Ch10 - Photosynthesis Chapter 10 Photosynthesis Converting...

Photosynthesis
Chapter 10

Photosynthesis
•
Converting solar energy (light) into
chemical energy (organic compounds)
•
Performed by autotrophs -- the producers
of the biosphere

Photoautotrophs
•
Plants are photoautotrophs : use energy of
sunlight to make organic molecules from water
and carbon dioxide
Figure 10.1

Photosynthesis
•
Occurs in plants, algae, certain other
protists, and some prokaryotes
These organisms use light energy to drive the
synthesis of organic molecules from carbon dioxide
and (in most cases) water. They feed not only
themselves, but the entire living world. (a) On
land, plants are the predominant producers of
food. In aquatic environments, photosynthetic
organisms include (b) multicellular algae, such
as this kelp; (c) some unicellular protists, such
as Euglena; (d) the prokaryotes called
cyanobacteria; and (e) other photosynthetic
prokaryotes, such as these purple sulfur
bacteria, which produce sulfur (spherical
globules) (c, d, e: LMs).
(a) Plants
(b) Multicellular algae
(c) Unicellular protist
10 μ m
40 μ m
(d) Cyanobacteria
1.5 μ m
(e) Purple sulfur
bacteria
Figure 10.2

Heterotrophs
•
Heterotrophs obtain organic material from
other organisms
•
Consumers (like us!)

The sites of
photosynthesis
Stomata, mesophyll, veins…
Vein
Leaf cross section
Figure 10.3
Mesophyll
CO
2
O
2 Stomata

Thylakoids, grana, stroma…
Chloroplast
Mesophyll
5 µm
Outer
membrane
Intermembrane
space
Inner
membrane
Thylakoid
space
Thylakoid
Granum
Stroma
1 µm

The Overall Reaction
6 CO
2
+ 12 H
2
O + Light energy →
C
6
H
12
O
6
+ 6 O
2
+ 6 H
2
O

Where does everything come
from???
6 CO
2
12 H
2
O
Reactants:
Products:
C
6
H
12
O
6
6 H
2
O 6 O
2
Figure 10.4

Photosynthesis is a Redox
Reaction
•
Remember cellular respiration:
•
In photosynthesis:
C
6
H
12
O
6
+ 6O
2
6CO
2
+ 6H
2
O + Energy
becomes oxidized
becomes reduced
C
6
H
12
O
6
+ 6O
2
6CO
2
+ 6H
2
O + Energy
becomes reduced
becomes oxidized

Two Processes
•
The light reactions
•
Occur in the grana (thylakoids)
•
In: H
2
O, sunlight
•
Out: O
2
, ATP, NADPH
•
The dark reactions (Calvin Cycle)
•
Occur in the stroma
•
In: ATP, NADPH, CO
2
•
Out: Sugar

An Overview
H
2
O
CO
2
Light
LIGHT
REACTIONS
CALVIN
CYCLE
Chloroplast
[CH
2
O]
(sugar)
NADPH
NADP
+
ADP
+ P
O
2 Figure 10.5
ATP

Purpose of the Light Reaction
•
To convert solar energy into chemical
energy
•
In the form of high energy electrons stored as
•
ATP
•
NADPH

Light
•
Electromagnetic energy, in the form of waves
•
Wavelength : the distance between crests; the
smaller the wavelength, the higher the energy
•
The spectrum
Gamma
rays
X-rays UV Infrared
Micro-
waves
Radio
waves
10
–5
nm 10
–3
nm 1 nm 10
3
nm 10
6
nm
1 m
10
6
nm
10
3
m
380 450 500 550 600 650 700 750 nm
Visible light
Shorter wavelength
Higher energy
Longer wavelength
Lower energy
Figure 10.6

Visible Light
•
The color we can see
•
We see what is
reflected
•
Photosynthesis is done with visible light waves

Pigments
•
Determine what light waves are absorbed
•
Spectrophotometer : sends light through
pigments and measures the light that is
transmitted
•
Gives you an absorption spectrum

Figure 10.8