Transcript CHAPTERS 6 & 7

CHAPTERS 6 & 7
Cellular Respiration
&
Photosynthesis
Photosynthesis and Cellular Respiration provide energy
for life
All Living Organisms Must Take in Energy and Use
It:
 Life Processes Require Energy:
– These include growth, transport, manufacture,
movement, reproduction, and others
– Energy that supports life on Earth is captured from
sun rays reaching Earth through plant, algae, protist,
and bacterial photosynthesis
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Photosynthesis and cellular respiration provide energy
for life
• Energy in sunlight is used in photosynthesis to
make glucose from CO2 and H2O with release of
O2
• Other organisms use the O2 and energy in sugar
and release CO2 and H2O through cellular
respiration
• Together, these two processes are responsible
for the majority of life on Earth
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Sunlight energy
ECOSYSTEM
Photosynthesis
in chloroplasts
CO2
Glucose
+
+
H2O
O2
Cellular respiration
in mitochondria
ATP
(for cellular work)
Heat energy
Breathing supplies oxygen to our cells for use in
cellular respiration and removes carbon dioxide
• Breathing and cellular respiration are closely
related
– Breathing is necessary for exchange of CO2 produced
during cellular respiration for atmospheric O2
– Cellular respiration uses O2 to help harvest energy
from glucose and produces CO2 in the process
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O2
Breathing
CO2
Lungs
CO2
Bloodstream
Muscle cells carrying out
Cellular Respiration
Glucose + O2
CO2 + H2O + ATP
O2
Cellular respiration banks energy in ATP molecules
• Cellular respiration is an exergonic/degradative
process that transfers chemical energy from
glucose to ATP
– Cellular respiration produces 38 ATP molecules from
each glucose molecule
– Other foods (organic molecules) can be used as a
source of energy as well
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C6H12O6
Glucose
+ 6
O2
Oxygen
6 CO2
Carbon
dioxide
+ 6
H2O
Water
+
ATPs
Energy
The human body uses energy from ATP for all its activities
• The average adult human needs about 2,200
kcal (nutritional calories) of energy per day
– A kilocalorie (kcal) is the quantity of heat required
to raise the temperature of 1 kilogram (kg) of water
by 1oC
– This energy is used for body maintenance and for
voluntary activities
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Cells tap energy from electrons “falling” from organic
fuels to oxygen
• Energy can be released from glucose
by simply burning it
• The energy is dissipated as heat and
light and is not available to living
organisms
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Cells tap energy from electrons “falling” from organic
fuels to oxygen
• On the other hand, cellular respiration is
the controlled breakdown of organic
molecules
– Energy is released in small amounts that
can be captured by a biological system
and stored in ATP
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Cells tap energy from electrons “falling” from organic
fuels to oxygen
• There are electron “carrier” molecules that
carry the electrons released from the
breakdown of the glucose molecule in cellular
respiration
– They form a staircase where the electrons pass from
one to the next down the staircase
– These electron carriers collectively are called the
electron transport chain, and as electrons are
transported down the chain, ATP is generated
– The final acceptor of the electrons is OXYGEN
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NADH
NAD+
+
ATP
2e–
Controlled
release of
energy for
synthesis
of ATP
H+
2e–
H+
H 2O
1

2
O2
STAGES OF CELLULAR RESPIRATION
AND FERMENTATION
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Overview: Cellular respiration occurs in three main
stages
• Stage 1: Glycolysis
– Glycolysis begins respiration by breaking
glucose, a six-carbon molecule, into two
molecules of a three-carbon compound called
pyruvate
– This stage occurs in the cytoplasm
– Only 2 ATPs are produced (NO oxygen is
involved)
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Overview: Cellular respiration occurs in three main
stages
• Stage 2: The Citric Acid Cycle
– The citric acid cycle breaks down
pyruvate into carbon dioxide and
supplies the third stage with electrons
– This stage occurs in the mitochondria
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Overview: Cellular respiration occurs in three main
stages
• Stage 3: Oxidative Phosphorylation (electron
transport system)
– During this stage, electrons are shuttled through the
electron transport chain
– As a result, ATP is generated through oxidative
phosphorylation (OXYGEN is REQUIRED = AEROBIC)
– This stage occurs in the mitochondria
– Another 36 ATPs are produced in stages 2 and 3
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NADH
Mitochondrion
High-energy electrons
carried by NADH
NADH
FADH2
and
OXIDATIVE
GLYCOLYSIS
Glucose
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
CITRIC ACID
CYCLE
Pyruvate
Cytoplasm
Inner
mitochondrial
membrane
CO2
CO2
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
ATP
Oxidative
phosphorylation
Fermentation enables cells to produce ATP without
oxygen
• Fermentation is an anaerobic (without
oxygen) energy-generating process
– It takes advantage of Glycolysis,
producing 2 ATP molecules for every
glucose molecule
– Why can’t humans survive by
fermentation alone???
