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PHOTOSYNTHESIS
6.1
The main form of energy from the sun is in the form of electromagnetic radiation
Visible radiation (white light) used for photosynthesis
Remember : ROY G. BIV?
The electromagnetic spectrum
A Red Object absorbs the blue and green wavelengths and reflects the red wavelengths
Why are plants green?
pigment a compound that absorbs light different pigments absorb different wavelengths of white
light.
chlorophyll is a pigment that absorbs red & blue light (photons) so green is reflected or transmitted.
Chlorophyll is located in the thylakoid membranes
So, Plants are green because the green wavelength is reflected, not absorbed.
2 types of chlorophyll Chlorophyll a – involved in light reactions
Chlorophyll b – assists in capturing light energy – accessory pigment
Carotenoids – accessory pigments – captures more light energy Red, orange & yellow
The electromagnetic wavelengths and the wavelengths that are absorbed by the chlorophyll
During the fall, what causes the leaves to change colors?
Fall Colors In addition to the chlorophyll
pigments, there are other pigments present
During the fall, the green chlorophyll pigments are greatly reduced revealing the other pigments
Carotenoids are pigments that are either red, orange, or yellow
Photosynthesis is -
conversion of light energy into chemical energy that is stored in organic compounds (carbohydrates > glucose)
Used by autotrophs such as: Plants Algae Some bacteria (prokaryotes)
glucose - energy-rich chemical produced through photosynthesis C6H12O6
Biochemical pathway – series of reactions where the product of one reaction is consumed in the next
E.g. photosynthesis product is glucose which is used in cellular respiration to make ATP
(carbohydrate)
Remember Redox Reaction
reduction/oxidation The transfer of one or more electrons from one reactant to another
Two types:1. Oxidation is the loss of e-
2. Reduction is the gain of e-
Oxidation Reaction
The loss of electrons from a substance or the gain of oxygen.
glucose
6CO2 + 6H2O C6H12O6 + 6O2
Oxidation
Carbon dioxide Water
Oxygen
Reduction Reaction
The gain of electrons to a substance or the loss of oxygen.
glucose
6CO2 + 6H2O C6H12O6 + 6O2
Reduction
Photosynthesis equation
Light energy
6CO2 + 6H2O C6H12O6 + 6O2
Chlorophyll
Reactants: Carbon dioxide and water
Products: glucose and oxygen which is a byproduct
Where does photosynthesis
take place?
Plants Mainly occurs in the leaves:
a. stoma - poresb. mesophyll cells
StomaMesophyllCell
Chloroplast
Mesophyll Cell of Leaf
Cell Wall
Nucleus
Chloroplast
Central Vacuole
Photosynthesis occurs in these cells!
Stomata (stoma)Pores in a plant’s cuticle through
which water vapor and gases (CO2 & O2) are exchanged between the plant and the atmosphere.
Guard CellGuard CellCarbon Dioxide (CO2)
Oxygen (O2)
Found on the underside of leaves
Stoma
Chloroplast
Organelle where photosynthesis takes place.
GranumThylakoid
Stroma
Outer Membrane
Inner Membrane
Thylakoid stacks are connected together
Partschloroplasts – dbl membrane organelle that
absorbs light energyThylakoids – flattened sacs contain pigment -
chlorophyllGrana (pl: granum) – layered thylakoids (like
pancakes)Stroma – solution around thylakoidsStomata – pore on underside of leaf where O2 is
released and CO2 enters
Stroma : chloroplast :: cytosol : cytoplasm
Thylakoid
Thylakoid Membrane
Thylakoid SpaceGranum
Grana make up the inner membrane
What do cells use
for energy?
Energy for Life on Earth
Sunlight is the ULTIMATE energy for all life on Earth
Plants store energy in the chemical bonds of sugars
Chemical energy is released as ATP during cellular respiration
Structure of ATP ATP stands for adenosine
triphosphate It is composed of the nitrogen
base ADENINE, the pentose (5C) sugar RIBOSE, and three PHOSPHATE groups
The LAST phosphate group is bonded with a HIGH ENERGY chemical bond
This bond can be BROKEN to release ENERGY for CELLS to use
Removing a Phosphate from ATP
Breaking the LAST PHOSPHATE bond from ATP, will --- Release ENERGY for cells to use Form ADP (adenosine diphosphate) Produce a FREE PHOSPHATE
GROUP
High Energy Phosphate Bond
FREE PHOSPHATE can be re-attached to ADP reforming ATP
Process called Phosphorylation
Phosphorylation
Photosynthesis
1. Light Reaction -Produces energy from solar power (photons) in the form of ATP and NADPH.
2. Calvin Cycle Also called Carbon Fixation or
Carbon Cycle, Uses energy (ATP and NADPH) from light reaction to make sugar (glucose).
