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Chapter 6
Photosynthesis and
Respiration
Living things need energy to
survive.
Where do living
things get the energy
they need?
Energy comes in many forms
including light, heat, and
electricity.
Energy can be stored in
chemical compounds, too.
Cells use Adenosine
TriPhosphate to store and
release energy
ATP
ATP is used by all types of cells
as their basic energy source.
10 Producers (Autotrophs)
Convert the Carbon in CO2 Into
Sugars (C6H12O6) using the
Energy in SunlightPhotosynthesis
ALL CELLS Convert the Energy in
the Bonds of Glucose into the
Energy of ATP - Respiration
• Autotroph
• Producer
• Heterotroph
• Consumer
• Chemotroph
• Chemosynthesis
CO2  C6H12O6 Using Energy of
Inorganic Compounds
ATP consists of:
•adenine
•ribose (a 5-carbon sugar)
•3 phosphate groups
Adenine
ATP
Ribose
3 Phosphate groups
Storing Energy
ADP has two phosphate groups instead of
three.
A cell can store small amounts of energy
by adding a phosphate group to ADP.
ATP
ADP
+
Adenosine Diphosphate
(ADP) + Phosphate
Partially
charged
battery
Energy
Energy
Fully
charged
battery
Adenosine Triphosphate (ATP)
Releasing Energy
Energy stored in ATP is released by
breaking the chemical bond between
the second and third phosphates.
2 Phosphate groups
P
ADP
What is the role of ATP
in cellular activities?
The energy from ATP is needed for
many cellular activities, including
active transport across cell
membranes, protein synthesis
and muscle contraction.
ATP’s characteristics make it
exceptionally useful as the basic
energy source of all cells.
Using Biochemical Energy
Most cells have only a small
amount of ATP
It is not a good way to store large
amounts of energy.
Cells can regenerate ATP from
ADP as needed by using the
energy in foods like glucose.
Quiz 6-1
Organisms that make their own food are called
a. autotrophs.
b. heterotrophs.
c. decomposers.
d. consumers.
Most autotrophs obtain their energy from
a. chemicals in the environment.
b. sunlight.
c. carbon dioxide in the air.
d. other producers.
How is energy released from ATP?
a. A phosphate is added.
b. An adenine is added.
c. A phosphate is removed.
d. A ribose is removed.
How is it possible for most cells to function
with only a small amount of ATP?
a. Cells do not require ATP for energy.
b. ATP can be quickly regenerated from
ADP and P.
c. Cells use very small amounts of
energy.
d. ATP stores large amounts of energy.
Compared to the energy stored in a molecule of
glucose, ATP stores
a. much more energy.
b. much less energy.
c. about the same amount of energy.
d. more energy sometimes and less at others.
Photosynthesis
Photosynthesizers use the
energy of sunlight to convert
water and carbon dioxide into
high-energy carbohydrates and
oxygen.
H2O
CO2
Light
NADP+
ADP + P
Lightdependent
reactions
Calvin
Calvin
cycle
Cycle
Chloroplast
O2
Sugars
Electron Carriers
When electrons in chlorophyll
absorb sunlight, the electrons gain a
great deal of energy.
Cells use electron carriers to
transport these high-energy
electrons from chlorophyll to other
molecules.
NADP+
Electron carriers, such as
NADP+, transport electrons.
NADP+ accepts and holds 2 highenergy electrons along with a
hydrogen ion (H+). This converts
the NADP+ into NADPH.
The Photosynthesis Equation
The equation for photosynthesis is:
6CO2 + 6H2O
Light
carbon dioxide + water
C6H12O6 + 6O2
Light
sugars + oxygen
Light energy
H2O
Light-Dependent
Reactions
(thylakoids)
ADP
+
NADP
Sugar
O2
ATP
NADPH
Calvin Cycle
(stroma)
CO2
+
H20
Inside a Chloroplast
In plants, photosynthesis takes
place inside chloroplasts.
Plant
Chloroplast
Plant cells
Chloroplasts contain thylakoids—saclike
photosynthetic membranes.
Single
thylakoid
Thylakoids are arranged in stacks
called grana, Or singular granum.
Granum
Photosystems, which are the lightcollecting units of the chloroplast
are in the thylakoid membrane.
Photosystems
What is the role of light
and chlorophyll in
photosynthesis?
Light and Pigments
How do plants capture the
energy of sunlight?
In addition to water and carbon
dioxide, photosynthesis requires
light and chlorophyll.
Plants gather the sun's energy with
light-absorbing molecules called
pigments.
The main pigment in plants is
chlorophyll.
There are two main types of
chlorophyll:
–chlorophyll a
–chlorophyll b
Chlorophyll absorbs light well in the
blue-violet and red regions of the visible
spectrum.
