly or indirectly on these organic nutrients to sustain themselves.
Photosynthetic organisms provide food for other organisms, known as consumers.
The bodies of plants became the coal or other fossil fuels used today.

4. Structure and Function of Chloroplasts
Chloroplasts are the organelles that carry on photosynthesis.
Mesophyll cells in the middle of a leaf house chloroplasts
Mesophyll cells are protected from drying out by a waxy cuticle.
Pores called stomata allow CO2 and O2 to enter the leaf.

5. Mesophyll cells of a leaf

7. The xylem is responsible for the transport of water and soluble mineral nutrients from the roots throughout the plant. It is also used to replace water lost during transpiration and photosynthesis.
The phloem is concerned mainly with the transport of soluble organic material made during photosynthesis.

8. Structure of Chloroplasts
Bounded by a double membrane.
The inner membrane encloses a large central space called the stroma that houses enzymes used to reduce CO2 to carbohydrate.
A membranous system of thylakoids lies within the stroma; some thylakoids are stacked into grana; thylakoids contain chlorophyll and other pigments.
All thylakoids are connected – single inner compartment within chloroplasts called the thylakoid space
Chlorophyll and other pigments absorb solar energy.

9. Chloroplast structure

10. Stepped Art Figure 7.3d,e Page 116
Overview of Photosynthesis
two outer membranes
inner membrane system
(thylakoids connected by channels)
stroma
channel
stacked part of thylakoid membrane
Stepped Art Figure 7.3d,e Page 116

11. Visible Light
Radiant energy from the sun (solar energy) can be described in terms of its wavelength and its energy content.
The colors in visible light range from violet (the shortest wavelength and highest energy) to blue, green, yellow, orange, and red (the longest wavelength and lowest energy).

12. Visible Light Spectrum

13. Pigments (chlorophylls and carotenoids) found within photosynthesizing cells, are capable of absorbing various portions of visible light.
Both chlorophyll a and chlorophyll b absorb violet, blue, and red light best.
Carotenoids absorb light in the violet-blue-green range and reflect yellow or orange
Leaves appear green because green light is reflected and only minimally absorbed.

15. In the fall when the pigment chlorophyll breaks down (chlorophyll needs warm weather to be created; is created continually during warm months), the remaining pigment (carotenoids) become unmasked, reflecting the colors like orange and yellow

17. Photosynthesis is an oxidation-reduction reaction, or redox reaction for short.
Oxidation is the loss of electrons; hydrogen atoms are removed from glucose.
Reduction is the gain of electrons; oxygen atoms gain electrons.
Remember OIL RIG (oxidation is loss, reduction is gain)

18. Overview of Photosynthesis
A simplified overall equation for photosynthesis is:
Solar energy + 6CO2 + 6H2O → C6H12O6 + 6O2
During photosynthesis, water molecules are oxidized; they lose electrons (e-) along with hydrogen ions (H+).
Also, CO2 is reduced and gains electrons given up by H2O.
Electrons from H2O are energized by the sun.

19. Enzyme involved
NADP+
Nicotinamide adenine dinucleotide phosphate
Accepts 2 electrons and H+ to become NADPH

20. The ATP cycle

21. Two Sets of Reactions
Photosynthesis is divided into two sets of reactions, as implied by the term “photosynthesis”:
“Photo” refers to the light-dependent (needs light) reactions that capture energy from the sun
Photosystem II
Photosystem I
“Synthesis” refers to the light-independent (does not need light) reactions that produce carbohydrate (glucose).
Calvin Cycle

22. Photosynthesis – Light-dependent and Light-independent Reactions
CO2
H2O
Chloroplast
LIGHT
REACTIONS
(in thylakoids)
CALVIN
CYCLE
(in stroma)
NADP+
ADP + P
ATP
NADPH O
Sugar
Electrons
Light-independent
Light-dependent

23. Animation of light-dependent reactions
Simplified animated steps of light-dependent reactions
Animation of overall light-dependent and animation of cyclic & noncyclic flow
Overview of light-independent reactions (Calvin cycle)
A photosynthesis rap!!!!!!!!!
Musical lecture part I
Musical lecture part II

24. Light-Dependent Reactions
Light energy is absorbed by chlorophyll.
Electrons are energized.
Energized electrons move down an electron transport system, release energy, and produce ATP.
NADP+ accepts electrons to produce NADPH.
Water is split to produce oxygen, hydrogen ions, and electrons
Photosystem II occurs first
Photosystem I occurs second (II and I were named for the order in which they were discovered, NOT the order in which they occur).

