CHAPTERS 6 & 7 Cellular Respiration & Photosynthesis.
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Transcript of 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
Copyright © 2009 Pearson Education, Inc.
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
Copyright © 2009 Pearson Education, Inc.
Sunlight energy
ECOSYSTEM
Photosynthesisin chloroplasts
Glucose
Cellular respirationin mitochondria
H2O
CO2
O2
(for cellular work)
ATP
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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Breathing
Cellular Respiration
Muscle cells carrying out
CO2 + H2O + ATP
Lungs
BloodstreamCO2O2
CO2O2
Glucose + 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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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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ATPNAD+
NADH
H+
H+2e–
2e–
Electron transport
chain
Controlledrelease ofenergy forsynthesis
of ATP
+
O2
H2O
12
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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Mitochondrion
CO2 CO2
NADH
ATP
High-energy electronscarried by NADH
NADH
CITRIC ACIDCYCLE
GLYCOLYSIS
PyruvateGlucose
andFADH2
Substrate-levelphosphorylation
Substrate-levelphosphorylation
OXIDATIVEPHOSPHORYLATION
(Electron Transportand Chemiosmosis)
Oxidativephosphorylation
ATPATP
CytoplasmInnermitochondrialmembrane
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 aspeanuts
ProteinsFatsCarbohydrates
Glucose
OXIDATIVEPHOSPHORYLATION(Electron Transportand Chemiosmosis)
CITRICACID
CYCLE
AcetylCoA
GLYCOLYSIS
Pyruvate
Amino acidsGlycerolSugars Fatty acids
Amino groups
G3P
ATP
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 AcidWhy 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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CO2 O2Stoma
Mesophyll Cell
Vein
Chloroplast
Mesophyll
Leaf Cross Section
Leaf
Outer and innermembranes
IntermembranespaceGranumStroma Thylakoid
space
Thylakoid
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
Copyright © 2009 Pearson Education, Inc.
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
Copyright © 2009 Pearson Education, Inc.
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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H2O
ADP
P
LIGHTREACTIONS
(in thylakoids)
Light
Chloroplast
NADPH
ATP
O2
CALVINCYCLE
(in stroma)
Sugar : GLUCOSE
CO2
NADP+
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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Wavelength (nm)
10–5 nm
Increasing energy
Visible light
650nm
10–3 nm 1 nm 103 nm 106 nm 1 m 103 m
380 400 500 600 700 750
Radiowaves
Micro-waves
InfraredX-rays UVGammarays
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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Stroma
O2
H2O 12 H+
NADP+ NADPHLIGHT ENERGY
Photosystem II
Electron transport chainProvides energy forsynthesis of
+ 2
Primaryacceptor
1
Thylakoidmem-brane
P680
2
4
3Thylakoidspace
e–e–
5
Primaryacceptor
P700
6
LIGHT ENERGY
Photosystem IATP
H++
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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NADPH
ATP
RuBP
3
P
G3P
P
Input:CO2
1
Rubisco
3 P
Step Carbon fixation
3-PGA6 P
CALVINCYCLE
6
6
6
6
P
Step Reduction
2
2
G3P5 P
3
3
G3P1 P
Glucoseand othercompounds
Output:
Step Release of one
molecule of G3P
1
Step Regeneration of RuBP4
4ATP3
3 ADP
NADP+
6 ADP +
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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