Download Photosynthesis - Jocha

Photosynthesis
Photosynthesis
Making
the fuel of life
 Sunlight energy is trapped and
converted into chemical energy in
the form of glucose
 Energy is stored in organic molecules
made of inorganic raw materials
 Photosynthesis is considered and anabolic process: Involves the synthesis of
new, larger compounds
 Organisms that are able to make their
own food in this way are called
autotrophs
 Plants, Algae, and Cyanobacteria
Specific organelle (Eukaryotes):
Chloroplast
Photosynthesis
Making the fuel of life
What is used?
What is produced?
+ 6CO2 + 6H2O
C6H12O6 + 6O2
Glucose
autotrophs
What living things make photosynthesis?
 Algae (seaweeds) and plants: The entire
process takes place in the chloroplast
Kelp
 Some unicellular Eukaryotes (Phytoplankton)
make photosynthesis, and some bacteria
(Cyanobacteria, that lack chloroplasts)
Anabaena, a
cyanobacteria
Mosses, ferns, pine trees,
and flowering plants
Euglena, inside the
group Protista, is
an unicellular
Eukaryote
How much is produced? 160,000,000,000 tons per year… or…
352,000,000,000,000 pounds
1
Photosynthesis
Why are these living things autotrophs?
•They have chlorophyll
•A green pigment
that absorbs light
energy and
initiates the
sequence of
reactions
(Able to produce their own food)
 Chlorophyll
 Is contained folded membranous structures called thylakoids in
chloroplasts
 Sunlight provides the energy
 Chlorophyll molecules absorb photons (units of energy)
 Electrons in the covalent bonds of the chlorophyll gain energy
 With this energy, electrons are able of entering into chemical reactions responsible for
the production of ATP + NADPH
ATP + NADPH are used in turn to produce glucose
Why is chlorophyll green?
•Light consists of high-speed particles called photons.
•Photons are packets of electromagnetic energy
Electromagnetic spectrum
shows the full range of radiation types
 Chlorophylls (a and b)
 Absorb mostly blue and red light
 But reflect 100% of the green
light
2
Photosynthesis
Why do color of leaves turn to different colors in fall?
Why are there brown and red algae?
 Other pigments absorb slightly different
wavelengths and “help” the chlorophyll!
 Carotenoids: in plants and algae
 Phycobilins: in algae and bacteria
 Chlorophyll c & d: in algae
Why having accessory pigments?
 With only chlorophyll
Visible spectrum
 With accessory pigments
Visible spectrum
Ergo…
 The more pigments
 The more “types” (different wavelengths)
of energy autotrophs can absorb
Stages of photosynthesis
(1) Light dependent reactions
 Need light to happen
 Take place in the membrane of the
thylacoids
 The light reactions convert solar
energy to chemical energy (ATP,
NADPH)
(2) Light independent reactions
 or “Dark”reactions or “Calvin cycle”
 DOES NOT need light to happen
 Takes place in the stroma (matrix) of
the chloroplast
 Uses the products of the light reactions to
make sugar from carbon dioxide
3
Photosynthesis
How do plants exchange the gases involved in photosynthesis?
 Stomata are
tiny pores in
leaves where
carbon dioxide
enters and
oxygen exits.
Produced in the
stroma of chloroplast
“in” using
stomata
“in”
using
roots
“in” and “out” using
stomata
(1) Light dependent reactions
How chlorophyll traps sunlight and passed the energy to the ETC…
 Chlorophyll is arranged in plants in photosystems
 Which are molecular light-capturing devices
 Two sequential photosystems are needed to
complete the light reactions
Why splitting
water?
 e- (electrons)
released are used to
replace those lost by
the chlorophyll
 H+ and O2 are also
produced
ETC
ETC
NADPH
production
ATP
production
Water-splitting
photosystem
NADPH-producing
photosystem
Both are used in
the dark reactions
to produce
glucose
4
Photosynthesis
 (1) The “excited”
electrons are passed
through two electron
transport chains
 (2) This results, as in cellular respiration, in H+ being
pumped into the cavity of the thylacoid…
 and electron “jumping” from one acceptor molecule to
another, with each “jump” meaning higher energy levels
 (3) Also as in cellular respiration, H+ return to the exterior of the
thylacoid down a gradient concentration and ATP is generated
(2) “Dark” reactions or Calvin Cycle
Input
 Functions like a sugar factory
within the stroma of a chloroplast
enzyme
Three CO2
CARBON
FIXATION
 Regenerates the starting material
with each turn
Six
Three ADP
Three
Six ADP + Six
Calvin
cycle
Six
Six NADP
ATP (energy) and NADPH ( H+) generated
in the previous stage, atmospheric CO2, and
a starter sugar molecule allow to build
organic molecules (ex:glucose)
One G3P
Output
Glucose and
other compounds
5
Photosynthesis
 The first real product of photosynthesis is
Glyceraldehyde 3-P instead of glucose!
 This molecule is the main intermediate
product of glycolisis in cellular respiration
 The surplus of Glyceraldehyde 3-P
is used to build glucose and a
diversity of molecules
How do plants adapt to water scarcity?
Plants open their stomata in the
epidermis to take in the CO2, but
H2O may be lost by dehydration
CO2
CARBON FIXATION
Calvin
Cycle
enzyme
“C3” photosynthesis
Sugar
(most plants)
The enzyme that “fixes” the CO2 works
very well when CO2 is abundant, but
poorly when CO2 concentration is low
“C4” photosynthesis
“CAM” photosynthesis
(Hot and dry areas)
(also in hot and dry areas)
stomata slightly open in the
epidermis to take in the CO2, this
minimizes water loss
stomata open at night
to take in the CO2
CO2
CO2
C CARBON FIXATION
uptake  Different enzyme, very
Calvin
Cycle
Sugar
Night
efficient when CO2
concentration is low (when
stomata are slightly open
Calvin
Cycle
 But there are extra steps
needed and more ATP is
used…
 more energy is spent
C
uptake
Day
CARBON
FIXATION
stomata
closed
during the
day, this
minimizes
water loss
Sugar
6