1. Picture Guide to Chapter 8
Photosynthesis

2. 8-1 Energy and Life

3. Objectives
Explain where plants get the energy they need to produce food
Describe the role of ATP in cellular activities

4. Q: Where does energy come from?
A: Our food, but originally the energy in food comes from the sun

5. Autotrophs
Make their own food

6. Heterotrophs
Cannot make their own food

7. Chemical Energy and ATP
The principal chemical compounds that cells use to store and release energy is called ATP adenosine triphosphate

8. Storing Energy ATP stores energy in the third phosphate
ATP is like a fully charged battery

9. Releasing Energy Q: How is the energy in ATP released?
A: Break bond between the second and 3rd phosphates 2
ADP

11. Using Biomechanical Energy
Active Transport
Movement of organelles throughout cell
Synthesis of proteins and nucleic acids
Produce light
Blink of firefly caused by an enzyme powered by ATP

12. ATP Availability
Most cells only have enough ATP for a few seconds of activity
Why?
Not good at storing energy over the long term
Glucose stores 90 times the chemical energy of ATP
Cells generate ATP from ADP as needed by using the energy in foods like glucose

13. Biology in History
1643 – van Helmont: trees gain most of their mass from water 1771 – Priestly: discovered plants release oxygen 1779 – Ingenhousz: plants need sunlight to make oxygen 1845 – Mayer: proposed plants convert light energy into chemical energy

14. Bio in History pt. 2
1948 – Calvin: traces chemical path that carbon follows to make glucose
1992 – Marcus: describes electron carrier molecules in electron transport chain
2004 – Iwata & Barber: identify the mechanism for splitting water in photosynthesis

15. 8-2 Photosynthesis:
An Overview

16. Photosynthesis
The process in which plants use the energy of sunlight to convert water and carbon dioxide into high energy carbohydrates – sugars and starches – and oxygen as a waste product

17. Photosynthesis

18. The Photosynthesis Equation
light
CO2 +
H2O
C6H12O6 + O2
(Carbon Dioxide)
(Water)
(Sun)
(Glucose)
(Oxygen)

19. Chlorophyll
The plant’s principle pigment, absorbs light energy in the blue-violet and red spectrum of visible light

20. Chlorophyll a and Chlorophyll b Absorption of Light by V B G Y O R

21. Because light is a form of energy…
Anything that absorbs light also absorbs the energy from that light
When chlorophyll absorbs light, much of the energy is transferred to electrons in the chlorophyll molecule, raising the energy level of these electrons
These high-energy electrons make photosynthesis work

23. Thylakoids
Sac-like photosynthetic membranes arranged in stacks

24. Grana
Stacks of thylakoids

25. Stroma
The fluid filled region outside the thylakoid

26. Scientists describe the reactions of photosynthesis in two parts
Light – dependent reactions (takes place in the thylakoid membranes)
Light – independent reactions (takes place in stroma)

28. Carrier Molecule
Compound that can accept a pair of high energy electrons and transfer them along with most of their energy to another molecule
Ex.) NADP+

30. Q: What does this do? NADP+ NADPH
A: this traps sunlight in chemical form

31. Light Dependent Reactions
Uses energy from light to produce
Oxygen gas
ATP
NADPH

32. 8-3 The Reactions of Photosynthesis

33. Light-Dependent Rxns
Function: use energy from sun to make oxygen and convert ADP & NADP+ into ATP and NADPH
Thylakoids have clusters of chlorophyll and proteins called photosystems

35. Steps for L-D Rxns Photosystem II –
a. Light energy absorbed & excited electrons
b. Water is split to replace electrons, releases Hydrogens (H+) and Oxygen

37. Steps for L-D Rxns
2. Electron Transport Chain (ETC) – a. High energy electrons move to photosystem I b. Energy from electrons pumps H+ ions into thylakoid space

39. Steps for L-D Rxns
3. Photosystem I – a. Electrons get reenergized by sunlight b. 2nd ETC transfers electrons to NADP+, makes NADPH

41. Steps for L-D Rxns
4. ATP Synthase – a. H+ ions build up creating + charge b. Each H+ crosses membrane rotating ATP synthase converting ADP to ATP

43. The Calvin Cycle
The ATP and NADPH formed by the light-dependent reactions contain an abundance of chemical energy
Not stable enough to store that energy for more than a few minutes.
The Calvin cycle uses ATP and NADPH from light – dependent reactions to produce high energy sugars

44. The Calvin Cycle
These reactions don’t require light, therefore these reactions are called
Light – independent reactions

46. Light Indep. Rxns/The Calvin Cycle

47. Steps for L-ID Rxns CO2 Enters the Cycle –
a. CO2 enters the stroma & combines with 5-Carbon compounds
b. Get twelve 3-Carbon compounds from 6 CO2

49. Steps for L-ID Rxns
2. Sugar Production – a. Midcycle, two of the 3-Carbon compounds removed. i. Used to make sugars, lipids, aminos & etc… b. Remaining ten 3-Carbon compounds go back to six 5-carbon compounds to cycle through again

51. Steps for L-ID Rxns
3. Summary– a. Calvin Cycle used 6 CO2 to make a single 6-Carbon sugar b. Energy needed to make this sugar comes from light-dependent rxns

53. Photosynth – End Results
Light-dependent rxns trap light & convert it to chemical energy
Light-independent rxns use that chem energy to make high energy sugars
END RESULT: Plenty of food and oxygen for animals

54. Factors Affecting Photosynthesis
Not enough water
Temperature
Light intensity

55. 1. Temperature High or low temps can slow or stop it
- Enzymes for Photosynth work best between 0°C - 35°C

56. 2. Light Intensity Light intensity - speed it up or slow it down
High intensity would naturally increase the rate (to a certain point)

57. 3. Amount of Water Shortage could stop photosynth completely
Can also damage plant tissues
Desert plants & conifers have waxy coating to protect from moisture loss

58. Extreme Conditions Photosynth
C4 Photosynth
CAM Plants

59. C4 Photosynth
Special pathway to gather CO2 in low light to pass to Calvin Cycle
- 1st molecule has 4 carbon (C4)
Allows photosynth under harsh light and high temps
Requires extra ATP to work
Ex. Corn, sugar cane, and sorghum

60. C.A.M. Plant Crassulacean Acid Metabolism (C.A.M.)
Named after family of plants
Bring in air only at night
CO2 combines with other molecules to make organic acids that trap Carbon
- During the day, the plants squeeze leaves shut & use trapped Carbon for food.
Ex. Pineapple trees & some cacti

61. Fun Fact
C.A.M. plants are often planted along freeways to help “retard” brushfires

62. THE END