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How organisms get energy
 Autotrophs
 Organisms that make
their own energy by
absorbing light from the
sun (photosynthesis)
 Plants and some fungi
 Heterotrophs
 Organisms that get
energy by eating other
organisms
Adenosine Triphosphate (ATP)
 Energy used by cells is called ATP
 ATP is made of a sugar (ribose), (adenine), and 3
phosphate groups (triphosphate)
 Adenosine Diphosphate (ADP) has 2 phosphate groups
 The chemical bonds between the phosphate groups
contain A LOT of energy
 ATP has more energy than ADP because it has more
phosphate groups
ATP
Section 8-1
Adenine
Ribose
3 Phosphate groups
Figure 8-3 Comparison of ADP and
ATP to a Battery
Section 8-1
ADP
ATP
Energy
Adenosine diphosphate (ADP) + Phosphate
Partially
charged
battery
Energy
Adenosine triphosphate (ATP)
Fully
charged
battery
Figure 8-3 Comparison of ADP and
ATP to a Battery
Section 8-1
ADP
ATP
Energy
Adenosine diphosphate (ADP) + Phosphate
Partially
charged
battery
Energy
Adenosine triphosphate (ATP)
Fully
charged
battery
Photosynthesis
 Photosynthesis - the process where plants use
sunlight to convert water and CO2 to make sugars to
use for energy
 Oxygen (O2) is also created as a waste product
 Photosynthesis occurs in the chloroplasts of plant cells
 6CO2 + 6H2O + sunlight→ C6H12O6 + 6O2
 Carbon dioxide + water + sunlight = sugars + oxygen
Photosynthesis: Reactants and Products
Light Energy
Chloroplast
CO2 + H2O
Sugars + O2
Chloroplasts
 Chloroplasts consist of thylakoids and stroma
Thylakoids
 Stacks of sac-like membranes where light-dependent
reactions occur
 Stacks are called grana
 Pigments are molecules that can capture sunlight
 Chlorophyll is the main pigment of plant cells

Appears green because it does not absorb green light, but
reflects it
 Thylakoids organize chlorophyll and other pigments
into light-collecting units called photosystems
Stroma
 The area outside the thylakoids
 Where the light-independent reactions, or dark
reactions, occur
 Light-independent reactions are called the Calvin
cycle
Electron Carriers
 Sunlight gives electrons in chlorophyll a lot of energy
 In order to move these high-energy electrons, they need a
special molecule called an electron carrier
 The process of moving electrons is called electron
transport and the carriers themselves are called the
electron transport chain
 NADP+ is an electron carrier
 NADP+ can carry 2 high-energy electrons and a hydrogen ion
(H+)

When NADP+ carries H+ and 2 electrons, it forms NADPH
 NADPH carries electrons to parts of the cell where they are
needed to help build needed molecules, such as sugars
Concept Map
Section 8-3
Photosynthesis
includes
Lightdependent
reactions
Calvin cycle
use
take place in
Energy from
sunlight
Thylakoid
membranes
to produce
ATP
NADPH
O2
takes place in
Stroma
uses
ATP
NADPH
of
to produce
Chloroplasts
High-energy
sugars
3 Stages of Photosynthesis
 Stage 1: Light Capturing (part of light-dependent reactions)
 Pigments capture sunlight that excites electrons


Electrons are supplied by H2O
Products of light capturing are high-energy electrons, H+ ions, and
oxygen (O2)
 Oxygen is a waste product (not needed by plant cell)
 Stage 2: Light-Dependent Reactions
 Utilizes H+ ions and high-energy electrons to turn ADP and
NADP+ into ATP and NADPH
 Stage 3: Calvin Cycle
 Utilizes ATP and NADPH to produce sugars that hold more
energy than ATP
Sunlight
H2O
CO2
Chloroplast
Chloroplast
NADP+
ADP + P
LightDependent
Reactions
Calvin
Cycle
ATP
NADPH
O2
Sugars
Light-Dependent Reactions
 Light is captured by the pigments in photosystem II
 Light excites electrons (from chlorophyll, provided by
H2O)
 Electrons move along the electron transport chain to
photosystem I. As electrons move along the chain,
their energy is used to move H+ ions from the stroma
into the thylakoids
 Light is captured in photosystem I to re-energize the
electrons. NADP+ picks up 2 of these electrons and a
H+ ion to form NADPH
Light-Dependent Reactions cont.
 Remember that while electrons move along the chain,




H+ ions are pumped into the thylakoid
Eventually, the thylakoid fills up with H+ ions, leaving
inside the thylakoid positive and outside the thylakoid
negative
H+ ions then move through a protein channel called
ATP synthase from inside the thylakoid to outside the
thylakoid
This movement causes ATP synthase to spin
As it spins, it adds a phosphate group to ADP, creating
ATP
Photosystem II
Hydrogen
Ion Movement
ATP synthase
Inner
Thylakoid
Space
Thylakoid
Membrane
Stroma
Electron
Transport Chain
Photosystem I
Calvin Cycle
 6 CO2 molecules combine with six 5-carbon molecules
to form twelve 3-carbon molecules
 The twelve 3-carbon molecules are energized by ATP
and NADPH
 2 of the 3-carbon molecules are removed to make
sugars, lipids, amino acids, or other molecules the
plant cell needs
 The ten 3-carbon molecules that are left over are
converted back into six 5-carbon molecules to start the
Calvin cycle all over again
CO2 Enters the Cycle
Energy Input
5-Carbon
Molecules
Regenerated
6-Carbon Sugar
Produced
Sugars and other compounds