1. Using Light to make Food
Photosynthesis:
Using Light to make Food

2. OVERALL, PHOTOSYNTHESIS...
6 CO2 + 6 H2O 
SUNLIGHT (light energy)
C6H12O6 + 6O2

3. Capturing Free Energy without Light
Photoautotrophs- organism use sunlight as the source of energy to drive photosynthesis and produce carbohydrates.
Chemoautotrophs- prokaryotes that use inorganic substances (hydrogen sulfide, ammonia, nitrite) as a source of energy.
Example:
CO2 + 4 H2S + O CH2O + 4 S + 3 H2O

4. Important details…. Light is required. It is the source of energy.
The reaction takes place in the chloroplast of the plant cell.
The chloroplast is filled with green pigment called chlorophyll.

5. PHOTOSYNTHESIS TAKES PLACE IN...
CHLOROPLASTS

7. Photosynthesis occurs in chloroplasts in plant cells
Chloroplasts are the major sites of photosynthesis in green plants.
Chlorophyll
is an important light-absorbing pigment in chloroplasts,
is responsible for the green color of plants, and
plays a central role in converting solar energy to chemical energy.
Teaching Tips
1. The authors note the analogous roles of the thylakoid space and the intermembrane space of a mitochondrion. Students might be encouraged to create a list of the similarities in structure and function of mitochondria and chloroplasts through these related chapters.
2. The living world contains many examples of adaptations to increase surface area. Some examples are the many folds of the inner mitochondrial membrane, the highly branched surfaces of plant roots, fish gills, and human lungs, and the highly branched system of capillaries in the tissues of our bodies. Consider relating this broad principle to the extensive folding of the thylakoid membranes. 7

8. Chloroplast – Internal Structure
Pigments are located in the membranes of the thylakoids.

9. Photosynthesis occurs in chloroplasts in plant cells
Thylakoids
Function analogous to the inter-membrane space of mitochondria (cellular respiration).
Contain needed enzymes and other proteins.
Chlorophyll molecules are built into the thylakoid membrane and capture light energy.
Teaching Tips
1. The authors note the analogous roles of the thylakoid space and the intermembrane space of a mitochondrion. Students might be encouraged to create a list of the similarities in structure and function of mitochondria and chloroplasts through these related chapters.
2. The living world contains many examples of adaptations to increase surface area. Some examples are the many folds of the inner mitochondrial membrane, the highly branched surfaces of plant roots, fish gills, and human lungs, and the highly branched system of capillaries in the tissues of our bodies. Consider relating this broad principle to the extensive folding of the thylakoid membranes. 9

10. Photosynthesis occurs in chloroplasts in plant cells
Stoma (singular), Stomata (plural)
Teaching Tips
1. The authors note the analogous roles of the thylakoid space and the intermembrane space of a mitochondrion. Students might be encouraged to create a list of the similarities in structure and function of mitochondria and chloroplasts through these related chapters.
2. The living world contains many examples of adaptations to increase surface area. Some examples are the many folds of the inner mitochondrial membrane, the highly branched surfaces of plant roots, fish gills, and human lungs, and the highly branched system of capillaries in the tissues of our bodies. Consider relating this broad principle to the extensive folding of the thylakoid membranes.
Guard cells contain chlorophyll.
Most stomata are on the lower epidermis.
Lower concentrations of stomata indicate lower rates of photosynthesis and growth or adaptations for dry weather. 10

11. Essential Leaf Parts for Photosynthesis
Structure
Function
Chloroplasts
Veins
Stomata

12. Photosynthesis is a redox process, as is cellular respiration
Photosynthesis, like respiration, is a redox (oxidation-reduction) process.
CO2 becomes reduced to sugar as electrons along with hydrogen ions from water are added to it.
Water molecules are oxidized when they lose electrons along with hydrogen ions.
Teaching Tips
In our world, energy is frequently converted to a usable form in one place and used in another. For example, electricity is generated by power plants, transferred to our homes, and used to run computers, create light, and help us prepare foods. Consider relating this common energy transfer to the two-stage process of photosynthesis. 12

