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2. Biology for a Changing World
Michèle Shuster • Janet Vigna • Gunjan Sinha • Matthew Tontonoz
Biology for a
Changing World
SECOND EDITION
Lecture PowerPoint
CHAPTER 5
Energy Flow and Photosynthesis
Copyright © 2014 by W. H. Freeman and Company

3. Stuff to understand What things do photosynthesis
Why is photosynthesis important to ecosystems
List the types of energy & what types are involved in photosynthesis
How does photosynthesis convert energy from sunlight into energy stored in energy filled molecules

4. Energy basics Energy = capacity to do work Making molecules
Moving stuff in and out of cells
Without a constant source of energy, all life on Earth would stop (new energy always being added to system)

5. Types of Energy
Kinetic energy - the energy of motion or movement (e.g. photons of light moving)
Heat - the kinetic energy generated by random movement of molecules or atoms
Potential energy - stored energy in the chemical bonds

6. Energy basics Autotrophs don’t create energy, they convert it
Chemical energy
potential energy stored in chemical bonds
break bonds to release energy
Light reactions convert sunlight
To chemical energy
kinetic energy
potential energy
potential energy

7. Energy basics
Humans and other animals obtain energy by eating food (we’re heterotrophs)
Chemical energy
potential energy is stored in bonds of biological molecules
break bonds to release – and use – energy

8. Two kinds of reactions
Anabolic uses energy to Add atoms (build molecules)
Catabolic reactions Cut bonds & release energy

9. Energy basics Algae and plants get energy from sun
Trap energy and store it in molecules
lots of biofuel stuff in this chapter.
will end of powerpoint

10. Sunlight energy
Light energy is the energy of the electromagnetic spectrum of radiation

11. Sunlight energy
Light energy is made of particles called photons, or packets of light energy
Photons of different wavelengths contain different amounts of energy

12. Photosynthesis: a closer look
Chlorophyll is a pigment present in the green parts of plants
It absorbs photons of light energy

13. Photosynthesis Overview Sun’s energy  chemical energy used to make complex molecules (anabolic RX)
Algae capture energy in their molecules.

14. Energy transformation is not efficient
With each energy transformation, some energy is lost as heat
Every transformation looses some energy
This is why we need to keep supplying energy to any system

15. Photosynthesis (one of two opposite paths)
Nutrients cycle, energy passes through
Photosynthesis (one of two opposite paths)
Figure 9.1b The Relationship Between Photosynthesis and Cellular Respiration
Next powerpoint

16. Energy: two major paths
Photosynthesis:
Cellular
Respiration:
Most producers (autotrophs) do both
Most consumers (Heterotrophs) don’t use photosynthesis
BOTH PATHS USE ELECTRON TRANSPORT CHAINS

17. Where do we find photosynthesis
Most common in these three kingdoms
Bacteria
Plants
Protists
Biology always has weird exceptions
 pea aphids!!

18. Photosynthesis (producers)
most ecosystems based on photosynthesis
Photosynthesizers are producers
Consumers must eat

19. Producers (autotrophs)
Take energy from the environment, store it in molecules they make
Chemosynthesis – less common
Photosynthesis = uses light to make sugar (it is G3P!!!)
Photosynthesis Overview:
Inputs
Outputs
Use own sugars for their OWN respiration
Eukaryotes use mitochondria for respiration

20. Molecular Energy Carriers: ATP
Adenosine triphosphate (ATP)
ATP is the main energy source of cell
Requires energy
Photosynthesis
Respiration

21. Molecular Energy Carriers
ATP (used for MANY types of reactions)
NADPH (some energy for anabolic reactions)
NADH (absorbs energy released in catabolic)

22. NADPH & NADH NADPH: electrons & hydrogen to anabolic react.
NADH: picks up electrons and hydrogen released from catabolic reactions

23. Leaves Stomata – how plants “breath” Many cells full of Chloroplasts
Take in CO2, release O2 (opposite of respiration) carbon dioxide to make sugars
Many cells full of Chloroplasts
Photosynthesis organelle
Calvin Cycle (sugar production) happens here

24. Light: energy to make Carbohydrates
Chloroplast – photosynthesis organelles for plant/algae
Have chlorophyll to absorb light energy
Light reactions – make energy molecules
Calvin cycle – make sugars

25. Photosynthesis: a two stage process
You must know “light reactions” and “Calvin Cycle”

26. Photosynthesis: Two Stages
Photosynthesis stages:
Light reactions
Use light energy to make ATP, NADPH, and break water
broken water molecules: source of oxygen
Calvin cycle
CO2  sugar using energy from ATP and NADPH
Entire ecosystem depends on this sugar!!!

27. Chloroplasts Light reactions in Thylakoids
The Calvin cycle (CO2  sugar) in stroma
Thylakoid space = where we put the hydrogen

28. First Stage: the light reactions
This is where we make ATP

29. Light Reaction: 1st Part
Photons of light are absorbed by chlorophyll
Electrons in the chlorophyll atoms become “excited”
Excited electrons help generate an energy-carrying molecule known as adenosine triphosphate (ATP)
ATP will be used in the Calvin Cycle to make sugar
When red and blue photons of sunlight hit chlorophyll during the light (“photo”) reactions, the electrons in its atoms become excited.

