2. Photosynthesis: Life from Light and Air

3. Energy needs of life All life needs a constant input of energy
Heterotrophs (Animals)
get their energy from “eating others”
eat food = other organisms = organic molecules
make energy through respiration
Autotrophs (Plants)
produce their own energy (from “self”)
convert energy of sunlight
build organic molecules (CHO) from CO2
make energy & synthesize sugars through photosynthesis
consumers
producers

4. Important Vocabulary ATP: Adenosine triphosphate
Three phosphates attached, energy is stored between the carbon bonds
ADP: Adenosine diphosphate
Two phosphates attached

5. How are they connected?   glucose + oxygen  carbon + water + energy
Heterotrophs (Do cellular respiration to produce energy)
making energy & organic molecules from ingesting organic molecules
glucose + oxygen  carbon + water + energy
dioxide
C6H12O6
6O2
6CO2
6H2O
ATP  +
Autotrophs (Do photosynthesis to store sunlight energy into glucose, then do cellular respiration
Label the products and reactants
making energy & organic molecules from light energy
So, in effect, photosynthesis is respiration run backwards powered by light.
Cellular Respiration
oxidize C6H12O6  CO2 & produce H2O
fall of electrons downhill to O2
exergonic
Photosynthesis
reduce CO2  C6H12O6 & produce O2
boost electrons uphill by splitting H2O
endergonic
+ water + energy  glucose + oxygen
carbon
dioxide
6CO2
6H2O
C6H12O6
6O2
light
energy  +

6. Simple Song 

7. What does it mean to be a plant
Need to…
collect light energy
transform it into chemical energy
store light energy
in a stable form to be moved around the plant or stored
need to get building block atoms from the environment
C,H,O,N,P,K,S,Mg
produce all organic molecules needed for growth
carbohydrates, proteins, lipids, nucleic acids
ATP
glucose
CO2
H2O N P K …

9. Plant structure Obtaining raw materials sunlight CO2 H2O nutrients
leaves = solar collectors
CO2
stomates = gas exchange
H2O
uptake from roots
nutrients
N, P, K, S, Mg, Fe…

10. stomate
transpiration
gas exchange

11. Let’s take a quick break and do a stomata peeling to see what they look like!

12. Pigment Molecules
Pigment molecules give organisms their color because of selective absorption
The color they DON’T absorb is the color they appear
Plants have pigment molecules called chlorophyll in them
Examples of pigment molecules that animals have are retinal in human eyes and melanin in human skin

13. A Look at Light
The spectrum of color V I B G Y O R

14. Light: absorption spectra
Photosynthesis gets energy by absorbing wavelengths of light
chlorophyll a
absorbs best in red & blue wavelengths & least in green
accessory pigments with different structures absorb light of different wavelengths
chlorophyll b, carotenoids, xanthophylls
Why are plants green?

15. chloroplasts in plant cell chloroplasts contain chlorophyll
absorb sunlight & CO2
cross section of leaf
leaves
CO2
chloroplasts in plant cell
chloroplasts contain chlorophyll
chloroplast
make energy & sugar

16. Plant structure Chloroplasts Thylakoid membrane contains
ATP
thylakoid
Chloroplasts
double membrane
stroma
fluid-filled interior
thylakoid sacs
grana stacks
Thylakoid membrane contains
chlorophyll molecules
electron transport chain
ATP synthase
H+ gradient built up within thylakoid sac
outer membrane
inner membrane
granum
stroma
thylakoid
A typical mesophyll cell has chloroplasts, each about 2-4 microns by 4-7 microns long.
Each chloroplast has two membranes around a central aqueous space, the stroma.
In the stroma are membranous sacs, the thylakoids.
These have an internal aqueous space, the thylakoid lumen or thylakoid space.
Thylakoids may be stacked into columns called grana.

17. Photosynthesis – 2 parts
1. Light reactions
light-dependent reactions
energy conversion reactions
convert solar energy to chemical energy
ATP & NADPH
2. Calvin cycle “dark reactions”
light-independent reactions
sugar building reactions
uses chemical energy (ATP & NADPH) to turn CO2 & C6H12O6 (glucose)
It’s not the Dark Reactions!