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Fermentation enables cells to produce ATP without
oxygen
• Human muscle cells and certain bacteria
perform lactic acid fermentation
• Lactic Acid produces some of the burning
sensation in your muscles after you’ve
exercised
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Fermentation enables cells to produce ATP without
oxygen
• The baking and winemaking industry have used
alcohol fermentation for thousands of years
– Yeasts are single-celled fungi that not only
can use respiration for energy but can
ferment under anaerobic (NO OXYGEN)
conditions
– They convert pyruvate to CO2 (gas) and
ethanol
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Fermentation enables cells to produce ATP without
oxygen
• Some bacteria perform acetic acid
fermentation
– They convert pyruvate to acetic acid
(VINEGAR)
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EVOLUTION CONNECTION: Glycolysis evolved early in
the history of life on Earth
• Glycolysis is the universal energy-harvesting
process of living organisms
– So, all cells can use glycolysis for the energy
necessary for viability
– The fact that glycolysis has such a widespread
distribution is good evidence for evolution
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Cells use many kinds of organic molecules as fuel for
cellular respiration
• Although glucose is considered to be the
primary source of sugar for cellular respiration
and fermentation, there are actually three
sources of molecules for generation of ATP
– Carbohydrates (disaccharides)
– Proteins (after conversion to amino acids)
– Ammonia (a TOXIN) is generated by the use of amino
acids for energy
– Fats
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Food, such as
peanuts
Carbohydrates
Fats
Glycerol
Sugars
Proteins
Fatty acids
Amino acids
Amino
groups
Glucose
G3P
GLYCOLYSIS
Pyruvate
Acetyl
CoA
ATP
CITRIC
ACID
CYCLE
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
CHAPTER 6 & 7 (continued)
PHOTOSYNTHESIS
Light
energy
6 CO2
+6
Carbon dioxide
H2 O
Water
C6H12O6
Photosynthesis
Glucose
+ 6
O2
Oxygen gas
PLANT POWER
• “Plant Power” would be an excellent energy solution,
because air pollution, acid precipitation, and
greenhouse gases could be significantly reduced
(plant power is also RENEWABLE)
• Fossil Fuels contain contaminants that lead to the
production of other greenhouse gases and
pollutants that cause acid rain:
– Sulfur Dioxide + Water  Sulfuric Acid
– Nitrogen Oxide + Water  Nitric Acid
Why is acid rain harmful to life???
Autotrophs are the producers of the biosphere
• Autotrophs (PRODUCERS) are living things that
are able to make their own food without using
organic molecules derived from any other living
thing
– Autotrophs that use the energy of light to produce
organic molecules are called photoautotrophs
– Most plants, algae and other protists, and some
prokaryotes are photoautotrophs
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Photosynthesis occurs in chloroplasts in plant cells
• Chloroplasts are the major sites of photosynthesis
in green plants
– Chlorophyll, an important light absorbing pigment in
chloroplasts, is responsible for the green color of plants
– Chlorophyll plays a central role in converting solar
energy to chemical energy
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Leaf Cross Section
Leaf
Mesophyll
Vein
CO2 O2 Stoma
Mesophyll Cell
Chloroplast
Outer and inner
membranes
Thylakoid
Stroma Granum
Thylakoid
space
Intermembrane
space
Photosynthesis is a biosynthetic & endergonic process; cellular
respiration is the opposite (degradative & exergonic)
• Photosynthesis is a biosynthetic &
endergonic process
– Water molecules are split apart; they
lose electrons and produce hydrogen
ions (H+)
– Then 6 CO2 molecules are built into a
sugar (GLUCOSE) molecule as electrons
and hydrogen ions are added to them
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Photosynthesis is a biosynthetic & endergonic process; cellular
respiration is the opposite (degradative & exergonic)
• Photosynthesis is a biosynthetic &
endergonic process
– Water molecules are split apart; they
lose electrons and produce hydrogen
ions (H+)
– Then 6 CO2 molecules are built into a
sugar (GLUCOSE) molecule as electrons
and hydrogen ions are added to them
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The two stages of photosynthesis are linked by
ATP
• Actually, photosynthesis occurs in two metabolic
stages
