Post on 11-Jan-2016
Photosynthesis
PS Learning Targets 1-9
Photosynthesis Outline
LT’s 1-3: Energy and Old Dead Dudes
LT’s 4 & 5: Light and Structures of PS
LT’s 6-8: Reactions and Factors of PS
ENERGYAll living things need energy to live!– Heterotrophs-get their food by eating other
organisms and turning them into energy (Ex: herbivores, carnivore, decomposers, etc)
– Autotrophs-get their energy by converting light or chemical energy into sugar, and then converting that into energy
(Ex: plants, bacteria, and some protists)
LT 1
ENERGY• The cell will store energy in molecules like
sugars and ATP– Most cells have small stores of ATP that only last
a few seconds, but cannot store energy there long-term.
– Cells will store it long term in carbohydrates/ sugars– Sugar energy > ATP energy 90x greater
ENERGYWhat are the uses for ATP in biochemical
reactions?• Active Transport• Energy to move cell organelles• Making proteins or nucleic acids• PHOTOSYNTHESIS!!!
Understanding PhotosynthesisVan Helmont
**Water and CO2
are needed tomake plants grow**
Do plants grow by taking material out of the soil?• Thought most of it came from the water absorbed•Did not know that the bulk of the mass came from CO2 absorbed from the air.
Priestley
**O2 is made from PS **
Put a flame under a jar and watched it burn out.•Found there was something in the air that caused the flame to burn•Put a mint plant in the jar and found it produced something flames needed.
Ingenhousz
**Plants need light for PS**
•Found that Priestley’s experiment needed light to occur.
LT 2
Photosynthesis Reaction
6 CO2 + 6 H2O light C6H12O6 + 6 O2
From the air
From the roots
From the sun
Made in the dark
rxn
Made in the light
rxn
Will be made into ATP later in
Cellular Respiration
LT 3
Light and Pigments6 CO2 + 6 H2O light C6H12O6 + 6 O2
• Photosynthesis starts with SUNLIGHT!• The light that comes from the sun is WHITE
LIGHT or ROYGBIV (R O Y G B I V)
• The red end is lowerenergy and longer wavelength
• The violet end has higher energy and smaller wavelength
LT 4
Light and Pigments? If plants use visible light, are all
colors/wavelengths/energies equally valuable to PS?
Let’s see…
Read the results of the experiment from Thomas Engelmann in 1803
Light and Pigments• Most plants are GREEN. This means that ROY BIV is absorbed and G is reflected.
• This means that if ROY and BIV are absorbed these are the colors of light that power PS
Pigment – any substance that absorbs light Chlorophyll a – the main pigment in plants that absorbs the sun’s light to power PS
Light and Pigments• There are also other pigments, beside
chlorophyll a, called ACCESSORY PIGMENTS chlorophyll b and carotenoids
• Each pigment has its optimal portion of ROYGBIV for absorption and to fuel PS
• Chlorophyll a is the main pigment for PS, while the accessory pigments help chlorophyll a by expanding the portion of ROYGBIV it can use!
Light and PigmentsChlorophyll a best absorption
occurs around 425nm AND 660nm
Chlorophyll b best absorption occurs around
475nm AND 640nm
Carotenoids best absorption occurs
around 450nm AND 490nm
Therefore, the accessory pigments expand the absorption from about 425nm (V) to 425-490nm (V-B) AND from 660nm (R) to 640-660nm (O-R). More light absorbed = More PSing!!
Cell Structures We Already Know….
Cell Membrane• A phospholipid bilayer embedded with proteins• Selectively permeable • Maintains homeostasis for the cell via – PASSIVE (diffusion, osmosis, or facilitated diffusion)– ACTIVE TRANSPORT (active transport, endocytosis or
exocytosis)
Now…The Leaf and Chloroplasts• The structures plants use for PS
LT 5
The LeafCuticle- the waxy outer covering of a leaf that prevents water loss
Palisdade Layer-layer of long cells where chloroplasts are found and where most of PS occurs
Spongy Mesophyll-random collection of cells with large spaces in between them. Some PS occurs here, but mostly this is where the gases taken in & given off by PS are exchanged between palisade layer and stoma
The Leaf (cont.)
Stoma- openings on the underside of leaves that allow for gas
exchange between the leaf and atmosphere.
Guard Cells-the cells on either side of the stoma that open/close them to let gases in or out OR to keep gases in
The Chloroplast• Organelle responsible for
PHOTOSYNTHESIS!• Disc-like in shape• Green due to the presence of
the pigment Chlorophyll a • Found mostly within the
palisade layer, but some are in the mesophyll too.
• Internal structures include– Thylakoids– StRoma– Granum (sing.) or Grana (pl.)– Lumen
Let’s see this
The Chloroplast (cont.)1 of 2 membranes that surround the
organelle
Fluid between
the thylakoids where the dark rxn occurs
Disc where the pigments of PS are. Where the light rxn
occurs
How Photosynthesis Occurs? So what about the rest of the PS equation; like CO2,
Water, Glucose and O2 ?
