1. Where It Starts – Photosynthesis
Chapter 6
Where It Starts – Photosynthesis

2. 6.1 How Do Photosynthesizers Absorb Light?
Energy flow through ecosystems begins when photosynthesizers intercept sunlight
Autotrophs are producers
Make food using energy from environment and carbon from inorganic molecules
Heterotrophs are consumers
Obtain carbon from organic compounds assembled by other organisms
Insert label and caption for any figures here.

3. ultraviolet radiation near-infrared radiation
Properties of Light
visible light
gamma rays
x-rays
ultraviolet radiation
near-infrared radiation
infrared radiation
microwaves
radio waves
shortest wavelengths (highest energy)
longest wavelengths (lowest energy)
Figure 6.1 – Properties of light.
400 nm
500 nm
600 nm
700 nm A B

4. Capturing a Rainbow
Photosynthesizers use pigments to capture light of specific wavelengths
Chlorophyll α: most common photosynthetic pigment in plants and protists
Absorbs violet, red, and orange light
Reflects green light (appears as green)
Accessory pigments harvest additional light wavelengths

5. 6.2 Why Do Cells Use More Than One Photosynthetic Pigment?
In 1882, Theodor Engelmann tested the hypothesis that the color of light affects the rate of photosynthesis
Used motile, oxygen-requiring bacteria to identify where photosynthesis was taking place
Directed a spectrum of light across individual strands of green algae

6. Why Do Cells Use More Than One Photosynthetic Pigment?
In Engelmann’s experiment, oxygen- requiring bacteria gathered where blue and red light fell across the algal cells
Conclusion:
Blue and red light are best light for driving photosynthesis in these algal cells

7. Why Do Cells Use More Than One Photosynthetic Pigment?
phycoerythrobilin
phycocyanobilin
chlorophyll b
chlorophyll a
bacteria
β-carotene
algae
Figure {Animated} Discovery that photosynthesis is driven best by particular wavelengths of visible light.
400nm
500nm
600nm
700nm
400nm
500nm
600nm
700nm
Wavelength B C

8. Why Do Cells Use More Than One Photosynthetic Pigment?
The combination of pigments used for photosynthesis differs among species
Photosynthetic species are adapted to the environment in which they evolved
Light that reaches different environments varies in its proportions of wavelengths

9. 6.3 What Happens During Photosynthesis?
Photosynthesis converts the energy of light into the energy of chemical bonds
Unlike light, chemical energy can power the reactions of life, and it can be stored for use at a later time

10. What Happens During Photosynthesis?
In eukaryotes, photosynthesis takes place in chloroplasts
Thylakoid membrane: a chloroplast’s continuous highly folded inner membrane system
Stroma: cytoplasm-like fluid between the thylakoid membrane and the two outer membranes of a chloroplast

11. What Happens During Photosynthesis?
Photosynthesis is often summarized as:
CO2 + water sugars + O2
light energy

12. Adaptations to Climate
Stomata are tiny gateways for gases
Open stomata:
Allow CO2 to diffuse from the air into photosynthetic tissues
Allow O2 to diffuse out of these tissues into the air
Closed stomata:
Conserve water on hot, dry days
Limit the availability of CO2 for the light- independent reactions; sugar synthesis slows

14. 6.6 Application: Green Energy
With fossil fuel prices soaring, there is an increasing demand for biofuels:
Oils, gases, or alcohols made from organic matter that is not fossilized
Most materials we use for biofuel production today consist of food crops:
Mainly corn, soybeans, and sugarcane

15. Application: Green Energy
Fossil fuels:
Petroleum, coal, and natural gas
Formed from the remains of ancient swamp forests that decayed and compacted over millions of years
Consist of molecules originally assembled by ancient plants
“Non-renewable”

16. Application: Green Energy
The process of using fossil fuels or biofuels are fundamentally the same:
Release energy by breaking the bonds of organic molecules
Use oxygen to break those bonds
Produce carbon dioxide

17. Application: Green Energy
Biofuels are a renewable source of energy
Growing more plants creates more sources of biofuels

18. Application: Green Energy
Biofuels do not contribute to global climate change
Growing plant matter for fuel recycles carbon that is already in the atmosphere

19. Application: Green Energy
Corn and other food crops are rich in oils, starches, and sugars that can be easily converted to biofuels
Starch from corn kernels can be broken down to glucose, which is converted to ethanol by bacteria or yeast

20. Application: Green Energy
Making biofuels from some plants require additional steps, because these materials contain a higher proportion of cellulose
Researchers are currently working on cost- effective ways to break down the abundant cellulose in fast-growing weeds

21. Application: Green Energy
Figure Switchgrass growing wild in a North American prairie.

22. Application: Green Energy
According to tropical forest scientist Willie Smits, the Arenga sugar palm has the potential to serve as the core of a waste- free system
Produces premium organic sugar and ethanol for fuel
Provides food products and jobs to villagers
Helps preserve the existing native rain forest

23. How Cells Release Chemical Energy
Chapter 7
How Cells Release Chemical Energy

24. 7.1 How Do Cells Access the Chemical Energy in Sugars?
In order to use the energy stored in sugars, cells must first transfer it to ATP
The energy transfer occurs when the bonds of a sugar’s carbon backbone are broken, driving ATP synthesis
Chemical Energy Usable Energy

25. How Do Cells Access the Chemical Energy in Sugars?
There are two main mechanisms by which organisms break down sugars to make ATP:
Aerobic respiration
Fermentation (anaerobic respiration)

