1. Using light to make food
PHOTOSYNTHESIS
Using light to make food

2. PHOTOSYNTHESIS Autotrophs are the producers of the biosphere
Autotrophs are the producers of the biosphere
Plants are autotrophs
Producing their own food and sustaining themselves without eating other organisms
What are we?
We are heterotrophs

3. Plants, algae, and some bacteria are photoautotrophs
Plants, algae, and some bacteria are photoautotrophs
Producers of food consumed by virtually all organisms
Figure 7.1A–D

4. Plants are AUTOTROPHS :make their own food
PLANTS USE ENERGY FROM THE SUN TO TRANSFORM CO2 AND WATER INTO ENERGY RICH CARBOHYDRATES(glucose).
Plants are AUTOTROPHS :make their own food
Plants supply all the energy (food) for life on earth and the oxygen that most
organisms need

5. How old is photosynthesis? How important is it?
Evidence of photosynthesis exists in rocks 3.5 billion years old.
Photosynthesis is the largest biochemical process on earth.
Importance?
Photosynthesis supplies OXYGEN to earth atmosphere and FOOD to all organisms

6. Photosynthesis is the process by which certain organisms use light energy to make sugar and oxygen gas from carbon dioxide and water.
Light
energy
PHOTOSYNTHESIS 6
CO2 +
H2O
Carbon dioxide
Water
C6H12O6 O2
Glucose
Oxygen gas

7. Where in the plant does photosynthesis occur?
In the CHLOROPLAST. The leaf is a food factory. The light trapping pigments are inside the chloroplasts embedded in the thylakoid membranes.
STOMATA or STOMA are openings on the leaf surface through which CO2 and O2 as well as water vapor go in and out of leaves.

8. Photosynthesis occurs in chloroplasts
Where does it occur?
Photosynthesis occurs in chloroplasts
Occurs primarily in the leaves, in the chloroplasts, which contain stroma, and stacks of thylakoids called grana
Leaf Cross Section
Leaf
Mesophyll Cell
Mesophyll
Vein
Stoma
CO2 O2
Chloroplast
Grana
Stroma
TEM 9,750 
Granum
Thylakoid
space
Outer
membrane
Inner
Intermembrane
LM 2,600 
Figure 7.2

9. ENERGY-CONVERTING ORGANELLES
Chloroplasts conver t solar energy to chemical energy (in sugars).
. Found in plants and some protists. This is where PHOTOSYNTHESIS takes place
TEM 9,750
Chloroplast
Stroma
Intermembrane space
Inner and outer membranes
Granum

10. Sites to check:

11. ENERGY-CONVERTING ORGANELLES
Chloroplasts conver t solar energy to chemical energy (in sugars).
. Found in plants and some protists. This is where PHOTOSYNTHESIS takes place
TEM 9,750
Chloroplast
Stroma
Intermembrane space
Inner and outer membranes
Granum

12. Thylakoids
Thylakoids are membranes that look like green flattened sacs stacked upon each other.
Granum is a stack of these sacs
The STROMA is the fluid between the membranes.

13. Plants produce O2 gas by splitting water
The O2 liberated by photosynthesis
Is made from the oxygen in water
Reactants:
Products:
6 CO2
12 H2O
C6H12O6
6 H2O
6 O2
Labeled
Experiment 1
Experiment 2
Not
labeled +
Figure 7.3A–C

14. Photosynthesis is a redox process, as is cellular respiration
Photosynthesis is a redox process, as is cellular respiration
In photosynthesis
H2O is oxidized and CO2 is reduced
Reduction
Oxidation
6 O2
6 H2O
6 CO2 
C6H12O6
Figure 7.4A, B

15. PHOTONS AND PIGMENTS
PHOTONS are packets of light energy
Light: electromagnetic energy waves that travel in waves of different lengths
PIGMENTS are molecules that absorb light energy (photons)
CHLOROPHYLL is the main pigment in plants. Absorbs the blue and red portions of the visible light spectrum and scatters or reflects back the green wave length. This is why plants look green.
CAROTENOIDS reflect the reds and yellows