13. Photosynthesis is a redox process, as is cellular respiration
Cellular respiration uses redox reactions to harvest the chemical energy stored in a glucose molecule.
This is accomplished by oxidizing the sugar and reducing O2 to H2O.
The electrons lose potential energy as they travel down the electron transport chain to O2.
The food-producing redox reactions of photosynthesis require energy.
Teaching Tips
In our world, energy is frequently converted to a usable form in one place and used in another. For example, electricity is generated by power plants, transferred to our homes, and used to run computers, create light, and help us prepare foods. Consider relating this common energy transfer to the two-stage process of photosynthesis. 13

14. Compare Cellular Respiration with Photosynthesis
Becomes oxidized
Becomes reduced
Figure 7.4B Cellular respiration (releases chemical energy)
photosynthesis 14

15. Photosynthesis is a redox process, as is cellular respiration
In photosynthesis,
light energy is captured by chlorophyll molecules to boost the energy of electrons,
light energy is converted to chemical energy, and
chemical energy is stored in the chemical bonds of sugars.
Teaching Tips
In our world, energy is frequently converted to a usable form in one place and used in another. For example, electricity is generated by power plants, transferred to our homes, and used to run computers, create light, and help us prepare foods. Consider relating this common energy transfer to the two-stage process of photosynthesis.
Go to…….. Photosynthesis Animation 15

16. Overview: The two stages of photosynthesis are linked by ATP and NADPH
Photosynthesis occurs in two metabolic stages.
The light reactions occur in the _________ ________.
_______ is split, providing a source of electrons and giving off oxygen as a by-product,
______ is generated from ADP and a phosphate group, and
________energy is absorbed by the chlorophyll molecules to drive the transfer of electrons and H+ from water to the electron acceptor NADP+ reducing it to NADPH.
NADPH produced by the light reactions provides the electrons for reducing carbon in the Calvin cycle.
Student Misconceptions and Concerns
Students may understand the overall chemical relationships between photosynthesis and cellular respiration, but many struggle to understand the use of carbon dioxide in the Calvin cycle. Photosynthesis is much more than gas exchange.
Teaching Tips
1. In our world, energy is frequently converted to a usable form in one place and used in another. For example, electricity is generated by power plants, transferred to our homes, and used to run computers, create light, and help us prepare foods. Consider relating this common energy transfer to the two-stage process of photosynthesis.
2. Figure 7.5 is an important visual organizer, which notes the key structures and functions of the two stages of photosynthesis. This figure demonstrates that water and sunlight are used in the thylakoid membranes to generate oxygen, ATP, and NADPH. The second step, in the stroma, reveals the use of carbon dioxide, ATP, and NADPH to ultimately generate carbohydrates. 16

17. Overview: The two stages of photosynthesis are linked by ATP and NADPH
The second stage is the Calvin cycle, which occurs in the ______________ of the chloroplast.
The Calvin cycle is a cyclic series of reactions that assembles ______________ molecules using CO2 and the energy-rich products of the light reactions.
During the Calvin cycle, ____________ is incorporated into organic compounds in a process called carbon fixation.
After carbon fixation, enzymes of the cycle make _________ by further reducing the carbon compounds.
The Calvin cycle is often called the dark reactions or light-independent reactions, because none of the steps requires light directly.
Student Misconceptions and Concerns
Students may understand the overall chemical relationships between photosynthesis and cellular respiration, but many struggle to understand the use of carbon dioxide in the Calvin cycle. Photosynthesis is much more than gas exchange.
Teaching Tips
1. In our world, energy is frequently converted to a usable form in one place and used in another. For example, electricity is generated by power plants, transferred to our homes, and used to run computers, create light, and help us prepare foods. Consider relating this common energy transfer to the two-stage process of photosynthesis.
2. Figure 7.5 is an important visual organizer, which notes the key structures and functions of the two stages of photosynthesis. This figure demonstrates that water and sunlight are used in the thylakoid membranes to generate oxygen, ATP, and NADPH. The second step, in the stroma, reveals the use of carbon dioxide, ATP, and NADPH to ultimately generate carbohydrates. 17

18. An overview of the two stages of photosynthesis in a chloroplast
CO2
Light
NADP+
ADP P
Calvin Cycle
Light Reactions
(in stroma)
(in thylakoids)
ATP
Figure 7.5_s3 An overview of the two stages of photosynthesis in a chloroplast (step 3)
NADPH
Chloroplast O2
Sugar
An overview of the two stages of photosynthesis in a chloroplast 18

