1. Chapter 6- Energy

2. What Is Energy? Types of energy (Jumping Penguins or log in a hearth)
Kinetic: energy of movement
Potential: stored energy

3. What Is Energy? First Law of Thermodynamics
“Energy cannot be created nor destroyed, but it can change its form.”
Example: potential energy in gasoline can be converted to kinetic energy in a car, but the energy is not lost

4. What Is Energy? Second Law of Thermodynamics
“When energy is converted from one form to another, the amount of useful energy decreases.”
No process is 100% efficient.
Example: more potential energy is in the gasoline than is transferred to the kinetic energy of the car moving
Where is the rest of the energy? It is released in a less useful form as heat—the total energy is maintained.

5. What Is Energy?
Sunlight provides an unending supply of new energy to power all plant and animal reactions, leading to increased entropy.

6. How Does Energy Flow In Chemical Reactions?
Chemical reaction: the conversion of one set of chemical substances (reactants) into another (products)
Exergonic reaction: a reaction that releases energy; the products contain less energy than the reactants

7. How Does Energy Flow In Chemical Reactions?
Exergonic reaction
energy released +
reactants +
products
(a)
Exergonic reaction

8. How Does Energy Flow In Chemical Reactions?
Burning glucose releases energy.
energy released
C6H12O6 +
6 O2
(glucose)
(oxygen)
6 CO2 +
6 H2O
(carbon dioxide)
(water)

9. How Is Energy Carried Between Coupled Reactions?
Breakdown of ATP releases energy.
energy A P P P
ATP A P P + P
ADP
phosphate

10. How Does Energy Flow In Chemical Reactions?
Endergonic reaction: a reaction that requires energy input from an outside source; the products contain more energy than the reactants

11. How Does Energy Flow In Chemical Reactions?
Endergonic reaction
energy used +
products +
reactants
(b)
Endergonic reaction

12. How Does Energy Flow In Chemical Reactions?
Photosynthesis requires energy.
energy
C6H12O6 +
6 O2
(glucose)
(oxygen)
6 CO2 +
6 H2O
(carbon dioxide)
(water)

13. How Is Energy Carried Between Coupled Reactions?
ATP is made from ADP (adenosine diphosphate) and phosphate plus energy released from an exergonic reaction (e.g., glucose breakdown) in a cell.
energy A P P P
ATP A P P + P
ADP
phosphate

14. How Does Energy Flow in Chemical Reactions?
Exergonic reactions may be linked with endergonic reactions.
Endergonic reactions obtain energy from energy-releasing exergonic reactions in coupled reactions.
Example: the exergonic reaction of burning gasoline in a car provides the endergonic reaction of moving the car
Example: exergonic reactions in the sun release light energy used to drive endergonic sugar-making reactions in plants

15. How Is Energy Carried Between Coupled Reactions?
The job of transferring energy from one place in a cell to another is done by energy-carrier molecules.
ATP (adenosine triphosphate) is the main energy carrier molecule in cells, and provides energy for many endergonic reactions.

16. How Is Energy Carried Between Coupled Reactions?
ATP is the principal energy carrier in cells.
ATP stores energy in its phosphate bonds and carries the energy to various sites in the cell where energy-requiring reactions occur.
ATP’s phosphate bonds then break yielding ADP, phosphate, and energy.
This energy is then transferred to the energy-requiring reaction.

17. How Is Energy Carried Between Coupled Reactions?
Breakdown of ATP releases energy.
energy A P P P
ATP A P P + P
ADP
phosphate

18. How Is Energy Carried Between Coupled Reactions?
Electron carriers also transport energy within cells.
Besides ATP, other carrier molecules transport energy within a cell.
Electron carriers capture energetic electrons transferred by some exergonic reaction.
Energized electron carriers then donate these energy-containing electrons to endergonic reactions.

19. How Is Energy Carried Between Coupled Reactions?
Common electron carriers are NAD+ and FAD.
high-energy reactants
energized
NADH e– e–
high-energy products
depleted
NAD+ + H+
low-energy products
low-energy reactants

20. How Is Energy Carried Between Coupled Reactions?
A biological example of coupled reactions
Muscle contraction (an endergonic reaction) is powered by the exergonic breakdown of ATP.
During energy transfer in this coupled reaction, heat is given off, with overall loss of usable energy.

21. How Is Energy Carried Between Coupled Reactions?
To summarize:
Exergonic reactions (e.g., glucose breakdown) drive endergonic reactions (e.g., the conversion of ADP to ATP).
ATP moves to different parts of the cell and is broken down exergonically to liberate its energy to drive endergonic reactions.

