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Cellular Respiration &
AP Biology
• _______________ is the process of converting energy from sunlight into
energy in chemical bonds:
• Light + 6 H20 + 6CO2 --> C6H12O6 + 6 O2
• C6H12O6 is ______________.
• The process of photosynthesis occurs in the ____________.
• Chloroplasts have sac structures inside them called ____________.
• A stack of thylakoids is called a ____________(grana)
• The fluid inside a thylakoid is called ____________
• The light reactions of photosynthesis occur on the thylakoid membranesthe dark reactions occur in the stroma.
• Light is unique in that it acts as a ____________, but also
acts as a particle (called a ____________).
• Plants utilize blue and red light, but reflect ____________
light (which is why they appear green to us)
• The process of photosynthesis begins with light- absorbing pigments in plant
• A pigment molecule is able to absorb energy from light within a narrow range
of wavelengths.
• Because of this, plants use a variety of pigments to absorb different
wavelengths. These include:
– Green ____________ a and chlorophyll b
– The ____________ - which are red, orange and yellow
• When light is absorbed into one of these pigments the energy from the light
is incorporated into electrons within the atoms of that molecule.
• These energized/excited electrons are ____________ and almost
immediately re-emit the absorbed energy.
• This energy bounces from one pigment molecule to another.
• The process ends when the energy is absorbed by one of two special
chlorophyll a molecules- P680 or P700.
• Together with other pigments, these pigments form clusters called
____________. Photosystem I contains P700, Photosystem II contains
A Photosystem
• Photosynthesis is divided into two stages:
1. The ____________ reactions- occur on the thylakoid membranes.
Convert solar energy into chemical energy. The light reactions are
divided into two processes- cyclic electron flow and noncyclic electron
2. ____________ Cycle- occurs in the stroma. produces sugar.
Light Reaction- Noncyclic
• ____________ - the process of making ATP from ADP and
inorganic phosphate (Pi) using energy from light. Noncyclic
electron flow begins with photosystem II and follows these
1. ____________ II- electrons trapped are energized by light.
2. ____________ electron acceptor- two energized electrons are
passed to a molecule called a primary electron acceptor.
3. Electron ____________ chain- those electrons are passed from
one protein to another in a chain.
4. ____________ - as the electrons move “down” the chain they
lose energy. The energy lost by the electrons is used to
phosphorylate (add a phosphate to) ATP molecules
5. ____________ I- The electron transport chain terminates with
photosystem I. The electrons are again energized by sunlight
and passed to another primary electron acceptor.
Light Reaction- Noncyclic
• 6. ____________ - the electrons pass through a short electron
transport chain. At the end of the chain, the electrons
combine with NADP+ and H+ to form NADPH. NADPH is a
coenzyme. Since the electrons have a considerable amount
of energy left, NADPH is an energy-rich molecule.
• 7. ____________ - the electrons that originated in photosystem
II have now been incorporated in NADPH. The loss of these
two electrons from photosystem II is replaced when water is
split into two electrons (2 H+ and 1/2 02) This is why water is
needed and oxygen is produced from photosynthesis.
• In summary, photophosphorylation take the energy in
____________ and electrons in water to make the energy rich
molecules ____________ and ____________ :
• Water + ADP + phosphate + NADP + light--> ATP + NADPH
+ oxgygen
Noncyclic Photophosphorylation
Cyclic Photophosphorylation
• A second photophosphorylation sequence occurs when the
electrons energized in photosystem I are “recycled.”
• Energized electrons join with protein carriers and generate
____________ as they pass through another electron transport
chain. The electrons then return to photosystem I (in a circle).
• This process is necessary because the calvin-benson cycle
requires more ATP than NADPH.
Calvin Benson Cycle
Uses NADPH and ATP to convert carbon dioxide into sugar.
Occurs in the stroma.
Is broken into three phases:
1. ____________ fixation- CO2 is attached to the protein RuBPthis reaction is catalyzed by the enzyme rubisco. The
molecule of CO2 bound to RuBP is so unstable that it
immediately splits into half - into 3-phosphoglycerate.
• 2. ____________ - 3 Phosphoglycerate receives a phosphate
from ATP and then a pair of electrons from NADPH. The
resulting molecule is called G3P. Its the form of sugar
produced by photosynthesis.
• 3. ____________ of CO2 acceptor (RuBP) - The carbon
skeletons of 5 molecules of G3P are rearranged into 3
molecules of RuBP using 3 molecules of ATP. This is why
cyclic photophosphorylation must occur.
Calvin Benson Cycle
Calvin Cycle
• In summary, the calvin benson cycle takes ____________
____________ from the atmosphere and ____________ from
ATP and NADPH to create a ____________ molecule. The
energy in ATP and NADPH was captured from the sun
through photophosphorylation (cyclic and noncyclic):
• 6CO2 + 18 ATP + 12 NADPH --> 18 ADP + 12 NADP
+ 1 glucose
• Each step of the calvin cycle is catalyzed by a specific
Chemiosmotic Theory
• Chemiosmotic theory describes the process by which ADP is
phosphorylated to ATP:
– 1. H+ ions (____________) accumulate inside the thylakoids.
The H+ ions come from photolysis during the light reactions.
