Chapter 9Photosynthesis: Capturing Energy

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Chapter 9Photosynthesis: Capturing Energy

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Heterotrophs: biotic consumers; obtains organic food by eating other organisms ... night, close during day (crassulacean acid metabolism); cacti, pineapples, etc. ... – PowerPoint PPT presentation

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Title: Chapter 9Photosynthesis: Capturing Energy

1

Chapter 9 Photosynthesis Capturing Energy

2
Photosynthesis in nature

Autotrophs biotic producers photoautotrophs
chemoautotrophs obtains organic food without
eating other organisms
Heterotrophs biotic consumers
obtains organic food by eating other organisms or
their by-products (includes decomposers)

3
The chloroplast

Sites of photosynthesis
Pigment chlorophyll
Plant cell mesophyll
Gas exchange stomata
Double membrane
Thylakoids, grana, stroma

4
Leaf Structure
5

Outer membrane
Inner membrane
Stroma
1 µm
Granum (stack of thylakoids)
Thylakoid membrane
Thylakoid lumen
Intermembrane space
(c) In the chloroplast, pigments necessary for
the light-capturing reactions of photosynthesis
are part of thylakoid membranes, whereas the
enzymes for the synthesis of carbohydrate
molecules are in the stroma.
Fig. 9-4c, p. 194
6
Electromagnetic Spectrum
7

One wavelength
Longer wavelength
760 nm
TV and radio waves
Red
700 nm
Micro- waves
Orange
Infrared
Color spectrum of visible light
600 nm
Visible
Yellow
UV
Green
X-rays
500 nm
Blue
Gamma rays
Violet
400 nm
380 nm
Electromagnetic spectrum
Shorter wavelength
Fig. 9-1, p. 192
8
Photosynthesis an overview

Redox process
H2O is split, e- (along w/ H) are transferred to
CO2, reducing it to sugar
2 major steps
light reactions (photo) v NADP
(electron acceptor) to NADPH
vPhotophosphorylation ADP ---gt ATP
Calvin cycle (synthesis) v Carbon fixation
carbon into organics

9
Photosystems

Light harvesting units of the thylakoid membrane
Composed mainly of protein and pigment antenna
complexes
Antenna pigment molecules are struck by photons
Energy is passed to reaction centers (redox
location)
Excited e- from chlorophyll is trapped by a
primary e- acceptor

10
Noncyclic electron flow

Photosystem II (P680) v
photons excite chlorophyll e- to an acceptor
v e- are replaced
by splitting of H2O (release of O2)
v e-s travel to Photosystem
I down an electron transport chain
(PqcytochromesPc) v as e-
fall, ADP ---gt ATP (noncyclic photophosphorylation
)
Photosystem I (P700) v
fallen e- replace excited e- to primary e-
acceptor v 2nd ETC ( FdNADP
reductase) transfers e- to NADP ---gt NADPH
(...to Calvin cycle)
These photosystems produce equal amounts of ATP
and NADPH

11
Noncyclic Electron Transport

Light-dependent reactions
form ATP and NADPH

12
The Calvin cycle

3 molecules of CO2 are fixed into
glyceraldehyde 3-phosphate (G3P)
Phases 1- Carbon fixation each CO2 is
attached to RuBP (rubisco enzyme) 2-
Reduction electrons from NADPH reduces to G3P
ATP used up 3- Regeneration G3P
rearranged to RuBP ATP used cycle continues

13
The Calvin Cycle
14
Calvin Cycle, net synthesis

For each G3P (and for 3 CO2). Consumption of
9 ATPs 6 NADPH (light reactions regenerate
these molecules)
G3P can then be used by the plant to make glucose
and other organic compounds

15
Cyclic electron flow

Alternative cycle when ATP is deficient
Photosystem I used but not II produces ATP but
no NADPH
Why? The Calvin cycle consumes more ATP than
NADPH.
Cyclic photophosphorylation

16
Cyclic Electron Transport

Electrons from photosystem I
return to photosystem I
ATP produced by chemiosmosis
No NADPH or oxygen generated

17
Alternative carbon fixation methods, I

Photorespiration hot/dry days stomata close
CO2 decrease, O2 increase in leaves O2 added to
rubisco no ATP or food generated
Two Solutions..
1- C4 plants 2 photosynthetic cells,
bundle-sheath mesophyll PEP carboxylase
(instead of rubisco) fixes CO2 in mesophyll new
4C molecule releases CO2 (grasses)

18
C3 and C4 Plants
19
Alternative carbon fixation methods, II