Download Photosynthesis Cellular Respiration

Chapter 8
Photosynthesis
and Cellular
Respiration
Section 8.1
Energy and Life
• Daily Question: What do you think of
when you hear the word “energy”?
• All living organisms must be
able to obtain energy from
the environment in which
they live.
• The law of conservation of
energy states that energy
can neither be created nor
destroyed.
Chemical Energy and ATP
• The principal chemical
compound that cells use to
store and release energy is
called ATP - adenosine
triphosphate.
• ATP is a quick energy source for
any cell’s organelle that needs
it.
• ATP is made of an adenosine
molecule, a ribose (sugar),
and three phosphate groups.
• Reminder- the three phosphate
groups have the same charge and
particles of the same charge repel
each other (opposites attract).
ATP
Charged phosphate
groups
Adenine
Ribose
Storing Energy In ATP
• ATP stores energy in the third
phosphate group.
• ATP is like a fully charged battery
storing energy until needed.
Third
phosphate
group
Releasing Energy From ATP
• The energy of ATP becomes
available to a cell when the bonds
between the 2nd and 3rd phosphate
groups are broken.
• Loss of the third phosphate group
results in ADP (adenosine
diphosphate) and the release of
stored energy.
ATP – ADP Cycle
• ADP can form ATP again by
bonding with another phosphate
group.
• This cycle allows the cell to make
more ATP when phosphates are
available, instead of having to
store enough of ATP; which is very
difficult.
ATP – ADP Cycle
Uses of Cell Energy
• ATP fuels cellular activities
which drives the organism and
maintains homeostasis.
• Ex. Active Transport,
movement of organelles
throughout the cell, synthesis
of proteins and nucleic acids
• All organisms will get their energy
either directly or indirectly from the
sun. (**remember food = energy)
• Organisms that can make their own
food are called autotrophs/producers
(green plants).
• Organisms that rely on other
organisms for food are called
heterotrophs/consumers (animals).
Autotrophs
• Make their own food
Heterotrophs
• Cannot make their own food
Section 8.2 & 8.3
Photosynthesis
• Daily Question: How does ATP differ
from ADP?
Photosynthesis
• Using energy from
sunlight, plants take light
energy and convert it into
chemical energy in the
form of carbohydrates.
Because light is a form of energy…
• Anything that absorbs light also
absorbs the energy from that light.
• When chlorophyll in the plant absorbs
light, much of the energy is transferred
to electrons in the chlorophyll
molecule, raising the energy level of
these electrons.
• These high-energy electrons make
photosynthesis work.
Photosynthesis Definition
• The process in which plants use the
energy of sunlight to convert water
and carbon dioxide into high energy
carbohydrates and oxygen as a waste
product.
• In other words – the sun’s energy is
converted into carbohydrates.
Photosynthesis
Photosynthesis
• General equation for
photosynthesis:
6CO2 + 6H2O -> C6H12O6 +6O2
Scientists describe the
reactions of photosynthesis
in two parts.
1. Light dependent reactions
2. Light Independent reactions
Light Dependent Reactions
• Converts light energy from
the sun into chemical energy
in the form of ATP and
NADPH.
• Occurs in the thylakoid discs
of the chloroplast in the plant
cells.
Structure of the Chloroplast
Structure of the Chloroplast
• Remember – the chloroplasts in
the plant cells are plastids that
store the pigment Chlorophyll.
• The chlorophyll in the grana of the
thylakoid discs absorbs light
energy in the blue-violet and red
spectrum of visible light. (they
reflect green that is why plants
appear green)
Absorption of Light by
Chlorophyll a and Chlorophyll b
Chlorophyll b
Chlorophyll a
V B GYO R
Photolysis
• Reaction taking place in the thylakoid
membranes where two molecules of
water are split to form oxygen, hydrogen
ions, and electrons.
– The oxygen is released into the air and
supplies the oxygen we breathe.
– The electrons are returned to the chlorophyll
replenishing energy.
– The hydrogens are pumped into the thylakoid
where they accumulate, form a concentration
gradient, and then diffuse out of the thylakoid
where they are coupled with ATP in a process
called chemiosmosis.
The Light – Independent
Reactions or Calvin Cycle
• The ATP and NADPH formed by the lightdependent reactions contain an abundance
of chemical energy, but they are not stable
enough to store that energy for more than a
few minutes.
• The Calvin cycle uses CO2, and the ATP and
NADPH from light – dependent reactions to
produce high energy sugars.
• This cycle does not require light.
• Calvin Cycle takes place in the Stroma of
chloroplast.
Structure of the Chloroplast
• The Calvin cycle occurs in a series of reactions
or cyles. Basically:
– Carbon fixation – CO2 carbon is “fixed” into a
six – carbon sugar.
– This sugar is broken down into two 3 Carbon
sugars called phosphoglyceraldehyde or
PGAL.
– After three cycles the sixth PGAL is made
available to make sugars, complex
carbohydrates, or other organic compounds.
Factors Affecting Photosynthesis
Many factors influence the rate of photosynthesis.
1. Temperature – the enzymes that drive
photosynthesis work best between 0 and 35
degrees Celsius. (32-95 Fahrenheit)
Photosynthesis will not occur if it is too cold or
too hot.
2. Light Intensity – high light intensity increases
the rate of photosynthesis until saturation
occurs.
3. Availability of Water – a shortage of water will
stop or slow photosynthesis.
Draw a diagram of
photosynthesis
CO2
Oxygen
Glucose
Sunlight
Water
A plant
Arrows representing what is going in
and out.