Chlorophyll does not absorb light in the
green region of the spectrum. Green light
is reflected by leaves, which is why
plants look green.
Light is a form of energy, so any compound
that absorbs light also absorbs energy from
that light.
When chlorophyll absorbs light, much of the
energy is transferred directly to electrons in the
chlorophyll molecule, raising the energy levels
of these electrons.
These high-energy electrons are what make
photosynthesis work.
Photosynthesis Video
Quiz 6-2
Most of the added mass of a tree comes from
a. soil and carbon dioxide.
b. oxygen and carbon dioxide.
c. water and carbon dioxide.
d. soil and oxygen.
Plants use the sugars produced in
photosynthesis to make
a. oxygen.
b. carbon dioxide.
c. starches.
d. protein.
The raw materials required for plants to carry out
photosynthesis are
a. carbon dioxide and oxygen.
b. carbon dioxide and water.
c. oxygen and sugars.
d. oxygen and water.
The principal pigment in plants is
a. chloroplast.
b. carotene.
c. chlorophyll.
d. carbohydrate.
The colors of light that are absorbed by
chlorophylls are
a. green and yellow.
b. blue, violet, and red.
c. green, blue, and violet.
d. red and yellow.
Light-Dependent Reactions
The light-dependent reactions
require light.
The light-dependent reactions
produce oxygen gas and convert
ADP and NADP+ into the energy
carriers ATP and NADPH.
Inside the Thylokoid (Lumen)
Outside the Thylokoid (Stroma)
Photosynthesis begins when pigments in
photosystem II absorb light, increasing their
energy level.
Photosystem II
These high-energy electrons are passed on to the
electron transport chain.
Photosystem II
High-energy
electron
Electron
carriers
Enzymes on the thylakoid membrane break water
molecules into:
Photosystem II
2H2O
High-energy
electron
Electron
carriers
– hydrogen ions
– oxygen atoms
– energized electrons
Photosystem II
+
O2
2H2O
High-energy
electron
Electron
carriers
The energized electrons from water replace the
high-energy electrons that chlorophyll lost to the
electron transport chain.
Photosystem II
+
2H2O
High-energy
electron
O2
As plants remove electrons from water, oxygen is
left behind and is released into the air.
Photosystem II
+
2H2O
High-energy
electron
O2
The hydrogen ions left behind when water is
broken apart are released inside the thylakoid
membrane.
Photosystem II
+
2H2O
High-energy
electron
O2
Energy from the electrons is used to transport H+
ions from the stroma into the inner thylakoid
space.
Photosystem II
+
2H2O
O2
High-energy electrons move through the electron
transport chain from photosystem II to
photosystem I.
Photosystem II
+
O2
2H2O
Photosystem I
Pigments in photosystem I use energy from
light to re-energize the electrons.
+
O2
2H2O
Photosystem I
NADP+ then picks up these high-energy
electrons, along with H+ ions, and becomes
NADPH.
+
O2
2H2O
2 NADP+
2
2
NADPH
As electrons are passed from chlorophyll to
NADP+, more H+ ions are pumped across the
membrane.
+
O2
2H2O
2 NADP+
2
2
NADPH
Soon, the inside of the membrane fills up with
positively charged hydrogen ions, which makes
the outside of the membrane negatively charged.
+
O2
2H2O
2 NADP+
2
2
NADPH
The difference in charges across the membrane
provides the energy to make ATP
+
O2
2H2O
2 NADP+
2
2
NADPH
H+ ions cannot cross the membrane directly.
ATP synthase
+
O2
2H2O
2 NADP+
2
2
NADPH
The cell membrane contains a protein called ATP
synthase that allows H+ ions to pass through it
ATP synthase
+
O2
2H2O
2 NADP+
2
2
NADPH
As H+ ions pass through ATP synthase, the
protein rotates.
ATP synthase
+
O2
2H2O
2 NADP+
2
2
NADPH
As it rotates, ATP synthase binds ADP and a
phosphate group together to produce ATP.
ATP synthase
+
O2
2H2O
ADP
2 NADP+
2
2
NADPH
Because of this system, light-dependent electron
transport produces not only high-energy electrons
but ATP as well.
ATP synthase
+
O2
2H2O
ADP
2 NADP+
2
2
NADPH
The Calvin Cycle
 uses ATP and NADPH from
the light-dependent reactions to
produce high-energy sugars.
The Calvin cycle does not require
light
 Light-Independent reactions.
Six carbon dioxide molecules enter the cycle from
the atmosphere and combine with six 5-carbon
molecules.
