Transcript Photosynthesis

Chapter 4
Photosynthesis and Respiration
4.1
• KEY CONCEPT
All cells need chemical energy.
Energy
• All cells need energy
• That energy is carried by ATP, adenosine
triphosphate.
• That energy is held in chemical bonds.
• Example: the chemical bonds in wood are
broken when wood burns and that bond
energy is released.
Glucose molecule and starch
Starch molecule
Glucose molecule
ATP
• ATP transfers energy from the breakdown of
food molecules to cell functions.
– Energy is released when a phosphate group is
removed.
– The third phosphate bond is called a high energy
bond
– ADP is changed into ATP when a phosphate group
is added
ATP
phosphate removed
ATP
adenosine
triphosphate
tri=3
adenosine
di=2
diphosphate
Chemical Energy and ATP
• Fats store the most energy
– 80 percent of the energy in your body
– About 146 ATP to form a triglyceride
• Proteins are least likely to be broken down to
make ATP.
– Amino acids are usually not needed for energy
– About the same amount of energy as a
carbohydrate
Energy Comparison
Alternatives
• A few types of organisms do not need sunlight
and photosynthesis as a source of energy.
• Photosynthesis:
– Uses sunlight to build carbon based molecules.
• Chemosynthesis
– Chemical energy is used to build carbon-based
molecules.
– Similar to photosynthesis
– Some organisms live in places that never get sunlight.
For Example
4.2
• KEY CONCEPT
The overall process of photosynthesis
produces sugars that store chemical energy.
Photosynthesis
• Producers make their
own source of chemical
energy.
• Plants use
photosynthesis and are
producers.
• Photosynthesis captures
energy from sunlight to
make sugars
Chlorophyll
• Chlorophyll is a pigment
molecule that absorbs
light energy.
• Found in chloroplasts in
plants
The chloroplast
• Photosynthesis occurs two
parts of the chloroplasts
grana (thylakoids)
chloroplast
–Grana (thylakoids)
–Stroma (fluid
around the
thylakoids)
stroma
Overview of Photosynthesis
– The light-dependent reactions capture energy
from sunlight take place in thylakoids
– water and sunlight are needed
– chlorophyll absorbs energy
– energy is transferred along thylakoid membrane
then to light-independent reactions
– oxygen is released
– P 104
Overview of Photosynthesis
• The light independent reactions make sugars
– Take place in stroma
– Needs carbon dioxide from atmosphere
– Use energy to build sugar in cycle of chemical
reactions
Overview of photosynthesis
The equation for the overall process is:
6CO2 + 6H2O  C6H12O6 + 6O2
granum (stack of thylakoids)
1
chloroplast
6H2
O
2
thylakoid
6CO2
3
6O2
energy
Stroma
1 six-carbon sugar
4
C6H12O6
Summary of photosynthesis
• Requires
– Water: all life requires water
– CO2: Uses the CO2 that we produce
– Sunlight: the ultimate source of all food energy
• Produces
– Sugar: the food
– Oxygen: for organisms to breathe
3.3
Photosynthesis in detail
• KEY CONCEPT:
Photosynthesis requires a series of chemical
reactions.
Light dependent reactions
• Capture light energy
• Splits water
• Produces oxygen gas
and hydrogen ions
Photosystem II
Captures and transfers energy
– chlorophyll absorbs
energy from sunlight
– energized electrons
enter electron transport
chain
– water molecules are
split
– oxygen is released as
waste
– hydrogen ions are
transported across
thylakoid membrane
Photosystem I
Captures energy and produces energycarrying molecules.
– chlorophyll absorbs
energy from sunlight
– energized electrons are
used to make NADPH
– NADPH is transferred to
light-independent
reactions
Light reactions overview
• The Light dependent reactions produce ATP
– hydrogen ions flow through a channel in the
thylakoid membrane
– ATP synthase attached to the channel makes ATP
Light Independent reactions
• The second stage of photosynthesis uses
energy from the first stage to make sugars.
• Light-independent reactions occur in the
stroma and use CO2 molecules.
• Enzyme RuBisCo fixes carbon dioxide carbon
into the cycle.
Light independent reactions
Light independent Reactions
• A molecule of glucose is formed as it stores
some of the energy captured from sunlight.
– carbon dioxide molecules enter the Calvin cycle
– energy is added and carbon molecules are
rearranged
– a high-energy three-carbon molecule leaves the
cycle
– Two three carbon molecules bond to form a sugar
– Remaining molecules stay in the cycle
Light independent Reactions
• A molecule of glucose is formed as it stores
some of the energy captured from sunlight.