22. How Does Energy Flow In Chemical Reactions?
All reactions require an initial input of energy.
The initial energy input to a chemical reaction is called the activation energy.
Activation energy needed to ignite glucose
Activation energy captured from sunlight
high
glucose
Energy level of reactants
glucose + O2
energy content of molecules
CO2 + H2O
CO2 + H2O
Energy level of reactants
low
progress of reaction
progress of reaction
(a)
Burning glucose (sugar): an exergonic reaction
(b)
Photosynthesis: an endergonic reaction
Fig. 5-6

23. How Do Cells Control Their Metabolic Reactions?
Catalysts reduce activation energy.
Catalysts are molecules that speed up a reaction without being used up or permanently altered.
They speed up the reaction by reducing the activation energy.
high
Activation energy without catalyst
Activation energy with catalyst
energy content of molecules
reactants
products
low
progress of reaction

24. How Do Cells Control Their Metabolic Reactions?
Three important principles about all catalysts
Catalysts speed up a reaction.
They speed up reactions that would occur anyway, if their activation energy could be surmounted.
Catalysts are not altered by the reaction.

25. How Do Cells Control Their Metabolic Reactions?
At body temperature, many spontaneous reactions proceed too slowly to sustain life.
A reaction can be controlled by controlling its activation energy (the energy needed to start the reaction).
At body temperature, reactions occur too slowly because their activation energies are too high.
Molecules called catalysts are able to gain access to energy that is not produced spontaneously.

26. How Do Cells Control Their Metabolic Reactions?
Enzymes are biological catalysts.
Almost all enzymes are proteins.
Enzymes are highly specialized, generally catalyzing only a single reaction.
In metabolic pathways involving multiple reactions, each reaction is catalyzed by a different enzyme.

27. How Do Cells Control Their Metabolic Reactions?
The structure of enzymes allows them to catalyze specific reactions.
Enzymes have an active site where the reactant molecules, called substrates, enter and undergo a chemical change as a result.
The specificity of an enzyme reaction is due to the distinctive shape of the active site, which only allows proper substrate molecules to enter.

28. How Do Cells Control Their Metabolic Reactions?
Enzyme structure
substrate
Many enzymes have both active sites and allosteric regulatory sites
active site
enzyme
allosteric regulatory site
(a)
Enzyme structure

29. Chapter 7-Photosynthesis

30. What Is Photosynthesis?
Life on earth depends on photosynthesis.
Photosynthesis is the capturing of sunlight energy and the conversion of it into chemical energy.
Before photosynthesis, there was little oxygen on Earth, and therefore, no organisms that used oxygen.

31. How Does Energy Flow In Chemical Reactions?
Photosynthesis requires energy.
energy
C6H12O6 +
6 O2
(glucose)
(oxygen)
6 CO2 +
6 H2O
(carbon dioxide)
(water)

32. What Is Photosynthesis?
Life on earth depends on photosynthesis (continued).
All present-day organisms that use oxygen as their respiratory gas depend upon photosynthesis to generate new oxygen.
Equally important to life is the energy captured by plants and stored as sugars, since virtually all life depends on this energy, either directly or indirectly.

33. What Is Photosynthesis?
Photosynthesis converts carbon dioxide and water to glucose.
The chemical reaction for photosynthesis:
6 CO2 + 6 H20 + light energy  C6H12O6 + 6 O2
Plants, seaweeds, and single-celled organisms all show the basic aspects of photosynthesis.

34. What Is Photosynthesis?
Plant photosynthesis takes place in leaves.
Leaves are the main location of photosynthesis.
Plants have thin leaves so sunlight can penetrate.
Plant leaves have a large surface area to expose them to the sun.
Plant leaves have pores to admit CO2, called stomata (singular, stoma).

35. What Is Photosynthesis?
Leaf cells contain chloroplasts.
Photosynthesis occurs in chloroplasts, in layers of cells called the mesophyll.
Chloroplasts contain a semifluid medium called stroma, which contains sacs called thylakoids within which photosynthesis occurs.

36. What Is Photosynthesis?
An overview of photosynthetic structures
mesophyll cells
(a)
Leaves
outer membrane
chloroplasts
inner membrane
vein
stoma
(b)
thylakoid
Internal leaf structure
stroma
(c)
Chloroplast in mesophyll cell

37. What Is Photosynthesis?
Photosynthesis consists of light-dependent and light-independent reactions.
These reactions occur at different locations in the chloroplast.
The two types of reactions are linked by the energy-carrier molecules adenosine triphosphatase (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH).

38. What Is Photosynthesis?
Light-dependent reactions
Occur in the membranes of the thylakoids
Light is captured here and stored in ATP and NADPH.
Water is consumed and oxygen is given off.

