1. Chapter 8 Cellular Energy
Biology

2. Section 8.1 How Organisms Obtain Energy
Main idea – All living organisms use energy to carry out all biological processes
Objectives
Summarize the two laws of thermodynamics
Compare and contrast autotrophs and heterotrophs
Describe how ATP works in a cell

3. Transformation of Energy
All cellular activities require energy; the ability to do work
Thermodynamics is the study of the flow and transformation of energy in the universe

4. Laws of Thermodynamics
The 1st Law – “Law of conservation of energy” – Energy can be converted from one form to another, but it cannot be created nor destroyed
The 2nd Law – Energy that is “lost” is generally converted to thermal energy – “entropy increases”
Entropy – measure of disorder or unusable energy, in a system.

5. Autotrophs & Heterotrophs
Autotrophs – organisms that make their own food
Chemoautotrophs – uses chemicals as a source of energy
Photoautotrophs – convert light energy from the Sun into chemical energy
Heterotrophs – organisms that need to ingest food to obtain energy

6. Metabolism
All of the chemical reactions in a cell are referred to as the cell’s metabolism
Metabolic pathway is a series of chemical reactions in which the product of one reaction is the substrate for the next reaction
Catabolic pathways – releases energy by breaking down larger molecules into smaller ones
Anabolic pathways –uses the energy released by catabolic pathways to build larger molecules from smaller molecules
The continual flow of energy within an organism is the result of the relationship of catabolic and anabolic pathways

7. Photosynthesis
Photosynthesis is the anabolic pathway in which light energy from the Sun is converted to chemical energy for use by the cell
6CO2 + 6H2O  C6H12O6 + 6O2

8. Cellular Respiration
Cellular Respiration is the catabolic pathway in which organic molecules are broken down to release energy for use by the cells
C6H12O6 + 6O2  6CO2 + 6H2O + ATP

9. Photosynthesis & Cellular Respiration Form a Cycle

10. ATP: The Unit of Cellular Energy
Adenosine Triphosphate (ATP) is the most important biological molecule that provides chemical energy
ATP is made of an adenine base, a ribose sugar, and three phosphate groups
ATP releases energy when the bond between the second and third phosphate groups is broken, forming adenosine diphosphate (ADP) and a free phosphate group
Energy is stored in the phosphate bond formed when ADP receives a phosphate group and becomes ATP

11. ATP: The Unit of Cellular Energy

12. Section 8.2 Photosynthesis
Main idea – Light energy is trapped and converted into chemical energy during photosynthesis
Objectives
Summarize the two phases of photosynthesis
Explain the function of a chloroplast during the light reactions
Describe and diagram electron transport

13. Overview of Photosynthesis
Photosynthesis is a process in which light energy is converted into chemical energy
6CO2 + 6H2O  C6H12O6 + 6O2
Photosynthesis occurs in two phases
Phase 1-Light-dependent reactions-light energy is absorbed and then converted into chemical energy in the form of ATP and NADPH
Phase 2-Light-independent reactions-the ATP and NADPH formed in phase 1 is used to make glucose

14. Phase 1: Light Reactions
Chloroplasts – capture light energy in photosynthetic organisms; disc-shaped organelles that contain two main compartments
Thylakoids are flattened saclike membranes that are arranged in stacks (grana) and are the location of light-dependent reactions
Stroma are the fluid spaces outside the grana and are the location of light-independent reactions

15. Phase 1: Light Reactions

16. Pigments
Pigments are light-absorbing molecules found in the thylakoid membranes of chloroplasts
Chlorophylls are the major light-absorbing pigments in plants; reflecting green light
Accessory pigments allow plants to trap additional light energy
Carotenoids – reflect yellow, orange and red light

17. Electron Transport
Activated electrons are passed from one molecule to another along the thylakoid membrane in a chloroplast. The energy from electrons is used to form a proton gradient. As protons move down the gradient, a phosphate is added to ADP, forming ATP

18. Electron Transport (cont.)
Light energy absorbed by photosystem II is used to split a molecule of water. When water splits, oxygen is released from the cell, protons (H+; hydrogen ions) stay in the thylakoid space and an activated electron enters the electron transport chain
As electrons move through the membrane, protons are pumped into the thylakoid space
At photosystem I, electrons are re-energized and NADPH is formed

19. Electron Transport (cont.)
Chemiosmosis: Protons accumulate in the thylakoid space, creating a concentration gradient
When protons move across the thylakoid membrane through ATP synthase, ADP is converted to ATP

20. Phase 2: Calvin Cycle Light-independent Reactions
Calvin Cycle – the second phase of photosynthesis in which energy is stored in organic molecules such as glucose

