Photosynthesis and Cellular Respiration

Trapping the Sun’s Energy

• The process by which plants capture energy from the sun to build carbohydrates through chemical pathways is called photosynthesis – Solar energy converts water and

carbon dioxide into chemical energy stored in simple sugars

• The simple sugar that photosynthesis produces is glucose which the plant uses to store energy.

• The equation that represents photosynthesis is:

6CO2 + 6H2O C6H12O6 + 6O2

Solar energy

Chapter 6

Comparing Autotrophs and Heterotrophs

Section 1 The Light Reactions

Visual Concept

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Phases of Photosynthesis

• Photosynthesis requires energy from the sun, but the sun is not available 24 hours a day.

• Photosynthesis must occur in two phases– Light-dependent Reactions (light

reactions)• Convert light energy into chemical energy

(ATP and NADPH)– Light-independent Reactions (dark

reactions)• Uses the ATP and NADPH from the light-

dependent reactions to build glucose

6CO2 + 6H2O C6H12O6 + 6O2

Solar energy

The Role of Chloroplasts and Pigments

• Photosynthesis takes place in the chloroplasts

• Light-dependent reactions take place in the membranes of the thylakoid disks (contain chlorophyll)

• Light-independent reactions take place in the stroma (thick fluid that forms the framework of a chloroplast)

The Role of Chloroplasts and Pigments

• The thylakoid membranes contain the pigments that can absorb certain wavelengths of sunlight.

• The most common pigment in the chloroplasts is chlorophyll.

• Chlorophyll a and b absorb most wavelengths of light except for green. Green is reflected making the plants appear green.

• In the fall, plants reabsorb chlorophyll leaving other pigments that reflect other wavelengths of light – making the leaves appear red, yellow, or orange.

Chapter 6

Spectrum of Light and Plant Pigments

Section 1 The Light Reactions

Visual Concept

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Light-dependent Reactions

• Sunlight strikes the chlorophyll molecules in the thylakoid membrane.

• Light energy is transferred to electrons• The electrons become highly energized

and are passed down an Electron Transport Chain

Light-dependent Reactions

• The Electron Transport Chain is a series of proteins in the thylakoid membrane

• As the electrons are transferred from one protein to another, some energy is released which – helps join ADP and Phosphate to form ATP – Pump hydrogen ions into the center of the

thylakoid disk to join H+ and NADP+ forming NADPH (electron carrier)

– ATP and NADPH will be used during the light-independent reactions

Light-dependent Reactions

• The electrons excited by the light energy that passed down the electron transport chain and left with NADPH need to be replaced so the reaction can happen again.

• To replace those electrons, a water molecule is split (photolysis), sending electrons back to the chlorophyll and releasing Oxygen and Hydrogen ions into the atmosphere – this supplies the oxygen that we breathePhotolysis

Light-dependent ReactionsSolar Energy absorbed by chloroplasts

NADPH released

Oxygen released

ATP Released

Products of Light Reactions (ATP and NADPH) fuel the dark reactions

Light-independent Reactions

• The second phase of photosynthesis does not require light and is called the Calvin Cycle.

• The Calvin Cycle occurs in the stroma of the chloroplast.

• The Calvin Cycle uses the ATP and NADPH that was built during the light-dependent reactions

The Calvin Cycle

Uses Carbon Dioxide from the air

Uses ATP and NADPH from light reactions

Builds a glucose molecule

Uses another ATP to replenish RuBP

Photosynthesis Equation

6CO2 + 6H2O C6H12O6 + 6O2

Carbon Dioxide

from the air – Used in

the Calvin Cycle

during the Dark

Reactions

Water Split during

Photolysis in the Light Reactions

Glucose Made in the

Calvin Cycle during the

Dark Reactions

Oxygen Released during

Photolysis in the Light Reactions

Light Energy

chlorophyll

Plants can use this glucose molecule for energy during Cellular Respiration. Plants can also convert this glucose molecule into other

organic compounds such as proteins and fats/lipids or other carbohydrates like starch and cellulose

3 Factors that Affect Photosynthesis

• Carbon Dioxide (CO2)– Without CO2, the plant would not have

one of the raw materials needed in the photosynthesis equation

– CO2 is used in the first step of the Calvin Cycle

• Temperature– The temperature must be in the

appropriate range for the plant in order for photosynthesis to properly occur

3 Factors that Affect Photosynthesis

• Intensity of Light– If the intensity of light is lower, the

available energy for photosynthesis is lower. • In a greenhouse, if the light source is

further away, intensity is lower and less photosynthesis can occur

• If light is not available at all, the light-dependent reactions cannot occur (nor can they provide the materials used in the light-independent reactions)

