1. Photosynthesis and Cellular Respiration
Chapter 5
Photosynthesis and Cellular Respiration

2. I. Energy in Living Systems
Directly or indirectly, almost all of the energy in living systems needed for metabolism comes from the sun
Building molecules that store energy
Metabolism can help organisms use energy to build molecules
Photosynthesis is the process by which light energy is converted to chemical energy

3. Autotrophs use energy from sunlight or from chemical bonds in inorganic substances to make organic compounds

4. B. Breaking down food for energy
Metabolism can also help organisms break down molecules in which energy is stored
Chemical energy in organic compounds can be transferred to other organic compounds or to organisms that consume food

5. Heterotrophs must get energy from food such as plants or other heterotrophs
Heterotrophs obtain energy from food through a process called cellular respiration
- cellular respiration releases energy from food to make ATP
- ATP provides cells with the energy they need to carry out the activities of life

6. C. Transfer of Energy to ATP
Chemical energy stored in food molecules is released gradually in a series of enzyme – assisted chemical reactions
When cells break down food molecules, some of the energy in the molecules is released as heat
The remaining energy is stored temporarily in molecules of ATP
ATP delivers energy wherever energy is needed in a cell
- enough energy is released from ATP to drive most of a cell’s activities

7. II. ATP
Adenosine triphosphate is a nucleotide with two extra energy-storing phosphate groups
The three phosphate groups form a chain, or phosphate “tail,” that branches from a five-carbon sugar called ribose and a base called adenosine

8. Cells use the energy released to power metabolism
The phosphate “tail” is unstable because the phosphate groups are negatively charged and repel each other
These phosphate groups store energy which is released when the bonds between the groups are broken
Breaking the outer phosphate group off requires an input of energy but releases more energy
ATP  ADP + P + energy
Cells use the energy released to power metabolism
Directed Reading p. 1

9. III. Photosynthesis
Photosynthesis occurs in the chloroplasts of plant cells and algae and in the cell membrane of certain prokaryotes

10. The equation for photosynthesis can be summarized as:
6 CO2 + 6H2O C6H12O6 + 6O2
- 6 carbon dioxide molecules, 6 water molecules, and light are needed to form one 6-carbon sugar and 6 molecules of oxygen

11. Some of the sugar molecules are used to form starch, which can be stored in stems or roots
Other sugar molecules are used to form proteins, nucleic acids, and other molecules

12. Stage One: Absorption of Light Energy
Light energy is used to make energy-storing compounds
Light is a form of radiation, or energy in the form of waves that travel through space
Radiation you can see is known as visible light and contains a mixture of wavelengths, or colors

13. Pigments
Pigments are light-absorbing substances that allow leaves or human eyes to absorb light
Pigments absorb only certain wavelengths, or colors, and reflect all the others
Chlorophyll in plants absorb blue and red light and reflect green and yellow light
Sunlight
Reflected
Light

14. Plants contain two types of chlorophyll, chlorophyll a and chlorophyll b, that are both used in plant photosynthesis
Carotenoids absorb wavelengths different from those absorbed from chlorophyll
- green light is also absorbed, allowing yellow and orange light to be reflected in the fall

15. 2. Production of Oxygen
Chlorophyll is embedded in the membranes of thylakoids which are structures found in the chloroplasts of leaf cells
When light strikes a thylakoid, energy is transferred to electrons in chlorophyll
These electrons with extra energy are said to be “excited”
Excited electrons jump from the thylakoid membrane to power the second stage of photosynthesis

16. The plant must replace the electrons that left by splitting water molecules
- when water molecules split, chlorophyll molecules take the electrons from the hydrogen atoms, H+
- the remaining oxygen atoms, O, combine to form oxygen gas, O2
2H2O  4e- + 4H+ +O2

18. B. Stage Two: Conversion of Light Energy
Excited electrons that leave chlorophyll molecules are used to produce new molecules, such as ATP, that temporarily store chemical energy
Electron Transport Chains
The processes of electrons being passed through a series of molecules along the thylakoid membrane to produce molecules such as ATP and NADPH

