Do NowWhat does a chloroplast look like?How do plants obtain energy?What is the formula for glucose?How do autotrophs obtain energy?How do heterotrophs obtain energy?

Chapter 6Photosynthesis: Capturing and

Converting Energy

Energy – the ability to do work

Photosynthesis

•Plants use the energy of sunlight to produce carbohydrates

•Energy is now in the chemical bonds

Jan Van Helmont•Where does a tree’s increased mass come

from?

•Seedling – 5 years – soil same mass – tree gained 75 kg

•Conclusion water “hydrate”

Priestly•Candle and a jar candle goes out – no

oxygen

•Candle + jar + plant candle does not go out

IngenhouszOxygen produced in light

Equation for Photosynthesis

Requirements for

Photosynthesis

1. Sunlight•Autotrophs – can use sunlight to make food

– Ex. Plants obtain energy

•Heterotrophs – obtain energy by eating other organisms

– Ex. Animals

•All organisms on earth depend on the sun for energy

•Sunlight is “white” light

•Many wavelengths of light

•ROYGBIV – visible spectrum

2. Pigments•Colored substances that absorb or reflect

light

•Photosynthesis begins when light is absorbed by pigments

•Chlorophyll – principle pigment of green plants

•Absorbs red and blue and reflects green light

ChromatographyPaper chromatography is a way to separate

chemical components of a solution.

How it Works

1.A drop of solution is placed at the bottom of a paper.

2.The paper is put in a solvent (tip only).3.The solvent rises through the paper.4.As it rises it carries the solution with it.5.The parts of the solution move at different

speeds depending on their mass. Lighter molecules move faster.

3. Energy Storing Compounds• Like solar cells• Electrons are raised to higher energy levels

– then trapped in bonds• Two ways that energy from the sun is

trapped in chemical bonds

1. High energy e- are passed to an electron carrier

(NADP +) NADPH– Electron carrier – a molecule that can

accept a pair of high energy electrons and later transfer them with most of their energy to another compound

– Conversion of NADP+ to NADPH – one way that energy from the sun can be trapped in a chemical form

2.Second way light energy is trapped ATP (Adenosine Triphosphate) – 3 phosphates

Fig 6-6Green plants produce ATP in photosynthesisATP energy storage compound used by every

cell

Producing ATP1.AMP (mono) – one phosphate2.AMP + P ADP (two – di)3.ADP + P ATP

• Energy is stored in the P bonds

• Energy is released when P bonds are broken

Adenosine

Adenosine

P P P

P

P

P P

Adenosine triphosphate (ATP)

Adenosine diphosphate (ADP)

Forming and Breaking Down ATPForming and Breaking Down ATP

6-2 Photosynthesis: The Light and Dark Reactions

•Light Reaction – energy of sunlight captured to make energy storing compounds

•ATP and NADPH

•Short term energy storage

Light-Dependent ReactionsLight-Dependent Reactions

Sun

Chlorophyll passes energy down through the electron transport chain.

for the use in light-independent reactions

bonds P to ADP

forming ATPoxygen

released

splitsH2O

H+

NADP+

NADPH

Light energy transfers to chlorophyll.

Energized electrons provide energy that

At each step along the transport chain, the electrons lose energy.

•Dark Reaction – energy from ATP and NADPH to make glucose (100 x the energy)

•Long term energy storage

The Light Reactions

ChloroplastParts of a chloroplastStroma – “cytoplasm”Grana – pancakeThylakoid – stacks of pancakes (grana)

Thylakoid = photosynthetic membrane

4 Parts of the Light Reaction1. Light absorption2. Electron transport3. Oxygen production4. ATP formation

Photosystems•Clusters of pigment molecules that capture

energy from the sun

•Two in plants – Photosystems I and II

Photosynthesis – plants - autotrophs•Occurs in the chloroplast

•Absorbs light

•Light reaction occurs in the thylakoid (photosynthetic environment) – needs sun to occur

Light Absorption•Photosystem I & II – absorb sunlight

•Pigment molecules pass the energy to other pigment molecules

•Reach a special pair of chlorophyll molecules in the reaction center

•High energy electrons released and passed to many electron carriers

Electron Transport•Electron transport – electron transport chain

•e- passed from one carrier to another (bucket brigade)

•Passed to electron carrier NADP+

•NADPH

Electron Transport Chain

NADPH – restoring electrons

•Water is split (photolysis)