19. Visible radiation absorbed by pigments drives the light reactions
Sunlight contains energy called electromagnetic energy or electromagnetic radiation.
Visible light is only a small part of the electromagnetic spectrum, the full range of electromagnetic wavelengths.
Electromagnetic energy travels in waves, and the wavelength is the distance between the crests of two adjacent waves.
Student Misconceptions and Concerns
1. The authors note that electromagnetic energy travels through space in waves that are like ripples made by a pebble dropped in a pond. This wave imagery is helpful, but can confuse students when energy is also thought of as discrete packets called photons. The dual nature of light, which exhibits the properties of waves and particles, may need to be discussed further, if students are to do more than just accept definitions.
2. The authors note that sunlight is a type of radiation. Many students think of radiation as a result of radioactive decay, a serious threat to health. The diverse types of radiation and the varying energy associated with each might need to be explained.
Teaching Tips
Consider bringing a prism to class and demonstrating the spectrum of light. Depending on what you have available, it can be a dramatic reinforcement. 19

20. Light, microwaves, x-rays, and TV and radio transmissions are all kinds of electromagnetic waves. They are all the same kind of wavy disturbance that repeats itself over a distance called the wavelength.
One thing that all the forms of electromagnetic radiation have in common is that they can travel through empty space. This is not true of other kinds of waves; sound waves, for example, need some kind of material, like air or water, in which to move.
Visible Light is nm

21. Gamma rays Micro- waves Radio waves 650 nm
Increasing energy
105 nm
103 nm
1 nm
103 nm
106 nm
1 m
103 m
Gamma rays
Micro- waves
Radio waves
X-rays UV
Infrared
Visible light
Figure 7.6A The electromagnetic spectrum and the wavelengths of visible light
380
400
500
600
700
750
Wavelength (nm)
650 nm 21

22. Relate wavelength of light to color and energy
Visible Light
light travels in waves
shorter
waves
more energy
longer
waves
less energy
as wavelength increases, energy decreases
Remember:
white light separates into color when going thru prism or water droplets
energy travels in waves
wavelength refers to distance between crest of two waves
short wavelengths have more energy, wavelengths below 500nm breaks chemical bonds in DNA and proteins
Wavelength Energy

23. Visible radiation absorbed by pigments drives the light reactions
We see the color of the wavelengths that are transmitted. For example, chlorophyll transmits green wavelengths.
Student Misconceptions and Concerns
1. The authors note that electromagnetic energy travels through space in waves that are like ripples made by a pebble dropped in a pond. This wave imagery is helpful, but can confuse students when energy is also thought of as discrete packets called photons. The dual nature of light, which exhibits the properties of waves and particles, may need to be discussed further, if students are to do more than just accept definitions.
2. The authors note that sunlight is a type of radiation. Many students think of radiation as a result of radioactive decay, a serious threat to health. The diverse types of radiation and the varying energy associated with each might need to be explained.
Teaching Tips
Consider bringing a prism to class and demonstrating the spectrum of light. Depending on what you have available, it can be a dramatic reinforcement. 23

24. Visible radiation absorbed by pigments drives the light reactions
Chloroplasts contain several different pigments, which absorb light of different wavelengths.
_____________absorbs blue-violet and red light and reflects green.
_____________absorbs blue and orange and reflects yellow-green.
_____________and other pigments
broaden the spectrum of colors that can drive photosynthesis
Some provide photoprotection, absorbing and dissipating excessive light energy that would otherwise damage chlorophyll
Student Misconceptions and Concerns
1. The authors note that electromagnetic energy travels through space in waves that are like ripples made by a pebble dropped in a pond. This wave imagery is helpful, but can confuse students when energy is also thought of as discrete packets called photons. The dual nature of light, which exhibits the properties of waves and particles, may need to be discussed further, if students are to do more than just accept definitions.
2. The authors note that sunlight is a type of radiation. Many students think of radiation as a result of radioactive decay, a serious threat to health. The diverse types of radiation and the varying energy associated with each might need to be explained.
Teaching Tips
Consider bringing a prism to class and demonstrating the spectrum of light. Depending on what you have available, it can be a dramatic reinforcement.
© 2012 Pearson Education, Inc. 24

25. Accessory Pigments-
Absorb light that chlorophyll a and b cannot!

26. Leaves have different pigments. other pigments become visible.
When (green) chlorophyll begins to breakdown due to colder temperatures and shorter days,
other pigments become visible.