Chapter 6

Environmental Influences on Photosynthesis

Section 2 The Calvin Cycle

Visual Concept

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Cellular Respiration• Cellular Respiration: Process by which

mitochondria break down food molecules to produce ATP in plants and animals Nutrients + oxygen water + ATP + CO2

• Changes organic chemical energy (glucose) into inorganic chemical energy (ATP)

• There are three stages of Cellular Respiration– Glycolysis

• Anaerobic – does not require oxygen– Citric Acid (Krebs) Cycle

• Aerobic – does require oxygen– Electron Transport Chain

• Aerobic – does require oxygen

Glycolysis• Glycolysis: Breaks down glucose into two

molecules of pyruvic acid (a colorless acid formed as an important intermediate in metabolism or fermentation)

• This reaction uses enzymes and takes place in the cytoplasm of the cell (anaerobic reaction)

• Produces – 2 pyruvic acid molecules (used in the next step

of Cellular Respiration)– 2 ATP molecules (energy the cell can use)– 2 NADH (electron carrier)

Chapter 7

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Visual Concept

Glycolysis

Section 1 Glycolysis and Fermentation

Into the Mitochondria…

• Before the next step of Cellular Respiration can occur, the pyruvic acid molecules must go into the mitochondria

• The two oxygen-dependent (aerobic) reactions are the Citric Acid Cycle (or Krebs Cycle) and the electron transport chainPyruvic acid CO2 + water + ATP

Citric Acid/Krebs Cycle (see page

138 in your book) CO2 is released

Pyruvate from Glycolysis fuels the cycle

CO2 is released

ATP is released

NADH and FADH2 is released

Electron Transport Chain• Electron Transport Chain uses the

electron carriers (NADH and FADH2) to pass electrons down the protein chain and slowly release energy that is used to form ATP and water molecules

• Electron Transport Chain transfers the most energy

Cellular Respiration

Glycolysis

Citric Acid Cycle

Electron Transport Chain

Glucose

Pyruvic Acid

ATP

Pyruvic Acid

CO2

ATP

ATP

NADH and FADH

NADH and FADH

Oxygen

Water

Cellular Respiration Equation

C6H12O6 + 6O2 6CO2 + 6H2O + energy

Water – released

from Electro

n Transpo

rt Chain

Oxygen from the

atmosphereUsed in

Electron Transport

Chain

Carbon Dioxide –

waste product of the Citric Acid Cycle

ATP released from

Glycolysis, Citric Acid Cycle, and Electron

Transport Chain

Between 34-36 ATP can be made with this process. This ATP can be used by the cells for cellular metabolism.

Glucose made in

photosynthesis by

plants or consumed by animals

Used in Glycolysis

Fermentation

• When oxygen is not available anaerobic respiration, fermentation, can follow glycolysis in order to continue to produce energy.

• This is not as efficient as aerobic respiration and produces far fewer ATP’s

• Two types of fermentation:– Lactic acid Fermentation– Alcoholic Fermentation

Lactic acid Fermentation

• Lactic acid fermentation occurs in muscle cells during strenuous exercise when a lot of energy is required and oxygen is scarce (oxygen debt).

Glucose pyruvic acid lactic acid + ATP

• The lactic acid is transferred from the muscle cells to the liver where it will be converted back into pyruvic acid

• The build up of lactic acid in the muscles is what causes them to be fatigued and sore.

Alcoholic Fermentation

• Yeast and some bacteria cells are capable of alcoholic fermentation during which glucose is broken down to release CO2 and ethyl alcoholGlucose pyruvic acid alcohol +

CO2 + ATP

• The bubbles formed by the CO2 make bread rise

• The alcohol released turns grape juice into wine

Chapter 7

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Visual Concept

Comparing Aerobic and Anaerobic Respiration

Section 1 Glycolysis and Fermentation

Photosynthesis vs. Cellular Respiration

Photosynthesis Cellular Respiration

Stores Energy as glucose

Releases Energy in glucose

Occurs in Living Cells

Uses an Electron Transport Chain

Occurs in Plant Cells

Occurs in Animal Cells

Releases Oxygen

Releases Carbon Dioxide

Creates Energy Neither!