1. Ch. 9 Photosythesis and Cellular Respiration
Honors Biology I
Loulousis

2. Leaves Optimized for absorbing light and carrying out photosynthesis.
Consist of:
BLADE – thin, flattened section that absorbs sunlight
PETIOLE – thin stalk that attaches the blade to the stem
Covered by epidermis and cuticle
Creates water-proof barrier

3. Leaf Functions PHOTOSYNTHESIS
Occurs in the Mesophyll (specialized ground tissue)
STOMATA – pores in the underside of a leaf that allows for the diffusion of O2 and CO2.
GUARD CELLS – control the opening and closing of stomata

5. Leaf Functions TRANSPIRATION
The loss of water from a plant through its leaves.
Replaced by water drawn into the leaf

6. Leaf Functions GAS EXCHANGE Take in CO2 and release O2.
Keep stomata open just enough to allow photosynthesis to take place
Can’t leave them open too long… can lead to water loss by transpiration

7. What type of organisms utilize photosynthesis
What type of organisms utilize photosynthesis? Plants, some bacteria, and algae (protista) Photoautotrophs- autotrophs that depend on photosynthesis for both energy and carbon compounds NOT chemoautotrophs- live in areas where it is too extreme – get energy by oxidizing inorganic substances such as iron or sulfur

8. Where does photosynthesis take place?
Leaves : the photosynthetic organs of the plant
Mesophyll: main photosynthetic tissue
a. Palisade cells: full of chloroplasts
b. Spongy cells: fewer chloroplasts and
many air spaces

9. Photosynthesis – An Overview
Living things get energy from food
Food is broken down and energy is stored as ATP
Heterotrophs have to consume other organisms for energy
Autotrophs are able to make their own food – Sugar (C6H12O6)/ glucose

10. How do Autotrophs Make Their Own Food?
Through photosynthesis – the process of using energy from the sun to convert Water and Carbon Dioxide into Oxygen and Sugar.
Equation:
6H2O + 6CO O2 + C6H12O6

11. An organism’s metabolism is part of Earth’s carbon cycle

12. Carbohydrates
Sugars are a type of organic molecule called carbohydrates
Carbohydrates are:
used for short term energy storage
Made up of basic units called monosaccharides
More complex sugars are disaccharides & polysaccharides
Plants make glucose through photosynthesis, also have an important polysaccharide called cellulose that makes up their cell walls

13. Cellular Energy
Cells use a form of chemical energy called Adenosine Triphosphate (ATP)
Cells store & use ATP to fuel necessary metabolic reactions
Such as maintaining internal chemical conditions (homeostasis)
10 MILLION molecules of ATP are consumed & regenerated per second per cell!
Cells store & use ATP to fuel necessary functions biosynthesis reactions, remove wastes, take in nutrients, maintain internal chemical conditions (homeostasis) & also for locomotion!

14. Adenosine Triphosphate (ATP)
Nucleotide
3 Energy Rich Phosphate Bonds
Sugar

15. ATP-Energy Currency
Holt Slide 13
ATP (adenosine triphosphate) -nucleotide with two extra energy-storing phosphate groups
Energy is released when the bonds that hold the phosphate groups together are broken
The removal of a phosphate group from ATP produces adenosine diphosphate -ADP:
H2O + ATP  ADP + P + energy

16. ATP Synthase An enzyme that catalyzes the synthesis of ATP
Recycles ADP by bonding a third phosphate group to the molecule to create ATP
Energy is stored when a phosphate is added to ADP to become ATP
Is a carrier protein for hydrogen ions (H+)
Flow of H+ ions through ATP synthase powers the production of ATP

17. ATP – ADP Cycle:

18. Light and Pigment
Plants also need light and chlorophyll to undergo photosynthesis.
Plants absorb the sun’s light with chlorophyll. There is chlorophyll a and chlorophyll b.
Sunlight is a mixture of colors (ROYGBIV)

19. Light and Pigment cont.
The color we see with our eyes is the result of colors being reflected and absorbed.
A red flower appears red because all of the colors from the spectrum are being absorbed, EXCEPT red. Red is the color being reflected.
Both chlorophylls absorb the red and blue spectrums easily. They DO NOT ABSORB green light, they reflect green light. (See the previous color spectrum chart)

20. Why Leaves Change Color?
A color palette needs pigments, and there are 3 types:
1. Chlorophyll
2. Carotenoids
3. Anthocyanins

21. Stop & Think 1. Why are light & chlorophyll needed for photosynthesis?
2. Why are plants green?
3. How well would a plant grow under pure yellow light?
4. Write the equation for photosynthesis. Identify reactants and products.
5. Use the graph below to figure…
In which regions of the spectrum will chlorophyll a absorb the most light?
In which regions of the spectrum will chlorophyll b absorb the most light?
Chlorophyll b
Chlorophyll a

22. What are Chloroplasts?
Organelles that house photosynthetic material and enzymes necessary for photosynthesis
Stroma – large central compartment, where Calvin cycle takes place
Thylakoids – flattened sacs within stroma that contain chlorophyll
Grana – stacks of thylakoids
Thylakoid space – within thylakoid, where light reactions take place

23. Chloroplast Structure

24. What is the first reaction of photosynthesis?
Light dependent reactions-
occurs in thylakoid membrane
pigments release electrons as light hits
photolysis- water is split and electrons replace pigment electrons
electrons move down electron transport system producing ATP
NADP+ pick up electrons and H+, holds energy
NADPH and ATP carried to Calvin Cycle

25. What are photosystems?
pigment complex that serves as antennae to gather solar energy in the form of photons
energy is passed from one pigment to the next until it reaches chlorophyll a
electrons escape as they become excited
picked up by nearby electron carrier

26. Light Dependent Reactions
There are two Electron Transport Chains (ETC)
Chlorophyll in Photosystem II (PSII) absorbs photons
Energy is passed along the (ETC)
The electrons lost to the chain from PSII are replaced by electrons from the splitting of water (photolysis)
Produces 4 electrons, 2 H+, O2 is released through stomata
High concentration of H+ in thylakoid, so move out to stroma by attaching to electrons, creating ATP in ATP synthase (from the ADP hanging around)
ATP move on to Calvin Cycle by a electron carrier molecule

27. Light Dependent Reactions cont.
Photosystem I receives photons from sunlight
Electrons are excited and move down the ETC
Electrons from PSII replace the lost electrons from PSI
The electrons are used by NADP reductase to change NADP+ to NADPH
NADPH is transported (carrier molecule) to the Calvin Cycle.

31. Calvin Cycle Aka the dark cycle or light independent reaction
The products from the light reaction , ATP and NADPH, fuel cycle
After energy released from ATP and NADPH, the now ADP and NADP+ go back to the light reaction to be used again
The product of the Calvin Cycle is glucose

32. Calvin Cycle Steps
1. Carbon Dioxide (CO2) enters leaf through stomata from atmosphere
2. Combines with a 5-carbon molecule called RuBP in process called carbon fixation
RuBP stands for ribulose biphosphate
3. Catalyzed by rubisco, RuBP becomes a temporary unstable 6-carbon molecule
4. The 6-carbon molecule quickly splits in half and forms two 3-carbon molecules called PGA

33. Calvin Cycle steps
5. The energy from ATP and NADPH is used to convert PGA into PGAL
6. Three turns of cycle, each picking up CO2, makes six molecules of PGAL
7. Five PGAL go to make more RuBP
8. 1 molecule of PGAL is used to make larger compounds such as starch, glucose (simple sugars), or cellulose for plant cell walls

35. H2O
Light
NADP+
ADP + P i
Light
Reactions
Chloroplast

36. H2O
Light
NADP+
ADP + P i
Light
Reactions
ATP
NADPH
Chloroplast O2

37. i CO2 Light NADP+ ADP Calvin Cycle Light Reactions ATP NADPH
H2O
CO2
Light
NADP+
ADP + P i
Calvin
Cycle
Light
Reactions
ATP
NADPH
Chloroplast O2

38. i CO2 Light NADP+ ADP Calvin Cycle Light Reactions ATP NADPH
H2O
CO2
Light
NADP+
ADP + P i
Calvin
Cycle
Light
Reactions
ATP
NADPH
Chloroplast
[CH2O]
(sugar) O2

39. Grand Totals During the Light Reactions: Enters = H2O Leaves = O2
During the Calvin Cycle:
Enters = CO2 Leaves = C6H12O6
_____________________________
Total Equation:
6CO2 + 6H O2 + C6H12O6

40. Stop & Think 1. Summarize the light dependent reactions.
2. Summarize the events of the Calvin Cycle.
3. What is the function of NADP+?
4. Why must the light reactions take place before the Calvin Cycle can occur?

41. Rates of Photosynthesis (limiting factors)
Four things affect rate of Photosynthesis
1. Light intensity
2. temperature
3. CO2 concentration
4. Oxygen concentration

42. Rates of Photosynthesis (limiting factor)
Four things affect rate of P.S.
Light intensity increases rate of p.s. up to light saturation point
as temperature increases, p.s. rate increases to point, then decreases
concentration of CO2 increases rate of p.s.
as oxygen increases, p.s. rate decreases

43. Light Intensity
As light intensity increases, rate increases until the saturation point, leveling off, then decreasing slightly
Why level off?
Light reactions are saturated with light electrons and are proceeding as fast as possible
Photoinhibition:
chlorophyll takes on energy faster than it can transfer e- to ETS. O2 reacts with e- and H2O to make OH- and H2O2 (hydrogen peroxide)
Products cause damage to chloroplast
Decline in rate

45. Temperature
As the temperature increases, rate increases until a point, then decreases
If temperature gets too high,
enzymes involved (Rubisco),
which is a protein, become
denatured

46. Concentration of Carbon dioxide
As CO2 increased, rate increases to a maximum until it reaches the saturation point.
After that, there is no effect on photosynthesis
What would the graph for this look like?

47. Oxygen Concentration
Increasing the level of oxygen, decreases the rate of photosynthesis in C3 Plants.
As a result
the plants undergo
photorespiration.

48. Photorespiration
Enzyme rubisco is needed to incorporate CO2 into the Calvin Cycle.
Rubisco can bind to CO2 or O2
If there is a higher concentration of oxygen than carbon dioxide, oxygen interferes with Carbon Fixation.
The enzyme rubisco will bind with oxygen and combines with RuBP which produces only 1 PGA molecule and glycolate.
PGA will eventually be used to form simple sugar
RuBP releases CO2 which resembles cellular respiration
Overall rate of photosynthesis slows

50. Inefficient C3 Pathway
Under conditions such as hot dry days, which cause water stress in plants
Plants close their stomata to conserve water
Photosynthesis in the chloroplasts rapidly uses up the CO2 remaining in the leaf
Also, oxygen produced during photosynthesis accumulates in the chloroplasts
Thus, the conditions are perfect for photorespiration

51. Special Heat Adaptations
Two groups of plants have evolved adaptations that reduce photorespiration : C4 & CAM Plants
C4 Plants:
a. 2 systems of CO2 fixation occur in
different parts of leaves
b. CO2 is 1st incorporated into a 4C acid in the
mesophyll cells (no Rubisco is there)
c. 4C acid is transported to the bundle
sheath where Calvin cycle resumes
Examples: sugar cane, corn, crabgrass

52. What is the advantage of C4 plants?
Can reduce amount photorespiration because CO2 is delivered to bundle sheath cells that have chloroplasts
No air space to allow rubisco to come in contact with oxygen

53. What is the advantage of partitioning space in a C4 plant?
1. Avoid photorespiration and can keep stomates open longer
2. CO2 is converted to oxaloacetate and delivered to bundle
sheath cells which reduces O2 being fixed
Disadvatage
1. water is lost as stomates are opened

54. Special Heat Adaptations
CAM Plants:
a. Opens stomates at night
b. Incorporates CO2 into a 4C acid
(malate) which is stored in vacuole
for use later
c. Not very efficient
d. Found in snake plants, jade, and cactus
e. Slow growers

55. What is the advantage of partitioning in time?
CAM Plants
What is the advantage of partitioning in time?
Can keep stomates open longer because CO2 is stored as malate in vacuoles during the evening and used by Calvin cycle during the day once ATP and NADPH get made
Stomates closed during day, reduces water loss by plant