CO2 Enters the Cycle
The result is twelve 3-carbon molecules, which
are then converted into higher-energy forms.
The energy for this conversion comes from ATP
and high-energy electrons from NADPH.
Energy Input
12
12 ADP
12 NADPH
12 NADP+
Two of twelve 3-carbon molecules are removed
from the cycle.
Energy Input
12
12 ADP
12 NADPH
12 NADP+
The molecules are used to produce sugars, lipids,
amino acids and other compounds.
12
12 ADP
12 NADPH
12 NADP+
6-Carbon sugar
produced
Sugars and other compounds
The 10 remaining 3-carbon molecules are
converted back into six 5-carbon molecules,
which are used to begin the next cycle.
12
12 ADP
6 ADP
12 NADPH
6
12 NADP+
5-Carbon Molecules
Regenerated
Sugars and other compounds
The two sets of photosynthetic
reactions work together.
–The Light-Dependent reactions trap
sunlight energy in chemical form.
Light & H2O  NADPH & ATP
–The Calvin Cycle uses that chemical
energy to produce stable, high-energy
sugars from carbon dioxide and water.
NADPH, ATP, & CO2  Glucose
Quiz 6-3
In plants, photosynthesis takes place inside the
a. thylakoids.
b. chlorophyll.
c. chloroplasts.
d. photosystems.
Energy to make ATP in the chloroplast comes
most directly from
a. electrons transferred directly from NADPH.
b. transfer of a phosphate from ADP.
c. hydrogen ions flowing through an enzyme in
the thylakoid membrane.
d. electrons moving through the electron
transport chain.
NADPH is produced in light-dependent reactions
and carries energy in the form of
a. ATP.
b. ADP.
c. high-energy electrons.
d. low-energy electrons.
What is another name for the Calvin cycle?
a. light-dependent reactions
b. light-independent reactions
c. electron transport chain
d. photosynthesis
Which of the following factors does NOT directly
affect photosynthesis?
a. light intensity
b. water supply
c. wind
d. temperature
Cellular Respiration
Chemical Energy and Food
One gram of glucose (C6H12O6), when burned,
releases 3811 calories of heat energy.
Both plant and animal cells carry out the final
stages of cellular respiration in the
mitochondria.
Mitochondrion
Animal Cells
Outer membrane
Inner
membrane
Matrix
Plant Cells
Intermembrane
space
Electrons carried in NADH
Pyruvic
acid
Glucose
Electrons carried
in NADH and
FADH2
Glycolysis
Cytoplasm
Mitochondrion
Cellular respiration
releases energy by
breaking down glucose
and other food molecules
in the presence of oxygen.
A Cellular Respiration Video
Another Cellular Respiration Video
The equation for cellular respiration is:
6O2 + C6H12O6 → 6CO2 + 6H2O +
Energy
oxygen + glucose → carbon dioxide + water +
Energy
Glycolysis takes place in the
cytoplasm. The Krebs cycle and
electron transport take place in the
mitochondria.
Glycolysis
Cytoplasm
Mitochondrion
ATP and NADH Production in Glycolysis
2 ATP
2 ADP
4 ADP
2NAD+
4 ATP
2
2 Pyruvic
acid
To the electron
transport chain
The Advantages of Glycolysis
The process of glycolysis is so fast that
cells can produce thousands of ATP
molecules in a few milliseconds.
Glycolysis does not require oxygen.
Quiz 6-4
Aerobic respiration produces ATP in …
a. eukaryotic animal cells.
b. eukaryotic plant cells.
c. all eukaryotic cells.
d. all prokaryotic and eukaryotic cells.
The raw materials required for cellular
respiration are
a. glucose and oxygen.
b. glucose and water.
c. carbon dioxide and oxygen.
d. carbon dioxide and water.
Glycolysis occurs in the
a. cytoplasm.
b. mitochondria.
c. nucleus.
d. chloroplasts.
The net gain of ATP molecules after glycolysis is
a. 2 ATP molecules.
b. 3 ATP molecules.
c. 3 pyruvic acid molecules.
d. 4 pyruvic acid molecules
The carbon product of glycolysis is …
a. pyruvic acid.
b. pyruvate.
c. two, three carbon molecules.
d. All of the above.
Oxygen is required for the
final steps of cellular
respiration.
Because the pathways of
cellular respiration require
oxygen, they are aerobic.
During the Krebs Cycle,
pyruvic acid is broken
down into carbon
dioxide in a series of
energy-extracting
reactions.
The Krebs cycle
begins when
pyruvic acid
produced by
glycolysis enters
the mitochondrion.
One carbon
molecule is
removed, forming
CO2, and
electrons are
removed,
changing NAD+ to
NADH.
