presentation spring 2021

1. Energy of Life - Photosynthesis

2. Review
• Describe the energy transfers that are common to life.
• Describe how cells use energy to do work.
• Compare and contrast potential and kinetic energy.
• Explain how physical laws constrain energy use in organisms.
• Compare and contrast exergonic and endergonic reactions.
• Explain how oxidation and reduction reactions are linked.
• Explain how ATP is used in coupled reactions.

3. Energy Has Different Forms
Section 4.1 Figure 4.1
High potential energy
High kinetic energy

5. Thermodynamics
1st Law
• Energy can neither be
created nor destroyed.
• (always present in some
form)
2nd Law
• Conversion of energy is
not 100% efficient
• (some energy converted
to heat rather than
“work”)

6. Sunlight
(kinetic
energy)
Heat
energy
Potential
energy
Chemical energy
(potential energy)
available for
cellular tasks
Heat
energy
Cellular
respiration Sugar
Photosynthesis
H2O
CO2
O2
Figure 4.2

7. Chemical Reactions Sustain Life
Section 4.2 Figure 4.4
Endergonic (energy
requiring) reaction:
photosynthesis
Exergonic (energy
releasing) reaction:
cellular respiration

8. Section 4.2 Figure 4.5
Most energy transformations in organisms occur in
oxidation-reduction reactions.
Oxidation is the loss of electrons from an atom or molecule;
these reactions release energy.

9. Chemical Reactions Sustain Life
Section 4.2 Figure 4.5
Reduction is the gain of electrons (and whatever energy is
contained in the electrons) by an atom or molecule.
These reactions require energy.

10. ATP Is the Cellular Energy Currency
Section 4.3 Figure 4.7
All cells rely on the potential energy stored in ATP to power
chemical reactions.
Bond with high
potential energy

11. ATP Is the Cellular Energy Currency
Section 4.3 Figure 4.8
Removing the endmost phosphate group by hydrolysis
releases the potential energy stored in ATP.
The cell uses this energy to do work.

12. ATP Is the Cellular Energy Currency
Section 4.3 Figure 4.9
ATP must then be reformed. Mitochondria release energy
from food, producing ATP from ADP.

13. ATP Is the Cellular Energy Currency
Section 4.3
ATP formation is coupled with exergonic reactions.
ATP breakdown is coupled with endergonic reactions.
Producing ATP
“Spending” ATP

14. ATP Hydrolysis Is Coupled with
Endergonic Reactions
Section 4.3 Figure 4.10
Phosphorylation

15. ATP Hydrolysis Is Coupled with
Energy-Requiring Reactions
Section 4.3 Figure 4.10

16. The Big Picture
Photosynthesis
1. “Photo” reactions
2. “Synthesis” reactions
Equation:
Cellular Respiration
1. Glycolysis
2. Acetyl-CoA production
3. Krebs Cycle
4. Electron Transport Chain
Equation:

18. Learning Outcomes
Photosynthesis
• Predict the effects of various factors on the rate of photosynthesis, e.g.
– light intensity
– color of light
– temperature
– pH (concentration of hydrogen ions)
– presence of inhibitors
• Describe the function of photosynthesis
• Describe the structures in a leaf that are involved in photosynthesis
• Describe the components of the chloroplast and their roles in photosynthesis
• Describe the components of the light-dependent & light-independent portions
of photosynthesis
• Identify the reactants (chemical inputs) and products (chemical outputs) of the
light-dependent & light-independent portions of photosynthesis
• Describe how to measure photosynthesis in various ways
• Explain how the light-dependent & light-independent portions of
photosynthesis work, how they are linked, and their similarities to cellular
respiration

21. Photosynthesis Occurs in the Chloroplasts
Gas exchange occurs at leaf pores called stomata.
Leaves ©Steve Raymer/National Geographic Stock
+ H2O
CO2 O2
Mesophyll
cells
Stoma
Section 5.2 Figure 5.5

24. Photosynthesis Occurs in the Chloroplasts
Section 5.2 Figure 5.5
15 µm
Mesophyll cell
Chloroplasts
Central
vacuole
Pigment molecules in the thylakoid membrane capture sunlight.
DNA
Outer
membrane
Inner
membrane
Granum
Stroma
Ribosomes
Chloroplast
Granum
Pigment molecules
embedded in
thylakoid membrane
Thylakoid
Thylakoid
space
Electron micrograph by Wm. P. Wergin, courtesy of Eldon H. Newcomb, University of Wisconsin-Madison.

