CHAPTER 8 PHOTOSYNTHESIS SECTION 8-1 ENERGY and LIFE

AUTOTROPHS AND HETEROTROPHS What is the key source of energy for most things? THE SUN Plants and other organisms such as blue-green algae use light energy from the sun to produce food. These organisms are called AUTOTROPHS. Use simple inorganic molecules to do this.

AUTOTROPHS and HETEROTROPHS Heterotrophs are organisms that obtain energy from the food they consume. Unable to use sunlight directly. ALL organisms must release energy in sugars and other compounds.

CHEMICAL ENERGY and ATP What are three forms of energy? Light, heat, and electricity Energy can be stored in compounds. Electrons release energy when a piece of wood is set on fire. When chemical bonds are broken and electrons shift from higher energy levels to lower energy levels, the extra energy is released as light and heat.

CHEMICAL ENERGY and ATP How do organisms such as humans store and release energy? Chemical compounds are used to do this. What is ATP? Adenosine Triphosphate (ENERGY storing molecule) ATP consists of ADENOSINE, a 5-CARBON SUGAR, and 3 PHOSPHATE GROUPS

What is ATP? https://www.youtube.com/watch?v=bbtqF9q_pFw

RELEASING ENERGY How is stored energy released from ATP to be used by the cell? Energy stored in chemical bond between the second and third phosphate groups. Breaking this bond releases the energy stored in it.

STORING ENERGY What is ADP? Key molecule used to store excess energy. ADENOSINE DIPHOSPHATE 2 PHOSPHATE GROUPS Partially charged battery Key molecule used to store excess energy. To store energy… P + ADP  ATP ATP is like a fully charged battery. WHY?

RELEASING ENERGY ATP is the basic energy source for all cells. What are different cellular functions that ATP can power within the cell? ACTIVE TRANSPORT PROTEIN SYNTHESIS MUSCLE CONTRACTION

USING BIOCHEMICAL ENERGY What is a SODIUM – POTASSIUM Pump? Used during Active Transport Pumps Na- ions out of the cell and K+ ions in Assists in transport of glucose into cell Maintains muscle movement and control Controls cell volume Why do most cells only have a small amount of ATP? Not a good molecule for storing large amounts of energy over a long period of time. Cells regenerate ATP How do cells store energy for long periods of time? Glucose stores 90 times more energy than ATP

8-2 Photosynthesis: An Overview What is PHOTOSYNTHESIS? Plants use the energy of sunlight to convert water and carbon dioxide into high energy carbohydrates Sugars and starches And Oxygen, a waste product.

Investigating Photosynthesis As a tree grows bigger and bigger in size, where does the tree’s increase in mass come from? SOIL, WATER, AIR? This simple question asked hundreds of years ago began the research into photosynthesis. Let’s take a closer look at some of the experiments that led to the discovery of photosynthesis…

Van HELMONT’S Experiment 1643, Belgian physician Jan van Helmont. What did he do? Experiment to investigate if plants grew by taking materials out of the soil. His experiment? 1. Determined mass of a pot of dry soil and a seedling.

Van HELMONT Experiment 2. Planted the seedling in the pot of soil. Watered regularly. 3. At the end of 5 years, the seedling had grown into a small tree. Mass gain of 75 grams. 4. Mass of soil remained almost unchanged. His Conclusion Mass of the tree came from the water – only thing he added. Accounted for the “HYDRATE” portion of a CARBOHYDRATE Where does the “CARBO” portion come from? Carbon Dioxide

Priestley’s Experiment 1771, English minister Joseph Priestley What did he do? Lit a candle, placed a jar over it, and watched the flame gradually die out. What did he reason about the candle flame? Something in the air was necessary to keep the candle burning.

Priestley’s Experiment What was his next step? He placed a spring of mint underneath the jar with the candle. After a few days, candle could be relit. Burned for a longer period of time. His conclusion? The mint sprig released something needed to keep the candle flame burning. What was this mystery substance? OXYGEN

The Ingenhousz Experiment 1779, Dutch scientist Jan Ingenhousz What did he do? Showed the effect observed by Priestley only occurred when plant exposed to light. What did these experiments show? When a plant is exposed to light, it transforms carbon dioxide and water into carbohydrates and releases oxygen.

PHOTOSYNTHESIS EQUATION What is the balanced equation of photosynthesis? Compare the equation of photosynthesis with another cellular process.

Light and Pigments White light - mixture of different wavelengths of light visible spectrum Different wavelengths = different colors.

Light and Pigments What are colored substances that absorb or reflect light? PIGMENTS Why are plants green? chlorophyll: principle pigment in green plants Absorbs red and blue-violet light Chlorophyll a and Chlorophyll b Reflect green light which is why plants look green.

Absorption of Light B – carotene Red and orange pigments that absorb light in other regions of the spectrum.

SECTION 8-3: The Reactions Where do they occur? The Chloroplast Contains Thylakoids Photosynthetic membranes. Arranged in stacks called GRANA (GRANUM) Photosystems: chlorophyll and pigments in the thylakoid LIGHT-Collecting Units of the Chloroplast

8-3: Reactions of Photosynthesis 1. Light-Dependent Reactions In the thylakoid membranes 2. Light-Independent Reactions or The Calvin Cycle Take place in the stroma

NADP+ AN ELECTRON CARRIER Carries 2 High-energy electrons (e-) and a hydrogen ion (H+). Converts NADP+ into NADPH Sunlight energy is trapped in chemical form. NADPH carries HE e- produced in chlorophyll to chemical reactions in the cell.