– 2. An ____________ gradient is created across the thylakoid
membrane as H+ is concentrated in the stroma.
– 3. As protons pass through the enzyme ATP
____________(embedded in the thylakoid membrane) the
enzyme uses the energy to phosphorylate ATP from ADP.
Chemiosmotic Theory
is the most abundant protein on Earth.
• In addition to being able to ____________ carbon
dioxide, it can also fix oxygen if the oxygen levels are
too high in a plant. This is called ______________________.
• This doesn’t lead to production of useful molecules
and the waste products are instead broken down by
organelles called ____________.
• ____________
Photosynthesis in Hot, Arid Climates
• The plants that photosynthesize in the methods we’ve
discussed so far are called ____________ plants. In these
plants, on hot and dry days their stomata close and oxygen
builds up. Also, CO2 levels decrease. This causes rubisco to
bind to oxygen instead of carbon dioxide-photorespiration.
• Alternative methods of carbon fixation have evolved to prevent
excess water loss in hot, arid climates.
C4 Plants
• C4 plants have a unique ____________ anatomy. They
have two types of photosynthetic cells.
• 1. ____________ Sheath cells: are where the calvin
cycle occurs.
• 2. ____________ cells: are where carbon dioxide is
fixed. In Mesophyll cells, CO2 is bound to the
molecule ____________ by the enzyme PEP
carboxylase which has a higher affinity for CO2
than rubisco does. The product (CO2 bound to
PEP) is called oxyloacetate.
• ____________ then moves into Bundle sheath cells
through plasmodesmata. This keeps CO2 levels
high in Bundle sheath cells so that ____________
accepts it even when stomata are closed.
CAM Plants
• Succulents and many cacti are ____________ Plants.
• They deal with hot, arid environments with a different
strategy. They open their ____________ at night and
close them during the day. This is just the reverse of
how other plants behave. Carbon dioxide is
____________ in a variety of molecules at night and then
during the day when the light reactions supply ATP
and NADPH, carbon dioxide is released and the
Calvin cycle takes place.
Cellular Respiration
• _________________is the process of incorporating energy
from light into energy rich molecules like glucose.
_______________is the opposite process of extracting that
stored energy from glucose to form ATP (from ADP and Pi):
• C6H12O6 + 6 O2 --> 6 H2O + energy (ATP)
• Cellular respiration occurs in the ____________. The
mitochondria has two membranes. The inner membrane is
highly folded- the folds are called ____________. The inside of
the mitochondria is called the ____________ and the space
between the two membranes is called the
• Respiration in the presence of oxygen is called aerobic
respiration. It’s divided into three steps:
– 1. Glycolosis
– 2. Krebs Cycle
– 3. Oxidative Phosphorylation/Electron Transport Chain
Cellular Respiration
• ____________ is breaking down glucose into the molecule
pyruvate. Nine intermediate products are formed and
enzymes catalyze each step.
Glucose--> 2 pyruvate molecules
Glucose--> (net) 2 ATP + 2 NADH molecules
Releases < 25% of the energy in glucose- rest is stored in
pyruvate molecules
No CO2 is released
Takes place in the ____________ of the cell- outside the
The Krebs Cycle/ Citric Acid Cycle
• Takes place in the mitochondrial ____________.
• If oxygen is present- pyruvate enters the mitochondrion and
is converted to Acetyl CoA by coenzyme A. Krebs cycle has 8
steps, each catalyzed by a specific enzyme. Each acetylCoA
molecule that enters produces 3 molecules of NADH. Another
molecules is also reduced (gains electrons) FADH2. Both of
these molecules will donate their electrons in the 3rd step.
Carbon dioxide (that you will exhale) is produced as a
biproduct of this step.
Oxidative Phosphorylation/ Electron Transport Chain
• Oxidative ____________ is the process of extracting ATP form NADH
and FADH2.
• Occurs on the inner membrane of the mitochondria.
• Electrons from NADH and FADH2 pass along an electron transport
chain from one protein to another, losing energy at each step
• The last electron acceptor is _______. When it accepts the two
electron, with two H+, it forms water.
Overview of Cellular Respiration
• ____________ - makes 2 ATP
• ____________ Cycle- makes 2 ATP
• ____________ Transport Chain- makes approx. 34 ATP
• Total- ____________ made for each glucose molecule
Anaerobic Respiration
• If oxygen’s not present there is no ____________
acceptor to accept the electrons at the end of the
electron transport chain. If this occurs, ____________
accumulates. This causes the krebs cycle and
glycolosis to both stop. If this happens, the cells
soon ____________ as no ATP is made.
• ____________ respiration is a method cells use to
escape this fate. The pathways in plants and
animals, ____________ and ____________ fermentation,
respectively, are slightly different but the objective is
the same: to replenish NAD+ so that glycolysis can
proceed again.
• Anaerobic respiration occurs in the ____________.
Aerobic Respiration
Fermentation- Occurs in plants,
fungi (such as yeast) and bacteria. Produces
____________ as a biproduct. This process is
used to commercially produce alcoholic
____________ Fermentation- occurs in animals.
Pyruvate is converted to lactate (or ____________
acid). This molecule causes muscle
____________ after strenuous exercise.
• ____________