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Topic
25
Table of Contents
Topic
25
Topic 25: Biochemistry
Basic Concepts
Additional Concepts
Biochemistry: Basic Concepts
Topic
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Molecules of Life
• Many of the most important molecules in
your body are polymers.
• Proteins, carbohydrates, and nucleic acids,
all extremely large molecules, are formed
from small monomer subunits.
• Although lipids are usually not considered
to be polymers, they, too, are formed from
smaller molecules that have been linked
together.
Biochemistry: Basic Concepts
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Molecules of Life
• You need relatively large amounts of proteins,
carbohydrates, and lipids in your diet.
• Complex reactions in your cells use some
of these molecules and a few others to
make a fourth group of biomolecules, the
nucleic acids.
Biochemistry: Basic Concepts
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Biochemistry
• The study of the chemistry of living things is
called biochemistry.
• This science explores the substances
involved in life processes and the reactions
they undergo.
• Other than water, which can account for
80 percent or more of the weight of an
organism, most of the molecules of life—
the biomolecules—are organic.
Biochemistry: Basic Concepts
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Biochemistry
• The elemental
composition of living
things is different from the
relative abundance of
elements in Earth’s crust.
• Oxygen, silicon,
aluminum, and iron are
the most abundant atoms
in Earth’s crust.
Biochemistry: Basic Concepts
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Biochemistry
• However, more than 95 percent of the atoms
in your body are
hydrogen, oxygen,
carbon, and nitrogen.
• All four of these
elements can form
the strong covalent
bonds found in
organic molecules.
Biochemistry: Basic Concepts
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Biochemistry
• Along with two other elements, sulfur and
phosphorus, they are
the only elements
needed to make most
of the proteins,
carbohydrates, lipids,
and nucleic acids found
in every cell.
Biochemistry: Basic Concepts
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Proteins
• A protein is an organic polymer composed
of amino acids bonded together in one or
more chains.
• An amino acid has a central carbon atom, to
which are bonded a carboxyl group, an amino
group, a hydrogen atom, and a variable side
chain designated as R, as shown in the
following structural formula.
Biochemistry: Basic Concepts
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Structure of an Amino Acid
Biochemistry: Basic Concepts
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Structure of an Amino Acid
• Amino acids bond to each other by forming
a peptide bond, an amide group formed by
a condensation reaction between the
carboxyl group of one amino acid and the
amino group of another.
Biochemistry: Basic Concepts
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Structure of an Amino Acid
• Two amino acids linked by a peptide bond
form a dipeptide.
Biochemistry: Basic Concepts
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Structure of an Amino Acid
• A chain of two or more amino acids linked
by peptide bonds is called a peptide.
• The term polypeptide is applied to a chain of
ten or more amino acids.
• Proteins may have one or several polypeptide
chains, and each chain must have an exact
sequence of amino acids.
Biochemistry: Basic Concepts
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Structure of an Amino Acid
• Proteins can fold into either round, globular
structures or long, fibrous structures.
Biochemistry: Basic Concepts
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Structure of an Amino Acid
• The amino acid chains are held in place in
three-dimensional structures by attractive
forces between the side chains of different
amino acids, which
have been brought
close together by
the bending and
folding of the
polypeptide chains.
Biochemistry: Basic Concepts
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Enzymes
• Many of the proteins in an organism act as
enzymes. These proteins catalyze chemical
reactions—speeding up reactions or
allowing the reactions to take place at a low
temperature.
Biochemistry: Basic Concepts
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Enzymes
• The reactants in an enzyme-catalyzed
process are called substrates. The
substrate(s) bind to the enzyme at a location
called the enzyme’s active site, forming an
enzyme-substrate complex.
• This interaction enables the substrate(s) to
react with a much lower activation energy
than they would without an enzyme.
Biochemistry: Basic Concepts
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Enzymes
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Biochemistry: Basic Concepts
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Enzyme Action
• Substrates are brought close together in the
active sites of an enzyme, which lowers the
activation energy of the reaction by
facilitating the bonding together of the
substrates to form a product.
Biochemistry: Basic Concepts
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Enzyme Action
• After the substrates have reacted, the product
is released.
• The enzyme is then able to bind more
substrate molecules and continue catalyzing
the reaction.
Biochemistry: Basic Concepts
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Carbohydrates
• Familiar carbohydrates include sugars,
starches, and cellulose.
