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Section 2–4 Chemical Reactions and Enzymes
Date ______________
(pages 49–53)
TEKS FOCUS: 1A Safe lab practices; 1B Conserve resources; 2A Plan investigations; 2B Measure
precisely; 2C Make inferences; 2D Communicate valid conclusions; 3A Analyze scientific explanations;
4B Cellular processes
This section describes what happens to chemical bonds during chemical reactions. It also
explains how energy changes affect chemical reactions and describes the importance of enzymes.
Chemical Reactions
(page 49)
1. What is a chemical reaction? It is a process that changes one set of chemicals into another
set of chemicals.
2. Complete the table about chemicals in a chemical reaction.
CHEMICALS IN A CHEMICAL REACTION
Chemicals
Definition
Reactants
The elements or compounds that enter into a chemical reaction
Products
The elements or compounds produced by a chemical reaction
3. Chemical reactions always involve changes in chemical
Energy in Reactions
bonds
.
(page 50)
4. What is released or absorbed whenever chemical bonds form or are broken?
Energy
5. What do chemical reactions that absorb energy need to occur? They need a source of
energy.
6. Chemists call the energy needed to get a reaction started the
activation energy
.
Energy-Releasing Reaction
Energy
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7. Complete the graph of an energy-releasing reaction by adding labels to show the energy
of the reactants, the energy of the products, and the activation energy.
Activation
energy
Reactants
Products
Course of Reaction
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Enzymes
(pages 51–52)
8. What is a catalyst? A catalyst is a substance that speeds up the rate of a chemical reaction.
9. Proteins that act as biological catalysts are called
enzymes
.
10. What do enzymes do? Enzymes speed up chemical reactions that take place in cells.
11. From what is part of an enzyme’s name usually derived? It is derived from the reaction it
catalyzes.
Enzyme Action
(pages 52–53)
12. The reactants of enzyme-catalyzed reactions are known as
substrates
.
13. Why are the active site and the substrates in an enzyme-catalyzed
reaction often compared to a lock and key? The active site and the substrates have
complementary shapes, and the fit is very precise.
14. The binding together of an enzyme and a substrate forms a(an)
enzyme-substrate complex
.
15. How do most cells regulate the activity of enzymes? Most cells contain proteins that help
turn key enzymes “on” or “off” at critical stages in the life of the cell.
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Class __________________
Date ______________
WordWise
Answer the questions by writing the correct vocabulary term in the blanks.
Use the circled letter(s) in each term to find the hidden vocabulary word.
Then, write a definition for the hidden word.
Clues
Vocabulary Terms
What is a negatively charged subatomic particle?
e
l
e
c
What is the basic unit of matter?
a
t
o
m
p
o
l
l
i
What is an element or compound called that is
produced by a chemical reaction?
p
What is the type of mixture whose components are
evenly distributed throughout?
What is an atom called that has a positive or negative
charge as a result of gaining or losing electrons?
What is a large compound formed from
combinations of many monomers?
What is an organic compound called that is used
to store energy and forms important parts of
biological membranes?
What is a monomer of nucleic acids called?
Hidden Word: c
Definition:
o
m
p
o
u
n
t
r
o
n
y
m
e
r
p
i
d
r
o
d
u
c
t
s
o
l
u
t
i
o
n
i
o
n
n
u
c
l
e
o
t
i
d
e
d
A substance formed by the chemical combination of two or more elements in definite
© Pearson Education, Inc. All rights reserved.
proportions
Guided Reading and Study Workbook/Chapter 2
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Date ______________
Chapter 8 Photosynthesis
Section 8–1 Energy and Life
(pages 201–203)
TEKS FOCUS: 4B Cellular processes; TEKS SUPPORT: 9A Structure and function of biomolecules
This section explains where plants get the energy they need to produce food.
It also describes the role of the chemical compound ATP in cellular activities.
Autotrophs and Heterotrophs
(page 201)
1. Where does the energy of food originally come from? Energy in most food comes from
the sun.
2. Complete the table describing the types of organisms.
TYPES OF ORGANISMS
Type
Description
Examples
Autotrophs
Organisms that make their own food
Plants
Heterotrophs
Organisms that obtain energy from
the food they eat
Animals, mushrooms
Chemical Energy and ATP
(pages 202–203)
3. What is one of the principal chemical compounds that cells use to store energy?
Adenosine triphosphate, or ATP
4. How is ATP different from ADP? ATP has three phosphate groups, whereas ADP has two
phosphate groups.
5. Label each part of the ATP molecule illustrated below.
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Adenine
Ribose
3 Phosphate groups
P
P
P
6. When a cell has energy available, how can it store small amounts of that energy?
It can add a phosphate group to ADP molecules, producing ATP molecules.
Guided Reading and Study Workbook/Chapter 8
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Class __________________
Date ______________
7. When is the energy stored in ATP released? It is released when the chemical bond between
the second and third phosphates is broken.
8. For what purpose do the characteristics of ATP make it exceptionally useful
to all types of cells? All types of cells use ATP as their basic energy source.
9. What are two ways in which cells use the energy provided by ATP?
a. Active transport
b. Movement within the cell
Using Biochemical Energy
(pages 202–203)
10. Why is it efficient for cells to keep only a small supply of ATP on hand?
ATP is not very good for storing large amounts of energy over the long term. A single sugar
molecule stores more than 90 times the chemical energy of an ATP molecule.
