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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

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Photosynthesis and Cellular Respiration

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Photosynthesis and cellular respiration

Photosynthesis and Cellular Respiration

Trapping the sun s energy

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

Comparing autotrophs and heterotrophs

Section 1 The Light Reactions

Chapter 6

Comparing Autotrophs and Heterotrophs

Click below to watch the Visual Concept.

Visual Concept

Phases of photosynthesis

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

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 pigments1

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.

Spectrum of light and plant pigments

Section 1 The Light Reactions

Chapter 6

Spectrum of Light and Plant Pigments

Click below to watch the Visual Concept.

Visual Concept

Light dependent reactions

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 reactions1

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 reactions2

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 breathe

Photolysis 

Light dependent reactions3

Light-dependent Reactions

Solar Energy absorbed by chloroplasts

Oxygen released

ATP Released

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

NADPH released

Light independent 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

The Calvin Cycle

Uses Carbon Dioxide from the air

Uses ATP and NADPH from light reactions

Uses another ATP to replenish RuBP

Builds a glucose molecule

Photosynthesis equation


Photosynthesis Equation

Light Energy

6CO2 + 6H2O C6H12O6 + 6O2

Carbon Dioxide from the air – Used in the Calvin Cycle during the Dark Reactions

Glucose Made in the Calvin Cycle during the Dark Reactions

Oxygen Released during Photolysis in the Light Reactions

Water Split during Photolysis in the Light Reactions

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

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 photosynthesis1

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)

Environmental influences on photosynthesis

Section 2 The Calvin Cycle

Chapter 6

Environmental Influences on Photosynthesis

Click below to watch the Visual Concept.

Visual Concept

Cellular respiration

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: 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)

Photosynthesis and cellular respiration

Section 1 Glycolysis and Fermentation

Chapter 7


Click below to watch the Visual Concept.

Visual Concept

Into the mitochondria

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 chain

    Pyruvic acid  CO2 + water + ATP

Citric acid krebs cycle see page 138 in your book

Citric Acid/Krebs Cycle (see page 138 in your book)

CO2is released

Pyruvate from Glycolysis fuels the cycle

CO2is released

NADH and FADH2is released

ATP is released

Electron transport chain

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 respiration1

Cellular Respiration




Pyruvic Acid


Citric Acid Cycle

Pyruvic Acid





Electron Transport Chain



Cellular respiration equation

Cellular Respiration Equation

C6H12O6 + 6O2 6CO2 + 6H2O + energy

Carbon Dioxide – waste product of the Citric Acid Cycle

Water – released from Electron Transport Chain

Glucose made in photosynthesis by plantsor consumed by animals

Used in Glycolysis

ATP released from Glycolysis, Citric Acid Cycle, and Electron Transport Chain

Oxygen from the atmosphereUsed in Electron Transport Chain

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



  • 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

  • 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

Alcoholic Fermentation

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

    Glucose  pyruvic acid  alcohol + CO2 + ATP

  • The bubbles formed by the CO2 make bread rise

  • The alcohol released turns grape juice into wine

Photosynthesis and cellular respiration

Section 1 Glycolysis and Fermentation

Chapter 7

Comparing Aerobic and Anaerobic Respiration

Click below to watch the Visual Concept.

Visual Concept

Photosynthesis vs cellular respiration

Photosynthesis vs. Cellular Respiration


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