Cell Energy Adapted from A. Anguiano & J. Zhen

All organisms need energy to live.

Autotrophs Organisms that make their own food.  They use sunlight to produce food.  Example: Plants Autotrophs

Heterotrophs Organisms that get energy from the food they eat. Examples: animals Heterotrophs

Photosynthesis …. Process by which plants convert water and carbon dioxide to high- energy carbohydrates (glucose). Plants = “autotrophs” (make their own food) Carbohydrates are: Glucose, starch and cellulose What are examples of carbohydrates?

Glucose is used to store energy (ATP) 1 Glucose gives 36 ATP 36 ATP

6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 PRODUCTS REACTANTS Reactants: are what goes into a chemical reaction Products: Are what is produced at the end of the chemical reaction. Photosynthesis Equation light

Photosynthesis Equation 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 Carbon Dioxide Water Glucose Oxygen light

Light 6 CO 2 6 H 2 O 6 O 2 C 6 H 12 O 6

Where Photosynthesis happens

Chloroplast Site of photosynthesis Contains chlorophyll, a pigment that absorbs energy from sunlight

Structure of a chloroplast: 1)Double membrane 2)Thylakoid: contain chlorophyll; where light rxn takes place 3)Granum: stacks of thylakoids 4)Photosystems: light-collecting units of the chloroplast (a cluster of chlorophyll in the thylakoid) 5)Stroma: space outside the thlakoid membrane

Plants  plant cells  Chloroplast  Chlorophyll a

Chlorophyll is a pigment* found in the Chloroplast. This is what gives it the green color.  *A pigment is a molecule that absorbs light.

The sun shines white light. White light is made up of a rainbow of colors. SUN

Each drop of water acts like a prism.

Why do plants look green? α Plants look green because they contain chlorophyll α which reflects green light. Photosynthesis

Plant Pigments Main pigment = chlorophyll a (absorbs blue/red light reflects green/yellow)

Photosynthesis

Plant Pigments Accessory pigments =  chlorophyll b (absorbs blue/red light reflects green/yellow  carotene(absorbs blue/green light reflects yellow/orange)

Photosynthesis is divided into 2 parts: 1. Light Dependent reactions 2. Dark reaction (Calvin Cycle) In (Light Independent ~ no Light is needed)

Light Dependent Reactions Light Independent Reactions

Two Reactions Occurs in 2 stages: 1) Light reaction (requires sunlight) 2) Dark reaction (does not require sunlight; also called the Calvin Cycle)

1. Light Dependent Reactions - Requires sunlight; occurs in thylakoids Sunlight Electron excited Chlorophyll ATP, NADPH

1)Chlorophyll in each thylakoid absorbs energy (in the form of photons) from sunlight 2)The energy is transferred to electrons and they leave the chlorophyll 3)Water (H 2 O) gets split. Electrons from water replace the electrons that chlorophyll lost and Oxygen (O 2 ) is released as a waste product 4)Thylakoid uses the energy to make two products to be used in Dark rxn later: - ATP (Adenosine Triphosphate) = energy-carrying molecule - NADPH = a temporary energy storage molecule Reactant Product Energy carrying molecules

NADPH: molecule that carries electrons NADPH holds 2 electrons NADP + is ready to accept 2 electrons & H+ Photosynthesis

Chemical Energy and ATP  Storing Energy ADP has two phosphate groups instead of three. A cell can store small amounts of energy by adding a phosphate group to ADP. ADP ATP Energy Partially charged battery Fully charged battery + Adenosine Diphosphate (ADP) + Phosphate Adenosine Triphosphate (ATP)

Chemical Energy and ATP  Releasing Energy Energy stored in ATP is released by breaking the chemical bond between the second and third phosphates. P ADP 2 Phosphate groups

Light-Dependent Reactions

Photosystem II Photosynthesis begins when pigments in photosystem II absorb light, increasing their energy level.

Photosystem II These high-energy electrons are passed on to the electron transport chain. Electron carriers High-energy electron

Photosystem II 2H 2 O Enzymes on the thylakoid membrane break water molecules into: Electron carriers High-energy electron

Photosystem II 2H 2 O  hydrogen ions  oxygen atoms  energized electrons + O 2 Electron carriers High-energy electron

Photosystem II 2H 2 O + O 2 The energized electrons from water replace the high-energy electrons that chlorophyll lost to the electron transport chain. High-energy electron

Photosystem II 2H 2 O As plants remove electrons from water, oxygen is left behind and is released into the air. + O 2 High-energy electron

Photosystem II 2H 2 O The hydrogen ions left behind when water is broken apart are released inside the thylakoid membrane. + O 2 High-energy electron

Photosystem II 2H 2 O Energy from the electrons is used to transport H + ions from the stroma into the inner thylakoid space. + O 2

Photosystem II 2H 2 O High-energy electrons move through the electron transport chain from photosystem II to photosystem I. + O 2 Photosystem I

2H 2 O Pigments in photosystem I use energy from light to re- energize the electrons. + O 2 Photosystem I

2H 2 O NADP + then picks up these high-energy electrons, along with H + ions, and becomes NADPH. + O 2 2 NADP + 2 NADPH 2

2H 2 O As electrons are passed from chlorophyll to NADP +, more H + ions are pumped across the membrane. + O 2 2 NADP + 2 NADPH 2

2H 2 O Soon, the inside of the membrane fills up with positively charged hydrogen ions, which makes the outside of the membrane negatively charged. + O 2 2 NADP + 2 NADPH 2

2H 2 O The difference in charges across the membrane provides the energy to make ATP + O 2 2 NADP + 2 NADPH 2

2H 2 O H + ions cannot cross the membrane directly. + O 2 ATP synthase 2 NADP + 2 NADPH 2

2H 2 O The cell membrane contains a protein called ATP synthase that allows H + ions to pass through it + O 2 ATP synthase 2 NADP + 2 NADPH 2

2H 2 O As H + ions pass through ATP synthase, the protein rotates. + O 2 ATP synthase 2 NADP + 2 NADPH 2

2H 2 O As it rotates, ATP synthase binds ADP and a phosphate group together to produce ATP. + O 2 2 NADP + 2 NADPH 2 ATP synthase ADP

2H 2 O Because of this system, light-dependent electron transport produces not only high-energy electrons but ATP as well. + O 2 ATP synthase ADP 2 NADP + 2 NADPH 2

2. Dark Reactions (Calvin Cycle) - Does not require sunlight; occurs in stroma (CO2 enters)

LightDark NADPHUsed to form glucose ATPstored or used elsewhere 1)ATP & NADPH from Light rxn are used to take carbon atoms from CO 2 to make glucose 2)It takes 6 turns of Calvin cycle to fix CO 2 (1 carbon) into C 6 H 12 O 6 (6 carbons) ReactantProduct

Six carbon dioxide molecules enter the cycle from the atmosphere and combine with six 5-carbon molecules. CO 2 Enters the Cycle

The result is twelve 3-carbon molecules, which are then converted into higher-energy forms.

The energy for this conversion comes from ATP and high- energy electrons from NADPH. 12 NADPH ADP 12 NADP + Energy Input

Two of twelve 3-carbon molecules are removed from the cycle. Energy Input 12 NADPH ADP 12 NADP +

The molecules are used to produce sugars, lipids, amino acids and other compounds. 12 NADPH ADP 12 NADP + 6-Carbon sugar produced Sugars and other compounds

The 10 remaining 3-carbon molecules are converted back into six 5-carbon molecules, which are used to begin the next cycle. 12 NADPH ADP 12 NADP + 5-Carbon Molecules Regenerated Sugars and other compounds 6 6 ADP