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Copyright © by Holt, Rinehart and Winston. All rights reserved.

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Energy in Living Systems• Directly or indirectly, almost all of the energy in living systems

needed for metabolism comes from the _______________.

Section 1 Energy and Living ThingsChapter 5



Energy in Living Systems, continued

Building Molecules That Store Energy

• Metabolism involves either using energy to __________ molecules or breaking down molecules in which energy is stored.

• Photosynthesis is the process by which ____________ energy is converted to chemical energy.

• Organisms that use energy from sunlight or from chemical bonds in inorganic substances to make organic compounds are called __________________________.





Breaking Down Food for Energy

• The chemical energy in organic compounds can be _____________________ to other organic compounds or to organisms that consume food.

• Organisms that must get energy from food instead of directly from sunlight or inorganic substances are called ________________________________.

• Cellular respiration is a metabolic process similar to burning _________________.





Transfer of Energy to ATP

• When cells break down food molecules, some of the energy in the molecules is released as __________. Much of the remaining energy is stored temporarily in molecules of ATP.

• Like money, ATP is a portable form of energy “currency” inside cells. ATP delivers ____________________ wherever energy is needed in a cell.




ATP

• ATP (adenosine triphosphate) is a nucleotide with two extra energy-storing ____________________ groups.

• Energy is released when the bonds that hold the phosphate groups together are _______________.

• The removal of a phosphate group from ATP produces adenosine diphosphate, or ADP:

H2O + ATP ADP + P + energy




Using the Energy in Sunlight

The Stages of Photosynthesis

• Stage 1 Energy is captured from _______________.

• Stage 2 Light energy is converted to chemical energy, which is temporarily ___________________ in ATP and the energy carrier molecule NADPH.

• Stage 3 The chemical energy stored in ATP and NADPH powers the formation of ________________ compounds, using carbon dioxide, CO2.

Section 2 PhotosynthesisChapter 5



Using the Energy in Sunlight

The Stages of Photosynthesis

• Photosynthesis can be summarized by the following ___________________________________:

6CO2 + 6H2O C6H12O6 + 6O2

Carbon dioxide water sugars oxygen gas




Stage One: Absorption of Light Energy

• Sunlight contains a mixture of all the __________________ (colors) of visible light. When sunlight passes through a prism, the prism separates the light into different colors.




Stage One: Absorption of Light Energy, continuedPigments

• How does a human eye or a leaf absorb light? These structures contain light-absorbing substances called ______________________________.

• Chlorophyll the primary pigment involved in photosynthesis, absorbs mostly blue and red light and reflects _______________________ and yellow light.

• Plants contain two types of chlorophyll, chlorophyll a and chlorophyll b.




Stage One: Absorption of Light Energy, continuedPigments

• The pigments that produce yellow and orange fall leaf colors, as well as the colors of many fruits, vegetables, and flowers, are called _________________________________.

• Carotenoids absorb wavelengths of light different from those absorbed by chlorophyll, so having ____________ pigments enables plants to absorb more light energy during photosynthesis.




Stage One: Absorption of Light Energy, continued

Production of Oxygen

• Clusters of pigments are embedded in the membranes of disk-shaped structures called _____________________.

• When light strikes a thylakoid in a chloroplast, energy is transferred to electrons in _______________________.

• This energy transfer causes the electrons to jump to a higher energy level. This is how plants first capture energy from sunlight.




Stage One: Absorption of Light Energy, continued

Production of Oxygen

• The excited electrons that leave chlorophyll molecules must be replaced by other electrons.

• Plants get these replacement electrons from ___________ molecules, which are split by thylakoid.

• The oxygen atoms, O, from the _________________ water molecules combine to form oxygen gas, O2.




Stage Two: Conversion of Light Energy

• Excited electrons that leave chlorophyll molecules are used to produce new molecules that temporarily store chemical _________________.

• First an excited electron jumps to a nearby molecule in the thylakoid membrane. Then the electron is _____________ through a series of molecules along the thylakoid membrane.

• The series of molecules through which excited electrons are passed along a thylakoid membrane are called electron transport _______________________.




Stage Two: Conversion of Light Energy, continuedElectron Transport Chains

• While one electron transport chain provides energy used to make ATP, a second electron transport chain provides energy used to make __________________.

• NADPH is an electron _______________ that provides the high-energy electrons needed to make carbon-hydrogen bonds in the third stage of photosynthesis.

• In this second chain, excited electrons combine with _______________ ions as well as an electron acceptor called NADP+, forming NADPH.




Stage Three: Storage of Energy

• In the third (final) stage of photosynthesis, carbon atoms from __________ ______________ in the atmosphere are used to make organic compounds in which chemical energy is stored.

• The transfer of carbon dioxide to organic compounds is called carbon dioxide fixation.




Stage Three: Storage of Energy, continuedCalvin Cycle

• The Calvin cycle is a series of enzyme-assisted chemical reactions that produces a three-carbon _____________:

Step 1 Each molecule of carbon dioxide is added to a five-carbon compound by an enzyme.

Step 2 The resulting compound splits into two three-carbon compounds. ___________________________ groups and electrons are added to the compounds.

