8.2 photosynthesis: an overview 4.2 overview of photosynthesis · 4.2 overview of photosynthesis...
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4.2 Overview of Photosynthesis
Photosynthesis – process by which plants make food using energy from the sun
• Plants are autotrophs that make their own source of chemical energy.
• Chemical equation of photosynthesis:
• Occurs in chloroplasts
6CO2 + 6H2O C6H12O6 + 6O2
H2O sugars
ATP
enzymes
CO2
sun
O2
8.2 Photosynthesis: An Overview
4.2 Overview of Photosynthesis
chloroplast
stroma
grana (thylakoids)
chloroplastleaf cellleaf
Chloroplast structure:• Double membrane structure• Light-dependent reactions take place
in the membrane of the thylakoids(stacks of thylakoids = grana)
• Light-independent reactions take place in stroma (fluid interior of chloroplast)
8.2 Photosynthesis: An Overview
4.2 Overview of Photosynthesis
Plant pigments in chloroplasts absorb sunlight.
• Absorb light at different wavelengths (what you don’t see)• Reflect what is not absorbed (what you see).
8.2 Photosynthesis: An Overview
4.2 Overview of Photosynthesis
Plant pigments absorb sunlight.• Main pigment
– chlorophyll a– absorb at blue and red region
and reflect green• Accessory pigments
– chlorophyll b, carotenoid, xanthophyll, carotene
– absorb closer to green region allowing plant to use light energy across spectrum
8.2 Photosynthesis: An Overview
4.2 Overview of Photosynthesis
Photosynthesis occurs in two stages.
ENERGYbuilding reactions(Light Rxn)
SUGARbuilding reactions
(Dark Rxn)
ATPNADPH
ADPNADP
sugar
sun
used immediatelyto synthesize sugars
H2O CO2
8.2 Photosynthesis: An Overview
4.2 Overview of Photosynthesis
Photosynthesis occurs in two stages.
• Light-dependent reaction - requires sunlight (aka “light reaction”)- only runs during daytime- energy-building reaction (making ATP & NADPH)- occurs in thylakoid of chloroplast
• Light-independent reaction- does not require sunlight (aka “dark reaction” or “Calvin Cycle”)
- runs all day- sugar-building reaction (making glucose)- occurs in stroma of chloroplast
8.2 Photosynthesis: An Overview
4.3 Photosynthesis in Detail
Light-Dependent Reactions• First set of reactions – depend on sun for energy
– Occur in membrane of thylakoids– Produces ATP and NADPH – energy carrier
molecules which will be used to run Light Independent Reactions
8.3 The Reactions of Photosynthesis
4.3 Photosynthesis in Detail
Light-Dependent Reactions• The light-dependent reactions include groups of
molecules called photosystems.• Photosystem II absorbs sunlight at 680 nm (P680).• Photosystem I absorbs sunlight at 700 nm (P700).
8.3 The Reactions of Photosynthesis
4.3 Photosynthesis in Detail
• Photosystem II captures and transfers energy.
1) PS II absorbs sunlight at 680 nm.
2) H2O molecules are split; O2 is released; energized e- enter ETC.
3) H+ ions are transported down ETC and pumped across thylakoid membrane
8.3 The Reactions of Photosynthesis
PS II
4.3 Photosynthesis in Detail
• Photosystem I captures energy and produces energy-carrying molecules.
4) PS I absorbs sunlight at 700 nm
5) energized electrons are used to make NADPH
6) hydrogen ions flow through ATP synthase in the thylakoid membrane
7) ATP synthase makes ATP from ADP
8) NADPH and ATP are sent to stroma to run Light-Independent Reaction
8.3 The Reactions of Photosynthesis
PS I
4.3 Photosynthesis in Detail
Summary of Light-Dependent Reaction
8.3 The Reactions of Photosynthesis
4.3 Photosynthesis in Detail
Light-Independent Reactions• Second set of reactions
– Do not depend on sunlight– Occur in stroma– Use CO2 as source of carbon to build glucose via
Calvin Cycle
8.3 The Reactions of Photosynthesis
4.3 Photosynthesis in Detail
1
2
3
4
• The Calvin Cycle (aka “Carbon Fixation”)1) Carbon from CO2 enter the cycle and add to 5-C molecule to
form 6-C molecules.2) ATP and NADPH from Light-Dependent Reactions are used
to split the 6-C molecules to 3-C molecules.3) 3-C molecules are rearranged to form high-energy 3-C
molecules. Two 3-Cmolecules formone 6-C glucose.
4) 3-C molecules arechanged back to5-C molecules tocontinue the cycle.
Light-Independent Reactions
SIX CO2 make ONE glucose!!
8.3 The Reactions of Photosynthesis
4.1 Chemical Energy and ATP
The chemical energy used for most cell processes is carried by ATP.
• Molecules in food store chemical energy in their bonds.
Starch molecule
Glucose molecule
8.1 Energy and Life
4.1 Chemical Energy and ATP
Adenosine Triphosphate (ATP)
• ATP is the energy molecule most cells use for cellular processes
• ATP is made up of 3 parts:- a nitrogen base (adenine)- a 5-carbon sugar (ribose)- 3 phosphate groups
triphosphateadenosine
adenosine diphosphate
8.1 Energy and Life
4.1 Chemical Energy and ATP
• ATP transfers energy from the breakdown of food molecules to cell functions.– Energy is released when a phosphate group is removed.
(ATP ADP)– Energy is stored when a phosphate group is added.
(ADP ATP)
8.1 Energy and Life
4.4 Overview of Cellular Respiration
Cellular respiration makes ATP by breaking down sugars.• All cells have to use cellular respiration to make energy in the form of ATP.