27. Reactions of Photosynthesis
2 Reaction Stages (sets)
light dependent reactions
sun energy chemical energy
light independent reactions
or Calvin Cycle
carbon fixation or the synthesis of glucose

28. Photosystems capture solar energy
Pigments in chloroplasts absorb photons (unit of solar power), which
increases the potential
energy of the pigment’s
electrons and
sends the electrons
into an unstable state.
These unstable electrons
drop back down to their “ground state,”
and as they do, release their excess
energy as heat.
Student Misconceptions and Concerns
Even at the college level, students struggle to understand why we perceive certain colors. The authors discuss the specific absorption and reflection of certain wavelengths of light, noting which colors are absorbed and which are reflected (and thus available for our eyes to detect). Consider spending time to make sure that your students understand how photosynthetic pigments absorb and reflect certain wavelengths.
Teaching Tips
The authors discuss a phenomenon that most students have noticed: dark surfaces heat up faster in the sun than do lighter-colored surfaces. This is an opportunity to demonstrate to your students the various depths of scientific explanations and help them appreciate their own educational progress. In elementary school, they might have learned that the sun heats darker surfaces faster than lighter surfaces. In high school, they may have learned about light energy and the fact that dark surfaces absorb more of this energy than lighter surfaces. Now, in college, they are learning that at the atomic level, darker surfaces absorb the energy of more photons, exciting more electrons, which then fall back to a lower state, releasing more heat. 28

29. Cyclic Photophosphorylation
Animation- first part- Cyclic

30. Pair of chlorophyll a molecules
A light-excited pair of chlorophyll molecules in the reaction center of a photosystem passing an excited electron to a primary electron acceptor (it becomes reduced)
Photosystem
Reaction-center complex
Light-harvesting complexes
Light
Primary electron acceptor
Thylakoid membrane
Figure 7.7B A light-excited pair of chlorophyll molecules in the reaction center of a photosystem passing an excited electron to a primary electron acceptor
Transfer of energy
Pair of chlorophyll a molecules
Pigment molecules 30

31. Noncyclic Photophosphorylation
Two types of photosystems (photosystem I and photosystem II) cooperate in the light reactions.
Each type of photosystem has a characteristic reaction center.
Photosystem II, which functions first, is called P680 because its pigment absorbs light with a wavelength of 680 nm.
Photosystem I, which functions second, is called P700 because it absorbs light with a wavelength of 700 nm.
Student Misconceptions and Concerns
Even at the college level, students struggle to understand why we perceive certain colors. The authors discuss the specific absorption and reflection of certain wavelengths of light, noting which colors are absorbed and which are reflected (and thus available for our eyes to detect). Consider spending time to make sure that your students understand how photosynthetic pigments absorb and reflect certain wavelengths.
Teaching Tips
The authors discuss a phenomenon that most students have noticed: dark surfaces heat up faster in the sun than do lighter-colored surfaces. This is an opportunity to demonstrate to your students the various depths of scientific explanations and help them appreciate their own educational progress. In elementary school, they might have learned that the sun heats darker surfaces faster than lighter surfaces. In high school, they may have learned about light energy and the fact that dark surfaces absorb more of this energy than lighter surfaces. Now, in college, they are learning that at the atomic level, darker surfaces absorb the energy of more photons, exciting more electrons, which then fall back to a lower state, releasing more heat. 31

32. Noncyclic Photophosphorylation-Two photosystems connected by an electron transport chain generate ATP and NADPH
In the light reactions, light energy is transformed into the chemical energy of ATP and NADPH.
To accomplish this, electrons are
removed from water,
passed from photosystem II to photosystem I, and
accepted by NADP+, reducing it to NADPH.
Between the two photosystems, the electrons
move down an electron transport chain and
provide energy for the synthesis of ATP.
Teaching Tips
The authors develop a mechanical analogy for the energy levels and movement of electrons in the light reaction. Figure 7.8B equates the height of an electron with its energy state. Thus, electrons captured at high levels carry more energy than electrons in lower positions. Although this figure can be very effective, students might need to be carefully led through the analogy to understand precisely what is represented. 32