16. THE LIGHT REACTIONS: CONVERTING SOLAR ENERGY TO CHEMICAL ENERGY
wavelengths of visible light (red,blue), absorbed by pigments drive the light reactions of photosynthesis
Increasing energy
10–5 nm
10–3 nm
1 nm
103 nm
106 nm
1 m
103 m
Gamma
rays
X-rays UV
Infrared
Micro-
waves
Radio
Visible light
400
500
600
700
750
650 nm
Wavelength (nm)
Transmitted
light
Absorbed
Reflected
Light
Chloroplast
380
Figure 7.6A, B

17. Overview: Photosynthesis occurs in two stages linked by ATP and NADPH
Overview: Photosynthesis occurs in two stages linked by ATP and NADPH
The complete process of photosynthesis consists of two linked sets of reactions
The Light Dependent Reactions and
The Calvin Cycle (discovered by Calvin and Benson)

18. Photosynthesis: H2O + CO2   O2 + C6H12O6 + H2O
water carbon light oxygen glucose water vapor
dioxide energy

19. STEPS OF PHOTOSYNTHESIS
capture sun light
use light energy to make ATP
use ATP to make carbohydrate molecules from CO2(carbon dioxide) and H2O (water)

20. LIGHT DEPENDENT REACTIONS
is the first stage of photosynthesis.
It takes place in the thylakoid membranes.
Oxygen is released, Water molecules are split. Oxygen gas diffuses out
ATP and electrons are carried to the next stage. Electrons are used to make ATP.

21. Light Dependent Reactions (In thylakoids of chloroplasts)
This is where light energy is converted to a form that can be used by plants to build Carbon compounds (sugars)
1.The energy of sunlight hits the photosystems (cluster of pigment molecules) and excites chlorophyll (pigment) electrons to a higher energy state. Light energy is absorbed by the photosystems
2. Water molecules split, oxygen is released.
Light energy is converted to chemical energy (ATP formation)
NADPH electron carrier take electrons from chlorophyll to the Calvin Cycle.

22. The Calvin cycle assembles sugar molecules from CO2
The light reactions
Convert light energy to chemical energy and produce O2
The Calvin cycle assembles sugar molecules from CO2
Using ATP and NADPH from the light reactions
Figure 7.5
Light
CO2
H2O
Chloroplast
LIGHT
REACTIONS
(in thylakoids)
CALVIN
CYCLE
(in stroma)
NADP+
ADP + P
ATP
NADPH O
Sugar
Electrons

23. THE CALVIN CYCLE: CONVERTING CO2 TO SUGARS
ATP and NADPH power sugar synthesis in the Calvin cycle
The Calvin cycle occurs in the chloroplast’s stroma
Consists of carbon fixation, reduction, release of G3P, (glyceraldehyde 3-phosphate)and regeneration of RuBP
Figure 7.10A
Input
CO2
ATP
NADPH
CALVIN
CYCLE
G3P
Output:

24. LIGHT INDEPENDENT REACTIONS-CALVIN CYCLE
(In stroma of chloroplasts ) This is a cyclic pathway where the final products are also the first reactants on the cycle
The Calvin Cycle uses the energy in ATP and NADPH to synthesize carbohydrates.
Carbon enters the cycle as a molecule of CO2

25. LIGHT INDEPENDENT REACTION or CALVIN CYCLE
Takes place in the stroma of the chloroplasts.
This is the “synthesis” part of photosynthesis. Making food (glucose) and trapping CO2 to incorporate carbon into living things.

26. CALVIN CYCLE- making glucose
The energy from ATP and NADPH+ go into the bonds of a glucose molecule.
Electrons ( hydrogens) from the carrier molecule are put together with CO2 to make glucose.
An enzyme called RUBISCO fixes the CO2 ( from the air) by bringing together the CO2 and the sugar.

