photosynthesis vs. respiration

Photosynthesis vs. Respiration

Free Energy – Enthalpy (heat of reaction) is the amount of energy

released or absorbed during a chemical reaction Symbol is ΔH Think of it as energy needed

Entropy is a measure of randomness, tendency toward disorder Symbol is ΔS More disorder = more entropy If reaction leads to more disorder, the entropy change

(ΔS) is positive, if it becomes more ordered, ΔS is negative

Example: melting ice, condensing water, cleaning your room (+,-,-)

Temperature – T measured in K (273 + ºC) Free Energy – spontaneity of a reaction

Spontaneous - is negative Not spontaneous - is positive. Would be spontaneous

if reversed.

Things in Common Both photosynthesis and respiration

make ATP. Both involve, CO2, oxygen, sugar

(C6H12O6), and water (H2O) Almost all cells go through respiration

phosphate removed

ATP transfers energy from the breakdown of food molecules to cell functions.– Energy is released when a phosphate group is removed.

– ADP is changed into ATP when a phosphate group is added.

Organisms break down carbon-based molecules to produce ATP.

Carbohydrates are the molecules most commonly broken down to make ATP.

– not stored in large amounts– up to 36 ATP from one glucose

molecule

triphosphateadenosine

adenosine diphosphate

tri=3

di=2

Fats store the most energy.– 80 percent of the energy in your body– about 146 ATP from a triglyceride

• Proteins are least likely to be broken down to make ATP.

– amino acids not usually needed for energy– about the same amount of energy as a carbohydrate

The light-dependent reactions capture energy from sunlight.– take place in thylakoids– water and sunlight are needed– chlorophyll absorbs energy– energy is transferred along thylakoid membrane then to light-

independent reactions– oxygen is released

The light-independent reactions make sugars.– take place in stroma (fluid outside the thylakoids)– needs carbon dioxide from atmosphere– use energy to build a sugar in a cycle of chemical reactions

Photosystem II captures and transfers energy.– chlorophyll absorbs

energy from sunlight– energized electrons enter

electron transport chain– water molecules are split– oxygen is released as

waste– hydrogen ions are

transported across thylakoid membrane

Photosystem I captures energy and produces energy-carrying molecules.– chlorophyll absorbs energy

from sunlight– energized electrons are

used to make NADPH– NADPH is transferred to

light-independent reactions

Summary of Light Dependent Reactions Energy is captured from the sun. Energy goes into electrons into the

electron transport chain. Water is broken down H+ ions are transported and form

NADPH Flow of H+ ions through ATP synthase

makes ATP Electron Transport

Summary of Light Independent Reactions (Calvin Cycle) CO2 enters cycle ATP and NADPH from light-dependent

transfer energy 1 3-carbon molecule made for every 3 CO2 2 3-carbon molecules bonded to make

sugar Products – 6-carbon sugar, NADP+, and

ADP

A molecule of glucose is formed as it stores some of the energy captured from sunlight.– carbon dioxide molecules enter the Calvin cycle (this is what has

sugar as an end product– energy is added and carbon molecules are rearranged– a high-energy three-carbon molecule leaves the cycle

two three-carbon molecules bond to form a sugar– remaining molecules stay in the cycle

o A molecule of glucose is formed as it stores some of the energy captured from sunlight.

Cellular respiration makes ATP by breaking down sugars. Cellular respiration is aerobic, or requires oxygen. Aerobic stages take place in mitochondria.

mitochondrion

animal cell

Glycolysis must take place first.– anaerobic process (does not require oxygen)– takes place in cytoplasm– splits glucose into two three-carbon molecules– produces two ATP molecules

Cellular respiration is like a mirror image of photosynthesis.

The Krebs cycle transfers energy to an electron transport chain. takes place in

mitochondrial matrix breaks down three-carbon

molecules from glycolysis– makes a small

amount of ATP– releases carbon

dioxide– transfers energy-

carrying molecules

6H O2

6CO 2

6O 2

mitochondrionmatrix (area enclosedby inner membrane)

inner membrane

ATP

ATP

energy

energy from glycolysis

1

2

4

3

and

and

and

Krebs Cycle

6H O2

6CO 2

6O 2

mitochondrionmatrix (area enclosedby inner membrane)

inner membrane

ATP

ATP

energy

energy from glycolysis

1

2

4

3

and

and

and

• The electron transport chain produces a large amount of ATP.

– takes place in inner membrane

– energy transferred to electron transport chain

– oxygen enters process– ATP produced

– water released as awaste product

Electron Transport

The Krebs cycle is the first main part of cellular respiration.

Pyruvate is broken down before the Krebs cycle. carbon dioxide

released NADH produced coenzyme A (CoA)

bonds to two-carbon molecule

The Krebs cycle produces energy-carrying molecules.

The electron transport chain is the second main part of cellular respiration.

The electron transport chain uses NADH and FADH2 to make ATP. high-energy electrons enter electron transport chain energy is used to transport hydrogen ions across the

inner membrane hydrogen ions

flow through achannel in themembrane

The electron transport chain is the second main part of cellular respiration.

The breakdown of one glucose molecule produces up to36 molecules of ATP. (2 from glycolysis, 2 from Kreb, 32 from ETC)

– ATP synthase produces ATP

– oxygen picks up electrons and hydrogen ions

– water is released as a waste product

o The electron transport chain uses NADH and FADH2 to make ATP.

ATP Products of Cellular Respiration including glycolysis Glycolysis – uses 2 ATP and make 4 ATP.

Net gain of 2 ATP Kreb Cycle – 2 ATP, 8 NADH, 2 FADH2 Electron Transport Chain – 32ATP Net gain – 36 ATP for every glucose

molecule.

Comparison of Photosynthesis & Cellular Respiration

Photosynthesis Cellular Respiration

Organelle for process

Chloroplast Mitochondrion

Reactants CO2 and H2O Sugars (C6H12O6) and O2

Cycle of chemical reactions

Calvin cycle in stroma of chloroplasts builds sugar molecules

Krebs cycle in matrix of mitochondria breaks down carbon-based molecules

Electron Transport Chain

Proteins within thylakoid membrane

Proteins within inner mitochondrial membrane

Products Sugars (C6H12O6) and O2

CO2 and H2O

Fermentation allows glycolysis to continue when oxygen is unavailable. Fermentation is an anaerobic process.

occurs when oxygen is not available for cellular respiration

does not produce ATP

Fermentation allows glycolysis to continue making ATP when oxygen is unavailable.

• Lactic acid fermentation occurs in muscle cells.– glycolysis splits glucose into two pyruvate molecules– pyruvate and NADH enter fermentation– energy from NADH converts pyruvate into lactic acid– NADH is changed back into NAD+

• NAD+ is recycled to glycolysis

Fermentation is used in food production.– yogurt

– cheese

– bread

Project In teams of 2, students will create a

visual representation (e.g., poster or PowerPoint) to explain the interdependent relationships of cellular respiration and photosynthesis, and how the processes of cellular respiration and photosynthesis affect a runner in a marathon race.

Students should use few words and focus on using graphics to represent the cyclic processes. Visual representations will be peer and teacher reviewed.