33. Noncyclic Photophosphorylation-Two photosystems connected by an electron transport chain generate ATP and NADPH
Electron transport chain Provides energy for synthesis of ATP by chemiosmosis
NADP  H
NADPH
Light
Light
Photosystem I 6
Photosystem II
Stroma 1
Primary acceptor
Primary acceptor 2
Thylakoid membrane 4 5
P680
P700
Figure 7.8A Electron flow in the light reactions: light energy driving electrons from water to NADPH
Thylakoid space 3
H2O 2 1 O2 H  2 33

34. Chemiosmosis powers ATP synthesis in the light reactions
Chemiosmosis is the mechanism that
generates ATP in chloroplasts.
In photophosphorylation, using the initial energy input from light,
the electron transport chain pumps H+ into the thylakoid space, and
the resulting concentration gradient drives H+ back through ATP synthase, producing ATP.
Teaching Tips
Module 7.9 notes the similarities between oxidative phosphorylation in mitochondria and photophosphorylation in chloroplasts. If your students have not already read or discussed chemiosmosis in mitochondria, consider assigning Modules 6.6 and 6.10 to show the similarities of these processes. (As noted in Module 7.2, the thylakoid space is analogous to the intermembrane space of mitochondria.) 34

35. 3 VERY Important Concepts
How is oxygen produced in the light dependent reaction?
Energy carried by the e- is captured in _____________.
Chemiosmosis produces __________

36. Nicotinamide Adenine Dinucleotide Phosphate
In chloroplasts, NADP is reduced in last step of the electron chain of the light dependent reactions of photosynthesis. The NADPH formed is used in the light independent reactions.

37. Noncyclic Photophosphorylation Dependent Reaction Steps1. 2. 3. 4. 5.

38. ATP and NADPH power sugar synthesis in the Calvin cycle (does not need light)
The Calvin cycle makes sugar within a chloroplast.
To produce sugar, the necessary ingredients are 1. 2. 3.
The Calvin cycle produces an energy-rich, three-carbon sugar called glyceraldehyde-3-phosphate (G3P). A plant cell then uses G3P to make glucose.
Student Misconceptions and Concerns
The terms light reactions and dark reactions can lead students to conclude that each set of reactions occurs at different times of the day. However, the Calvin cycle in most plants occurs during daylight, when NADPH and ATP from the light reactions are readily available.
Teaching Tips
Glucose is not the direct product of the Calvin cycle, as might be expected from the general equation for photosynthesis. Instead, as noted in the text, G3P is the main product. Clarify the diverse uses of G3P in the production of many important plant molecules for students. 38

39. Step Release of one molecule of G3P 6 NADP 6 P 5 P G3P G3P
Step Carbon fixation 1
Input: 3
CO2
Rubisco 1 3 P P 6 P
RuBP
3-PGA
Step Reduction 2 6
ATP 3
ADP 6
ADP P
Calvin Cycle 4 2 3
ATP 6
NADPH
Step Release of one molecule of G3P 3
Figure 7.10B_s4 Details of the Calvin cycle, which takes place in the stroma of a chloroplast (step 4) 6
NADP 6 P 5 P
G3P
G3P 3
Glucose and other compounds
Step Regeneration of RuBP 4
Output: 1 P
G3P 39

40. Calvin-Benson Cycle animation

41. Noncyclic Photophosphorylation Light inDependent Reaction Steps1. 2. 3. 4. 5.

42. Different Carbon Fixing Pathways
The carbon fixing pathway previously described is more accurately called the C3 pathway due to the first stable compounds formed in the Calvin-Benson Cycle being 2, 3-carbon molecules (PGA)
Different environments have adapted a different pathway.
_____________: high daytime temperatures, high intensity of sunlight, ex.- corn, sugarcane
_____________: high daytime temperatures, intense sunlight, low soil moisture, ex.- cacti, pineapples

43. EVOLUTION CONNECTION: Other methods of carbon fixation have evolved in hot, dry climates
Most plants use CO2 directly from the air, and carbon fixation occurs when the enzyme rubisco adds CO2 to RuBP.
Such plants are called C3 plants because the first product of carbon fixation is a _______-carbon compound, 3-PGA.
Teaching Tips
1. If you can find examples of C3, C4, and CAM plants, consider bringing them to class. Referring to living plants helps students understand these abstract concepts. Nice photographs can serve as a substitute.
2. Relate the properties of C3 and C4 plants to the regions of the country where each is grown. Students might generally understand that crops have specific requirements, but may not specifically relate these physiological differences to their geographic sites of production or specific evolutionary histories. 43