18. Light Reactions Electron Transport Chain
Pigments (proteins) in the chloroplast membrane called chlorophyll absorb light waves
Not all wavelengths of light are absorbed

19. Light Reactions Chlorophyll molecules absorb photons of light
This photon of light splits a water molecule inside the membrane into oxygen gas and strips off electrons from the hydrogen to be passed on
1 photosystem is not enough.
Have to lift electron in 2 stages to a higher energy level. Does work as it falls.
First, produce ATP -- but producing ATP is not enough.
Second, need to produce organic molecules for other uses & also need to produce a stable storage molecule for a rainy day (sugars). This is done in Calvin Cycle!
generates O2

20. Light Reactions
The electrons get excited within the chlorophyll and passed on to the next protein
The proteins in the electron transport chain raise the electrons to a higher energy level
As the electron gets passed along one of the proteins it passes through generates ATP
Eventually it gets passed on through all the proteins and the energy filled electron gets stores as NADPH (money in the bank… aka we will be using later)
1 photosystem is not enough.
Have to lift electron in 2 stages to a higher energy level. Does work as it falls.
First, produce ATP -- but producing ATP is not enough.
Second, need to produce organic molecules for other uses & also need to produce a stable storage molecule for a rainy day (sugars). This is done in Calvin Cycle!
ATP
Chlorophyll
Chlorophyll

21. ETC of Photosynthesis e e O split H2O H+ sun sun to Calvin Cycle ATP
Two places where light comes in.
Remember photosynthesis is endergonic -- the electron transport chain is driven by light energy.
Need to look at that in more detail on next slide O
to Calvin Cycle
split H2O
ATP

22. A little more complicated than you need to know it but a good animation…

23. Photosynthesis – Part 1 summary
Why do plants appear green? (use wavelengths in your answer)
What are the light absorbing pigments in plants called?
Where does the oxygen that plants give off come from?
Why are light reactions called light reactions? (Hint: what do they require?)
Where do the light reactions occur?
What do chlorophyll molecules do to electrons?
Where did the energy come from? The Sun
Where did the electrons come from? Chlorophyll
Where did the H2O come from?
The ground through the roots/xylem
Where did the O2 come from? The splitting of water
Where did the O2 go? Out stomates to air
Where did the H+ come from? The slitting of water
Where did the ATP come from?
Photosystem 2: Chemiosmosis (H+ gradient)
What will the ATP be used for?
The work of plant life! Building sugars
Where did the NADPH come from?
Reduction of NADP (Photosystem 1)
What will the NADPH be used for? Calvin cycle / Carbon fixation
…stay tuned for the Calvin cycle

24. Photosynthesis: The Calvin Cycle Life from Air

26. Remember what it means to be a plant…
Need to produce all organic molecules necessary for growth
carbohydrates, lipids, proteins, nucleic acids
Need to store chemical energy (ATP) produced from light reactions
in a more stable form
that can be moved around plant
saved for a rainy day
+ water + energy  glucose + oxygen
carbon
dioxide
6CO2
6H2O
C6H12O6
6O2
light
energy  +

27.   build stuff !! photosynthesis
Light reactions
Convert solar energy to chemical energy
ATP
NADPH
What can we do now?
ATP
 energy
 Stored power
  build stuff !!
photosynthesis

28. CO2 C6H12O6 What is the goal? Want to make C6H12O6 synthesis
How? From what? What raw materials are available?
CO2
CO2 contains little energy because it is fully oxidized
Reduce CO2 in a series of steps to synthesize a stable energy storage molecule
NADPH
reduces CO2
carbon fixation
NADP
NADP
C6H12O6

29. Calvin Cycle = “Dark Reactions”
CO2 is going to be converted into glucose during the Calvin Cycle
This is often referred to as the “Dark Reactions”
Calling it the “Dark Reactions” is misleading
It doesn’t only happen in the dark, but rather in the light AND dark!
Remember light reactions can only happen in the light!

30. From Light reactions to Calvin cycle
Takes place in the chloroplast stroma (which is like the cytoplasm of the chloroplast)
Need products of light reactions to drive the Calvin cycle
ATP
NADPH
stroma
ATP
thylakoid

31. Calvin Cycle summary Calvin cycle Consumed (used) CO2
Produced (made) glucose
Regenerated (recycled) ADP
Regenerated NADP
ADP
NADP

33. Putting it all together
CO2
H2O
C6H12O6 O2
light
energy  +
H2O
CO2
Plants make both:
energy
ATP & NADPH
sugars
sunlight
ADP
NADP
Energy Building
Reactions
Sugar Building
Reactions
NADPH
ATP O2
sugars

34. The Great Circle of Life,Mufasa!
sun
Energy cycle
Photosynthesis
CO2
H2O
C6H12O6 O2
light
energy  +
H2O
plants
CO2
glucose O2
animals, plants
CO2
H2O
C6H12O6 O2
ATP
energy  +
Cellular Respiration
ATP
The Great Circle of Life,Mufasa!

35. If plants can do it… You can learn it!
Ask Questions!!