Respiration, Fermentation, and

Photosynthesis

Free Energy

• Free energy is the energy needed to do work.• It takes work to keep the cell organized and

functioning properly! • Ex: Active transport, muscle contractions, nerve

impulses…

Endergonic & Exergonic Reactions

• In a chemical reaction, the amount of energy in the reactants is usually different from the amount of energy in the products. • Energy is stored in the bonds between atoms

within a molecule.

• There are 2 type of reactions:• Endergonic – energy must be supplied

• The products have more energy than the reactants

• Exergonic – energy is released• The products have less energy than the reactants• Activation energy is still required!

Endergonic & Exergonic Reactions

Coupling Reactions• Endergonic and exergonic reactions are often coupled, or

linked, to each other.

• The energy released from the exergonic reaction is the same energy that is supplied for the endergonic reaction.

ATP

• ATP has 3 parts:• Adenine (a nitrogenous

base)• Ribose (the same sugar that

is found in RNA)• 3 phosphate groups

Adenine

*** Energy is stored in the bonds between the phosphate groups. The last bond (between the second and third phosphates) stores tons of energy!! The energy from food is not useful for the cell until it has been converted and stored in one of these high-energy bonds.

• ATP (adenosine triphosphate) is the energy “currency” for living things

ATP & ADP

• Energy is released when the bond between the second & third phosphate groups is broken.

• This also produces ADP (adenosine diphosphate) • We need to turn ADP back into ATP to do more work!

• Energy is required to reattach the 3rd phosphate group.

• ATP ADP + Pi Exergonic• ADP + Pi ATP Endergonic

(Pi = inorganic phosphate)

ATP & ADP

ATP & ADP

Figure 7.1

Energy from food isrequired to push a thirdphosphate group onto ADP.

1.

2.

3.

Energy from food is thenstored as a phosphate bondin ATP.

Energy is then released whenthe phosphate bond isbroken, and can be used tofuel our everyday activities.

ADPP

+ ADP

energy hill

P

+

energyout

energyin

ATP

• ATP ADP + Pi Exergonic• ADP + Pi ATP Endergonic

Aerobic Respiration

• (Aerobic = oxygen is required)

• In aerobic respiration, glucose provides the energy to make ATP from ADP and inorganic phosphate.

• The formula for cellular respiration is:

C6H12O6 + 6O2 + 38 ADP + 38 Pi 6CO2 + 6H2O + 38 ATP

3 Stages of Aerobic Respiration:

• Glycolysis• An anaerobic process that occurs in the cytosol• Uses 2 ATP but creates 4, for a net total of 2 ATP

• Krebs cycle (citric acid cycle, TCA cycle) • Takes place in the mitochondria• Produces 2 ATP

• Electron transport chain (ETC) • Takes place across the inner mitochondrial membrane• Produces up to 34 ATP• Oxygen is the terminal electron acceptor in the ETC.• Without oxygen, BOTH the ETC AND the Krebs cycle

shut down!

Cellular Respiration

Figure 7.4

2 ATP

2 ATP

34 ATP

glycolysis

38 ATP maximum per glucose molecule

Krebscycle

electrontransport

chain

glucose

(b) In schematic terms

(a) In metaphorical terms

mitochondrion H2O

O2

2 FADH2

2 NADH

2 NADH

6 NADH

CO2

CO2

glucose derivatives

cytosol

glycolysis

Krebscycle

electrontransport

chain

insert 1 glucose

2 energytokens

2 energytokens

34 energytokens

reactants products

Aerobic Respiration

Anaerobic Respiration

• Anaerobic = Oxygen is NOT required.

• Anaerobic respiration is also called fermentation.

• There are 2 types of fermentation:• A) Lactic acid fermentation

• C6H12O6 + 4 ADP + 4 Pi 2 lactic acid + 4 ATP

• This happens inside our muscles when we cannot get oxygen to them quickly enough (during strenuous exercise)

• Also used by many bacteria

• This is how yogurt, buttermilk, and sauerkraut are made!

Anaerobic Respiration

• B) Alcoholic fermentation• C6H12O6 + 4 ADP + 4 Pi 2 ethanol + 2 CO2 + 4

ATP• Used by yeast and some other microorganisms• Used to produce beer, wine, and bread

Autotrophs vs. Heterotrophs

• Autotrophs are organisms that can produce their own food (sugars) from CO2.

• Turning CO2 to sugar is an endergonic process.

• Photoautotrophs use energy from sunlight• Chemoautotrophs use energy from inorganic chemicals

• Heterotrophs are organisms that must consume food.

Photosynthesis

• During photosynthesis, photoautotrophic organisms like plants and cyanobacteria use energy from sunlight to convert carbon dioxide and water to glucose.

• Light is a form of electromagnetic radiation.

• Sunlight contains all wavelengths of the visible spectrum.

Electromagnetic Spectrum

Chloroplasts

• In plants, photosynthesis takes place in the chloroplasts.

• Chloroplasts contain the pigment chlorophyll, which makes them appear green.• There are 2 types of chlorophyll that absorb light in the red

and blue wavelengths.• Green and yellow wavelengths are reflected, so this is

what we see!

• Chloroplasts also contain pigments called carotenoids that reflect orange and yellow wavelengths of light. • These become visible when chlorophyll degrades in the

fall.

2 Stages of Photosynthesis

• The Light Reactions (Light-Dependent Reactions):• Sunlight absorbed by chlorophyll is used to activate

electrons, which enter an electron transport chain, producing ATP.

• The electrons come from water, forming oxygen as a by-product

• Takes place across the membranes of coin-shaped thylakoids that are stacked inside the chloroplasts - a stack of thylakoids is called a granum (plural = grana)

• The Calvin Cycle (Light-Independent Reactions):• Uses the ATP generated during the light reactions to

produce glucose from carbon dioxide (an endergonic reaction!)

• Takes place in the stroma, the liquid that fills chloroplasts.