CHAPTERS 6 & 7 Cellular Respiration & Photosynthesis

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


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


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


C6H12O6 + 6 O2

Glucose Oxygen

6 CO2

Carbondioxide

+ 6 H2O

Water

+ ATPs

Energy

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


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



• 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



• 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


ATPNAD+

NADH

H+

H+2e–

2e–

Electron transport

chain

Controlledrelease ofenergy forsynthesis

of ATP

+

O2

H2O

12

STAGES OF CELLULAR RESPIRATION AND FERMENTATION


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)



• 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



• 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


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???



• 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



• 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



• Some bacteria perform acetic acid fermentation – They convert pyruvate to acetic acid

(VINEGAR)


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


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


Food, such aspeanuts

ProteinsFatsCarbohydrates

Glucose

OXIDATIVEPHOSPHORYLATION(Electron Transportand Chemiosmosis)

CITRICACID

CYCLE

AcetylCoA

GLYCOLYSIS

Pyruvate

Amino acidsGlycerolSugars Fatty acids

Amino groups

G3P

ATP

CHAPTER 6 & 7 (continued)

PHOTOSYNTHESIS

Carbon dioxide

C6H12O6

Photosynthesis

H2OCO2 O2

Water

+ 66

Lightenergy

Oxygen gasGlucose

+ 6

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


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


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


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


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


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


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


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


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

Light

Chloroplast

Thylakoid

Absorbedlight

Transmittedlight

Reflectedlight

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


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++

THE CALVIN CYCLE: CONVERTING CO2 TO GLUCOSE


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


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, SOLAR RADIATION,

AND EARTH’S ATMOSPHERE


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



• 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


Atmosphere

Sunlight

Some heatenergy escapesinto space

Radiant heattrapped by CO2

and other gases


• Perhaps photosynthesis can mitigate the increase in atmospheric CO2 (Photosynthesis uses up Carbon Dioxide)– However, there is increasing widespread deforestation, which

aggravates the global warming problem


Documents

CHAPTERS 6 & 7 Cellular Respiration & Photosynthesis