PowerPoint Presentation Chapter 7

1
Photosynthesis
Principles of Biology Chapter 7
2
Photosynthesis

• 6 CO2 6 H2O --gt C6H12O6 6 O2
• Reactants of photosynthesis are products of
  respiration
• Instead of breaking bonds to release energy,
  photosynthesis takes in energy from the sun to
  build food molecules

3
(No Transcript)
4
Site of photosynthesis
5
(No Transcript)
6
(No Transcript)
7
Visible Light Spectrum
8
Sunlight

• Radiation energy photons - packets of light
  energy
• Electromagnetic energy that travels in waves
• Like ripples in water when stone is thrown
• Wavelengths distance between two ripples
• Visible light - wavelengths we can see
• Minor part of entire spectrum
• Color determined by wavelengths reflected
• Wavelengths absorbed not visible
• Why are leaves green?
• They absorb red, blue, reflect green

9
(No Transcript)
10
(No Transcript)
11
Pigments and energy

• Photon - packet of light energy
• Violet has twice as much energy as red
• Pigment molecules can absorb photon energy
• Energy gained excites an electron in pigment
  molecule
• Excited electron is unstable
• Most often heat is released as electron falls
  back to its normal position
• Excited chlorophyll electrons can pass on the
  energy instead of loosing it

12
(No Transcript)
13
Overview of photosynthesis
14
Photo Synthesis

• Photo - light required aka light reactions
• Light reactions - in thylakoid membrane
• Energy from sun converted to chemical energy
• ATP
• NADPH
• Synthesis - aka Calvin Cycle aka dark
  reactions/light INdependent reactions
• Makes sugar in stroma
• No light required
• CO2 to C6H12O6
• Uses ATP and NADPH

15
(No Transcript)
16
Structure of chloroplasts

• Double membrane
• Stroma-thick fluid in chloroplasts
• Membrane system
• Grana stack of thylakoids
• Membranous flattened sacs (thylakoid)
• Interconnected
• Chlorophylls and other pigments in membrane
• Light reactions occur in thylakoid membrane and
  in the inner space

17
(No Transcript)
18
Cyclic pathway

• aka photophosphorylation
• Two possible pathways to make ATP
• Two photosystems
• One can follow the cyclic pathway
• Or non-cyclic pathway
• Photosystem one (PS1) -discovered first
• Can go cyclic or non-cyclic
• Depending on need for ATP
• Excited electron to electron acceptor to ETS,
  then back to chlorophyll (cyclic pathway)
• (electron is recycled)
• Generates ATP

19
(No Transcript)
20
ETCs in photosynthesis

• Together the two photosystems use non-cyclic
  pathway
• Photons excite electons in pigment molecules
• Electrons passed to reaction center
• Then to electron acceptor molecule
• And on to ETS
• PS2 splits H2O to replace electrons lost by
  reaction center
• Splitting releases H and oxygen
• One oxygen joins another making O2
• This is where oxygen is generated- waste product
• Electrons passed to PS1
• Photons excite electrons.

21
(No Transcript)
22
Photosystems

• 100s of pigment molecules act as antenna
• To gather light energy
• Photon hits one pigment excited electrons jump
  from molecule to molecule
• Excited electron passed to reaction center
• Special chlorophyll A molecule
• With a primary electron acceptor next to it
• Which grabs the electron
• ETSs generate ATP and NADPH

23
Thylakoid organization
24
(No Transcript)
25
(No Transcript)
26
Discovery of Calvin Cycle steps

• Using algae and radioactive isotopes of C in CO2
• Radioactive CO2 added then algae killed
• By dropping into alcohol
• After 2 seconds, 5 seconds etc.
• Extracting the organic compounds collected after
  different lengths of time and determining which
  ones contained the radioactive C, could figure
  out pathway

27
(No Transcript)
28
Carbohydrate synthesis

• ATP and NADPH from light reactions drive the
  Calvin cycle
• Turning low energy reactants (CO2 H2O) into
  high energy glucose
• 1. CO2 combines with RuBP (a 5-C)
• 2. This 6-C splits into two 3-C PGA
• 3. PGAL(a 3-C molecule) actual final product of
  Calvin Cycle
• 4. Many other molecules can be made from PGAL

29
(No Transcript)
30
(No Transcript)
31
(No Transcript)
32
(No Transcript)
33
Fig. 6.14
34
Plant adaptations

• Control of water loss big problem for plants
• C3 plants form 3-C compound
• Ex. Soybeans, wheat, rice, oats
• Have problems in dry weather
• Closed stoma means no CO2 for Calvin Cycle
• C4 plants
• Has enzyme that takes CO2 in and saves it
• Can release CO2 while keeping stoma closed
• Conserves water while making sugar
• CAM plants - succulents
• Takes in CO2 at night for use during daytime
• Keeps stoma closed during day

35
Overview of Photosynthesis
36
(No Transcript)
37
(No Transcript)