26. Aerobic Respiration and Fermentation Compared
Aerobic respiration: requires oxygen to break down sugars to make ATP
Main energy-releasing pathway in nearly all eukaryotes and some bacteria

27. Aerobic Respiration and Fermentation Compared
The three stages of aerobic respiration produce thirty-six ATP:
Glycolysis
Occurs in the cytoplasm; net yield is two ATP
Krebs cycle
Occurs in the mitochondria; net yield is two ATP
Electron transfer phosphorylation
Occurs in the mitochondria; net yield is thirty-two ATP

28. Aerobic Respiration and Fermentation Compared
Fermentation: sugar breakdown pathway that does not require oxygen to make ATP
Like aerobic respiration, fermentation begins with glycolysis in cytoplasm
Unlike aerobic respiration, fermentation occurs entirely in cytoplasm, and does not include electron transfer chains
Net yield is two ATP, which provides enough ATP to sustain many single-celled species

29. How Did Energy-Releasing Pathways Evolve?

30. What Is Fermentation? Two fermentation pathways:
Alcoholic fermentation: anaerobic sugar breakdown pathway that produces ATP, CO2, and ethanol
Lactate fermentation: anaerobic sugar breakdown pathway that produces ATP and lactate

31. Alcoholic Fermentation
Alcoholic fermentation in a fungus, Saccharomyces cerevisiae, sustains these yeast cells as they grow and reproduce
Used to produce beer, wine, and bread

32. Lactate Fermentation
Animal muscle cells carry out aerobic respiration and/or lactate fermentation
Red muscle fibers: many mitochondria and myoglobin; produce ATP mainly by aerobic respiration
Sustains prolonged activity
White muscle fibers: contain few mitochondria and no myoglobin; most ATP produced by lactate fermentation
Useful for quick, strenuous activities

33. Lactate Fermentation B
Figure 7.8 Lactate fermentation. C

34. 7.7 Can the Body Use Any Organic Molecule for Energy?
Energy from dietary molecules
Aerobic respiration generates a lot of ATP by fully oxidizing glucose, completely dismantling it carbon by carbon
Cells also dismantle other organic molecules by oxidizing them
Complex carbohydrates, fats, and proteins in food can be converted to molecules that enter glycolysis or the Krebs cycle

35. Complex Carbohydrates
Starches and other complex carbohydrates are broken down into monosaccharides
Sugars are converted to glucose-6- phosphate for glycolysis
A high concentration of ATP causes glucose- 6-phosphate to be diverted away from glycolysis and into the formation of glycogen stores

36. Fats
Fats are dismantled by first breaking the bonds that connect the fatty acid tails to the glycerol head
Free fatty acids are oxidized by splitting their backbones into two-carbon fragments
These fragments are converted to acetyl– CoA, which can enter the Krebs cycle
Glycerol gets converted to PGAL, an intermediate of glycolysis

37. Proteins Dietary proteins are split into their amino acid subunits
Ammonia (NH3), formed as a waste product, is eliminated in urine
The carbon backbone is split, and acetyl– CoA, pyruvate, or an intermediate of the Krebs cycle forms
These molecules enter aerobic respiration’s second stage

38. 7.7 Can the Body Use Any Organic Molecule for Energy? (cont’d.)
Food
a triglyceride (fat)
glycerol head
Fats
Complex Carbohydrates
Proteins
fatty acids
glycerol
glucose, other simple sugars
amino acids 2 3 1 4
acetyl–CoA
PGAL
acetyl–CoA
fatty acid tails
NADH
pyruvate
intermediate
of Krebs cycle
Figure 7.9 {Animated} A variety of organic compounds from food can enter the reactions of aerobic respiration.
NADH, FADH2

39. Photosynthesis =
Light Energy Chemical Energy
Cell Respiration =
Chemical Energy Usable Energy

40. In the setup shown below, which color light will cause the plant to
produce the smallest number of gas bubbles?
A) red
B) orange
C) blue
D) green

41. In the setup shown below, which color light will cause the plant to
produce the smallest number of gas bubbles?
A) red
B) orange
C) blue
D) green

42. An investigation was carried out and the results are shown below.
Substance X resulted from a metabolic process that produces ATP in yeast (a single-celled fungus).
Which statement best describes substance X?
A) It is oxygen released by protein synthesis.
B) It is glucose that was produced in photosynthesis.
C) It is starch that was produced during digestion.
D) It is carbon dioxide released by respiration.

43. An investigation was carried out and the results are shown below.
Substance X resulted from a metabolic process that produces ATP in yeast (a single-celled fungus).
Which statement best describes substance X?
A) It is oxygen released by protein synthesis.
B) It is glucose that was produced in photosynthesis.
C) It is starch that was produced during digestion.
D) It is carbon dioxide released by respiration.

44. The diagram represents a system in a space station that includes a tank containing algae. An astronaut from a spaceship boards the space station.
A- State two changes in the chemical composition of the space station atmosphere that would result from turning on more lights.
B- State two changes in the chemical composition of the space station atmosphere as a result of the astronaut coming on board the space station.
C- Identify one process being controlled in the setup shown in the diagram.

45. The diagram represents a system in a space station that includes a tank containing algae. An astronaut from a spaceship boards the space station.
A- State two changes in the chemical composition of the space station atmosphere that would result from turning on more lights.
Less CO2 / More O2
B- State two changes in the chemical composition of the space station atmosphere as a result of the astronaut coming on board the space station.
Less O2 / More CO2 / More water vapor
C- Identify one process being controlled in the setup shown in the diagram.
Photosynthesis