Download Photosynthesis

PHOTOSYNTHESIS
PHOTOSYNTHESIS
Photosynthesis is ability of a plant to turn
sunlight, air, and water into sugar
(energy).
 The overall reaction is:

light
chlorophyll
H2O -------> CH2O
CO2 +
+ O2
 Photosynthesis is vital to life for two
reasons
–1. The oxygen in the air comes from
photosynthesis. The plants continue to
replenish the oxygen in the air.
–2. All of our food comes directly or
indirectly from photosynthesis.
Parts of a leaf
Stomata
palisade layer
spongy layer
veins
chloroplast
thylakoids
grana
stroma
Light
 Photosynthesis
uses visible light.
– Only visible light with intermediate
wavelengths has enough energy to cause
chemical change without destroying
biological molecules.
 What
are the colors of the visible
spectrum?
 Why does a leaf look green?
Light is captured by
pigments. The main
photosynthetic pigment is
chlorophyll. There is
chlorophyll a, b and c.
Chlorophyll a is the major
photosynthetic pigment and
is found in all
photosynthetic plants,
protist, and cyanobacteria.
Carotenoids are accessory pigments
found in all green plants. They absorb
blue and green wavelengths and give a
plant a yellow or orange color. In the fall
when chlorophyll breaks down, it is the
accessory pigments which give colors of
fall. The red color of some autumn leaves
is due to the anthocyanin pigments.
These are not photosynthetic.
Stages of Photosynthesis
LIGHT REACTIONS
DARK REACTIONS
Light absorption
Carbon Fixation
Electron transport
Oxygen production
Chemiosmotic ATP synthesis
The Energy-Capturing Reactions
 Light
absorption
– Chlorophyll a and b are antennae pigments
 Electron
transport
– Electrons lost by chlorophyll a end up at
NADP
– Produce oxygen
 Chemiosmotic
ATP synthesis
– Powered by H ion reservoir
The Dark Reactions
 The
dark reactions take place outside
the thylakoid membrane.
 Carbon fixation - The carbon dioxide is
incorporated into an organic molecule
(1C + 5C = 6C). This 6 carbon structure
is unstable and immediately splits into
2, 3 carbon molecules. These molecules
go through a series of reactions known
as the CALVIN CYCLE.
What controls photosynthesis?
Intensity
of light
Scarcity of water
Ecological Aspects

C4 PLANTS - Use more ATP but at high
temperatures they can photosynthesize
faster -allowing plants to grow and
reproduce faster. These include many
weeds and important crops such as corn.

A special variation of C4 plants are the
CAM plants. These are mostly desert
plants. These plants keep the stomata
closed during the day and open at
night. They must conserve water!
Vocabulary
 Glossary
– blade
– stipules
– petiole
– vein
– midrib
of terms
Vocabulary
carotenoids
chlorophyll
electromagnetic
spectrum
granum
NADP+
NADPH
photon
photosystem
photosystem I
photosystem II
pigment
stroma
thylakoid