•2 H2O 4 H+ + O2 + 4 e-

•Oxygen is released

•4 e- go to the chloroplast

•4 H+ are used to make ATP

ATP Formation•4 H+ released inside the membrane

•H+ build up

•Inside positive – outside is negative (charge difference is a source of energy)

•Enzymes use this energy to attach P to ADP ATP

9-2-GB4FASF.AVI

The Dark Reaction or Calvin Cycle

The Dark Reaction or Calvin Cycle•Does not need sunlight to happen

•Often happens with sunlight

•Uses products of the light reaction (ATP + NADPH)

•This series of reactions is particularly critical to living things

•Carbon dioxide is used to build complex organic molecules glucose

Dark Reaction or Calvin CycleOccurs in the stroma5 C sugar (RuBP) + CO2This reaction is slow and is catalyzed by

rubiscoNext two 3 C sugars are produced (PGA)ATP and NADPH from the light reaction are

used to convert PGA eventually into PGAL (3 C) – products P + ADP and NADP+

PGAL can use some ATP and become RuBP (5 C)

After several turns of the cycle 2 PGAL can leave and form glucose

6-3 Glycolysis and Respiration

•Enables organisms to release energy in glucose

•Breaks down food molecules

•C6H12O6 + 6O2 6CO2 + 6H2O + energy (ATP)

•1 g of glucose 3811 calories

•1 cal = amount of heat energy to raise

1 g of water 1 OC

Glycolysisoccurs in the cytoplasmChanges a molecule of glucose into many

different molecules step by step

•Glucose (6 C)

•2 ATP are used to make 2-3-C PGAL

•PGAL is converted into pyruvic acid and 4 ATP and 2 NADH are produced

•Pyruvic acid can enter aerobic or anaerobic respiration based on whether there is oxygen available or not

Presence of Oxygen – Cellular Respiration•Aerobic oxygen needed

•Takes place in the mitochondria

•Krebs cycle (Citric Acid Cycle)

•Starts with Pyruvic acid

•Carbon dioxide is removed

•Acetyl CoA is produced

•Citric acid is then produced

•9 reactions

•9 intermediate

•citric acid is produced and the cycle begins again

•Carbon dioxide is released

•Make FADH2 and NADH

•FADH2 and NADH go to the inner membrane of the mitochondria

•Electrons passed to enzymes

•Electron transport chain

•At the end – enzyme combines

• H+ + O2 H2O

•Therefore Oxygen is the final electron acceptor

•Mitochondrial membrane is charged (H+ ions pumped to one side)

•Provides energy to convert ADP ATP

•36 ATP are produced

6-4 Alcoholic Fermentation

•Glycolysis – net 2 ATP NAD+ NADH

•If you remove an electron from NADH glycolysis can continue

Fermentation – Anaerobic (no Oxygen)•NADH converted to NAD+ (acceptor molecule

take the H)

•Allows cells to carry out energy production in the absence of oxygen

•1 glucose 2 ATP

•Prokaryotes use many different acceptors

•Eukaryotes use two different acceptors1. Lactic acid fermentation2. Alcoholic fermentation

Alcoholic FermentationOccurs in yeast and a few other organismsPyruvic acid is broken down to produce 2-C

alcohol and carbon dioxidePyruvic acid + NADH alcohol + CO2 + NAD+Brewers and bakersCarbon dioxide produced causes bread to riseBubbles in beerYeast dies at 12% alcohol content

Lactic Acid FermentationPyruvic acid created in glycolysis can be

converted to lactic acidThe conversion regenerates NAD+Pyruvic acid + NADH lactic acid + NAD+Lactic acid produced in muscles during rapid

exercise when the body does not supply enough oxygen

Lactic acid – produced burning sensation in muscles

Comparing Photosynthesis and Cellular RespirationComparing Photosynthesis and Cellular Respiration

Photosynthesis Cellular RespirationFood synthesized Food broken down

Energy from sun stored in glucose Energy of glucose released

Carbon dioxide taken in Carbon dioxide given off

Oxygen given off Oxygen taken in

Produces sugars from PGAL Produces CO2 and H2O

Requires light Does not require light

Occurs only in presence of chlorophyll

Occurs in all living cells

Table 9.1 Comparison of Photosynthesis and Cellular Respiration

The End