30. Light Reactions: energy from light excites electrons
Electron  electron transport chains
PS II happens 1st!!

31. Chloroplast: Light Reactions
Light-absorbing molecules in thylakoid membrane collect energy from sunlight
Absorbed light gives energy to electron
Chloroplast ETC plays “hot potato” with electron
Uses energy to pump protons (hydrogen ions)

32. Chloroplast: Light Reactions
Thylacoid membranes full of hydrogen ions
From splitting water
From chloroplast electron transport chain

33. Making ATP : movment of H+ ions
Thylacoid membranes full of hydrogen ions H+ wants to move: high concentration  low H+ movement = energy (like water wheel) The movment of hydrogen ions powers the production of ATP (“ATP synthesis”) and NADPH

34. Figure 9.8c How the Light Reactions Generate Energy Carriers

35. Making Oxygen: byproduct
Splitting water frees Oxygen
Two broken H20 molecules
Two free oxygens combine
O + O  O2
Oxygen Gas
Needed for all life on earth!!!

36. Chloroplasts Light reactions in Thylacoids
The Calvin cycle (CO2  sugar) in stroma
Uses ATP made by light reactions!!!

37. Calvin Cycle: 2nd Part
Photosynthesis captures carbon dioxide gas from the air
Incorporates carbon atoms into sugar (G3P!!!)
“Carbon fixation”
Sugar is glucose, the building block of carbohydrates.

38. Carbon fixation
Conversion of inorganic gaseous carbon into an organic molecule
Sugars used by autotrophs and heterotrophs
Main way carbon enters the global energy chain

39. Calvin Cycle: making sugars
Part 2 of photosynthesis
Happens in Stroma
Uses carbon dioxide from air
“carbon fixation”
Makes a three carbon sugar
glyceraldehyde 3-phosphate (G3P)
Depends on an enzyme nickname “Rubisco”
Rubisco picks up the incoming CO2

40. Figure 9.9 The Calvin Cycle Converts Carbon Dioxide into Sugar
The Calvin cycle reactions fix carbon by turning CO2 into sugar molecules using energy delivered by ATP, and electrons and protons delivered by NADPH.

41. Calvin Cycle: making sugars
Calvin Cycle needs energy
Fixes one carbon each cycle
3 cycles to make each 3 carbon sugar (G3P)
G3P is the building block of all carbohydrates

42. G3P: building block of sugars
G3P is the building block of glucose and all the other carbohydrates
Leaves chloroplast, fuel chemical reactions
In plants, G3P can be stored as starch for use at night

43. Photosynthesis: a two stage process
You must know “light reactions” and “Calvin Cycle”

44. Hot or try conditions stress plants
Heat and low humidity increase water loss
Plants will die if they don’t have enough water

45. Closing the Stomata can reduce water loss…
…but CO2 down & O2 up
Plants need to take in
CO2 to make sugars!!!

46. Oxygen messes up RUBISCO
ATP used to make sugar
ATP used to fix RUBISCO!!
Photorespiration wastes the plant’s energy, makes it harder to grow in hot or dry conditions

47. Other ways to do photosynthesis
keep the oxygen away from the rubisco!!!

48. Using algae to make fuel
Algae are best known for the green, red, or brown hues
Also have ability to capture energy of sunlight and convert it into usable forms of energy
Much is in the form of oils ideally suited to making fuel
Photo bioluminescent algae glow in the tide along a beach.
The oil that microalgae produce is very similar to common vegetable oil. It accumulates inside the microbes’ tiny cells, and once extracted, it can be processed to make biodiesel.

49. costs, benefits, and sustainability?
The future of fuel: Scientists hope to make algae into the next global energy source.
Copyright © 2014 by W. H. Freeman and Company

50. Fossil fuels are limited
Demand for oil will increase over next 25 years
Sources of oil are finite
Takes millions of years to replenish
The gasoline used to power cars begins as oil formed deep in the ground over millions of years. The United States depends heavily on oil recovered from other countries for its fuel supply.

51. U.S. energy consumption
The United States is the largest consumer of fossil fuels
New energy sources being developed to reduce our demand
The United States is the largest consumer of fossil fuels. Fossil fuels are considered nonrenewable because they take millions of years to create by natural processes.

52. Energy basics
Algae capture energy in their molecules.

53. Biofuels Renewable fuels made from living organisms
In 2012, more than 150 companies were dedicated to making fuel from algae
The United States must produce 36 billion gallons of renewable fuels by 2022, of which 21 billion gallons must be advanced biofuels.

54. How green are biofuels?
Extracting fuel from algae is also less energy intensive than extraction from other biofuel sources. To make ethanol, for instance, farmers typically start with corn, which requires more energy to grow than algae.

55. Summary
All living organisms require energy to live and grow. The ultimate source of energy on Earth is the sun.
Energy is neither created nor destroyed, but converted from one form to another. Kinetic energy is the energy of motion and includes heat energy and light energy. Potential energy is stored energy and includes chemical energy.
Photosynthesis is a series of chemical reactions that captures the energy of sunlight and converts it to chemical energy in the form of sugar and other energy-rich molecules.
Photosynthetic organisms are known as autotrophs. MOST animals do not photosynthesize; they are known as heterotrophs.

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