How Organisms Obtain Energy
Energy is the ability to do work
Thermodynamics is the study of
the flow & transformation of
energy in the universe
Laws of Thermodynamics
First law—energy can be converted
from one form to another, but it
cannot be created nor destroyed.
Second law—energy cannot be
converted without the loss of usable
energy
Autotrophs and Heterotrophs
 Autotrophs use energy from sunlight or
chemical bonds in inorganic substances to
make organic compounds
 Heterotrophs are organisms that need to
ingest food to obtain energy
What was the best
item you ate for
lunch today?
Metabolism
 All of the chemical reactions in a cell
 Anabolic reactions- simpler substances
combine to make more complex molecules or
store energy-usually requires energy
 Catabolic reactions-break down more
complex molecules into simpler substancesusually releases energy-drives chemical rxns
Biochemical Pathways
Photosynthesis—light
energy
from the Sun is converted to
chemical energy for use by the
cell (anabolic)
Cellular respiration—organic
molecules are broken down to
release energy for use by the cell
(catabolic)
Photosynthesis
uses CO2 ,
water and sunlight (energy) to
make organic compounds and
O2
Cellular respiration uses
organic compounds and O2 to
make CO2, water and energy
In 1648, a Flemish alchemist, Jan van
Helmont, had a theory. To test it, he grew a
tree in a tub of soil, adding nothing but
measured quantities of water for five
years. During that time he kept track of
the weight of the soil and the tree. At the
end of the experiment the tree had gained
164 pounds and the soil had lost 2
ounces. What could von Helmont
conclude from his experiment?
140
120
130
30
40
50
60
70
10
480
5
6
7
8
9
180
20
160
90
170
150
100
110
Overview of Photosynthesis
Photosynthesis occurs in 2 phases:
Light reactions-light energy is
absorbed and temporarily stored in
ATP and NADPH
Calvin Cycle (carbon fixation)organic compounds formed using
CO2 and energy in ATP and
NADPH
What is an organic molecule?
Build a carbon dioxide – what type
of bonds does it have?
2. Build a water molecule- what type of
bonds does it have?
3. Begin bonding the 6 carbons
together for glucose-note 1 is not in the
ring
1.
Phase One: Light Reactions
The absorption of light is the first step
in photosynthesis
How does a leaf absorb light? They
contain light-absorbing pigments in
the chloroplasts
Chlorophyll the primary
pigment in photosynthesis,
absorbs mostly blue and
red light and reflects green
and yellow light
• Plants contain two types of
chlorophyll, chlorophyll a
and chlorophyll b
The pigments that produce yellow
and orange fall leaf colors, also the
colors of many fruits, vegetables,
flowers, are called carotenoids.
Carotenoids absorb
wavelengths different from
chlorophyll, both pigments
allow plants to absorb more
light energy
Absorption Spectra of Photosynthetic
Pigments
Pigments are embedded in the
membranes of thylakoidsphotosystem I and II
When
light strikes a thylakoid
in a chloroplast, energy is
transferred to electrons in
chlorophyll.
This
energy transfer causes
the electrons to jump to a
higher energy level.
The
excited electrons that leave
chlorophyll molecules must be
replaced by other electrons
Plants
get replacement electrons
from water molecules. Photolysis is
the splitting of water by light
form
oxygen gas, O2
2H2O
4 H+ + 4e- + O2
ions (H+, protons) are
released into the lumen of the
thylakoid
Here H+ ions build up and when H+
passes through ATP synthase into the
stroma of the chloroplast, ADP + Pi are
converted into ATP - chemiosmosis
Hydrogen
electrons are released into the electron
transport system
The excited electrons move from
photosystem II to an electron-acceptor
molecule in the thylakoid membrane
The electron-acceptor molecule
transfers the electrons along a series of
electron-carriers to photosystem I
Photosystem I transfers the
electrons to a protein called
ferrodoxin
Ferrodoxin transfers the electrons
and a proton to the electron carrier
NADP+, forming the energy-storing
molecule NADPH
Phase Two: The Calvin Cycle-Carbon Fixation
 In the second
phase of
photosynthesis,
called the Calvin
cycle, energy is
stored in organic
molecules such
as glucose
 Six CO2 molecules combine with six 5-carbon
compounds to form twelve 3-carbon molecules
called 3-PGA
 The chemical energy stored in ATP and
NADPH is transferred to the 3-PGA molecules
to form high-energy molecules called G3P
 Two G3P molecules leave the cycle to be used
for the production of glucose and other organic
compounds
 An enzyme called rubisco converts the
remaining ten G3P molecules into 5-carbon
molecules called RuBP
 These molecules combine with new carbon
dioxide molecules to continue the cycle
How does the essential
CO2 get into the plant?
How does O2 leave?
Alternative Pathways
C4 plants-corn, sugarcane, crabgrass –
plants that keep stomata partially closed
during the hottest part of the day
CAM plants-cacti, orchids, pineapplesstomata only open at night, grow slowly
but lose little water
Factors that affect
Photosynthesis
Light
Intensity
CO2 level
Temperature
All increase photosynthesis as
factor increases to a terminal
point