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Energy is defined as the ability to do work It exists in two states: kinetic and potential
Fig. 5.1
Potential Energy = stored energy Kinetic Energy = energy of motion Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

Energy flows from the sun into the earth Photosynthetic organisms capture part of it They then use it to generate sugars These sugars have potential energy due to the arrangement of their atoms into bonds A chemical reaction is the making or breaking of chemical bonds
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Chemical reactions (substrates) begin with reactants which are converted to products reactants products
A + B C Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

Fig. 5.4
Energy of Activation Extra energy required to destabilize chemical bonds and so initiate a chemical reaction
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Fig. 5.4
Catalysts lower the activation energy of a reaction, and thus increase its rate However, they cannot make an endergonic reaction exergonic
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Enzymes are proteins that serve as catalysts They speed up chemical reactions within cells Enzymes bind a specific molecule and stress bonds to make a particular reaction more likely Active site Site on enzyme surface where reactant fits Binding site Site on reactant where enzyme binds
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Fig. 5.5 Enzyme shapes determines its activity
Changes upon binding of the substrate The substrate is now bound more intimately Lysozyme
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Fig. 5.6 How enzymes work Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

Fig. 5.7 The catalytic cycle of an enzyme
Bond 1 The substrate, sucrose, consists of glucose and fructose bonded together.
2 Glucose The substrate binds to the enzyme, forming an enzyme substrate complex.
H 2 O Fructose 4 Products are released, and the enzyme is free to bind other substrates.
Active site Enzyme 3 The binding of the substrate and enzyme places stress on the glucose-fructose bond, and the bond breaks.
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Enzyme activity is affected by any change in condition that alters the enzyme’s 3-D shape The structural bonds of enzymes are sensitive to changes in temperature and pH Therefore, a temperature or pH beyond the optimal range will cause the enzyme to denature
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Fig. 5.8 Enzymes are sensitive to their environment
Digests proteins in the stomach
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Digests proteins in the intestine

Biochemical Pathways
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Due to electrostatic repulsion between phosphate groups Adenosine triphosphate (ATP) is the main energy currency of the cell Each ATP molecule is composed of three parts:
Fig. 5.11
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Most energy exchanges in the cell involve cleavage of only the outermost bond in ATP Provided through photosynthesis or aerobic respiration Used to power many of the cell’s activities
Fig. 5.12
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-
Reduction Many reactions involve the passage of electrons from one atom/molecule to another Oxidation is the loss of electrons Reduction is the gain of electrons Oxidation reduction reactions always take place together Note that the transfer of electrons through these redox reactions also transfers energy
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Fig. 5.13 Redox reactions
A o + Loss of electron (oxidation) o B A e – B A* + B* _ Gain of electron (reduction) Low energy High energy
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is the process that captures light energy and transforms into the chemical energy of carbohydrates.
Light photons supply energy to remove the carbon from carbon dioxide and link them together to form a compound of glucose.
6CO 2 +12H 2 O + light → C 6 H 12 O 6 +6H 2 O+6O 2
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Fig. 6.1
Journey into a leaf Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

Light consists of tiny packets of energy called photons Sunlight contains photons of many energy levels High energy photons have lower wavelength than low energy photons The full range of these photons is called the electromagnetic spectrum
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Fig. 6.2 Photons of different energy: the electromagnetic spectrum Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

Are molecules that absorb light energy The pigment in human eyes is retinal Absorption: ~ 380 (violet) – 750 (red) nm The main pigment in plants is chlorophyll Chlorophyll a and chlorophyll b Have slight differences in absorption spectra Carotenoids are accessory pigments They capture wavelengths not efficiently absorbed by chlorophyll
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Fig. 6.4 Absorption spectra of chlorophylls and carotenoids Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

Fig. 6.5 Fall colors are produced by pigments such as carotenoids Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

Chlorophyll is embedded in a protein complex in the thylakoid membrane This pigment-protein complex forms the photosystem
Fig. 6.6
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is the process that captures light energy and transforms into the chemical energy of carbohydrates.
Light photons supply energy to remove the carbon from carbon dioxide and link them together to form a compound of glucose.
6CO 2 +12H 2 O + light → C 6 H 12 O 6 +6H 2 O+6O 2
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Photosynthesis takes place in three stages:
Light-dependent reactions Light-independent reactions The Calvin cycle
1. Capturing energy from sunlight 2. Using energy to make ATP and NADPH 3. Using ATP and NADPH to power the synthesis of carbohydrates from CO 2
6 CO 2
+
12 H 2 O
+
carbon dioxide water Light energy C 6 H 12 O 6 glucose
+
6 H 2 O Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display water
+
6 O 2 oxygen

All three stages occur in the chloroplast Contain the pigment chlorophyll, which captures light
Fig. 6.1
Journey into a leaf (continued) Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display