Download Notes-Unit 6-photosynthesis

Unit 6
Chapter 8
Photosynthesis
Learning Target #1
•Describe the role of ATP in cellular
activity.
Energy currency –
ATP (adenosine triphosphate)
1. cell’s energy storage molecule=ATP
2. used for activation energy
3. Why is ATP useful?
•it can easily release and store energy
•Energy source for all cells
Structure of ATP
• adenosine
•ribose sugar and an adenine base
• 3 phosphates
• enzymes easily break bond between 2nd and
3rd phosphate to release energy
• phosphate transferred to another molecule
ATP-ADP cycle
-P
ATP
Releases energy
For cell to do work
ADP
+P
Comes from Energy in food
Formed during cellular respiration
Stores Energy for a little time
Where does ATP come from?
• autotroph - manufacture own food from inorganic
substance and energy
•photosynthesis - capture light energy to be stored
in organic compounds
•plants, algae, some bacteria
• heterotroph - cannot make own food
•eat autotrophs
•heterotrophs that feed on autotrophs
• For humans•ATP comes from the food we eat
• all life ultimately depends on SUN ENERGY and
autotrophs
Learning Target (8.2)
•Explain how cellular structures and
molecules are involved in
photosynthesis.
Leaf Anatomy and Terms
• See attached sheet given to you!
Structure of a chloroplast
• Chloroplast is the site of
photosynthesis
• thylakoids - system of
interconnected membranes,
flattened sacs
• contain chlorophyll
• contain electron transport
chain
• grana - stacks of thylakoids
• stroma - liquid surrounding
thylakoids
Light
• Light appears white :
•actually a variety of colors
•visible spectrum
• Light can be:
• reflected
•Transmitted
•Absorbed
Chloroplast pigments
• pigment - compound that absorbs light
• chlorophyll a (green) - absorbs less blue but more
red
• directly involved in light reactions
• chlorophyll b (green) - absorbs more blue and less
red
• assists chlorophyll a in light absorption
• accessory pigment
• accessory pigments
• carotenoids - yellow, orange, brown
• xanthophylls - yellow
• in leaves, chlorophyll masks others
• others show in fruits, flower
Learning Target (8.3).
•Describe how a photosynthetic
organism converts the sun’s energy
into chemical energy
An Overview of Photosynthesis
•
Photosynthesis uses the energy of sunlight to convert water and carbon
dioxide into high-energy sugars and oxygen.
•
In symbols:
•
6 CO2 + 6 H2O  C6H12O6 + 6 O2
•
In words:
• Carbon dioxide + Water  Sugars + Oxygen
Light Dependent Reaction
(A.K.A. Light Reaction)
• photosystem
• cluster of pigment molecules
• two photosystems: 1 and 2
1. light is absorbed by chlorophyll a in photosystem 2
• 2 electrons are energized (excited) to higher energy
level
2. electrons leave chlorophyll a (oxidized) (LEO)
• goes to primary electron acceptor in thylakoid membrane
(reduced)(GER)
3. electrons donated to electron transport chain - lose energy
• used to move protons into thylakoid
High-Energy Electrons
•
The high-energy electrons produced by chlorophyll are highly reactive
and require a special “carrier.”
• Think of a high-energy electron as being similar to a hot potato. If you wanted
to move the potato from one place to another, you would use an oven mitt—a
carrier—to transport it.
•
Plants use electron carriers to transport high-energy electrons from
chlorophyll to other molecules.
Light Dependent Reaction
(A.K.A. Light Reaction)
4. at same time photosystem 2 absorbs light, so does photosystem 1
• 2 electrons leave chlorophyll a to another primary electron
acceptor
• photosystem 1 electron replaced by electron from photosystem 2
5. primary electron acceptor of photosystem 1 sends 2 electrons
toward stroma and they combine with 2 protons (H+) and NADP+
(coenzyme) (reduced to NADPH)
6. electron of photosystem 2 replaced by splitting of water:
2H + 2e- + 1/2O2
• H2 O
• Products of the Light Rxn: O2 + NADPH + ATP
• H+ produced remain in thylakoid,
• O2 produced diffuses out of plant
• http://www.fw.vt.edu/dendro/forestbiology/photosynthesis.swf
High-Energy Electrons
•
NADP+ (nicotinamide adenine dinucleotide phosphate) is a carrier
molecule.
•
NADP+ accepts and holds two high-energy electrons, along with a
hydrogen ion (H+). In this way, it is converted into NADPH.
•
The NADPH can then carry the high-energy electrons to chemical
reactions elsewhere in the cell.
Light Reaction
Chemiosmosis
1. Process to synthesize ATP
•protons from splitting of water are pumped from
stroma into the thylakoid (ACTIVE TRANSPORT)
•concentration gradient of protons higher inside
thylakoid than in stroma (represents potential
energy)
• ATP synthase in thylakoid makes ATP by adding
phosphate to ADP
• movement of protons to stroma provides energy
2. NADPH and ATP needed to run dark reactions
Light Independent Reaction
A.K.A.-Calvin Cycle (do not need light) (in stroma)
Light Independent Reaction
A.K.A.-Calvin Cycle (do not need light) (in stroma)
Carbon fixation- inclusion of CO2 into organic compounds
1. CO2 diffuses through stomates (stoma) from atmosphere
into cells
• stomata- small pores on the leaf that allow CO2 and O2
through
2. CO2 diffuses into stroma from cytoplasm
• starting compound is RuBP (ribulose biphosphate)
• CO2 combines with RuBP(5C)
• 6C unknown formed
• splits immediately into two PGA (3C)
(phosphoglycerate)
Light Independent Reaction
A.K.A.-Calvin Cycle (do not need light) (in stroma)
Light Independent Reaction
3. PGA converted to PGAL (3C) (steps of how)
(phosphoglyceraldehyde)
•phosphate from ATP
•PGA + ATP
DPGA (PGA-P) + ADP
• H added from NADPH and phosphate released
producing PGAL
•ADP, P, and NADP+ cycled back to light
reactions
4. most PGAL converted back to RuBP
Light Independent Reaction
A.K.A.-Calvin Cycle (do not need light) (in stroma)
Light Independent Reaction:
Synthesis of Glucose
1. 2 PGAL join to form glucose, fructose, or galactose
• glucose used for cell respiration by plant
•excess glucose:
sucrose can be made
starch and cellulose can be formed
amino acids and lipids can be formed
• http://www.youtube.com/watch?v=OYSD1jOD1dQ&fe
ature=relate
• http://fdmcbiology12.weebly.com/calvin-cycle.html
Over all photosynthesis reaction:
C6H12O6 + 6O2 + 6H2O
6CO2+ 12H2O + light
Learning Target 8.3 c
•Identify the factors that affect the
rate of photosynthesis (8.3)
Rate of Photosynthesis
1. light intensity (when reaches certain
intensity, rate levels off)
2. level of CO2
3. temperature (too high inhibits enzyme
action)