21. Calvin Cycle (cont.)
First step – carbon fixation - 6CO2 + 6 RuBP (ribulose 1,5-biphosphate a 5-carbon compound) to form 12 3-PGA (3-phosphoglycerate, a 3-carbon molecule)
Second step – the chemical energy stored in 12 ATP and 12 NADPH is transferred to the 12 3-PGA to form 12 G3P (glyceraldehyde 3-phosphate, high energy molecules)

22. Calvin Cycle (cont.)
Third step – 2 G3P leave the cycle to form glucose and other organic compounds
Final step – An enzyme called rubisco converts the remaining 10 G3P into RuBP.
Plants use the sugars formed during the Calvin Cycle both as source of energy and as building blocks for complex carbohydrates, including cellulose, which provides structural support for the plant

23. Alternative Pathways
Many plants in extreme climates have alternative photosynthesis pathways to maximize energy conversion
C4 plants minimize water loss by closing stoma in hot days as they fix carbon dioxide into 4-carbon compounds instead of the 3-carbon molecules during the Calvin Cycle
CAM plants (crassulacean acid metabolism) occurs in water-conserving plants as CO2 enters leaves at night fixing it into organic molecules. During the day, CO2 is released and enters the Calvin Cycle

24. 8.3 Cellular Respiration
Main idea – Living organisms obtain energy by breaking down organic molecules during cellular respiration
Objectives
Summarize the stages of cellular respiration
Identify the role of electron carriers in each stage of cellular respiration
Compare alcoholic fermentation and lactic acid fermentation

25. Overview of Cellular Respiration
Organisms obtain energy in a process called cellular respiration
The function of cellular respiration is to harvest electrons from carbon compounds, such as glucose, and use that energy to make ATP
C6H12O6 + 6O2  6CO2 + 6H2O + ATP

26. Cellular Respiration (cont.)
Two main parts
Glycolysis
Anaerobic process – do not require oxygen
Aerobic Respiration
Krebs cycle & electron transport
Aerobic process – requires oxygen

27. Glycolysis
Glucose is broken down in the cytoplasm through the process of glycolysis, refer to Figure 8.12 on p. 229
First, 2 phosphate groups are joined to glucose
Second, the 6-carbon molecule is broken down into 2 G3P
Next, two phosphates are added and electrons and hydrogen ions combine to produce 4 ATP and 2 NADH, respectfully
Last, the 2 G3P are converted into 2 pyruvate molecules
Glycolysis has a net yield of 2 ATP molecules

28. Krebs Cycle
The series of reactions in which pyruvate is broken down into carbon dioxide is called the Krebs cycle or tricarboxylic acid (TCA) cycle.
This cycle is known as the citric acid cycle, too
The Krebs cycle occurs inside the mitochondria of cells.

29. Krebs Cycle (cont.)
Prior to the Krebs cycle, pyruvate reacts with coenzyme A (CoA) to form acetyl CoA
At the same time CO2 is released and NAD+ is converted into NADH
The reaction results in the production of 2 CO2 molecules and two NADH
The cycle begins with acetyl CoA combining with a 4-carbon compound to form citric acid, a 6 carbon compound

30. Krebs Cycle (cont.)
Then, citric acid is broken down in the next series of steps, releasing 2 molecules of CO2 and generating one ATP, three NADH, and one FADH2. FAD is another electron carrier similar to NAD+ and NADP+
Finally, acetyl CoA and citric acid are generated and the cycle continues
The net yield from the Krebs cycle is 6 CO2 molecules, 2 ATP, 8 NADH, and 2 FADH2.
NADH and FADH move on to play a significant role in the next stage of aerobic respiration

31. Krebs Cycle

32. Electron Transport Refer to Figure 8.14 on p. 231
Electrons move along the mitochondrial membrane from one protein to another
Electrons are transported to oxygen to form water
Electron transport produces 24 ATP
Each NADH molecule produces 3 ATP
Each group of 3 FADH2 produces 2 ATP
In eukaryotes, one molecule of glucose yields 36 ATP
In prokaryotes, one molecule of glucose produces 38 ATP

33. Anaerobic Respiration
The anaerobic pathway that follows glycolysis is anaerobic respiration, or fermentation
Fermentation occurs in the cytoplasm and regenerates the cell’s supply of NAD+ while producing a small amount of ATP
Two types
Lactic acid fermentation
Alcohol fermentation

34. Lactic acid fermentation & Alcohol fermentation
Enzymes convert the pyruvate made during glycolysis to lactic acid
When oxygen is absent or in limited supply, fermentation can occur
Skeletal muscles during strenuous exercise
Microorganisms to produce cheese, yogurt & sour cream
Alcohol fermentation
Occurs in yeast and some bacteria when pyruvate is converted to ethyl alcohol and CO2

35. Photosynthesis & Cellular Respiration
Processes cells use to obtain energy
Metabolic pathways that produce and break down simple carbohydrates
The products of Photosynthesis are oxygen and glucose – the reactants needed for cellular respiration
The products of cellular respiration – carbon dioxide and water – are the reactants for photosynthesis