• Simple carbohydrates consist of a chain of
carbon atoms having hydroxyl (–OH) groups
and a carbonyl group, often in the form of an
aldehyde group.
Biochemistry: Basic Concepts
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Monosaccharides
• The simplest carbohydrates are the simple
sugars, or monosaccharides, which
commonly have five or six carbon atoms.
• Glucose, the main ingredient in corn syrup,
is a familiar monosaccharide.
Biochemistry: Basic Concepts
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Monosaccharides
• Glucose has the molecular formula C6H12O6
and can be represented by the following
structures.
Biochemistry: Basic Concepts
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Monosaccharides
• The most common simple sugars are glucose,
fructose, and ribose.
Biochemistry: Basic Concepts
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Polysaccharides
• A polymer of many monosaccharides bonded
into a chain is called a polysaccharide.
• Starch is a
polysaccharide
that consists only
of glucose units.
Biochemistry: Basic Concepts
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Polysaccharides
• Plants also link glucose units together in a
different way to form the polysaccharide
cellulose, which
forms plant cell
walls.
Biochemistry: Basic Concepts
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Polysaccharides
• Animals store glucose as a polysaccharide
called glycogen, which is similar to starch.
Biochemistry: Basic Concepts
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Lipids
• Lipids are the nonpolar substances—fats,
waxes, and oils—produced by living things.
• Lipids are not
polymers,
and their
chemical
structures
vary widely.
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Biochemistry: Basic Concepts
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Fatty Acids
• The most familiar lipids are the plant oils
and animal fats.
• These lipids are esters of fatty acids, which
are carboxylic acids with long, straight
hydrocarbon chains usually having between
12 and 24 carbon atoms.
Biochemistry: Basic Concepts
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Saturated Fatty Acid
• The simplest fatty acids are the
saturated fatty acids, which have
no double bonds between carbon
atoms.
• Stearic acid is found in pork and
beef tissue.
Biochemistry: Basic Concepts
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Monounsaturated Fatty Acid
• Many other fatty acids have
one or more double bonds
between carbon atoms and,
as a result, are unsaturated
fatty acids.
• Oleic acid is a major
component of olive oil.
Biochemistry: Basic Concepts
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Triglycerides
• Animal fats and plant oils are made up
primarily of triglycerides, molecules in which
three fatty acids are bonded to a glycerol
molecule by ester
linkages, as shown
in the following
diagram.
Biochemistry: Basic Concepts
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Triglycerides
• Phospholipids are triglycerides in which a
polar phosphate group, instead of a third
fatty acid, is bonded to the glycerol.
• Cell membranes
consist of a
double layer of
phospholipid
molecules.
Biochemistry: Basic Concepts
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Triglycerides
• The membranes of
living cells are formed
by a double layer of
lipids called a bilayer.
Biochemistry: Basic Concepts
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Other Lipids
• Another class of lipids, steroids, consists
of compounds whose basic structure is
very different from those of other lipids,
as shown below.
• Cholesterol,
vitamin D, and
some hormones
are steroids.
Biochemistry: Basic Concepts
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The Functions of Lipids
• Lipids have two major biochemical roles
in the body.
• When an organism takes in and processes
more food than it needs, excess energy is
produced.
• The organism stores this excess energy
for future use by using it to bond atoms
together in lipid molecules.
Biochemistry: Basic Concepts
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The Functions of Lipids
• Later, when energy is needed, enzymes
break these same bonds, releasing the
energy used to form them.
• You have learned that carbohydrates also
store energy; however, the process is not
as efficient as in lipids.
• Therefore, long-term storage of energy is
usually in the form of lipids.
Biochemistry: Basic Concepts
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Nucleic Acids
• The sequence of amino acids in a protein
is determined by the genetic information
coded into long-chain polymers called
nucleic acids.
• The monomers that make up nucleic acids
are called nucleotides.
Biochemistry: Basic Concepts
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Nucleic Acids
• Each nucleotide is made up of three parts: a
phosphate group, a five-carbon sugar, and a
nitrogen-containing cyclic compound called
a nitrogen base.
• The structure of a nucleotide is shown.
Biochemistry: Basic Concepts
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Nucleic Acids
Biochemistry: Basic Concepts
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Nucleic Acids
Biochemistry: Basic Concepts
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Nucleic Acids
• The common nucleic acids are DNA
(deoxyribonucleic acid) and RNA
(ribonucleic acid).