SUN
3 stages of photosynthesis-
Stages:
STAGE 1 - LIGHT REACTIONS - energy from sun is used to split water into H+ an O2
STAGE 2 – energy is converted to chemical energy & stored in ATP & NADPH in stroma
STAGE 3 - CALVIN CYCLE where carbon is fixed into glucose
Light Reaction (Electron Flow)
Occurs in the Thylakoid membranes
2 possible routes for electron flow:Use Photosystem I and Electron Transport Chain (ETC) and generate ATP only
OR use Photosystem II and Photosystem I with ETC and generate O2, ATP and NADPH
Photosynthesis animation
http://www.mhhe.com/biosci/genbio/biolink/j_explorations/ch09expl.htm
ELECTRON TRANSPORT - LIGHT REACTIONS in 5 steps
Photosystem I and II Step 1 – light excites e- in photosystem II Step 2 – e- move to primary e- acceptor
Step 3 – e- move along electron transport chain (etc)
Step 4 – light excites e- in photosystem I Step 5 – e- move along 2nd (etc) End – NADP+ combine H+ to make NADPH
Light reaction animation
http://www.science.smith.edu/departments/Biology/Bio231/ltrxn.html
Electron transport chain song
Play the "Come On Down (The Electron Transport Chain)" song performed by Sam Reid.
Photolysis –photo-chemical splitting of water (restoring photosystem II)
Chemiosmosis – synthesis of ATP
Powers ATP synthesis Takes place across the
thylakoid membrane Uses ETC and ATP synthase H+ move down their
concentration gradient forming ATP from ADP
Concentration of protons is greater in thylakoid than stroma
ChemiosmosisH+ H+
ATP Synthase
H+ H+ H+ H+
H+ H+high H+
concentration
H+ADP + P ATP
PS II PS IE
TC
low H+
concentration
H+ThylakoidSpace
Thylakoid
SUN (Proton Pumping)
The Calvin Cycle
6.2
Calvin Cycle - Biochemical pathway in photosynthesis that
produces organic compounds using ATP & NADPH
Carbon fixation – carbon atoms from CO2 are bonded or ‘fixed’ into carbohydrates
occurs in stroma
Calvin Cycle Carbon Fixation C3 plants (80% of plants on
earth) Occurs in the stroma Uses ATP and NADPH from light
reaction as energy Uses CO2
To produce glucose: it takes 6 turns and uses 18 ATP and 12 NADPH.
Chloroplast
GranumThylakoid
STROMA– where Calvin Cycle occursOuter Membrane
Inner Membrane
Calvin Cycle (C3 fixation)
6CO2
6C-C-C-C-C-C
6C-C-C 6C-C-C
6C-C-C-C-C
12PGA
RuBP
12G3P
(unstable)
6NADPH 6NADPH
6ATP 6ATP
6ATP
C-C-C-C-C-CGlucose
(6C)(36C)
(36C)
(36C)
(30C)
(30C)
(6C)
6C-C-C 6C-C-C
C3
glucose
Calvin Cycle
Remember: C3 = Calvin Cycle
C3
Glucose
Step 1 -
CO2 diffuses fr cytosol & combines with RuBP which splits into pair of PGA
Step 2 -
PGA gets phosphate gr fr ATP gets proton fr NADPH to become PGAL
Reaction produces: ADP, NADP+ & phosphate to be used again
Step 3 -
PGAL converts back to RuBP
Allows Calvin cycle to continue
Alternates:
C3 plants – use Calvin cycle exclusively Form 3-carbon compounds
C4 pathway – evolved in hot, dry climate Form 4-carbon compounds Partially close stomata E.g. Corn, sugar cane, crabgrass
CAM – open stomata at night, close in day Grow slow, lose less water E.g. cactus, pineapple
C4 Plants Hot, moist
environments 15% of plants
(grasses, corn, sugarcane)
Photosynthesis occurs in 2 places: Light reaction -
mesophyll cells Calvin cycle -
bundle sheath cells
C4 Plants
Mesophyll Cell
CO2
C-C-C
PEP
C-C-C-CMalate-4C sugar
ATP
Bundle Sheath Cell
C-C-C
Pyruvic Acid
C-C-C-C
CO2
C3
Malate
Transported
glucoseVascular Tissue
CAM Plants Hot, dry environments 5% of plants (cactus and ice
plants) Stomates closed during day Stomates open during the
night Light reaction - occurs
during the day Calvin Cycle - occurs when
CO2 is present
CAM PlantsNight (Stomates Open) Day (Stomates Closed)
Vacuole
C-C-C-CMalate
C-C-C-CMalate Malate
C-C-C-CCO2
CO2
C3
C-C-CPyruvic acid
ATPC-C-CPEP glucose
Rate of photosynthesis is effected by - light intensity, CO2 or temperature
High intensity or high CO2 = high rate Growth graph levels off (plateau)
High temp = initial high rate but peaks Rate drops when stomata closes
Recap Photosynthesis converts light energy into chemical
energy thru series of biochemical pathways Electrons excite in photosystem II – move along
ETC to photosystem I electrons are replaced when water is split oxygen is byproduct ATP synthesized across thylakoid Calvin cycle – carbon is fixed & sugar produced 3 turns produce PGAL (PGAL keeps cycle going Other pathways – C3, C4, CAM
References
www.biologyjunction.com