LIGHT DEPENDENT REACTIONS PRODUCE Oxygen gas CONVERT ADP and NADP+ into energy carriers ATP and NADPH STEP A: Pigments in Photosystem II absorb light. Electrons absorb light energy making them HIGH-Energy electrons HIGH-Energy electrons passed to Electron Transport Chain (ETC)

LIGHT DEPENDENT REACTIONS STEP A CONTINUED: Does chlorophyll run out of electrons? No Where do the new electrons come from? WATER is broken down by enzymes. 1 WATER molecule  2 H+ ions and 1 O atom 2 H+ ions replace the HE electrons passed to the ETC Oxygen is released into the atmosphere

LIGHT DEPENDENT REACTIONS STEP B: HE e- move through ETC from Photosystem II to Photosystem I Energy used in ETC to transport H+ ions from Stroma to Thylakoid. STEP C: Pigments in Photosystem I use light energy to recharge electrons. NADP+ picks up HE e- and H+ ions NADP+ becomes NADPH

LIGHT DEPENDENT REACTIONS STEP D: H+ ions are pumped across the thylakoid membrane. Inside of membrane fills up with H+ ions Outside of membrane becomes negatively charged. This difference in charges provides the energy to make ATP. What is the importance of H+ ions?

LIGHT DEPENDENT REACTIONS STEP E: ENERGY MAKING STEP ATP SYNTHASE found in cell membrane. Allows H+ ions to pass through. ATP Synthase rotates and binds ADP with a Phosphate making ATP. LDR ETC produces HIGH-Energy electrons and ATP

ATP SYNTHASE

Photosynthesis Reactions

REVIEW of LDR What happens in LDR? LDR traps sunlight energy in a chemical form (A). HE e- give energy to ETC to move H+ ions into the thylakoid (B). PHOTOSYSTEM I recharges e- and are picked up by NADP+ with H+ ions making NADPH (C). H+ ions are pumped across the thylakoid membrane into the cell (D). H+ ions diffuse back through the membrane using ATP Synthase (E). Provides energy for ADP + P  ATP (FREE ENERGY)

The Calvin Cycle (Light-Independent Reactions) Discovered by Melvin Calvin in 1948. Involves an enzyme called RUBISCO The Calvin Cycle uses ATP and NADPH from LDR to produce high energy sugars.

The Calvin Cycle STEP A: CO2 Enters the Cycle 12 (3-C molecules) made STEP B: Energy Input 3-C molecules are converted into higher-energy forms. Uses ATP and HE electrons 12 ATP and 12 NADPH are used Returns 12 ADP and 12 NADP+

The Calvin Cycle STEP C: 6-Carbon Sugar Produced 3-C molecules produce SUGARS, lipids, amino acids, and other compounds. STEP D: 5-Carbon Molecules Regenerated 5-C molecules are returned to beginning of cycle 6 ATP are used here.

The Calvin Cycle LDR traps sunlight energy in a chemical form 6 CO2 are used to create a single 6-C SUGAR molecule Plants use the SUGARS to meet energy needs and build more macromolecules such as Cellulose. LDR traps sunlight energy in a chemical form ATP and NADHP CC uses this chemical energy to produce stable, high energy SUGARS from CO2 and H2O.

REVIEW of CALVIN CYCLE CO2 combines with 5-C molecules to make 3-C molecules (A) 3-C molecules converted into higher energy forms using ATP and NADPH (B) Two 3-C molecules removed from CC to make Glucose and other molecules (C) Ten 3-C molecules are converted back to Six 5-C molecules (D). Cycle repeats itself.

Bozeman Science Video http://www.youtube.com/watch?v=g78utcLQrJ4 Start 2:13 Stop 8:35

LDR and CC Why are they called LIGHT DEPENDENT REACTIONS? They require light energy to take place. Let’s look at the bigger picture. What would happen if plants do not get sunlight? Plants could not perform photosynthesis. They would not produce sugars or release Oxygen Gas Organisms like you and me(heterotrophs) would not be able to survive. Why is the Calvin Cycle called Light Independent Reactions? When does the CC take place?

The CALVIN CYCLE

THE CALVIN CYCLE 1. Where does the Calvin Cycle take place? 2. What enters the CC from the atmosphere? 3. Where do ATP and NADPH come from? 4. What is the product of the CC? 5. How is the cycle completed? (Why is the CC called a cycle?)

Factors that Affect Photosynthesis Water Provides electrons to the LDR How do plants in dry areas protect themselves from water loss? Temperature ENZYMES function best between 0 and 35 degrees C What effect will extreme temperatures have on enzymes? Intensity of Light More Light = More Photosynthesis

Why do leaves change color in the fall? Pigments carotene (red/orange) and xanthophyll (yellow) Help absorb sunlight with chlorophyll for photosynthesis. What major change occurs during winter? Carotene and xanthophyll are responsible for supplying light energy to the plant.

Name: EXIT PASS Nov 4 1. What materials enter the chloroplast that are used in the light-dependent reactions? 2. What material comes into the chloroplast that is used in the Calvin Cycle? 3. What material exits the chloroplast from the light-dependent reactions? 4. How do plants receive electrons for use in Photosystem II? 5. What materials move from the L-D reactions to the Calvin Cycle? Which steps produce these materials? 6. What materials move from the Calvin Cycle back to the LDR?