27. LIGHT INDEPENDENT REACTIONS-CALVIN CYCLE
Fixes Carbon (from CO2) using the enzyme rubisco. This enzyme catalizes the binding of carbon from CO2 to RuBP ( ribulose bisphosphate). This is how all carbon enters the world of life.
Put together sugars using ATP and NADPH as energy sources.
The final product is a three carbon sugar called G3P (glyceraldehyde 3-phosphate)
G3P is a sugar phosphate that can be modified to form glucose

28. PHOTOSYNTHESIS REVIEWED
Review: Photosynthesis uses light energy to make food molecules
Light
H2O
CO2
NADP+
Photosystem II
Photosystem I
Electron
transport
chains
ADP P +
RUBP
CALVIN
CYCLE
(in stroma)
3-PGA
Stroma
G3P
NADPH
ATP O2
LIGHT REACTIONS
CALVIN CYCLE
Sugars
Cellular
respiration
Cellulose
Starch
Other organic
compounds
Thylakoid
membranes
Chloroplast
Figure 7.11

29. C3 PLANTS
Plants that use CO2 directly from the air are called C3 plants. Soybeans, oats wheat and rice are C3 plants.
In hot dry weather these plants close their stomata ( pores in underside of leaves) to reduce water loss. Since no CO2 can enter, the rate of photosynthesis is reduced and your crop productivity is poor.

30. C4 and CAM plants have special adaptations that save water
In C3 plants a drop in CO2 and rise in O2 when stomata close on hot dry day divert the Calvin cycle to photorespiration
( Rubisco can bind oxygen in place of CO2 as CO2 becomes scarce. When Oxygen enters the Calvin cycle instead of CO2 so it cannot produce sugars )
C4 and CAM plants have special adaptations that save water

31. CAM PLANTS CAM PLANTS In hot and very dry climates. (deserts)
Examples: pineapple, cactus, orchids all the “succulent plants such as Aloe and Jade plants
When stoma opens to get CO2 the water can get out. Survival depends on water retention.
Adaptation: Stoma is closed during the day and open at night. Co2 is taken in at night and banked until the next day when it is given to the Calvin cycle to make carbohydrates.
The CO2 taken in at night stays “banked” until the sun’s energy comes in the next day.

32. CAM plants open their stomata at night
Making a four-carbon compound used as a CO2 source during the day
CO2
Figure 7.12 (right half)
CAM plant
Day
CALVIN
CYCLE
3-C sugar
CO2
4-C compound
Night
Pineapple

33. C4 PLANTS
Have special adaptations to save water without shutting down photosynthesis
In hot climates.
Examples: grasses , corn, sugarcane
In hot climates the stoma closes to keep water in. It also keeps CO2 out and oxygen builds up inside the leaves. Since there is not enough CO2 the enzyme rubisco (that normally binds CO2) binds oxygen and the plants would not grow well.
Adaptation : It continues to make sugars with closed stomata.
How? These plants use a different enzyme to bind CO2.This enzyme fix carbon twice to produce a 4 carbon compound which can then donate the C to the Calvin cycle

34. C4 plants first fix CO2 into a four-carbon compound
That provides CO2 to the Calvin cycle
Figure 7.12 (left half)
Sugarcane
C4 plant
CALVIN
CYCLE
3-C sugar
CO2
4-C compound
Mesophyll cell
Bundle-sheath cell

35. ENVIRONMENTAL IMPACT OF PHOTOSYNTHESIS
Food. Photosynthesis is the source of all the food that gives us energy ( from the sun)
Oxygen production
CO2 is the gas plants use to make sugars.
CO2 in the atmosphere retains heat from the sun that would otherwise radiate back into space

36. PHOTOSYNTHESIS, SOLAR RADIATION, AND EARTH’S ATMOSPHERE CONNECTION
Photosynthesis moderates global warming
Greenhouses used to grow plants trap solar radiation, raising the temperature inside
Figure 7.13A

37. Global warming and the Greenhouse effect
Global warming is the slow and steady rise in Earth surface temperatures.
Warming is caused by CO2 and other greenhouse gases.
It is called the green house effect because CO2 traps heat and keeps it warm near the earth surface.
When this occurs in moderation it is a good thing, otherwise the planet would be about 10 degrees colder all the time. The trouble is that we get overheating.

38. What are greenhouse gases?
All the cars and industries that burn fossil fuel produce so much CO2 that we now have 30% more than ever before. This causes global warming.
Some greenhouse gases are carbon dioxide CO2, methane CH4, water vapor and others

39. Web sites to check: