8.1 How Organisms Obtain
Energy
Mr. Purcell Biology I
Transformation of Energy
 Energy is the ability to do work.
 Thermodynamics is the study of the
flow and transformation of energy in
the universe.
Laws of Thermodynamics
 First law – Energy can not be created nor
destroyed only changed.
 Second law – Energy cannot be converted
without the loss of usable energy.
Autotrophs and Heterotrophs
 Autotrophs are organisms that make their own food.
 Heterotrophs are organisms that need to ingest food
to obtain energy.
Metabolism
 All of the chemical reactions in a cell.
 Photosynthesis –light energy from the sun is
converted to chemical energy for use by the cell.
 Cellular respiration – organic molecules are
broken down to release energy for use by the cell
ATP: The Unit of Cellular Energy
 Adenosine Triphosphate (ATP) – Cells use
ATP to store & use for Energy (Battery fully
charged)
 Adenosine Diphosphate (ADP) – Stores
Energy (Battery Not fully Charged)
ATP & ADP
-To release the
Energy, the
Phosphate Bonds
are Broken
-Cells only have
very small
amounts of ATP
on hand, most is
in ADP & is
easily converted
to ATP.
ATP Synthesis
8.2 Photosynthesis
Photosynthesis…
…way simplified
Photosynthesis
Photosynthesis
Overview of Photosynthesis
 Photosynthesis occurs in two phases.
 Light-dependent reactions
 Light–independent reactions (Calvin Cycle)
light
 6CO2 + 6H2O
C6H12O6 +6O2
Light Dependent Reactants
Need the light dependent reactants 3:25 clip
Have on Hadorn chapter 8
Light dependent reactants
Photosynthesis –
Absorption Spectra
Chlorophyll
Chlorophyll…
Phase One: Light Reactions
 The absorption of light is the first step in photosynthesis
 Chloroplasts capture light energy.
Chloroplast
Chloroplast
Calvin Cycle
Electron transport
 Light energy excites electrons in photosystem II
and also causes a water molecule to split, releasing
an electron into the electron transport system, H+
into the thylakoid space, and O2 as a waste
product.
No I will not…
Electron Transport
 The excited electrons move from photosystem II to
an electron –acceptor molecule in the thylakoid
membrane. That transfers the electrons along a
series of electron – carriers to photosystem I.
Electron Transport
 Photosystem I transfers the electrons to a protein
called ferrodoxin.
 Ferrodoxin transfers the electrons to the electron
carrier NADP+ forming the energy – storing molecule
NADPH.
 Need electron chain clip
ADP+  ATP
 The H+ from the split of water is used
by ATP Synthase to produce ATP from
ADP+.
Electron Transport
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Phase Two: The Calvin Cycle
 In the second phase of photosynthesis, called the
Calvin cycle, which takes place in the stroma, ATP and
NADPH from the light-dependent reactions are used to
produce high-energy sugars.
Phase Two: The Calvin Cycle
 The ‘Melvin’ Calvin cycle works steadily to
remove carbon dioxide from the atmosphere
and turns out energy-rich sugars.
 Six carbon dioxide molecules are needed to
make a single 6-carbon sugar.
The Calvin Cycle
Photosynthesis
Alternative pathways
 C4 plants
 CAM plants
C4 and CAM 4
Plants
Photosynthesis
The Musical
8.2 – Section Review
8.3 Cellular Respiration
Overview of Cellular Respiration
 Organisms obtain energy in a process called cellular
respiration.
 The equation for cellular respiration is the opposite of
the equation for photosynthesis.
 C6H12O6 + 6O2
6CO2 + 6H2O + Energy
Cellular respiration occurs in
three main parts.
1. Glycolysis
2. The Kreb Cycle
3. Electron Transport
Glycolysis

Glucose is broken down in the cytoplasm
through the process of glycolysis.

Two molecules of ATP and two
molecules of NADH are formed for each
molecule of glucose that is broken down.
Glycolysis
Krebs Cycle
 Glycolysis has a net result of only two ATP and 2
pyruvate.
 Most of the energy from the glucose is still
contained in the pyruvate.
 This series of reactions in which pyruvate is broken
down into carbon dioxide is called the Krebs cycle.
Krebs Cycle
 The net yield
from the
Krebs cycle is
six CO 2
molecules,
two ATP, eight
NADH, and
two F ADH2.
Electron Transport
 Final step in the breakdown of glucose
 Point at which most ATP is produced
 Produces 34 ATP
What happens when we run out of OXYGEN?
Anaerobic Respiration
 The anaerobic pathway that follows glycolysis.
 Two main types
 Lactic acid fermentation
 Alcohol fermentation
Fermentation
Fermentation
Chemiosmosis
Electron Transport
Photosynthesis and Cellular Respiration