– One stage involves the light reactions
(REQUIRES LIGHT)
– In the light reactions, light energy is
converted to chemical energy (ATP)
– Water is split to provide the O2 as well as
electrons
– Water  Hydrogen ions + Oxygen + electrons
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Overview: The two stages of photosynthesis are
linked by ATP
• The second stage is the Calvin cycle
– It is a cyclic series of reactions that builds sugar
molecules (GLUCOSE) from CO2 and the products of
the light reactions
– During the Calvin cycle, CO2 is incorporated into
organic compounds, a process called carbon fixation
– This is the endergonic/biosynthetic part of the
reaction that uses the ATP (energy) produced during
the Light Dependent Stage
– This is the Light Independent Stage
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CO2
H2O
Chloroplast
Light
NADP+
ADP
P
LIGHT
REACTIONS
CALVIN
CYCLE
(in stroma)
(in thylakoids)
ATP
NADPH
O2
Sugar : GLUCOSE
THE LIGHT REACTIONS:
CONVERTING SOLAR ENERGY TO
CHEMICAL ENERGY
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Visible radiation drives the light reactions
• Sunlight contains energy called electromagnetic
energy or radiation
– Visible light is only a small part of the
electromagnetic spectrum, the full range of
electromagnetic wavelengths
– Electromagnetic energy travels in waves, and the
wavelength is the distance between the crests of
two adjacent waves
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Increasing energy
10–5 nm 10–3 nm
Gamma
rays
X-rays
103 nm
1 nm
UV
106 nm
Infrared
103 m
1m
Microwaves
Radio
waves
Visible light
380 400
600
500
Wavelength (nm)
700
650
nm
750
Light
Reflected
light
Chloroplast
Absorbed
light
Thylakoid
Transmitted
light
Visible radiation drives the light reactions
• Chloroplasts contain several different pigments
and all absorb light of different wavelengths
– Chlorophyll a absorbs blue violet and red light and
reflects green
– Chlorophyll b absorbs blue and orange and reflects
yellow-green
– The carotenoids absorb mainly blue-green light and
reflect yellow and orange
– SO: Most leaves look GREEN
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LIGHT ENERGY
Photosystem II
Electron transport chain
Provides energy for
synthesis of ATP
NADP+ + H+
LIGHT ENERGY
Photosystem I
Stroma
1
Primary
acceptor
Primary
acceptor
2 e–
Thylakoid
membrane
e–
4
P700
P680
Thylakoid
space
3
H2O
1

2
5
O2 + 2 H+
6
NADPH
THE CALVIN CYCLE: CONVERTING
CO2 TO GLUCOSE
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ATP powers sugar (GLUCOSE) synthesis in the
Calvin cycle
• The Calvin cycle makes sugar (glucose) within a
chloroplast
– To produce sugar, the necessary ingredients are
atmospheric CO2, and ATP & Hydrogen ions which
were generated in the light reactions
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Step 1 Carbon fixation
Input:
3
CO2
Rubisco
1
Step 2 Reduction
P
3 P
P
6
RuBP
3-PGA
6
3 ADP
ATP
6 ADP + P
Step 3 Release of one
molecule of G3P
3
ATP
CALVIN
4
2
CYCLE
6 NADPH
6 NADP+
Step 4 Regeneration of RuBP
P
5
P
6
G3P
G3P
3
Output: 1
P
G3P
Glucose
and other
compounds
PHOTOSYNTHESIS,
SOLAR RADIATION,
AND EARTH’S ATMOSPHERE
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Photosynthesis moderates global warming
• The greenhouse effect results from solar energy
warming our planet
– Gases in the atmosphere (often called greenhouse
gases), including CO2, reflect heat back to Earth,
keeping the planet warm and supporting life
– However, as we increase the level of greenhouse
gases, Earth’s temperature rises above normal,
initiating problems
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Photosynthesis moderates global warming
• Increasing concentrations of greenhouse gases
lead to global warming, a slow but steady rise in
Earth’s surface temperature
– The extraordinary rise in CO2 is mostly due to the
combustion of carbon-based fossil fuels
– The consequences of continued rise will be melting
of polar ice, changing weather patterns, and spread
of tropical disease
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Some heat
energy escapes
into space
Sunlight
Atmosphere
Radiant heat
trapped by CO2
and other gases
Photosynthesis moderates global warming
• Perhaps photosynthesis can mitigate the
increase in atmospheric CO2 (Photosynthesis
uses up Carbon Dioxide)
– However, there is increasing widespread
deforestation, which aggravates the global warming
problem
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