25. Photosynthesis Occurs in the Chloroplasts
Section 5.2 Figure 5.6
A photosystem consists of antenna pigments and a reaction center that
contains chlorophyll.

27. Pigments

28. Why do leaves appear green?

29. The Sun Emits a Spectrum of Wavelengths
Section 5.2 Figure 5.3
Photons are packets of light energy. Plants capture
photons of visible light.
Wavelength
in
nanometers
Violet
Blue
Cyan
Green
Yellow
Orange
Red
Long wavelength (low energy)
Portion of
spectrum
that
reaches
Earth's
surface Wavelength
Visible light
Short wavelength (high energy)
Radio waves
Microwaves
Infrared
radiation
Ultraviolet
radiation
X-rays
Gamma rays
400
750
700
650
600
550
500
450

30. Light Energy

31. Photosynthetic Pigments Capture Sunlight
Section 5.2 Figure 5.4
No pigment
absorbs green
light.
0
Sunlight
Reflected
light
700
Wavelength of light (nanometers)
600
500
400
80
60
40
20
Chlorophyll a
Chlorophyll b
Carotenoids
Relative
absorption
(percent)

33. Sunlight + Water + Carbon dioxide = oxygen + sugar
Input Output

34. Photosynthesis Occurs in Two Stages
Section 5.3 Figure 5.7

35. 2 parts of Photosynthesis
• Photo Reactions
• Synthesis Reactions

36. The Light Reactions Begin Photosynthesis
Location:
Inputs:
Outputs:
Section 5.4 Figure 5.8

38. Section 5.4 Figure 5.8
The Light Reactions Begin Photosynthesis
The photosystems are part
of an electron transport
chain that converts light
energy into ATP and
NADPH.

39. Follow the
electrons!

45. Section 5.4 Figure 5.8
The Light Reactions Begin Photosynthesis

46. Section 5.4 Figure 5.A
The Light Reactions Begin Photosynthesis
Some chemicals, such as the weed killers
DCMU and Paraquat, block the light reactions.

47. Carbon Reactions Produce Carbohydrates
Section 5.5 Figure 5.9
Location:
Inputs:
Outputs:

49. Carbon Reactions Produce Carbohydrates
Section 5.5
Calvin Cycle
CO2
Figure 5.9

51. Glycolysis
2 Pyruvate
2
2
6
2
6 6
34
2
4
2
2 Acetyl CoA
Transition step
Krebs
cycle
Electron
transport
chain
Glucose
2
Cytosol
Mitochondrion
NADH
NADH
NADH
FADH2
ATP
ATP
ATP
CO2
CO2
H2O
O2
Recall that Cellular Respiration
began with a single glucose
molecule and yielded ~36 ATP.

52. Carbon Reactions Produce Carbohydrates
Section 5.6
Plants use glucose for
energy and to build
polysaccharides.
Glucose
Cellulose: © Dr. Dennis Kunkel; starch © Gary Gaugler/Visuals Unlimited

53. Plants Use Different Carbon Fixation
Pathways
Section 5.6 Figure 5.10
C3 plants, C4 plants,
and CAM plants all
use slightly different
carbon fixation
pathways.

55. Plants Use Different Carbon Fixation
Pathways
Figure 5.11
Tree: © Tony Sweet/Digital Vision/Getty Images RF; corn: © Joeseph Sohm-Visions of America/Getty Images RF; cactus: © Digital
Vision/Getty Images RF
Section 5.6

56. Plants Use Different Carbon Fixation
Pathways
Figure 5.11
Section 5.6
Tree: © Tony Sweet/Digital Vision/Getty Images RF; corn: © Joeseph Sohm-Visions of America/Getty Images RF; cactus: © Digital
Vision/Getty Images RF

57. Section 6.9
Photosynthesis and Respiration
Are Ancient Pathways
Figure 6.12
Both of these chemical
processes arose in
unicellular organisms over
3 billion years ago.

58. Section 6.9
Photosynthesis and Respiration
Are Related