Focus Activity What does a chloroplast do?

Chapter 8 Photosynthesis

Ch. 8 Photosynthesis  Section 8.1: Energy and Life  Section 8.2: Photosynthesis: An Overview  Section 8.3: The Reactions of Photosynthesis

8-1 Energy and Life  Remember:  There are two major “substances” in nature  Matter  Energy  Matter is neither created nor destroyed, just rearranged and changed  Energy is neither created nor destroyed, just rearranged and changed

Autotrophs and Heterotrophs  All living things require energy. The source of that energy is food.  Autotrophs  Heterotrophs  All plants are photoautotrophs (and some bacteria)  All other organisms must eat autotrophs or eat other organisms that eat autotrophs

Chemical Energy and ATP  Forms of energy  Light  Heat  Electricity  Chemical Compounds  ATP (adenosine triphosphate): The main chemical compound that cells use  Structure:  Adenine + Ribose + 3 phosphate groups

ATP structure AdenineRibose3 Phosphate groups

Chemical Energy and ATP  How ATP stores energy:  ADP (adenosine Diphosphate)  2 phosphates  Adding a third phosphate stores energy and produces ATP  Releasing Energy:  Breaking the third bond on an ATP, frees the third phosphate, making it available to go and energize other interactions in the cell  ATP is the energy currency for the cell

ADP vs ATP ADPATP Energy Adenosine triphosphate (ATP) Partially charged battery Fully charged battery

Using Biochemical Energy  What ATP provides energy for:  Active Transport  Synthesis of proteins and nucleic acids  Responses to chemical signals  ATP is a super energy source but it’s short term. Long term energy supplies are in the form of glucose and what other organic compound?  Cells continually regenerate ATP from ADP by using energy in glucose

8-2: Photosynthesis: An Overview  Photosynthesis  The Process plants go through to convert water and CO 2 into high energy carbohydrates using sunlight  Beginning Question:  Where does a tree’s increase in Mass come from?  The Water?  The Soil?

Investigating Photosynthesis  Van Helmont’s Experiment  In the 1600’s, Van Helmont tested this question.  He planted a seedling in a pot of soil that he massed and grew it for 5 years. The seedling grew to be 75 kg, but the mass of the soil was mostly unchanged.  Conclusion:  Gain in Mass came from Water

Investigating Photosynthesis  Where did the Carbon come from?  Priestly’s Experiment  Over 100 years later, Joseph Priestly put a candle in a jar, and it went out because some substance must be used up (oxygen). Then he put a plant under the jar for a few days, relit the candle and it stayed lit for a while.  The plant was recycling the CO 2 that the candle was emitting and releasing oxygen that the candle burned.

Priestly’s Exp. (con’t)  With the continued work of scientists, it was discovered that in the presence of light, plants transform CO 2 and H 2 O into carbohydrates and free oxygen.

The Photosynthesis Eq. 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2  Plants then use the sugars to produce more complex carbohydrates (like starches).  CO 2 comes from the air light

Lights and Pigments  Photosynthesis also requires Light and chlorophyll  Chlorophyll – a pigment found in plants that absorbs blue-violet light and red wavelengths of light, and reflects green and yellow wavelengths of light  Pigment – light-absorbing molecule  Two types of chlorophyll  Chlorophyll A  Chlorophyll B

Wavelength vs. Absorption Absorption of Light by Chlorophyll a and Chlorophyll b VBGYOR Chlorophyll b Chlorophyll a

Lights and Pigments (con’t)  Chlorophyll does not absorb green light well  it is reflected  Plants also contain red, orange, and yellow pigments  Where is chlorophyll located?  Chloroplasts

8-3 The Reactions of Photosynthesis  Inside the chloroplasts  Chloroplasts contain pancake-like structures called Thylakoids  Thylakoids are arranged in stacks called grana  The stroma is the space around the outside of the thylakoids (Syrup)

Chloroplast

Inside a chloroplast (con’t)  Proteins in the thylakoid membrane arrange chlorophyll & other pigments into photosystems:  Two Photosystems: I and II  Light collecting units of chloroplasts  Two Reactions of Photosynthesis  Light dependent reactions  Thylakoid membranes  Light Independent Reactions (Calvin Cycle)  Stroma

Electron Carriers  When Sunlight strikes the chlorophyll, the electrons (e-) get “excited”  When (e-) are excited, they “jump up” energy levels.  High Energy Electrons require a special carrier  A carrier molecule is a compound that can accept a pair of high energy (e-) & transfer them, along with their energy, to another molecule.  Electron Transport

Electron Carriers  Common Carrier Molecules  NADP +  NAD +  FAD +  NADP +  accepts 2(e-) and 1H +  NADPH  NADPH carries electrons which are an energy source used to help build carbohydrates like Glucose.

Light Dependent Reactions  Requires Light  Use energy from light to produce ATP & NADPH PRODUCT OF REACTION:  The light dependent reactions produce oxygen gas to convert ADP & NADP + into energy carriers ATP and NADPH

Steps of the Process 1.Pigments in photosystem II absorb light a.Electrons become excited b.The Electron passes into the Electron Transport Chain (ETC) c.The Electrons that were passed are replaced by the electrons lossed when Water is broken.  Enzymes on the inner surface of the thylakoid membrane break up a water molecule into 2 electrons.  What is left?

Steps of the RXN(con’t) 2. Electrons move through the ETC a.They “land” in photosystem I b.H + are pumped into thylakoids from the stroma 3.Electrons in Photosystem I are hit by light. a.The electrons get “excited” b.The electrons are picked up by NAD +  NADPH

Steps in the RXN (con’t) 4.Hydrogen Ions are pumped across the membrane a.As H + ions are pumped inside the thylakoid, it makes the inside more positive than the outside. b.The difference in charges across the membrane provides the energy to make ATP c.The H + ions can only exit the thylakoid membrane through one special protein channel, called ATP synthase  H + ions passing through ATP synthase powers the formation of ATP and ADP

Light dependent RXN Hydrogen Ion Movement Photosystem II Inner Thylakoid Space Thylakoid Membrane Stroma ATP synthase Electron Transport Chain Photosystem IATP Formation Chloroplast

The Calvin Cycle  Uses ATP and NADPH from light reactions to produce sugars  Doesn’t require light  Light INDEPENDENT reaction

Calvin Cycle ChloropIast CO 2 Enters the Cycle Energy Input 5-Carbon Molecules Regenerated Sugars and other compounds 6-Carbon Sugar Produced

Factors affecting Photosynthesis  Water  Temperature  Intensity of Light

Closure Concept Map Photosynthesis includes of take place in takes place in uses to produce use Light- dependent reactions Calvin cycle Thylakoid membranes StromaNADPH ATP Energy from sunlight ATPNADPHO2O2 Chloroplasts High-energy sugars