• These names reflect the fact that DNA
contains the sugar deoxyribose and RNA
contains the sugar ribose.
• DNA exists as a pair of polymer chains in
which the backbone of each chain consists of
alternating phosphate and deoxyribose units.
The bases stick out from the backbone.
Biochemistry: Basic Concepts
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The Structure of DNA
• This model of a
portion of a DNA
molecule clearly
shows its complexity.
• A single DNA
molecule contains
many thousands of
nucleotides.
Biochemistry: Basic Concepts
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Base Pairing
• The two chains of DNA are held together
because the nitrogen bases of one chain are
hydrogen-bonded to the nitrogen bases of
the other chain.
• Because of the change in angle from one
nucleotide to the next, the chains wind into
a spiral called a double helix.
Biochemistry: Basic Concepts
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Base Pairing
• Four different nitrogen bases are found
in DNA: adenine, guanine, cytosine, and
thymine.
• Adenine hydrogen bonds to thymine, and
guanine hydrogen bonds to cytosine.
Biochemistry: Basic Concepts
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Base Pairing
• The order of these four nitrogen bases
along one of the DNA chains provides the
information for the sequences of amino
acids in proteins.
• Cell mechanisms “read” the DNA sequence
in groups of three bases called triplets.
• Each triplet codes for a specific amino
acid or tells the cell to start or stop making
a protein.
Basic Assessment Questions
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Question 1
Label the amino group and the carboxyl
group of the dipeptide.
Basic Assessment Questions
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Answer
Basic Assessment Questions
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Question 2
Draw an arrow pointing to the peptide bond.
Basic Assessment Questions
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Answer
Basic Assessment Questions
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Question 3
Draw a square around each variable side chain.
Basic Assessment Questions
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Answer
Basic Assessment Questions
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Question 4
Glucose is a(n)
a. polysaccharide.
b. amino acid.
c. part of cellulose.
d. 5-carbon sugar.
Basic Assessment Questions
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Answer
The answer is C, part of cellulose.
Biochemistry: Additional Concepts
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Additional Concepts
Biochemistry: Additional Concepts
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Anabolism and Catabolism
• The set of reactions carried out by an
organism is its metabolism.
• Living organisms must accomplish two
major functions in order to survive.
• They have to extract energy from nutrients
in forms that they can use immediately as
well as store for future use.
Biochemistry: Additional Concepts
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Anabolism and Catabolism
• In addition, they have to use nutrients to
make building blocks for synthesizing all
of the molecules needed to carry out their
life functions.
Biochemistry: Additional Concepts
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Anabolism and Catabolism
• A large number of different metabolic
reactions take place in living cells.
• Some involve breaking down nutrients to
extract energy; these are catabolic processes.
Biochemistry: Additional Concepts
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Anabolism and Catabolism
• Others involve using energy to build large
biological molecules; these reactions are
anabolic processes.
Biochemistry: Additional Concepts
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Anabolism and Catabolism
• The term catabolism refers to the metabolic
reactions that break down complex biological
molecules such as proteins, polysaccharides,
triglycerides, and nucleic acids for the
purposes of forming smaller building blocks
and extracting energy.
• The term anabolism refers to the metabolic
reactions that use energy and small building
blocks to synthesize the complex molecules
needed by an organism.
Biochemistry: Additional Concepts
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ATP
• Catabolism and anabolism are linked by
common building blocks that catabolic
reactions produce and anabolic reactions use.
• A common form of potential chemical
energy also links the two processes.
Biochemistry: Additional Concepts
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ATP
• ATP (adenosine triphosphate) is a nucleotide
that functions as the universal energy-storage
molecule in living cells.
• During catabolic
reactions, cells harness
the chemical energy of
foods and store it in
the bonds of ATP.
Biochemistry: Additional Concepts
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Photosynthesis
• What is the source of the energy that fuels
metabolism? For most living things,
certain wavelengths of sunlight provide all
of this energy.
• Some bacteria and the cells of all plants and
algae, including the brown algae, are able to
capture light energy and convert some of it
to chemical energy.
Biochemistry: Additional Concepts
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Photosynthesis
• Animals can’t capture light energy, so they
get energy by eating plants or by eating
other animals that eat plants.
• The process that converts energy from
sunlight to chemical energy in the bonds of
carbohydrates is called photosynthesis.
Biochemistry: Additional Concepts
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Photosynthesis
• ATP is a nucleotide that contains an
adenine nitrogen base, a ribose sugar, and
three phosphate groups.