19. The first electron transport chain involves the excited electron passing through a protein
- the electron loses energy as it passes through this protein
- the energy lost by the electron is used to pump hydrogen ions, H+, into the thylakoid

21. As hydrogen ions become more concentrated inside the thylakoid, a concentration gradient is produced
- as hydrogen ions build up, they diffuse back out of the thylakoid down their concentration gradient through specialized carrier proteins
- these carrier proteins use energy of hydrogen ion movement to catalyze a reaction in which a phosphate group is added to ADP to make ATP

23. b. A second electron transport chain involves the excited electron combining with hydrogen ions and an electron acceptor called NADP+
This forms NADPH, an electron carrier that provides the high-energy electrons, needed to make carbon-hydrogen bonds in the third stage of photosynthesis

25. C. Stage Three: Storage of Energy
Carbon atoms from carbon dioxide (CO2) in the atmosphere are used to make organic compounds in which chemical energy is stored
- the transfer of carbon dioxide to organic compounds is called carbon dioxide fixation
- these are light independent reactions

26. Calvin Cycle
A series of enzyme-assisted chemical reactions that produces organic compounds
A common method of carbon dioxide fixation
These organic compounds provide the organism with energy for growth and metabolism
The energy used in the cycle is supplied by ATP and NADPH made during the second stage of photosynthesis

27. a. A carbon dioxide (CO2) molecule is added to a five-carbon compound by an enzyme

28. b. The resulting six-carbon compound splits into 2 three-carbon compounds - phosphate groups from ATP and electrons from NADPH are added to the three-carbon compounds - results in 2 three-carbon sugars

29. 2

30. 2
c. 1 of the three-carbon sugars is used to make organic compounds - i.e. starch and sucrose - stores energy for later use

31. d. The other three-carbon sugars are used to regenerate five-carbon compounds to begin the cycle again 2

32. IV. Factors that Affect Photosynthesis
The rate of photosynthesis increases as light intensity increases until all of the pigments are being used
The rate of photosynthesis also increases with increased concentrations of carbon dioxide (CO2)
Photosynthesis is most efficient within a certain range of temperatures
- unfavorable temperatures may inactivate certain enzymes
Directed Reading p. 3

33. V. Cellular Respiration
A process used by cells to transfer the energy in organic compounds such as glucose, to ATP
Oxygen in the air makes this process more efficient
- metabolic processes that require oxygen are called aerobic
- metabolic processes that do not require oxygen are anaerobic, or “without air”

34. Cellular respiration can be summarized by the equation:
C6H12O6 + 6O CO2 + 6H2O + energy
1 glucose molecule and 6 oxygen gas molecules are needed to form 6 molecules of carbon dioxide, 6 molecules of water, and energy in the form of ATP
enzymes

35. Connection Between Photosynthesis and Cellular Respiration
6CO2 + 6H20 + Light energy  C6H12O6 + 6O2
Carbon Water Glucose Oxygen dioxide
2. Cellular Respiration
C6H12O6 + 6O2  6CO2 + 6H2O + energy (ATP)
Glucose Oxygen Carbon Water
dioxide
Each process makes the materials that are needed for the other process to occur

36. Stage One: Breakdown of Glucose
Glucose is formed when carbohydrates such as starch and sucrose (products from photosynthesis) are broken down
Glucose enters the first stage of cellular respiration called glycolysis

37. Glycolysis
Takes place in the cell’s cytoplasm
1 six-carbon molecule of glucose is broken down to 2 three-carbon pyruvate ions
2 NADH molecules are produced
2 ATP molecules are used to produce 4 ATP (net gain of 2 ATP)

38. a. phosphate groups from 2 ATP molecules are transferred to a glucose molecule

39. b. Glucose is broken down to 2 three-carbon compounds, each with a phosphate group

40. c. Hydrogen atoms from glucose are transferred to an electron acceptor called NAD+, forming 2 NADH electron carriers
1 more phosphate group is transferred to each three-carbon compound

