Transcript CP Photosynthesis Power Point

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
Electron carriers
Coenzymes - carry H+ ions and electrons (H atoms)
– take from one molecule in a chain of reactions,
- give them to another molecule in a later reaction
In photosynthesis, carrier is NADP
- helps change sunlight to chemical energy
takes electrons and H+ ions from water
Gives them to CO2  makes glucose
NADP  NADPH  NADP
Carries (accepts) e- and H+ ions
Light –dependent reactions
In thylakoid membranes
#1. Chlorophyll
absorbs sunlight
a.Electrons from
chlorophyll
b.Make ATP
#2. Light Splits Water
• H2O 
2 H+ + 2 e- + O
• Hydrogens (H+) go to NADP  NADPH
• Oxygens  make O2 gas
• 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 energy
change to ATP?
• Light excites electrons
• Electrons start a series of reactions
–Electron Transport Chain
• Makes ATP
Electron Transport Chain
makes ATP
1. Electron energy concentrates H+ ions
2. Ions diffuse through a membrane enzyme
3. Enzyme makes ATP
Making ATP
ATP Synthase Enzyme
• In thylakoid membrane
• H ions move through it
• Adds P to ADP
• Makes ATP
chemiosmosis
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. H+ and e- go to NADP  NADPH
1) Later they become part of glucose molecule
Light
Reactions
make:
ATP
NADPH
O2
3
1
2
See oxygen gas made by
an aquatic plant
Light-Independent Reactions
“Dark” reactions, or
In stroma of chloroplast
• Uses ATP made in light
reactions
• Fixes CO2 from air
• Adds H+ ions and
electrons from water
• Makes GLUCOSE
Calvin Cycle
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
2) Joins to CO2
”fixed”
1) Start: 5-carbon
compound in
stroma
3) ATP and
NADPH are used
5) End:
Stroma
compound
returned
4) glucose made
Overview of Photosynthesis
LE 7-5
Photosynthesis uses light energy to make food molecules
H2O
Chloroplast
CO2
Light
1. Absorbs
light energy
4. “Fixes”
carbon
NADP
ADP

P
LIGHT
REACTIONS
(in thylakoids)
2. Makes
ATP, NADPH
CALVIN
CYCLE
(in stroma)
ATP
NADPH
3. Light splits
water makes O2
Starch
6. Makes
glucose
O2
5. Uses
energy
molecules
made in
light
Lipids
Sugar
proteins
cellulose
Environmental Factors affecting
Photosynthesis
1. Light – bright sun, more energy
a. Long days (summer), more light absorbed
b. Wavelength – cannot absorb green light
How amount of light affects
rate of photosynthesis
plateau
At high light intensity, rate stays
constant because all
chlorophyll are being used
At low light intensity, rate
increases as light increases
Factors Affecting Photosynthesis
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 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
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
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 stomata are open
- use stored carbon when stomata 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