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Photosynthesis: The Big Picture. Source of BOTH matter and energy for most living organismsCaptures light energy from the sun and converts it into chemical energySynthesized organic molecules from inorganic moleculeBOTTOM LINE: Makes FOOD. Autotroph:Organisms that make their own food (energy-rich organic molecules) from simple, inorganic moleculesPhotoautotroph:Organisms that make their own food through photosynthesis; obtain energy from the sunType of autotrophHeterotroph:Get carbon a9459
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1. How Cells Acquire Energy Chapter 7
2. Photosynthesis: The Big Picture Source of BOTH matter and energy for most living organisms
Captures light energy from the sun and converts it into chemical energy
Synthesized organic molecules from inorganic molecule
BOTTOM LINE: Makes FOOD
3. Autotroph:
Organisms that make their own food (energy-rich organic molecules) from simple, inorganic molecules
Photoautotroph:
Organisms that make their own food through photosynthesis; obtain energy from the sun
Type of autotroph
Heterotroph:
Get carbon and energy by eating autotrophs or one another Definitions
4. Photoautotrophs Capture sunlight energy and use it to carry out photosynthesis
Plants
Some bacteria
cyanobacteria
Many protistans
algae
5. Linked Processes Photosynthesis
Energy-storing pathway
Releases oxygen
Requires carbon dioxide Aerobic Respiration
Energy-releasing pathway
Requires oxygen
Releases carbon dioxide
6. Photosynthesis Equation
7. Where Atoms End Up
8. Chloroplast Structure
9. Light dependent reactions
Converts light energy into chemical energy (ADP? ATP)
Gathers e- and H+ from water (NADP+ ? NADPH)
Occurs in thylakoid membranes
Light independent reactions (Calvin-Benson Cycle)
Reduces CO2 to synthesize glucose using energy and hydrogens (i.e. ATP and NADPH) generated in the light dependent reaction
Occurs in Stroma
Notice that these reactions do not create NADH, but rather NADPH Two Stages of Photosynthesis
10. Two Stages of Photosynthesis
11. Electromagnetic Spectrum Shortest Gamma rays
wavelength X-rays
UV radiation
Visible light
Infrared radiation
Microwaves
Longest Radio waves
wavelength
12. Visible Light Electromagnetic energy with a wavelength of 308-750nm
Light energy is organized into packets called photons
The shorter the wavelength the greater the energy carried by the photons
13. Properties of Light White light (from the sun) contains all of the wavelengths of light
When light hits matter, it can be reflected (transmitted) or absorbed
White substances reflect all light
Black substances absorb all light
14. Pigments A substance that absorbs light
We see the color that is transmitted by pigment
The absorbed color disappears into pigment
15. Plant pigments Plant use a variety of pigments during photosynthesis:
Chlorophylls a and b
Carotenoids
Anthocyanins
Phycobilins
The main photosynthetic pigment is Chlorophyll a
16. Chlorophylls Chlorophyll a absorbs red and blue light, and reflects green light (what we see)
Note: The colors that are absorbed are used for photosynthesis
17. Effect of Light on Pigments What happens when light hits pigments?
The color disappears, but the energy does not
Absorbing photons of light excites electrons (e-), thus adding potential energy
Ground state: normal pigment
Excited state: pigment absorbing light (e- excited)
18. Photosystems In thylakoid membrane, pigments are organized in clusters called photosystems
These clusters contain several hundred pigment molecules
Two types of photosystems
Photosystem I = P700 (absorbs light at 700nm)
Photosystem II = P680 (absorbs light at 680nm)
19. Reaction Center Chlorophyll One of the pigments in each photosystem is known as the reaction center chlorophyll (RCC)
if any pigment within the photosystem gets hit by a photon, the energy is transferred to the RCC
The RCC will then transfer its excited e- into an electron transport chain
20. Pigments in a Photosystem
21. Light Dependent Reactions Location: the thylakoid membranes
Function: to generate ATP (energy!) and NADPH (reducing power!) that will be used in the light independent reaction
Two processes:
Non-cyclic electron flow
Generates ATP and NADPH
Cyclic electron flow
Generates only ATP
22. Noncyclic Electron Flow Two-step pathway for light absorption and electron excitation
Uses two photosystems: type I and type II
Produces ATP and NADPH
Involves photolysis - splitting of water
23. Machinery of Noncyclic Electron Flow
24. Steps of Non-cyclic electron flow Photosystem II gets hit by a photon; electron of RCC gets excited
