Transcript Light-Independent Reactions

CP Ch. 8 PHOTOSYNTHESIS
Uses energy
from sunlight
Converts water and carbon dioxide from
the environment into organic food
molecules and oxygen gas
Photosynthetic organisms – producers on
land and in the water
Two Sets of Reactions
In chloroplasts
1. Light-Dependent
(“light”) Reactions
- Chlorophyll absorbs sunlight
- Makes energy molecule ATP
- Makes O2 gas
2. Light-independent reactions
Calvin cycle
(“dark” reactions)
• Uses energy molecules
from light reactions
• Uses CO2
• Makes glucose
6 CO2 + 6 H2O  C6H12O6 + O2
Cells use ATP for energy
ATP - adenosine triphosphate
High-energy bond between phosphate groups
- breaks easily, bond energy is released
- energy is used by cell to do work
When a cell needs energy for work, 3rd phosphate
comes off ATP and attaches to molecule doing work
-Transfers ENERGY to new molecule
-“phosphorylate”
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ATP – ADP Cycle
• ATP breakdown products (ADP + P) stay in cell
• used again to make more ATP when needed
ATP made in
cell respiration
ATP used for
cellular work
Very fast!! A cell can make 10 million ATP/second
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Sunlight is white light, containing all colors
Color of light
Depends on wavelength (l)
-Shorter wavelength
 higher energy
- blue-violet end of spectrum
-Longer wavelength
 lower energy
-red-orange end of spectrum
Visible light: small part of Electromagnetic spectrum
travels as a wave ---- behaves as a particle (photon)
Shorter wavelength
Longer wavelength
Higher energy
Lower energy
Colors of light absorbed by photosynthetic pigments
Plants absorb blue and red light best
Photosynthetic pigments
•Plants have multiple pigments to absorb as
much sun energy as possible
•Chlorophyll a is the primary pigment –
starts the chain of reactions
•Chlorophyll b, carotenes, xanthophylls and
others are accessory pigments.
•They absorb wavelengths that chlorophyll a
cannot absorb  use more of sunlight
Chromatography
Separates a liquid mixture
by solubility
Colors of light absorbed by a chloroplast
Colors NOT absorbed are
reflected or transmitted
-- the colors we SEE
Absorbed light energy
is transferred to
electrons in pigment
-- energized electrons
Chlorophyll absorbs mostly from the red and blue ends
of the spectrum - reflects green.
Parts of a chloroplast
Thylakoid membranes
- have chlorophyll
- absorb sunlight
- site for 1st set of
reactions
Granum – stack of thylakoid sacs
Stroma – fluid surrounding thylakoids
- site for 2nd set of reactions
Parts of a Leaf
What are electron carriers?
Electron carriers are coenzymes that take electrons
(and H+ ions) from one molecule in a chain of
reactions and transfer them to another molecule
in a later reaction.
a. transfer energy
b. In photosynthesis, the carrier NADP accepts
electrons and H+, becoming NADPH
c. Helps change sunlight to chemical energy
What is NADP?
• NADP accepts electrons and H+ ions
from water in “light” reactions
NADP + H  NADPH
• Gives them to CO2 in Calvin cycle
NADPH - H  NADP
• CO2 + H + e-  glucose
Coenzyme – helps in a reaction but is not
the catalyst
NADP is an electron and hydrogen
“acceptor”
It carries e- and H+ ions until a later reaction
NADP + H  NADPH
NADPH – H  NADP
Light –dependent reactions
TWO things happen
1.Photosystems
absorb sunlight
a.excited electrons
from chlorophyll go to
Electron Transport
Chains
b.Make ATP
2. Light Splits Water
• H2O 
2 H+ + 2 e- + O
• Hydrogens (H+) reduce NADP  NADPH
• Oxygens  O2
• Electrons - replace electrons lost from chlorophyll
Light Reactions
reactant
products
1. Water
Also need
-Sunlight
-chlorophyll
1. ATP
2. NADPH
3. Oxygen gas
How does light make ATP?
