8.2 photosynthesis: an overview 4.2 overview of photosynthesis · 2015-06-23 · 4.2 overview of...

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


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)



Plant pigments in chloroplasts absorb sunlight.

• Absorb light at different wavelengths (what you don’t see)• Reflect what is not absorbed (what you see).



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



Photosynthesis occurs in two stages.

ENERGYbuilding reactions(Light Rxn)

SUGARbuilding reactions

(Dark Rxn)

ATPNADPH

ADPNADP

sugar

sun

used immediatelyto synthesize sugars

H2O CO2



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


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


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).



• 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


PS II


• 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


PS I


Summary of Light-Dependent Reaction



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



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!!


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


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


• 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


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



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



• 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


• 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



Anaerobic Respiration (Fermentation)

alcohol

lactic acid

4.6 Fermentation9.1 Chemical Pathways


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



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)



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



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



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


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



Summary of ATP Production per Glucose Molecule

• Glycolysis 2 ATP• Krebs Cycle 2 ATP• ETC 32 ATP

TOTAL: 36 ATP



• The reactants in photosynthesis are the same as the products of cellular respiration.

Comparing Photosynthesis and 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

8.2 photosynthesis: an overview 4.2 overview of photosynthesis · 2015-06-23 · 4.2 overview of...

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