25. Light-dependent reactions continued
Both occur within the thylakoid membranes inside the chloroplast
Each photosystem has a pigment system of green pigments (chlorophylls a and b) and accessory pigments.
Closely packed pigments serve as an “antenna” for gathering solar energy.
Electrons can follow one of two electron pathways – cyclic or noncyclic

26. Electron Pathways
Electrons can follow a cyclic electron pathway or a noncyclic electron pathway during the light-dependent phase of photosynthesis.
The cyclic electron pathway generates ATP only.
Used by some bacteria
The noncyclic electron pathway generates ATP, NADPH and oxygen.
Used by some bacteria and plants

27. Cyclic Electron Pathway
The cyclic electron pathway begins after PS I absorbs solar energy.
Electrons enter an electron transport system, generating the production of ATP.
Electrons return to PSI.

28. ATP Production
Each time water is split, two H+ remain in the thylakoid space.
As electrons move down the electron transport system, they give up energy, which is used to pump H+ from the stroma into the thylakoid space.
Thus, H+ build up in the thylakoid space.
The flow of H+ through an ATP synthase complex back into the stroma drives the production of ATP.

29. The light-dependent reactions: the cyclic electron pathway

30. Cyclic electron pathway – light-dependent reaction

31. Noncyclic Electron Pathway
In the noncyclic electron pathway, electrons move from H2O through PS II to PS I and then on to NADP+.
The PS II pigment complex first absorbs solar energy, and high-energy electrons (e-) leave the reaction-center chlorophyll a.
PS II takes replacement electrons from water, which splits, releasing oxygen.

32. The oxygen leaves the chloroplast as oxygen gas (O2), and the hydrogen ions (H+) temporarily remain in the thylakoid space.
The high-energy electrons enter an electron transport system, and energy is used to produce ATP (same as in cyclic pathway)
Low-energy electrons leaving the electron transport system enter PS I where they replace electrons that have left the PS I reaction center.

33. When the PS I pigment complex absorbs solar energy, high-energy electrons leaving the reaction-center chlorophyll a are captured by an electron acceptor.
This time, the electron acceptor passes the electrons on to NADP+, which accepts a hydrogen ion (H+) and becomes NADPH:
NADP+ + 2e- + H+ → NADPH

34. Results of the noncyclic electron pathway:
Water is split, yielding H+, e-, and O2
ATP is produced
NADP+ becomes NADPH

36. The light-dependent reactions: the noncyclic electron pathway

37. Noncyclic electron pathway – light-dependent reactions
Stroma

38. LIGHT-DEPENDENT REACTION
Requires Light and
Water
WHAT IT DOES:
WHERE IT HAPPENS:
SPLITS H2O
Leaf
Creates ATP and NADPH
For Calvin Cycle
Chloroplasts
Inside Thylakoids
Forms O2 as a byproduct

39. Light-Independent Reactions
The light-independent reactions do not need light
Take place in the stroma
Reactions make up the Calvin cycle.
Carbon dioxide (CO2) is taken up by the plant (from the atmosphere)
ATP and NADPH (made from the light dependant reactions) convert CO2 into glyceraldehyde 3- phosphate, or G3P (PGAL)
G3P is a type of sugar which a plant can easily be converted to glucose. This glucose can then be used as a source of stored energy for the plant

40. The Calvin Cycle
AKA G3P

41. Overview of the Calvin Cycle
Carbon dioxide is taken up by a 5-carbon sugar, RuBP.
The resulting 6-carbon molecule breaks into two 3-carbon PGA molecules.
Each 3 carbon molecule PGA is reduced to G3P/PGAL using NADPH and ATP during a redox reaction (CO2 is reduced while NADPH is oxidized).
Some of the resulting G3P/PGAL is used to form glucose, the rest is used to re-form RuBP.