44. EVOLUTION CONNECTION: Other methods of carbon fixation
In hot and dry weather, C3 plants
close their stomata to reduce water loss but
Problem is…._________________________________
As O2 builds up in a leaf, rubisco adds O2 instead of CO2 to RuBP, and a two-carbon product of this reaction is then broken down in the cell.
This process is called __________________ because it occurs in the light, consumes O2, and releases CO2.
But unlike cellular respiration, it uses ATP instead of producing it.
Teaching Tips
1. If you can find examples of C3, C4, and CAM plants, consider bringing them to class. Referring to living plants helps students understand these abstract concepts. Nice photographs can serve as a substitute.
2. Relate the properties of C3 and C4 plants to the regions of the country where each is grown. Students might generally understand that crops have specific requirements, but may not specifically relate these physiological differences to their geographic sites of production or specific evolutionary histories. 44

45. Photorespiration
If oxygen levels are high, Calvin’s cycle slows. Less glucose is produced and CO2
is actually released from the cycle instead of being fixed by the cycle.
Why does O2 build up in leaves?

46. EVOLUTION CONNECTION: Other methods of carbon fixation
C4 plants have evolved a means of
carbon fixation that saves water during photosynthesis while
optimizing the Calvin cycle.
C4 plants are so named because they first fix CO2 into a four-carbon compound.
When the weather is hot and dry, C4 plants keep their stomata mostly closed, thus conserving water.
Teaching Tips
1. If you can find examples of C3, C4, and CAM plants, consider bringing them to class. Referring to living plants helps students understand these abstract concepts. Nice photographs can serve as a substitute.
2. Relate the properties of C3 and C4 plants to the regions of the country where each is grown. Students might generally understand that crops have specific requirements, but may not specifically relate these physiological differences to their geographic sites of production or specific evolutionary histories. 46

48. EVOLUTION CONNECTION: Other methods of carbon fixation
Another adaptation to hot and dry environments has evolved in the CAM plants, such as pineapples and cacti.
CAM plants conserve water by opening their stomata and admitting CO2 only at night.
CO2 is fixed into a four-carbon compound,
which banks CO2 at night and
releases it to the Calvin cycle during the day.
Teaching Tips
1. If you can find examples of C3, C4, and CAM plants, consider bringing them to class. Referring to living plants helps students understand these abstract concepts. Nice photographs can serve as a substitute.
2. Relate the properties of C3 and C4 plants to the regions of the country where each is grown. Students might generally understand that crops have specific requirements, but may not specifically relate these physiological differences to their geographic sites of production or specific evolutionary histories. 48

49. Mesophyll cell
CO2
CO2
Night
4-C compound
4-C compound
Bundle- sheath cell
CO2
CO2
Calvin Cycle
Calvin Cycle
Figure 7.11 Comparison of C4 and CAM photosynthesis
3-C sugar
3-C sugar
Day
C4 plant
CAM plant
Sugarcane
Pineapple 49

50. Outline of C4 and CAM Pathways

51. Review: Photosynthesis uses light energy, carbon dioxide, and water to make organic molecules
Most of the living world depends on the food-making machinery of photosynthesis.
The chloroplast
integrates the two stages of photosynthesis and
makes sugar from CO2.
Student Misconceptions and Concerns
Some students do not realize that plant cells also have mitochondria. Instead, they assume that the chloroplasts are sufficient for the plant cell’s needs. As noted in the text, nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria).
Teaching Tips
1. Challenge students to explain how the energy in beef is ultimately derived from the sun.
2. The authors note that G3P is also used to produce cellulose, the most abundant organic molecule in a plant and probably on the surface of the Earth! 51

52. Review: Photosynthesis uses light energy, carbon dioxide, and water to make organic molecules
About half of the carbohydrates made by photosynthesis are consumed as fuel for cellular respiration in the mitochondria of plant cells.
Sugars also serve as the starting material for making other organic molecules, such as proteins, lipids, and cellulose.
Excess food made by plants is stockpiled as starch in roots, tubers, seeds, and fruits.
Student Misconceptions and Concerns
Some students do not realize that plant cells also have mitochondria. Instead, they assume that the chloroplasts are sufficient for the plant cell’s needs. As noted in the text, nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria).
Teaching Tips
1. Challenge students to explain how the energy in beef is ultimately derived from the sun.
2. The authors note that G3P is also used to produce cellulose, the most abundant organic molecule in a plant and probably on the surface of the Earth! 52