Cytoplasm
Pyruvicacid
Mitochondrion
Electrons carried in NADHElectrons carriedin NADH and
FADH2
GlycolysisGlucose
9.1 Chemical Pathways
4.4 Overview of Cellular Respiration
Chemical Equation of Cellular Respiration
Glucose Oxygen Water Energy
This is why we eat. Plants don’t eat; they make this with sunlight.
This is why we breathe oxygen.
This is why we breathe out carbon dioxide.
The waterwe can use.
The energy released from the glucose is stored in molecules of ATP for later use.
Carbon Dioxide
9.1 Chemical Pathways
4.4 Overview of Cellular Respiration
mitochondrion
animal cell
Two types of Cellular Respiration
• Aerobic Respiration - requires oxygen- aka “Oxidative Respiration”
• Anaerobic Respiration- does not require oxygen- aka “Fermentation”- Alcohol Fermentation
occurs in yeast cells- Lactic Acid Fermentation
occurs in muscle cells
9.1 Chemical Pathways
4.4 Overview of Cellular Respiration
• Both types of respiration begin with glycolysis– anaerobic process (does not require oxygen)– takes place in cytoplasm– glucose is broken down– 6-C glucose is split into two 3-C pyruvates
Cytoplasm
Pyruvicacid
Mitochondrion
Electrons carried in NADH
GlycolysisGlucose
Glycolysis
4.5 Cellular Respiration in Details9.1 Chemical Pathways
4.4 Overview of Cellular Respiration
• 2 pyruvates (or pyruvic acids) are produced• 4 ATP are produced, but 2 ATP are used
= net production of 2 ATP• 2 NADH produced (NADH is a temporary energy-
carrying molecule which will enter ETC to make ATP)• If no oxygen is available fermentation• If oxygen is available Krebs Cycle ETC
Glycolysis
4.5 Cellular Respiration in Details9.1 Chemical Pathways
4.4 Overview of Cellular Respiration
Anaerobic Respiration (Fermentation)
alcohol
lactic acid
4.6 Fermentation9.1 Chemical Pathways
4.4 Overview of Cellular Respiration
Anaerobic Respiration (Fermentation)• Two types:
1) Alcohol fermentation - pyruvate (3-C) is converted into alcohol (2-C) and CO2 (1-C)
- used by bacteria and yeast in food production(bread, wine, cheese)
- makes 2 ATPs from glycolysis
4.6 Fermentation9.1 Chemical Pathways
4.4 Overview of Cellular Respiration
2) Lactic Acid fermentation - pyruvate (3-C) is converted into lactic acid (3-C)- occurs in muscle cells during strenuous exercise for
short periods of time due to oxygen debt- makes 2 ATPs from glycolysis
Anaerobic Respiration (Fermentation)
4.6 Fermentation9.1 Chemical Pathways
4.4 Overview of Cellular Respiration
Aerobic Cellular Respiration
• Cellular respiration that requires O2
• Pyruvate from glycolysis enters the mitochondrion
• Many ATP are made – approx 36 ATP per glucose
• Much more efficient than anaerobic respiration (only 2 ATP)
6H O2
6CO2
6O2
mitochondrion
matrix (area enclosedby inner membrane)
inner membrane
ATP
ATP
energy
energy from glycolysis
1
2
4
3
and
and
and
C6H12O6 + 6 O2 6 CO2 + 6 H2O + 36 ATP
4.5 Cellular Respiration in Details9.1 Chemical Pathways
4.4 Overview of Cellular Respiration
Aerobic respiration occurs in three steps:
• Glycolysis (in the cytoplasm)• Krebs cycle (in the matrix of the mitochondria)• Electron Transport system (in the inner membrane of the
mitochondria)
Cytoplasm
Pyruvicacid
Mitochondrion
Electrons carried in NADH
GlycolysisGlucose
4.5 Cellular Respiration in Details9.1 Chemical Pathways
4.4 Overview of Cellular Respiration
Krebs Cycle• takes place in mitochondrial matrix• 2 pyruvates enter the cycle• 2 ATP, 8 NADH, 2 FADH2 and 1 CO2 (waste product)
are produced• NADH and FADH2 are temporary energy-carrying
molecules which will enter ETC to make ATP
4.5 Cellular Respiration in Details9.2 The Krebs Cycle and Electron Transport Chain
4.4 Overview of Cellular Respiration
Electron Transport Chain (ETC)• takes place in mitochondrial inner membrane• All NADH and FADH2 from glycolysis and Krebs Cycle
are converted to ATP• 32 ATPs are produced• O2 is necessary for aerobic respiration to act as the
final acceptor of the electrons to form H2O
4.5 Cellular Respiration in Details9.2 The Krebs Cycle and Electron Transport Chain
4.4 Overview of Cellular Respiration
Summary of ATP Production per Glucose Molecule
• Glycolysis 2 ATP• Krebs Cycle 2 ATP• ETC 32 ATP
TOTAL: 36 ATP
4.5 Cellular Respiration in Details9.2 The Krebs Cycle and Electron Transport Chain
4.4 Overview of Cellular Respiration
• The reactants in photosynthesis are the same as the products of cellular respiration.
Comparing Photosynthesis and Cellular Respiration
4.4 Overview of Cellular Respiration
Comparing Photosynthesis and Cellular RespirationPhotosynthesis Cellular Respiration
Occurs only in presence of light in plant cells
Occurs in all cells with or without light
Stores energy in glucose Releases energy from glucose to form ATP
CO2 and H2O are raw materials CO2 and H2O are productsGlucose and O2 are products Glucose and O2 are raw materialsChloroplast is double membrane organelle
Mitochondrion is double membrane organelle
Has an electron transport system Has an electron transport system