41. 2 pyruvate ions are formed
d. The 2 three-carbon compounds give up both of their phosphate groups to 4 ADP molecules
2 pyruvate ions are formed
4 ATP molecules are produced (2 net ATP molecules)

42. B. Stage Two: Production of ATP
Pyruvate produced during glycolysis enters a mitochondrion
1 carbon dioxide (CO2) molecule, 1 NADH molecule, and 1 two-carbon compound called acetyl-CoA is formed

43. Krebs Cycle
3 NADH molecules, 1 FADH2 molecule, and 1 ATP molecule are formed in a cyclic process

44. a. The two-carbon compound acetyl-CoA combines with a four-carbon compound and releases coenzyme A (CoA)

45. b. Carbon dioxide, CO2, is released from the six-carbon compound and electrons are transferred to NAD+ forming NADH
1 NADH

46. c. Carbon dioxide, CO2, is released from the five-carbon compound and an electron is given to NAD+ forming NADH
1 molecule of ATP is also formed
2 NADH
1 ATP

47. d. Electrons from the four-carbon compound are transferred to an electron acceptor called FAD, forming the electron carrier FADH2
2 NADH
1 ATP
1 FADH2

48. e. The new four-carbon compound is converted to the four-carbon compound that began the cycle while 1 molecule of NADH is produced
3 NADH
1 ATP
1 FADH2

49. 2. Electron Transport Chain
Located in the inner membranes of mitochondria in eukaryotic cells

50. a. NADH and FADH2 made by the Krebs Cycle donate electrons to pump hydrogen ions out of the inner mitochondrial compartment

51. b. As hydrogen ions accumulate in the outer compartment, they diffuse down their concentration gradient back into the inner mitochondrial compartment through a carrier protein

52. c. As hydrogen ions move through the protein, phosphate groups are added to ADP making ATP
34 ATP molecules are produced during the electron transport chain

53. d. At the end of the electron transport chain, hydrogen ions and used electrons combine with oxygen gas, O2, forming water molecules, H2O

54. VI. Fermentation in the Absence of Oxygen
The electron transport chain does not function because oxygen is not available to accept electrons or hydrogen ions at the end of the chain
NADH does not donate electrons to pump hydrogen ions out of the mitochondria in the electron transport chain

55. The recycling of NAD+ is called fermentation
NADH instead transfers an electron to pyruvate produced during glycolysis
- This process regenerates a NAD+ electron acceptor needed for the breakdown of glucose and further production of ATP
The recycling of NAD+ is called fermentation
*Remember there
is a net gain of
2 ATP molecules
made in Glycolysis

56. Lactic Acid Fermentation
Pyruvate accepts an electron from NADH
- pyruvate is converted to a three-carbon lactate
- NADH become NAD+
Pyruvate in muscles is converted to lactate during vigorous exercise when oxygen is not available
This fermentation process can continue as long as the glucose (sugar) supply lasts
Blood removes excess lactate from muscles
- if too much lactate builds up in muscles, you experience muscle soreness

57. B. Alcoholic Fermentation
Used in preparation of many foods and beverages
Pyruvate is converted to a two-carbon compound releasing carbon dioxide (CO2)
The two-carbon compound accepts an electron from NADH which becomes NAD+
The two-carbon compound is converted to the two-carbon compound called ethanol

59. VII. Production of ATP
The total amount of ATP that a cell is able to harvest from each glucose molecule that enters glycolysis depends on the presence or absence of oxygen

60. Glycolysis (First Stage of Cellular Respiration)
Anaerobic process that happens in all cells
Net gain of 2 ATP molecules

61. B. Second Stage of Cellular Respiration
1. Aerobic respiration
Oxygen must be present
Net gain of 2 ATP molecules during Krebs cycle
Net gain of 34 ATP molecules during electron transport chain

62. 2. Anaerobic Fermentation Oxygen is not present
No Krebs Cycle or electron transport chain
NADH is converted to NAD+ for every pyruvate ion made by glycolysis so that the cycle can continue
Directed Reading p. 5
Concept Mapping p. 17