53. Calvin Cycle (in stroma) Electron transport chain
H2O
CO2
Chloroplast
Light
NADP
ADP P
Light Reactions
RuBP
Photosystem II
Calvin Cycle (in stroma)
3-PGA
Electron transport chain
Thylakoids
Photosystem I
ATP
Stroma
Figure 7.12 A summary of photosynthesis
NADPH
G3P
Cellular respiration
Cellulose
Starch O2
Sugars
Other organic compounds 53

54. CONNECTION: Photosynthesis may moderate global climate change
The greenhouse effect operates on a global scale.
Solar radiation includes visible light that penetrates the Earth’s atmosphere and warms the planet’s surface.
Heat radiating from the warmed planet is absorbed by gases in the atmosphere, which then reflects some of the heat back to Earth.
Without the warming of the greenhouse effect, the Earth would be much colder and most life as we know it could not exist.
Student Misconceptions and Concerns
1. Students often do not fully understand how the burning of fossil fuels contributes to global warming. They might wonder, “How does the burning of fossil fuels differ from the burning of ethanol produced from crops?” Students might not realize that the carbon in fossil fuels was removed from the atmosphere hundreds of millions of years ago, while the carbon in crops was removed much more recently, when the crops were grown. The use of ethanol as an alternative is complicated by the typical reliance upon fossil fuels for ethanol production.
2. Students may confuse global warming with the breakdown of the ozone layer. Be prepared to explain both phenomena and the impact of human activities.
Teaching Tips
Some students might better relate the greenhouse effect to what happens inside their closed car on a sunny day. The glass in our automobiles functions like the glass of a greenhouse, trapping heat inside our car. This can be an advantage during the winter but is usually not welcome on a hot summer day! 54

55. CONNECTION: Photosynthesis may moderate global climate change
The gases in the atmosphere that absorb heat radiation are called greenhouse gases. These include
water vapor,
carbon dioxide
and methane.
Student Misconceptions and Concerns
1. Students often do not fully understand how the burning of fossil fuels contributes to global warming. They might wonder, “How does the burning of fossil fuels differ from the burning of ethanol produced from crops?” Students might not realize that the carbon in fossil fuels was removed from the atmosphere hundreds of millions of years ago, while the carbon in crops was removed much more recently, when the crops were grown. The use of ethanol as an alternative is complicated by the typical reliance upon fossil fuels for ethanol production.
2. Students may confuse global warming with the breakdown of the ozone layer. Be prepared to explain both phenomena and the impact of human activities.
Teaching Tips
Some students might better relate the greenhouse effect to what happens inside their closed car on a sunny day. The glass in our automobiles functions like the glass of a greenhouse, trapping heat inside our car. This can be an advantage during the winter but is usually not welcome on a hot summer day! 55

56. CONNECTION: Photosynthesis may moderate global climate change
Increasing concentrations of greenhouse gases have been linked to global climate change (also called global warming), a slow but steady rise in Earth’s surface temperature.
Since 1850, the atmospheric concentration of CO2 has increased by about 40%, mostly due to the combustion of fossil fuels including
coal,
oil, and
gasoline.
Student Misconceptions and Concerns
1. Students often do not fully understand how the burning of fossil fuels contributes to global warming. They might wonder, “How does the burning of fossil fuels differ from the burning of ethanol produced from crops?” Students might not realize that the carbon in fossil fuels was removed from the atmosphere hundreds of millions of years ago, while the carbon in crops was removed much more recently, when the crops were grown. The use of ethanol as an alternative is complicated by the typical reliance upon fossil fuels for ethanol production.
2. Students may confuse global warming with the breakdown of the ozone layer. Be prepared to explain both phenomena and the impact of human activities.
Teaching Tips
Some students might better relate the greenhouse effect to what happens inside their closed car on a sunny day. The glass in our automobiles functions like the glass of a greenhouse, trapping heat inside our car. This can be an advantage during the winter but is usually not welcome on a hot summer day! 56

