Picture Guide to Chapter 8
Photosynthesis
8-1 Energy and Life
Objectives
• Explain where plants get the
energy they need to produce food
• Describe the role of ATP in
cellular activities
Q: Where does energy come from?
A: Our food, but originally the
energy in food comes from the
sun
Autotrophs
• Make their own food
Heterotrophs
• Cannot make their own food
Chemical Energy and ATP
• The principal chemical compounds
that cells use to store and release
energy is called ATP adenosine
triphosphate
Storing Energy
• ATP stores energy in the third
phosphate
• ATP is like a fully charged battery
Releasing Energy
Q: How is the energy in ATP released?
A: Break bond between the second and 3rd
phosphates
2
ADP
ATP Formation - Using
Biomechanical Energy
• Active Transport
• Movement of organelles throughout
cell
• Synthesis of proteins and nucleic acids
• Produce light
– Blink of firefly caused by an enzyme
powered by ATP
ATP Availability
• Most cells only have enough ATP for a few
seconds of activity
• Why?
– Not good at storing energy over the long term
– Glucose stores 90 times the chemical energy
of ATP
– Cells generate ATP from ADP as needed by
using the energy in foods like glucose
Photosynthesis
• The process in which plants use
the energy of sunlight to convert
water and carbon dioxide into
high energy carbohydrates –
sugars and starches – and
oxygen as a waste product
Photosynthesis
The Photosynthesis
Equation
CO2 + H2O
(Carbon Dioxide)
(Water)
light
(Sun)
C6H12O6 + O2
(Glucose)
(Oxygen)
Chlorophyll
• The plants principal pigment,
absorbs light energy in the blueviolet and red spectrum of visible
light
Absorption of Light by
Chlorophyll a and Chlorophyll b
Chlorophyll b
Chlorophyll a
V
B
G
YO
R
Because light is a form of energy…
• Anything that absorbs light also absorbs
the energy from that light
• When chlorophyll absorbs light, much of
the energy is transferred to electrons in
the chlorophyll molecule, raising the
energy level of these electrons
• These high-energy electrons make
photosynthesis work
8-3 The Reactions of
Photosynthesis
Thylakoids
• Sac-like photosynthetic
membranes arranged in stacks
Grana
• Stacks of thylakoids
Stroma
• The region outside the thylakoid
Scientists describe the reactions
of photosynthesis in two parts
1. Light – dependent reactions
(takes place in the thylakoid
membranes)
2. Light – independent reactions
(takes place in stroma)
Carrier Molecule
• Compound that can accept a pair
of high energy electrons and
transfer them along with most of
their energy to another molecule
• Ex.) NADP+
Q: What does this do?
• NADP+
NADPH
A: this traps sunlight in chemical
form
Light Dependent Reactions
• Uses energy from light to
produce
1. Oxygen gas
2. ATP
3. NADPH
Fig. 8-10
The Calvin Cycle
• The ATP and NADPH formed by the lightdependent reactions contain an
abundance of chemical energy, but they
are not stable enough to store that energy
for more than a few minutes.
• The Calvin cycle uses ATP and NADPH
from light – dependent reactions to
produce high energy sugars
The Calvin Cycle
• These reactions don’t require
light, therefore these reactions
are called
• Light – independent reactions
Fig 8.11
Factors Affecting Photosynthesis
• Not enough water
• Temperature
• Light intensity