Step 3 ____________ of the resulting three-carbon sugars is used to make organic energy-storing compounds.


Step 4 The other three-carbon sugars are used to _______________________________ the initial five-carbon compound, thereby completing the cycle.



Stage Three: Storage of Energy, continued

Factors that Affect Photosynthesis

• Photosynthesis is directly affected by various environmental factors.

• In general, the rate of photosynthesis increases as light _________________ increases until all the pigments are being used.

• Photosynthesis is most efficient within a certain range of _____________________________.




Cellular Energy

• Oxygen in the air you breathe makes the production of ATP more _____________________, although some ATP is made without oxygen.

• Metabolic processes that require oxygen are called ______________________________.

• Metabolic processes that do not require oxygen are called _________________________________, which means “without air.

Section 3 Cellular RespirationChapter 5



Cellular Energy, continued

The Stages of Cellular Respiration

• Cellular respiration is the process cells use to harvest the energy in organic compounds, particularly ________________________________. The breakdown of glucose during cellular respiration can be summarized by the following equation:

C6H12O6 + 6O2 6CO2 + 6H2O + energyglucose oxygen gas carbon dioxide water ATP




Cellular Energy, continued

The Stages of Cellular Respiration

• Cellular respiration occurs in two stages:

Stage 1 Glucose is converted to _______________, producing a small amount of ATP and NADH.

Stage 2 When oxygen is present, pyruvate and NADH are used to make a ________ amount of ATP. When oxygen is not present, pyruvate is converted to either lactate or ethanol and carbon dioxide.




Stage One: Breakdown of Glucose

Glycolysis

• In the first stage of cellular respiration, glucose is broken down in the cytoplasm during a process called ______________________________.

• As glucose is broken down, some of its hydrogen atoms are _________________________________ to an electron acceptor called NAD+. This forms an electron carrier called NADH.




Stage One: Breakdown of Glucose, continuedGlycolysis

• Glycolysis occurs in four steps:

Step 1 Phosphate groups from _____________ ATP molecules are transferred to a glucose molecule.

Step 2 The resulting six-carbon compound is ________________ down to two three-carbon compounds.

Step 3 Two NADH molecules are produced, and each compound _______________ one more phosphate group.

Step 4 Each three-carbon compound is converted to a three-carbon pyruvate, producing _______________________ ATP molecules in the process.




Stage Two: Production of ATP

• When oxygen is present, pyruvate produced during glycolysis enters a _________________________ and is converted to a two-carbon compound.

• This reaction produces one _________________ dioxide molecule, one NADH molecule, and one two-carbon acetyl group.

• The acetyl group is attached to a molecule called coenzyme A (CoA), forming a _________________ called acetyl-CoA.




Stage Two: Production of ATP, continued

Krebs Cycle

• Acetyl-CoA enters a series of enzyme-assisted reactions called the ____________ cycle, which follows five steps:

Step 1 Acetyl-CoA combines with a four-carbon compound, forming a six-carbon compound and releasing coenzyme A.

Step 2 _________ dioxide is released from the six-carbon compound, forming a five-carbon compound. Electrons are transferred to NAD+, making a molecule of NADH.





Krebs Cycle

Step 3 Carbon dioxide is released from the compound. A molecule of __________ and a molecule of NADH are made.

Step 4 The existing four-carbon compound is converted to a new four-carbon compound. __________________________ are transferred to an electron acceptor called FAD, making a molecule of FADH2, another type of electron carrier.

Step 5 The new four-carbon compound is then converted to the four-carbon compound that began the cycle. Another molecule of _____________________________ is produced.





Electron Transport Train

• In aerobic respiration, electrons _______________ by NADH and FADH2 pass through an electron transport chain.

• In eukaryotic cells, the electron transport chain is located in the inner membranes of _______________________________.

• At the end of the electron transport chain, hydrogen ions and spent electrons combine with oxygen molecules forming ______________________________ molecules.




Respiration in the Absence of Oxygen

• When oxygen is not present, NAD+ is recycled in another way. Under anaerobic conditions, electrons carried by NADH are transferred to pyruvate produced during __________________________.

• This process _________________ NAD+ needed to continue making ATP through glycolysis.

• The recycling of NAD+ using an organic hydrogen acceptor is called fermentation.




Respiration in the Absence of Oxygen, continuedLactic Acid Fermentation

• In some organisms, a three-carbon pyruvate is converted to a three-carbon _______________ through lactic acid fermentation.

• Fermentation enables glycolysis to continue producing ATP in muscles as long as the glucose supply lasts.




Respiration in the Absence of Oxygen, continuedAlcoholic Fermentation

• In some organisms, the three-carbon pyruvate is broken down to ____________ (ethyl alcohol), a two-carbon compound, through alcoholic fermentation.

• As in lactic acid fermentation, NAD+ is recycled, and glycolysis can continue to produce ATP.




Respiration in the Absence of Oxygen, continuedLactic Acid and Alcoholic Fermentation

• When oxygen is not present, cells recycle NAD+ through ______________________________.




Respiration in the Absence of Oxygen, continuedProduction of ATP

• When oxygen is present, ___________________ respiration occurs to produce ATP. When oxygen is not present, fermentation occurs instead.


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