42. The Role of Glucose
The formation of glucose from G3P/PGAL is of interest because glucose is used by most organisms to produce ATP to supply energy needs.
Glucose can be stored as starch, or is used to as cellulose make to strengthen plant cell walls.
G3P/PGAL is converted to many organic molecules besides glucose, including plant oils.

43. Stages of the Calvin Cycle
The Calvin cycle can be divided into:
Fixation of CO2;
Reduction of CO2; and
Regeneration of RuBP.
Metabolites of the Calvin cycle include:
RuBP = ribulose bisphosphate
PGA = 3-phosphoglycerate
PGAP = 1, 3-bisphosphoglycerate
G3P/PGAL = glyceraldehyde-3-phosphate

44. 1. Fixation of Carbon Dioxide
The first event of the Calvin cycle is the fixation of carbon dioxide (CO2).
This occurs when CO2 is attached to an organic compound.
A 5-carbon molecule, RUBP, combines with CO2 to form a 6-carbon molecule.
An enzyme, RuBP carboxylase, speeds this reaction.

45. 2. Reduction of Carbon Dioxide
The 6-carbon molecule immediately breaks down into two 3-carbon PGA molecules.
Each of the two PGA molecules is reduced to G3P/PGAL with the help of NADPH and ATP (made during the light-dependent reactions).
This is a redox reaction in which CO2 is reduced to carbohydrate (CH2O) and NADPH is oxidized to NADP+.
ATP is oxidized to ADP

46. 3. Regeneration of RuBP
RuBP must be regenerated for the Calvin cycle to continue with the help of ATP (produced during the light-dependent reaction)
For every three turns of the Calvin cycle, five molecules of G3P/PGAL are used to re-form three molecules of RuBP.
ATP is oxidized to ADP

47. The light-independent reactions of the Calvin cycle (detailed)
Or G3P

48. Making 1 molecule of glucose requires:
6CO2 (from atmosphere)
18ATP (from light-dependent reactions)
12 NADPH (from light-dependent reactions)

49. Photosynthesis, like all energy transformations, results in a loss of usable energy.
Under ideal laboratory conditions, plants transform 25% of solar energy they absorb into carbohydrate.
Under natural conditions, the efficiency of photosynthesis ranges from less than 1% to a maximum of 8%.
Regardless, living things depend on photosynthesis as their ultimate source of chemical energy.

50. Calvin Cycle Overall reactants Overall products Carbon dioxide ATP
NADPH
Overall products
Glucose
ADP
NADP+
Reaction pathway is cyclic and ribulose bisphosphate (RuBP) is regenerated

51. (Thick Fluid inside Chloroplast)
DARK REACTION
Requires ATP, NADPH,
and CO2
WHAT IT DOES:
WHERE IT HAPPENS:
Produces High
Energy Sugars
Leaf
Combines CO2, ATP
and NADPH
Chloroplasts
In the Stroma
(Thick Fluid inside Chloroplast)
Forms a 6 carbon sugar
(Glucose)

52. Summary of Photosynthesis
Light-Dependent Reactions
Subset RXNS:
Cyclic Electron Flow (1 photosystem, ETS)
Noncyclic Electron Flow (2 photosystems, ETS)
Location: Thylakoid
Produces: O2, ATP, NADPH (only ATP for cyclic)
Light-Independent Reactions
Aka Calvin Cycle
Location: Stroma
Produces: glucose, ADP, NADP+

53. Overview of Photosynthesis

54. Photosynthesis Vs. Cellular Respiration
Overall equation for photosynthesis is:
Overall equation for cellular respiration is:

55. Photosynthesis Vs. Cellular Respiration
Occurs in plants, algae, & some bacteria
Occurs in all organisms
Occurs in chloroplasts
Occurs in mitochondria
Glucose is produced
Glucose is broken down

56. Photosynthesis Vs. Cellular Respiration (cont’d)
Occurs in plant cells during day
Occurs in plant cells day AND night
Uses electron transport system
Uses NADP+ and NADPH
Uses NAD+ and NADH, FAD and FADH2

57. Photosynthesis versus cellular respiration