39. What Is Photosynthesis?
Light-independent reactions
Enzymes in the stroma use ATP and NADPH produced by light-dependent reactions to make glucose and other molecules.
Carbon dioxide is consumed in the process.
ATP and NADPH are converted to low-energy ADP and NADP+.
These low-energy molecules are re-charged to ATP and NADPH by returning to light-dependent reactions.

40. What Is Photosynthesis?
An overview of photosynthesis: light-dependent and light-independent reactions
LIGHT-DEPENDENT REACTIONS (thylakoids)
H2O O2
depleted carriers (ADP, NADP+)
energized carriers (ATP, NADPH)
LIGHT-INDEPENDENT REACTIONS (stroma)
CO2
glucose

41. How Is Light Energy Converted To Chemical Energy?
Light is first captured by pigments in chloroplasts.
Membranes of choroplast thylakoids contain several types of pigments (light-absorbing molecules).
Chlorophyll is one light-absorbing molecule that absorbs violet, blue, and red light, but reflects green.
Other accessory pigments include carotenoids, which absorb blue and green light, but reflect yellow and orange.

42. How Is Light Energy Converted To Chemical Energy?
Light, chloroplast pigments, and photosynthesis
Absorbance of photosynthetic pigments
100 80 60
carotenoids
light absorption (percent) 40
chlorophyll 20
Wavelength (nanometers)
400
450
500
550
600
650
700
750
Visible light
Gamma rays
X-rays UV
Infrared
Micro- waves
Radio waves

43. How Does the Need To Conserve Water Affect Photosynthesis?
Photosynthesis requires carbon dioxide; porous leaves would allow the entry of CO2, but would also result in the loss of H2O.
Evolution of the stomata resulted in pores that could open, letting in CO2, but also to close, to restrict H2O losses.
Closing stomata to prevent H2O loss also restricts the release of O2, produced by photosynthesis, to the atmosphere.

44. Chapter 8- Cellular Respiration

45. What Is The Source Of A Cell’s Energy?
The energy for cellular activities is stored until use in bonds of molecules such as carbohydrates and fats.
In order to be used, stored energy is transferred to the bonds of energy-carrier molecules such as adenosine triphosphate (ATP).
Glucose is a key energy-storage molecule, and energy stored in this molecule is harvested to power many biological processes in cells.

46. What Is The Source Of A Cell’s Energy?
Glucose metabolism and photosynthesis are complementary processes.
The products of each reaction provide reactants for the other.
The symmetry is apparent by comparing the equations that describe each process.
Photosynthesis:
6 CO2 + 6H2O + sunlight energy  C6H12O6 + 6 O2
Complete glucose metabolism:
C6H12O6 + 6O2  6 CO2 + 6 H20 + ATP + heat energy

47. How Does Energy Flow In Chemical Reactions?
Burning glucose releases energy.
energy released
C6H12O6 +
6 O2
(glucose)
(oxygen)
6 CO2 +
6 H2O
(carbon dioxide)
(water)

48. Electron transport chain
(cytoplasmic fluid)
glucose
Glycolysis 2
ATP 2 C C C 2 C C C
lactate
pyruvate or 2 C C + 2 C
Fermentation
ethanol
CO2
Cellular respiration C C
2 acetyl CoA 4 C
CO2 C
2 CO2
Krebs cycle 2
ATP
electron carriers
intermembrane compartment
H2O
Electron transport chain
32 or 34
ATP
(mitochondrion) O2

49. How Do Cells Harvest Energy From Glucose?
Glucose metabolism occurs in stages; the first stage is glycolysis.
Glycolysis occurs in the cytoplasm of cells.
Glucose (a six-carbon sugar) is split into two three-carbon pyruvate molecules.
The split releases a small amount of energy that is used to make two ATP molecules.

50. Electron transport chain
(cytoplasmic fluid)
glucose
Glycolysis 2
ATP 2 C C C 2 C C C
lactate
pyruvate or 2 C C + 2 C
Fermentation
ethanol
CO2
Cellular respiration C C
2 acetyl CoA 4 C
CO2 C
2 CO2
Krebs cycle 2
ATP
electron carriers
intermembrane compartment
H2O
Electron transport chain
32 or 34
ATP
(mitochondrion) O2

51. How Do Cells Harvest Energy From Glucose?
Pyruvate produced by glycolysis is further processed in the second stage, called cellular respiration.
Cellular respiration occurs in the mitochondria.
Cellular respiration breaks pyruvate down to CO2 and H20, yielding 34 or 36 ATP molecules.
Oxygen is needed for cellular respiration to proceed.