The excited (high energy) e- gets picked up by an electron carrier and taken into an electron transfer chain (ETC)
The excited e- provides energy to pump protons (H+) into the thylakoid (tiny space)
Through chemiosmosis, ATP is generated
25. Chemiosmotic Model of ATP Formation Electrical and H+ concentration gradients are created between thylakoid compartment and stroma
H+ flow down gradients into stroma through ATP synthase
The energy driven by the flow of H+ powers the formation of ATP from ADP and Pi
26. Chemiosmotic Model for ATP Formation
27. Non-cyclic electron flow: Photolysis While Photosystem II gets hit by light, etc., water is split:
H2O ? ˝ O2 + 2H+ + 2e-
This process is called photolysis
The H+ are pumped into the thylakoid to create the proton gradient
The e- replace the excited e- that was taken away from the RCC
28. Non-Cyclic Electron Flow:The saga continues Photosystem I gets excited at the same time as photosystem II
Its excited e- gets taken into a second electron transfer chain that attaches the excited e- and the leftover H+ to NADP+ to make NADPH:
NADP+ + H+ + e- ? NADPH
29. Non-cyclic electron flow The electron hole in photosystem I is then filled with the used up, low energy e- from photosystem II
Now everything is back to normal, and we can start all over again
30. Energy Changes in Non-cyclic electron flow
31. Non-cyclic electron flow: Summary After two excited photosystems, two ETCs and the splitting of water, both ATP and NADPH are generated!!!
32. Cyclic electron flow The light independent reactions require more ATP than NADPH
Cyclic electron flow is like a short cut to making extra ATP
Involves only Photosystem I
33. Cyclic electron flow Photosystem I gets excited
Excited e- is carried into the first ETC; energy goes to pump H+ into thylakoid compartment
Chemiosmosis powers formation of ATP
The same e- (now low energy) replaces itself in the electron hole in Photosystem I
34. Cyclic electron flow
35. Light dependent reactions:Summary Non-cyclic electron flow
Generates ATP
36. Synthesis part of photosynthesis
Can proceed in the dark
Take place in the stroma
Calvin-Benson cycle Light-Independent Reactions
37. Calvin-Benson Cycle Overall reactants
Carbon dioxide
ATP
NADPH Overall products
Glucose
ADP
NADP+
38. Calvin-Benson Cycle Three Phases:
Carbon Fixation
Reduction
Regeneration of RUBP
39. Calvin-Benson Cycle: Carbon Fixation Capturing atmospheric (gaseous) CO2 by attaching it to RuBP, a 5-carbon organic molecule
This process forms two 3-carbon molecules
The enzyme that catalyzes this process is called Rubisco
40. Calvin Benson Cycle:Reduction The captured CO2 has very little energy and no hydrogens
In order to make sugar, energy and hydrogens need to be added to the molecules formed by Carbon fixation
ATP and NADPH (made in the light dependent reactions) break down to form ADP and NADP+ and, in the process, transfer energy and hydrogens to the 3-carbon compounds formed by carbon fixation, resulting in sugar formation
41. Calvin-Benson Cycle:Regeneration Some of the sugar created by reduction leaves the Calvin cycle, and is used to build up glucose and other organic molecules
The rest of the sugar is used to remake (regenerate) RuBP
This process requires ATP (which was made in the light dependent reactions)
42. Calvin-Benson Cycle:Summary The cycle proceeds 6 times to form each molecule of glucose
In the process, ATP and NADPH is used up
6CO2 are converted into C6H12O6 - glucose
43. In Calvin-Benson cycle, as described, the first stable intermediate is a three-carbon PGA
Because the first intermediate has three carbons, the pathway is called the C3 pathway The C3 Pathway
44. Photorespiration in C3 Plants On hot, dry days stomata (holes in the leaf) close to prevent evaporation of water
As a result, within the leaf oxygen levels rise, and Carbon dioxide levels drop
Rubisco attaches RuBP to oxygen instead of carbon dioxide
Results in a VERY wasteful process known as Photorespiration uses up ATP without generating sugar
45. C4 and CAM Plants To avoid photorespiration, plants that live in hot, dry climates evolved mechanisms to separate carbon fixation from the Calvin Cycle
The CO2 that enters the Calvin cycle is derived from the breakdown of previously synthesized organic acids
In this way, the enzyme that catalyzes the reaction that attaches CO2 to RuBP is not exposed to atmospheric oxygen
46. C4 and CAM Plants C4 plants do carbon fixation in a different location (cell type) than the Clavin cycle
CAM plants do carbon fixation at a different time (night) that the Calvin cycle (day)
47. Summary of Photosynthesis