57. CONNECTION: Photosynthesis may moderate global climate change
Some predicted consequences of continued warming include
melting of polar ice,
rising sea levels,
extreme weather patterns,
droughts,
increased extinction rates, and
the spread of tropical diseases.
Student Misconceptions and Concerns
1. Students often do not fully understand how the burning of fossil fuels contributes to global warming. They might wonder, “How does the burning of fossil fuels differ from the burning of ethanol produced from crops?” Students might not realize that the carbon in fossil fuels was removed from the atmosphere hundreds of millions of years ago, while the carbon in crops was removed much more recently, when the crops were grown. The use of ethanol as an alternative is complicated by the typical reliance upon fossil fuels for ethanol production.
2. Students may confuse global warming with the breakdown of the ozone layer. Be prepared to explain both phenomena and the impact of human activities.
Teaching Tips
Some students might better relate the greenhouse effect to what happens inside their closed car on a sunny day. The glass in our automobiles functions like the glass of a greenhouse, trapping heat inside our car. This can be an advantage during the winter but is usually not welcome on a hot summer day! 57

58. CONNECTION: Photosynthesis may moderate global climate change
Widespread deforestation has aggravated the global warming problem by reducing an effective CO2 sink.
Global warming caused by increasing CO2 levels may be reduced by
limiting deforestation,
reducing fossil fuel consumption, and
growing biofuel crops that remove CO2 from the atmosphere.
Student Misconceptions and Concerns
1. Students often do not fully understand how the burning of fossil fuels contributes to global warming. They might wonder, “How does the burning of fossil fuels differ from the burning of ethanol produced from crops?” Students might not realize that the carbon in fossil fuels was removed from the atmosphere hundreds of millions of years ago, while the carbon in crops was removed much more recently, when the crops were grown. The use of ethanol as an alternative is complicated by the typical reliance upon fossil fuels for ethanol production.
2. Students may confuse global warming with the breakdown of the ozone layer. Be prepared to explain both phenomena and the impact of human activities.
Teaching Tips
Some students might better relate the greenhouse effect to what happens inside their closed car on a sunny day. The glass in our automobiles functions like the glass of a greenhouse, trapping heat inside our car. This can be an advantage during the winter but is usually not welcome on a hot summer day! 58

59. SCIENTIFIC DISCOVERY: Scientific study of Earth’s ozone layer has global significance
Solar radiation converts O2 high in the atmosphere to ozone (O3), which shields organisms from damaging UV radiation.
Industrial chemicals called CFCs (chlorofluorcarbons) have caused dangerous thinning of the ozone layer, but international restrictions on CFC use are allowing a slow recovery.
Student Misconceptions and Concerns
Students may confuse global warming with the breakdown of the ozone layer. Be prepared to explain both phenomena and the impact of human activities.
Teaching Tips
1. Consider an analogy between the ozone layer and sunscreen applied to the skin. The thinning of the ozone layer is like putting on less and less sunscreen. In both situations, more harmful UV light penetrates the layers and causes damage.
2. Frustration can overwhelm concerned students alarmed by the many problems addressed in this chapter. One way to address this is to provide meaningful ways for students to respond to this information (for example, changes in personal choices and voting). The Earth Day Network, is just one of many Internet sites devoted to positive action.
Ozone hole 59

60. Animations for Review (click on the links):
Calvin Cycle animation
Cyclic and Non-Cyclic Photophosphorylation- step by step
C4 and CAM photosynthesis
ALSO read CliffsNotes Chapter 5

61. You should now be able to
Define autotrophs, producers, and photoautotrophs.
Describe the structure of chloroplasts and their location in a leaf.
Explain how plants produce oxygen.
Describe the role of redox reactions in photosynthesis and cellular respiration.
Compare the reactants and products of the light reactions and the Calvin cycle. 61

62. You should now be able to
Describe the properties and functions of the different photosynthetic pigments.
Explain how photosystems capture solar energy.
Explain how the electron transport chain and chemiosmosis generate ATP, NADPH, and oxygen in the light reactions.
Compare photophosphorylation and oxidative phosphorylation.
Describe the reactants and products of the Calvin cycle. 62

63. You should now be able to
Compare the mechanisms that C3, C4, and CAM plants use to obtain and use carbon dioxide.
Review the overall process of the light reactions and the Calvin cycle, noting the products, reactants, and locations of every major step.
Describe the greenhouse effect.
Explain how the ozone layer forms, how human activities have damaged it, and the consequences of the destruction of the ozone layer. 63