Photosynthesis and Cellular Respiration

1. Photosynthesis and Cellular Respiration Chapter 9

2. Energy in Living Systems Section 1

3. Chemical Energy • Organisms use and store energy in chemical bonds of organic compounds • Almost all energy in organic compounds comes from the sun • Solar energy enters living systems when plants, algae, and certain prokaryotes use sunlight to carry out photosynthesis

4. Chemical Energy • Photosynthesis: the process by which sunlight, carbon dioxide, and water are used to produce carbohydrates and oxygen • Organisms that are able to perform photosynthesis are called autotrophs

5. Chemical Energy • In order to survive, organisms that cannot make their own food must absorb food molecules made by autotrophs, eat autotrophs, or eat organisms that consume autotrophs • These food molecules supply energy for the cells • Energy is stored in molecular bonds

6. Metabolism and the Carbon Cycle • Metabolism involves either using energy to build organic molecules or breaking down organic molecules in which energy is stored • Organic molecules contain carbon • Therefore, an organism’s metabolism is part of Earth’s carbon cycle

7. Metabolism and the Carbon Cycle • Photosynthesis • Energy enters an ecosystem when organisms use sunlight during photosynthesis to convert carbon dioxide into glucose • Takes place in the chloroplasts

8. Metabolism and the Carbon Cycle • Cellular Respiration • Organisms extract energy stored in glucose molecules • Through cellular respiration, cells make the carbon in glucose into carbon dioxide molecules and produce energy

9. Metabolism and the Carbon Cycle • Cellular respiration • Inputs: • Glucose • Six oxygen molecules • Outputs: • Six carbon dioxide molecules • Six water molecules • Energy (ATP, which is the main energy source for all cell processes) • C6H12O6 + 6O2 6CO2 + 6 H2O + Energy

11. Transferring Energy • In chemical reactions, energy can be absorbed and released during the breaking and forming of bonds • In cells, chemical energy is gradually released in a series of chemical reactions that are assisted by enzymes • Enzymes: proteins that act as catalysts in reactions

12. Transferring Energy • ATP • When cells break down food molecules, some of the energy in the molecules is released as heat • Cells use much of the remaining energy to make ATP • Used to power chemical reactions • Portable form of energy • Can be made in one place and used in another • Nucleotide made up of a chain of three phosphate groups

13. Transferring Energy • ATP Synthase • An enzyme that catalyzes the synthesis of ATP • ATP synthase recycles ADP by bonding a third phosphate group to the molecule • Acts as a carrier protein and an enzyme for hydrogen ions

14. ATP Synthase

15. Transferring Energy • Hydrogen Ion Pump • Electron transport chain: a series of molecules is the inner membrane of a mitochondrion • Allows electrons to drop in energy as they are passed along and uses the energy released to pump H+ ions out of a mitochondrion’s inner compartment

16. Electron Transport Chain

17. Photosynthesis Section 2

18. Introduction • Plants, algae, and certain prokaryotes capture about 1% of the energy in the sunlight that reaches Earth and convert it to chemical energy through photosynthesis • Photosynthesis provides energy from almost all life

19. Harvesting Light Energy • The cells of many photosynthetic organisms have chloroplasts • Chloroplasts convert light energy into chemical energy

20. Harvesting Light Energy • Chloroplasts • Have an outer membrane and an inner membrane • Inner membrane is highly selective • Both allow light to pass through • Stroma: space inside the inner membrane • Inside the stroma are thylakoid membranes • Folded to produce flat, disc-like sacs called thylakoids • Thylakoids arranged in stacks • Photosynthesis starts when light hits these stacks • Thylakoids contain molecules that absorb light energy

21. Chloroplasts

22. Harvesting Energy • Electromagnetic radiation • Light is a form of electromagnetic radiation • A form of energy that can travel through empty space in the form of waves • Different wavelengths correspond to a certain amount of energy • Sunlight contains all wavelengths of visible light

23. Harvesting Energy • Pigments • Pigment: a substance that absorbs certain wavelengths (colors) of light and commonly reflects all of the others • In plants, light energy is harvested by pigments that are located in the thylakoid membrane of chloroplasts • Chlorophyll: a green pigment that absorbs light energy to start photosynthesis • Absorbs mostly red and blue light and reflects green and yellow

24. Harvesting Energy • Pigments • Plants have two types of chlorophyll: • Chlorophyll a • Chlorophyll b • Plants also have carotenoids • Reflect yellow, orange, and red light • Why do leaves change color in the fall? • Chlorophyll fades away, so the carotenoids are exposed