Coenzyme A joins
the 2-carbon
molecule, forming
acetyl-CoA.
Acetyl-CoA then
adds the 2-carbon
acetyl group to a 4carbon compound,
forming citric acid.
Citric acid
Citric acid is broken down into a 5-carbon
compound, then into a 4-carbon compound.
Two more molecules of CO2 are released and
electrons join NAD+ and FADH, forming NADH
and FADH2
In addition, one molecule of ATP is generated.
The energy tally from 1
molecule of pyruvic acid is
– 4 NADH
– 1 FADH2
– 1 ATP
Electron Transport
The electron transport chain
uses the high-energy electrons
from the Krebs cycle to convert
ADP into ATP.
High-energy electrons from NADH and FADH2 are
passed along the electron transport chain from one
carrier protein to the next.
At the end of the chain, an enzyme combines
these electrons with hydrogen ions and oxygen to
form water.
As the final electron acceptor of the electron
transport chain, oxygen gets rid of the low-energy
electrons and hydrogen ions.
When 2 high-energy electrons move down the
electron transport chain, their energy is used to
move hydrogen ions (H+) across the membrane.
During electron transport, H+ ions build up in the
intermembrane space, so it is positively charged.
The other side of the membrane, from which those
H+ ions are taken, is now negatively charged.
The inner membranes of the mitochondria contain
protein spheres called ATP synthases.
ATP
synthase
As H+ ions escape through channels into these
proteins, the ATP synthase spins.
Channel
ATP
synthase
As it rotates, the enzyme grabs a low-energy ADP,
attaching a phosphate, forming high-energy ATP.
Channel
ATP
synthase
ADP
The Totals
Glycolysis produces just 2 ATP
molecules per molecule of glucose.
The complete breakdown of glucose
through cellular respiration, including
glycolysis, results in the production
of ~36 molecules of ATP.
Comparing Photosynthesis and Cellular
Respiration
The energy flows in photosynthesis and cellular
respiration take place in opposite directions.
Fermentation
When oxygen is not present,
glycolysis is followed by a different pathway.
The combined process of this pathway
and glycolysis is called fermentation.
Fermentation releases energy from food
molecules by producing ATP in the absence
of oxygen.
During fermentation, cells convert NADH to
NAD+ by passing high-energy electrons back
to pyruvic acid.
This action converts NADH back into NAD+, and
allows glycolysis to continue producing a
steady supply of ATP.
Fermentation does not require oxygen—it is an
anaerobic process.
What are the two main
types of fermentation?
Alcoholic Fermentation
Yeasts and a few other microorganisms use
alcoholic fermentation, forming ethyl alcohol
and carbon dioxide as wastes.
The equation for alcoholic fermentation after
glycolysis is:
pyruvic acid + NADH → alcohol + CO2 + NAD+
Lactic Acid Fermentation
In many cells, pyruvic acid that accumulates as
a result of glycolysis can be converted to
lactic acid.
This type of fermentation is called lactic acid
fermentation. It regenerates NAD+ so that
glycolysis can continue.
The equation for lactic acid fermentation after
glycolysis is:
pyruvic acid + NADH → lactic acid + NAD+
The first part of the equation is glycolysis.
The second part shows the conversion of
pyruvic acid to lactic acid.
On a global level, photosynthesis and cellular
respiration are also opposites.
– Photosynthesis removes carbon dioxide from the
atmosphere and cellular respiration puts it back.
– Photosynthesis releases oxygen into the
atmosphere and cellular respiration uses that
oxygen to release energy from food.
Quiz 6-5
The Krebs cycle breaks pyruvic acid down into
a. oxygen.
b. NADH and FADH2.
c. alcohol.
d. carbon dioxide.
What role does the Krebs cycle play in the cell?
a. It transfers energy from molecules formed
during glycolysis.
b. It breaks down glucose and releases its
stored energy.
c. It combines carbon dioxide and water into
high-energy molecules.
d. It breaks down ATP and NADH, releasing
stored energy.
In respiration, the electron transport chain is
located in the
a. cell membrane.
b. cytoplasm.
c. inner mitochondrial membrane.
d. outer mitochondrial membrane.
To generate energy over long periods, the body
must use
a. cellular respiration.
b. lactic acid fermentation.
c. stored ATP.
d. glycolysis.
Which statement correctly describes
photosynthesis and cellular respiration?
a. Photosynthesis releases energy, while
cellular respiration stores energy.
b. Photosynthesis and cellular respiration use
the same raw materials.
c. Cellular respiration and photosynthesis
produce the same products.
d. Cellular respiration releases energy, while
photosynthesis stores energy.
Homework!!!
Chapter 6
Standardized Test Prep