52. Electron transport chain
(cytoplasmic fluid)
glucose
Glycolysis 2
ATP 2 C C C 2 C C C
lactate
pyruvate or 2 C C + 2 C
Fermentation
ethanol
CO2
Cellular respiration C C
2 acetyl CoA 4 C
CO2 C
2 CO2
Krebs cycle 2
ATP
electron carriers
intermembrane compartment
H2O
Electron transport chain
32 or 34
ATP
(mitochondrion) O2

53. How Do Cells Harvest Energy From Glucose?
When oxygen is not available, the second stage of glucose metabolism is fermentation.
In the absence of oxygen, pyruvate remains in the cytoplasm.
Cytoplasmic pyruvate may be converted to lactate or ethanol by fermentation.
Fermentation does not produce additional ATP energy.

54. Electron transport chain
(cytoplasmic fluid)
glucose
Glycolysis 2
ATP 2 C C C 2 C C C
lactate
pyruvate or 2 C C + 2 C
Fermentation
ethanol
CO2
Cellular respiration C C
2 acetyl CoA 4 C
CO2 C
2 CO2
Krebs cycle 2
ATP
electron carriers
intermembrane compartment
H2O
Electron transport chain
32 or 34
ATP
(mitochondrion) O2
Fig. 7-1

55. What Happens During Fermentation?
There are two types of fermentation: one converts pyruvate to ethanol and CO2, and the other converts pyruvate to lactate.
Alcoholic fermentation is the primary mode of metabolism in many microorganisms.
The reactions use hydrogen ions and electrons from NADH, thereby regenerating NAD+.
Alcoholic fermentation is responsible for the production of many economic products, such as wine, beer, and bread.

56. What Happens During Fermentation?
Other cells ferment pyruvate to lactate, and include microorganisms that produce yogurt, sour cream, and cheese.
Lactate fermentation also occurs in aerobic organisms when cells are temporarily deprived of oxygen, such as muscle cells during vigorous exercise.
These muscle cells ferment pyruvate to lactate, which uses H+ and electrons from NADH to regenerate NAD+.

57. What Happens During Cellular Respiration?
The Krebs cycle breaks down pyruvate in the mitochondrial matrix.
Pyruvate produced by glycolysis reaches the matrix and reacts with coenzyme A, forming acetyl CoA.
During this reaction, two electrons and a H+ are transferred to NAD+ to form NADH.
Acetyl CoA enters the Krebs cycle and produces one ATP, one FADH2, and three NADH.

58. Electron transport chain
(cytoplasmic fluid)
glucose
Glycolysis 2
ATP 2 C C C 2 C C C
lactate
pyruvate or 2 C C + 2 C
Fermentation
ethanol
CO2
Cellular respiration C C
2 acetyl CoA 4 C
CO2 C
2 CO2
Krebs cycle 2
ATP
electron carriers
intermembrane compartment
H2O
Electron transport chain
32 or 34
ATP
(mitochondrion) O2

59. What Happens During Cellular Respiration?
Steps of cellular respiration
Step 1: Two molecules of pyruvate produced by glycolysis are transported into the matrix of a mitochondrion.
Step 2: Each pyruvate is split into CO2 and acetyl CoA, which enters the Krebs cycle.
The Krebs cycle produces one ATP from each pyruvate, and donates electrons to NADH and flavin adenine dinucleotide (FADH2).

60. What Happens During Cellular Respiration?
Steps of cellular respiration (continued)
Step 3: NADH and FADH2 donate energized electrons to the electron transport chain of the inner membrane.
Step 4: In the electron transport chain, electron energy is used to transport hydrogen ions (H+) from the matrix to the intermembrane compartment.
Step 5: Electrons combine with O2 and H+ to form H2O.

61. What Happens During Cellular Respiration?
Steps of cellular respiration (continued)
Step 6: Hydrogen ions in the intermembrane compartment diffuse across the inner membrane, down their concentration gradient.
Step 7: The flow of ions into the matrix provides the energy to produce ATP from ADP.
Step 8: ATP moves out of mitochondrion into the cytoplasm.

62. Electron transport chain
(cytoplasmic fluid)
glucose
Glycolysis 2
ATP 2 C C C 2 C C C
lactate
pyruvate or 2 C C + 2 C
Fermentation
ethanol
CO2
Cellular respiration C C
2 acetyl CoA 4 C
CO2 C
2 CO2
Krebs cycle 2
ATP
electron carriers
intermembrane compartment
H2O
Electron transport chain
32 or 34
ATP
(mitochondrion) O2
Fig. 7-1