6 CO2 + 6 H2O light C6H12O6 + 6 O2
PS occurs in 2 parts1. Light Dependent (or Light Reaction)• This part of the rxn requires LIGHT, H2O, and gives off O2
2. Light Independent (or Dark Reaction)• This part of the rxn requires CO2 and produces the sugar
or glucose
LT’s
6 & 7
Photosynthesis
Reactants
Products
The Light Reaction“I’m So Excited!”
e- e-
electron carriers receive chlorophyll’s electrons the excited e-’s and pass
get very excited from the them along to other sun’s energy molecules. These e-’s
carriers molecules arecalled the ELECTRON TRANSPORT
CHAIN
LT 6
The Light ReactionExamples of a Carrier Molecule:
NADP+
• Takes 2e-’s from chlorophyll and 1H+ from water
NADP+ + 2e- + 1H+ NADPH• Takes energy with it to other cell rxns• Think of it like a UPS truck, picking up “packages” and
dropping them off
ATP
The Light Reaction: Key Concepts• Occurs in the thylakoid membrane of the
chloroplast• Includes Photosystem II and Photosystem I• Needs Light and H2O to start
• Produces O2, NADPH and ATP
Waste!
The Light Reaction: Photosystem II
PS II - In the Thylakoid Membrane (TM)• 1. e- absorb sun’s energy and get highly energized• 2. The proteins in the TM split a water (hydrolysis) to
make H+’s , e-’s , and O2
• 3. e-’s go to ETC (a series of protein carriers)
• 4. Energy from the e-’s pumps H+’s into the TM, changing the [H+] ions (low to high-active transport)
The Light Reaction: Photosystem I
PS I - In the Thylakoid Membrane (TM)• 5. Light is energized again
• 6. e-’s move to the final e- acceptor which adds them to NADP+ to make NADPH
• 7. High [H+] (left over from hydrolysis) diffuse through the enzyme protein ATP synthase to make ATP form ADP (H+ give energy to add a phosphate to ADP)
Let’s See This
The Light Reaction: The Thylakoid Membrane
The Light Reaction: The Thylakoid Membrane
A Little Quiz:1. Put a #1 where there is a higher concentration of H+
2. Draw a squiggly line between PSII and PSI3. Put a #2 on the thylakoid membrane4. Put a #3 in the stroma5. Put a #4 where the e-’s are first energized6. Put a #5 where the e-’s are re-energized7. Put a #6 where hydrolysis occurs8. Put a #7 where active transport is occurring.
The Dark Reaction: Key Concepts
• The second part of PS is called the Dark Reaction,the Calvin Cycle, or the Light Independent Cycle
• It is called the Dark Rxn because this part can take place without light (that is not to say it must be dark,
but if it were, this part could still proceed)
LT 7
The Dark Reaction: Key Concepts• The two products from the Light Reaction, NADPH and
ATP go to the Dark Reaction
• NADPH and ATP have lots of energy in their bonds but they can only hold it for a few minutes
• If the cell wants to hold the energy long-term, they will have to build high energy molecules that can hold it…like GLUCOSE (savings account!)
• This process takes place in the stRoma (outside of thylakoid)
The Dark Reaction
6-ATP
6-NADPH
3 -CO2
3-RuBP’s5 C’s
3-5C RuBP’s
3-6C Compound-Unstable!
6-3C PGA’s
6-3C PGAL’s
5 stay in cycle
1 exits and will become GLUCOSE
From Light Rxn
Calvin Cycle Video
3-ATP
Limiting Factors to PSThere are factors that limit the amount of PS
1. H2O –slow or decrease PS
2. Temperature– Recall that enzymes have particular optimal temperatures– Functions best between 0-35°C– Temperatures above or below these temps slow PS– Very low temps STOP PS
3. Light Intensity- increase intensity = increase PS4. Color of Light – RO and BV preferred
LT 8
Photosynthesis Review• Two rxns: Light and
Dark• Reactants: H2O, CO2,
and Light• Products: O2 and
Glucose• Two Locations: – Light –Thylakoid
Membrane– Dark- StRoma
LT’s
1-8
Photosynthesis Review
1.
2. 8.
3. 4.
5. 6. 7.
9. 10. 11.
12. 13.
Word BankPhotosynthesisATP (2)ThylakoidStromaLight Energy from the sunHigh energy sugarsNADPH (2)OxygenLight-depentdent reactionCalvin CycleChloroplast
Photosynthesis Review
Adaptations for Photosynthesis
• Recall, that normally stomata are OPEN…– during the day, – when light intensity is high, – CO2 levels are low – and/or water levels are high
Sometimes, during the day, the threat of water loss is too great. How do plants adjust for this?
LT’s 9
Some plants do open/close their stomata backwards!
AT NIGHT…• The stomata OPEN and CO2 comes into the plant’s leaves• Instead of RuBP, CO2 is attached to a molecule called PEP and they
become malic acid• Malic acid is stored in the cells’ central vacuoles
DURING THE DAY…• The stomata close. H2O stays in. • Malic acid leaves the central vacuole and is broken down to get CO2
again• The dark reaction then takes place.
Used by plants in very arid (dry) conditions. Called CAM plants