25. Harvesting Light Energy • Electron carriers • When light hits a thylakoid, energy is absorbed by many pigment molecules • They funnel the energy to the reaction center (a special chlorophyll molecule) • Energy causes electrons to become “excited” and move to a higher energy level; they are transferred down the chain to an electron carrier

26. Two Electron Transport Chains • The electron carrier transfers the electrons to the first of two electron transport chains in the thylakoid membrane • During photosynthesis, one electron transport chain provides energy to make ATP, while the other provides energy to make NADPH

27. Two Electron Transport Chains • Producing ATP • In mitochondria, electron transport chains pump H+ ions through a membrane, which produces a concentration gradient • Also happens in chloroplasts

28. Two Electron Transport Chains • Step 1: Water Splitting • Step 2: Hydrogen Ion Pump • Step 3: ATP Synthase • Step 4: Reenergizing • Step 5: Making NADPH

29. Two Electron Transport Chains • Step 1: Water Splitting • Excited electrons that leave the chlorophyll have to be replaced by other electrons • Replaced from H2O • Water is split by an enzyme • H+ ions and O2 molecules produced

31. Two Electron Transport Chains • Step 2: Hydrogen Ion Pumps • Protein acts as a membrane pump • Excited electrons transfer some energy to pump H+ ions into the thylakoid • Creates a concentration gradient

33. Two Electron Transport Chains • Step 3: ATP Synthase • The energy from the diffusion of H+ ions through the carrier protein is used to make ATP • As hydrogen ions pass through the channel portion of the protein, ATP synthase catalyzes a reaction in which a phosphate group is added to a molecule of ADP • Results in ATP

35. Two Electron Transport Chains • Producing NADPH • While one electron transport chain provides energy to make ATP, a second electron transport chain receives excited electrons from a chlorophyll molecule and uses them to make NADPH

37. Two Electron Transport Chains • Step 4: Reenergizing • In this second chain, light excites electrons in the chlorophyll molecule • The electrons are passed to the second electron transport chain

38. Two Electron Transport Chains • Step 5: Making NADPH • Excited electrons combine with H+ ions and NADP+ (an electron acceptor) • Both NADPH and the ATP made during the first stage of photosynthesis will be used to provide the energy to carry out the final stage of photosynthesis

40. Producing Sugar • The first two stages of photosynthesis depend directly on light because light energy is used to make ATP and NADPH • In the first stage of photosynthesis, ATP and NADPH are used to produce energy-storing sugar molecules from the carbon in carbon dioxide • The use of carbon dioxide is called carbon fixing

41. Producing Sugar • The reactions that fix carbon dioxide are light-independent reactions • Sometimes called dark reactions • Several ways in which carbon dioxide is fixed • Most common method is the Calvin Cycle

42. Producing Sugar • Calvin Cycle • Carbon Fixation • In CO2 fixation, an enzyme adds a molecule of CO2 to a 5-carbon compound • Occurs three times to yield three 6-carbon molecules • Transferring Energy • Each 6-carbon compound splits into two 3-carbon compounds • Phosphate groups from ATP and electrons from NADPH are added to the compounds to form higher energy 3-carbon compounds

43. Producing Sugar • Making Sugar • One of the 3-carbon sugars leaves the Calvin Cycle and is used to make organic compounds • Recycling • The remaining five 3-carbon sugars are rearranged • Using the energy from ATP, enzymes reform three molecules of the initial 5-carbon compound • Completes the cycle

44. Calvin Cycle

45. Factors that Affect Photosynthesis • Light intensity, carbon dioxide concentration, and temperature are three environmental factors that affect photosynthesis • The rate of photosynthesis increases and light intensity increases until all chlorophyll molecules are being used, which causes the process to level off • The concentration of CO2 affects the rate of photosynthesis in the same way as light intensity • Unfavorable temperatures may inactivate certain enzymes so reactions don’t take place

46. Cellular Respiration Section 3

47. Glycolysis • The primary fuel for cellular respiration is glucose • Formed when carbs are broken down • Proteins and nucleic acids can also be used to make ATP

48. Steps of Glycolysis • In the first stage of cellular respiration, glucose is broken down in the cytoplasm by glycolysis • Glycolysis: enzymes break down one 6-carbon molecule of glucose into two 3-carbon pyruvate molecules

49. Steps of Glycolysis • Breaking Down Glucose • Two ATP molecules are used to break glucose into two smaller units • A phosphate group from ATP is added to the 6-carbon compound • breaks into two 3-carbon sugars

50. Steps of Glycolysis • NADH Production • Each 3-carbon compound reacts with another phosphate group (not from ATP) • Hydrogen atoms are transferred to two molecules of NAD+ • Produces two molecules of NADH