Light energizes electrons
Electrons enter an
Electron Transport Chain
Series of membrane proteins transfer electrons
Electrons power ATP synthesis
Electrons pass from one membrane protein to the next
Electron energy concentrates H+ ions
Ions help make ATP
Chemiosmosis
How Cells make ATP
H+ ions diffuse through ATP Synthase
- (enzyme in thylakoid membrane)
• Phosphorylates ADP (ADP + P)
• Makes ATP
chemiosmosis
ADP + P  ATP
Summary of Light reactions
1. Capture light energy, make ATP
2. Split water (H2O) into 2 H+ + O + 2e1) Electrons replace those lost from chlorophyll
2) O makes oxygen gas
3. Add H+ and e- to NADP  NADPH
1) Later they become part of glucose molecule
Light
Reactions
make:
ATP
NADPH
O2
2
1
3
Bubbles –oxygen gas made by an
aquatic plant
Calvin Cycle
“Dark” reactions, or Light-Independent Reactions
In stroma of chloroplast
• Uses ATP made in light
reactions
• Fixes CO2 from air
• Adds H+ ions from water
• Adds electrons from ETC
Makes GLUCOSE
What is carbon fixing?
CO2 from air
becomes part of
organic molecule
Energy needed to
make glucose comes
from ATP made in the
light reactions
Calvin Cycle
in stroma
B) Carbon is “fixed”
 CO2 becomes part of
a 3-carbon molecule
A) Carbon
compounds in
stroma
(RuBP)
C) ATP and
NADPH are used
E) Stroma
compounds
returned
D) (2) 3-C compounds make 1 glucose
Overview of Photosynthesis
LE 7-5
Photosynthesis uses light energy to make food molecules
H2O
Chloroplast
CO2
Light
“Fixes” carbon
(CO2 becomes
part of organic
molecule)
NADP
ADP
Absorbs
light energy

P
LIGHT
REACTIONS
(in thylakoids)
Makes energy
molecules ATP,
NADPH
CALVIN
CYCLE
(in stroma) Uses energy
molecules
made in light
ATP
NADPH
Makes glucose
Light splits water
-makes O2
Starch
Lipids
O2
Sugar
proteins
cellulose
Factors Affecting Photosynthesis
1. Light – bright sun, more energy
a. Long days (summer), more light absorbed
b. Wavelength – cannot absorb green light
2. Temperature – warm, but not too hot
a. Hot days – stomata close to save water
3. Water – soil must be moist
a. Water comes up through xylem in veins
b. Exits through open stomata
c. Water low? – stomata close
How CO2 concentration affects
rate of photosynthesis
plateau
At high CO2 concentration, rate
is constant because all
coenzymes are being used
At low CO2 concentration, rate
increases as CO2 increases
How amount of light affects
rate of photosynthesis
plateau
At high light intensity, rate stays
constant because all
photosystems are being used
At low light intensity, rate increases
as light increases
How temperature affects rate of
photosynthesis
Rate increases
with increasing
temp (energy)
- To optimum
Rate drops above
optimum temp
- stomata close to
save water
- enzymes denature
Environmental Factors affecting
Photosynthesis
Ordinary plants in hot weather
C-3 – carbon fixed into a 3-carbon compound
In hot, dry weather, C-3 plants:
•
leaf openings close to save water
•
How can CO2 get inside?
Leaf epidermis, stomata
Guard cells open/close stomata
Open
Closed
Close when [CO2] or water is low in plant
C-4 Plants
C-4 plants store CO2 while stomates are open
- use stored carbon when stomates are closed
 Can still make sugar
Corn
Sugar Cane
crabgrass
CAM Plants
Succulents
cacti
pineapples
Fix CO2 during the night, when it is cool enough
for open stomates
- Do photosynthesis during the day, using the
stored carbon
Parasitic plants
Supplement nutrition by taking from other organisms
Dodder Plant
Cannot make its own food
Takes nutrients from host plant
Mistletoe – supplements photosynthesis
Carnivorous plants
Eat insects to get nitrogen
Venus Fly Trap
Insect walking on leaves touches trigger hairs
- Leaves close, insect digested
Pitcher plant
Insect climbs inside, can’t get out
Walls of tube are slippery
Sundew – eats insects
Sugary “dew” attracts
insects
Insects get stuck, plant closes
Carotenes in
nature
We can see carotenes,
xanthophylls, and other
pigments in places other
than autumn leaves
Is it a fruit or a vegetable?
Botanically speaking, a fruit is a seed-bearing structure that develops from the
ovary of a flowering plant, whereas vegetables are all other plant parts, such as
roots, leaves and stems. By those standards, seedy outgrowths such as apples,
squash and, yes, tomatoes are all fruits, while roots such as beets, potatoes and
turnips, leaves such as spinach, kale and lettuce, and stems such as celery and
broccoli are all vegetables.