Section 8.3
Cellular Respiration
• Daily Question: What is the goal of
photosynthesis? Has that been
accomplished in the light reaction
phase? Where will it be accomplished?
Food
• Food provides living things with
the chemical building blocks they
need to grow and reproduce.
• Food serves as a source of raw
materials used to synthesize new
molecules.
• Food serves as a source of
energy.
Cellular Respiration
• The process in which mitochondria
break down food molecules to
produce ATP.
• There are two stages of cellular
respiration: Glycolysis and Krebs
Cycle.
• Glycolysis is anaerobic – no oxygen is
required.
• Krebs Cycle is aerobic – oxygen is
required.
The equation for cellular
respiration is…
O2 + C6H12O6
Oxygen
Glucose
CO2 + H2O + ATP
Carbon
dioxide
Water
Energy
Glycolysis
2 Pyruvic acid
Glucose
• The process in which one molecule of
glucose is broken in half producing two
molecules of pyruvic acid.
 Energy yield from glycolysis is small.
• Doesn’t require oxygen.
• Occurs in the cytoplasm.
• 2 molecules of ATP are used up to get
glycolysis going.
• 4 molecules of ATP are produced at
the end of glycolysis.
• Net gain of 2 ATP molecules.
 One of the reactions of glycolysis
removes 4 high energy electrons and
passes them to a carrier called NAD+
which then becomes NADH.
 NADH holds the electrons until they
can be transferred to other molecules.
Chemical Pathways
Glucose
Glycolysis
Krebs
cycle
Fermentation
(without oxygen)
Electron
transport
Alcohol or
lactic acid
The Krebs Cycle
• At the end of glycolysis, about 90%
of the chemical energy that was
available in glucose is still unused,
locked in high energy electrons of
pyruvic acid.
• To export the rest of that energy,
the cell turns to the worlds most
powerful electron acceptor…
Oxygen.
Kreb’s Cycle (Citric Acid Cycle)
• Occurs in the mitochondria.
• Requires oxygen.
• Pyruvic acid from Glycolysis enters the
mitochondria and is converted to
Acetyl CoA. The Kreb’s cycle breaks
down this Acetyl CoA into CO2 and
ATP.
• Produces a net of 2 ATP.
• The carbon dioxide produced diffuses
out of the mitochondria, out of the cell
and into the bloodstream where it is
carried to the lungs and diffuses into
the air that we exhale.
Glucose
Glycolysis
Krebs
cycle
Fermentation
(without oxygen)
Electron
transport
Alcohol or
lactic acid
Fermentation
• Releases energy from food in the absence
of oxygen (anaerobic).
• Occurs when a cell can’t get the oxygen
that it needs to carry out aerobic
respiration.
• Less EFFECTIVE, doesn’t make as much
ATP.
• Waste products are left behind.
• Occurs in the cytoplasm.
• During fermentation, cells
convert NADH to NAD+ by
passing high energy electrons
back to pyruvic acid.
• Changes NADH back to NAD+.
• Allows glycolysis to keep
producing ATP.
There are 2 main types of
fermentation
1. Alcoholic Fermentation
2. Lactic Acid Fermentation
Alcoholic Fermentation
• Carried out by yeast
Pyruvic Acid + NADH
alcohol + CO2 NAD+
Fermentation
Yeast
Lactic Acid Fermentation
• Regenerates NAD+ so that
glycolysis can continue.
Pyruvic Acid + NADH
Glucose
lactic acid + NAD+
Pyruvic acid
Lactic Acid Fermentation
• Lactic acid is produced during
rapid exercise when the body is
low on Oxygen (O2)
• You quickly run out of Oxygen
(O2)
• The buildup of lactic acid causes
painful burning sensation (This is
why you feel sore).
Lactic acid makes you sore
• Your body
creates an
oxygen debt
• You must
repay that
debt with
heavy
breathing
after the
exercise
Good Lactic Acid
• Unicellular organisms that produce lactic
acid during fermentation are used to
make
• Cheese
• Yogurt
• Buttermilk
• Sour cream
• Pickles
• Sauerkraut
• Kimchi
Energy and Exercise
Quick Energy
• For short, quick bursts of energy, the body
uses ATP already in muscles as well as
ATP made by lactic acid fermentation.
Long – Term Energy
• For exercise longer than 90 seconds,
cellular respiration is the only way to
continue generating a supply of energy.
The whole process is divided into 2
parts:
• Anaerobic
– No Oxygen
– Occurs in cytoplasm
– Glycolysis is an
anaerobic process
– Glucose is broken
into pyruvic acid and
ATP
• Aerobic
– Oxygen
– Occurs in
mitochondria
– Divided into 2
stages:
• Kreb cycle (citric
acid cycle)
• Electron Transport
Chain
Comparing Photosynthesis
and Cellular Respiration
• They are almost the opposite
processes.
Photosynthesis
Cellular Respiration
Food synthesized
Food broken down
Energy from sun stored in glucose
Energy of glucose released
Carbon dioxide taken in
Carbon dioxide given off
Oxygen given off
Oxygen taken in
Produces sugars from PGAL
Produces CO2 and H2O
Requires light
Does not require light
Occurs only in presence of
chlorophyll
Occurs in all living cells
•
Photosynthesis
•
Cellular Respiration
Function
Energy capture
Energy release
Location
Chloroplast
Mitochondria
Reactants
CO2 and H2O
C6H12O6 and O2
Products
C6H12O6 and O2
CO2 and H2O
Equation
6CO2 + 6H2O 
C6H12O6 + 6O2
6O2 + C6H12O6 
6CO2 + 6 H2O