Biochemistry: Additional Concepts
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Photosynthesis
• When the final phosphate group is removed
from ATP, as modeled by the red dotted line,
ADP is formed and energy is released.
Biochemistry: Additional Concepts
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Photosynthesis
• During the complex process of
photosynthesis, carbon dioxide and water
provide the carbon, hydrogen, and oxygen
atoms that make up carbohydrates and
oxygen gas, which also is formed.
• The following net reaction takes place
during photosynthesis.
Biochemistry: Additional Concepts
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Photosynthesis
• Photosynthesis results in the reduction of
the carbon atoms in carbon dioxide as
glucose is formed.
• During this redox process, oxygen atoms
in water are oxidized to oxygen gas.
Biochemistry: Additional Concepts
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Cellular Respiration
• Most organisms need oxygen to live. Oxygen
that is produced during photosynthesis is
used by living things during cellular
respiration, the process in which glucose is
broken down to form carbon dioxide, water,
and large amounts of energy.
• Cellular respiration is a redox process; the
carbon atoms in glucose are oxidized while
oxygen atoms in oxygen gas are reduced to
the oxygen in water.
Biochemistry: Additional Concepts
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Cellular Respiration
• The net reaction that takes place during
cellular respiration is
• Note that the net equation for cellular
respiration is the reverse of the net equation
for photosynthesis.
• These two processes complement each other
in nature.
Biochemistry: Additional Concepts
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Fermentation
• During cellular respiration, glucose is
completely oxidized, and oxygen gas is
required to act as the oxidizing agent.
• Can cells extract energy from glucose in the
absence of oxygen?
• Yes, but not nearly as efficiently. Without
oxygen, only a fraction of the chemical
energy of glucose can be released.
Biochemistry: Additional Concepts
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Fermentation
• Whereas cellular respiration produces 38
moles of ATP for every mole of glucose
catabolized in the presence of oxygen, only
two moles of ATP are produced per mole of
glucose that is catabolized in the absence of
oxygen.
Biochemistry: Additional Concepts
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•
•
•
•
Fermentation
This provides enough energy for oxygendeprived cells so that they don’t die.
The process in which glucose is broken
down in the absence of oxygen is known
as fermentation.
There are two common kinds of fermentation.
In one, ethanol and carbon dioxide are
produced.
In the other, lactic acid is produced.
Biochemistry: Additional Concepts
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Alcoholic fermentation
• Yeast and some bacteria can ferment glucose
to produce the alcohol ethanol.
Biochemistry: Additional Concepts
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Alcoholic fermentation
Biochemistry: Additional Concepts
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Alcoholic fermentation
• Alcoholic fermentation is needed to make
bread dough rise, form tofu from soybeans,
and produce the ethanol in alcoholic
beverages.
• Another use of the ethanol that is produced
by yeast is as an additive to gasoline, called
gasohol.
Biochemistry: Additional Concepts
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Lactic acid fermentation
• During strenuous activity, muscle cells often
use oxygen faster than it can be supplied by
the blood.
• When the supply of oxygen is depleted,
cellular respiration stops.
Biochemistry: Additional Concepts
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Lactic acid fermentation
• Although animal cells can’t undergo
alcoholic fermentation, they can produce
lactic acid and a small amount of energy
from glucose through lactic acid
fermentation.
Biochemistry: Additional Concepts
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Lactic acid fermentation
Biochemistry: Additional Concepts
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Lactic acid fermentation
• The lactic acid that is produced is moved
from the muscles through the blood to
the liver.
• There, it is converted back into glucose
that can be used in catabolic processes to
yield more energy once oxygen becomes
available.
Biochemistry: Additional Concepts
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Lactic acid fermentation
• However, if lactic acid builds up in muscle
cells at a faster rate than the blood can
remove it, muscle fatigue results.
• Buildup of lactic acid is what causes a
burning pain in the muscle during strenuous
exercise.
Additional Assessment Questions
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Question 1
What effect do enzymes have on the chemical
reactions that take place in living things?
Additional Assessment Questions
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Answer
speed reactions by lowering activation energy
Additional Assessment Questions
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Question 2
Your cells carry out cellular respiration.
What is the function of this process?
Additional Assessment Questions
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Answer
releases energy for life processes
Additional Assessment Questions
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Question 3
What process is the reverse of cellular
respiration?
Additional Assessment Questions
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Answer
photosynthesis
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