Photosynthesis
Objectives
• Explain the
importance of
photosynthesis.
• Write and interpret
the chemical equation
for photosynthesis.
Check Your Understanding
How are plant cells different from animal cells?
In what organelle does photosynthesis take place?
All Energy on Earth comes from the
Sun!!
Light Energy Harvested by Plants &
Other Photosynthetic Autotrophs
6 CO2 + 6 H2O + light energy → C6H12O6 + 6
O2
THE BASICS OF PHOTOSYNTHESIS
• Almost all plants are photosynthetic autotrophs, as
are some bacteria and protists
– Autotrophs generate their own organic matter through
photosynthesis
– Sunlight energy is transformed to energy stored in the
form of chemical bonds
(c) Euglena
(b) Kelp
(a) Mosses, ferns, and
flowering plants
(d) Cyanobacteria
Food Chain
Overview
• Carbon dioxide and water are taken in by
plants
• Plants absorb light energy and convert it to a
usable form.
– ATP
• Energy is used to “fix” carbon dioxide into
sugar molecules
– Chemical energy
• Sugar is converted to starch and stored for
use by the plant, and by animals when they
eat plants.
WHY ARE PLANTS GREEN?
It's not that easy bein' green
Having to spend each day the color of the leaves
When I think it could be nicer being red or yellow or gold
Or something much more colorful like that…
Kermit the Frog
Electromagnetic Spectrum and
Visible Light
Gamma
rays
X-rays
UV
Infrared &
Microwaves
Visible light
Wavelength (nm)
Radio waves
WHY ARE PLANTS GREEN?
Different wavelengths of visible light are seen by
the human eye as different colors.
Gamma
rays
X-rays
UV
Infrared
Visible light
Wavelength (nm)
Microwaves
Radio
waves
The feathers of male cardinals
are loaded with carotenoid
pigments. These pigments
absorb some wavelengths of
light and reflect others.
Sunlight minus absorbed
wavelengths or colors
equals the apparent color
of an object.
Why are plants green?
Transmitted light
WHY ARE PLANTS GREEN?
Plant Cells
have Green
Chloroplasts
The thylakoid
membrane of the
chloroplast is
impregnated with
photosynthetic
pigments (i.e.,
chlorophylls,
carotenoids).
THE COLOR OF LIGHT SEEN IS THE
COLOR NOT ABSORBED
• Chloroplasts
absorb light
energy and
convert ito
chemical energy
Light
Reflected
light
Transmitted
light
Chloroplast
Absorbed
light
Chloroplasts
• Have TWO membranes
– A “bi-bilayer!”
• The inner membrane is
called the thylakoid.
• The thylakoid is folded
and looks like stacks of
coins called granum
(grana singular).
• The stroma is the space
surrounding the granum
Image source: http://www.daviddarling.info/encyclopedia/C/chloroplasts.html
Chloroplasts: Sites of Photosynthesis
• Photosynthesis
– Occurs in chloroplasts, organelles in certain
plants
– All green plant parts have chloroplasts and carry
out photosynthesis
• The leaves have the most chloroplasts
• The green color comes from chlorophyll in the
chloroplasts
• The pigments absorb light energy
Photosynthesis occurs in chloroplasts
• In most plants, photosynthesis occurs
primarily in the leaves, in the chloroplasts
• A chloroplast contains:
– stroma, a fluid
– grana, stacks of thylakoids
• The thylakoids contain chlorophyll
– Chlorophyll is the green pigment that captures
light for photosynthesis
• The location and structure of chloroplasts
Chloroplast
LEAF CROSS SECTION
MESOPHYLL CELL
LEAF
Mesophyll
CHLOROPLAST
Intermembrane space
Outer
membrane
Granum
Grana
Stroma
Inner
membrane
Stroma
Thylakoid
Thylakoid
compartment
Chloroplast Pigments
• Chloroplasts contain several pigments
– Chlorophyll a
– Chlorophyll b
– Carotenoids
Figure 7.7
Plants produce O2 gas by splitting H2O
• The O2 liberated by photosynthesis is made
from the oxygen in water (H+ and e-)
AN OVERVIEW OF PHOTOSYNTHESIS
• Photosynthesis is the process by which
autotrophic organisms use light energy to
make sugar and oxygen gas from carbon
dioxide and water
Carbon
dioxide
Water
Glucose
PHOTOSYNTHESIS
Oxygen
gas
• A Photosynthesis Road Map
Chloroplast
Light
Stroma
NADP
Stack of
thylakoids
ADP
+P
Light
reactions
Calvin
cycle
Sugar used for
 Cellular respiration
 Cellulose
 Starch
 Other organic compounds
Review: Photosynthesis uses light
energy to make food molecules
• A summary of
the chemical
processes of
photosynthesis
Chloroplast
Light
Photosystem II
Electron
transport
chains
Photosystem I
CALVIN
CYCLE
Stroma
Cellular
respiration
Cellulose
Starch
LIGHT REACTIONS
CALVIN CYCLE
Other
organic
compounds