11. Circle the letter of where cells get the energy to regenerate ATP.
a. ADP
b. phosphates
c. foods like glucose
d. organelles
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250
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Name __________________________________ Date _________ Class _________________
Section 8–2 Photosynthesis: An Overview
(pages 204–207)
TEKS FOCUS: 3F History of biology and contributions of scientists, 4B Cellular processes
This section describes what important experiments revealed about how plants
grow. It also introduces the overall equation for photosynthesis and explains
the roles light and chlorophyll have in the process.
Introduction
(page 204)
1. What occurs in the process of photosynthesis? Plants use the energy of sunlight to convert
water and carbon dioxide into high-energy carbohydrates—sugars and starches—and oxygen.
Investigating Photosynthesis
(pages 204–206)
2. What did Jan van Helmont conclude from his experiment? He concluded that most of
the mass a plant had gained had come from water, because that was the only thing he had added
to the pot.
3. Circle the letter of the substance produced by the mint plant in Joseph Priestley’s
experiment.
a. carbon dioxide
b. water
4. What did Jan Ingenhousz show?
c. air
d. oxygen
He showed that light is necessary for plants to produce
oxygen.
The Photosynthesis Equation
(page 206)
5. Write the overall equation for photosynthesis using words.
carbon dioxide + water
light
sugars + oxygen
6. Write the overall equation for photosynthesis using chemical
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formulas. 6CO2 + 6H2O
light
C6H12O6 + 6O2
7. Photosynthesis uses the energy of sunlight to convert water and
sugars
carbon dioxide into oxygen and high-energy
Light and Pigments
.
(page 207)
8. What does photosynthesis require in addition to water and carbon dioxide?
It requires light and chlorophyll, a molecule in chloroplasts.
9. Plants gather the sun’s energy with light-absorbing molecules called
pigments
.
10. What is the principal pigment of plants?
Guided Reading and Study Workbook/Chapter 8
Chlorophyll
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11. Circle the letters of the regions of the visible spectrum in which chlorophyll absorbs
light very well.
a. blue-violet region
b. green region
c. red region
d. yellow region
Reading Skill Practice
By looking at illustrations in textbooks, you can help yourself remember better what
you have read. Look carefully at Figure 8–4 on page 206. What important ideas does
this illustration communicate? Do your work on a separate sheet of paper.
Photosynthesis uses light energy to convert carbon dioxide and water into sugars and oxygen. This
takes place in chloroplasts.
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252
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Class __________________
Section 8–3 The Reactions of Photosynthesis
Date ______________
(pages 208–214)
TEKS FOCUS: 3F History of biology and contributions of scientists, 4B Cellular processes;
TEKS SUPPORT: 9A Structure and function of biomolecules
This section explains what happens inside chloroplasts during the process of
photosynthesis.
Inside a Chloroplast
(page 208)
thylakoids
1. Chloroplasts contain saclike photosynthetic membranes called
.
2. What is a granum? A granum is a stack of thylakoids.
3. The region outside the thylakoid membranes in the chloroplasts is called the
stroma
.
4. What are the two stages of photosynthesis called?
a. Light-dependent reactions
b. Light-independent reactions, or Calvin cycle
5. Complete the illustration of the overview of photosynthesis by writing the products
and the reactants of the process, as well as the energy source that excites the electrons.
H2O
CO2
Chloroplast
Light
NADP+
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ADP + P
Calvin
Cycle
LightDependent
Reactions
ATP
NADPH
O2
Guided Reading and Study Workbook/Chapter 8
Sugars
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Electron Carriers
Class __________________
Date ______________
(page 209)
6. When sunlight excites electrons in chlorophyll, how do the electrons change?
The electrons gain a great deal of energy.
7. What is a carrier molecule? A carrier molecule is a compound that can accept
a pair of high-energy electrons and transfer them along with most of their energy to another
molecule.
8. Circle the letter of the carrier molecule involved in photosynthesis.
a. H2O
c. CO2
+
b. NADP
d. O2
+
9. How does NADP become NADPH? NADP+ becomes NADPH when it accepts a pair
of high-energy electrons.
Light-Dependent Reactions
(pages 210–211)
10. Circle the letter of each sentence that is true about the light-dependent
reactions.
a. They convert ADP into ATP.
b. They produce oxygen gas.
c. They convert oxygen into carbon dioxide.
d. They convert NADP+ into NADPH.
11. Where do the light-dependent reactions take place? Within the thylakoid membranes
of chloroplasts
12. Circle the letter of each sentence that is true about the light-dependent reactions.
b. Photosynthesis begins when pigments in photosystem I absorb light.
c. The difference in charges across the thylakoid membrane provides the energy to
make ATP.
d. Pigments in photosystem I use energy from light to reenergize electrons.
+
13. How does ATP synthase produce ATP? ATP synthase allows H ions to pass through
the thylakoid membrane. As the ions pass through, ATP synthase rotates, binding ADP and
a phosphate group together to produce ATP.
254
Guided Reading and Study Workbook/Chapter 8
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a. High-energy electrons move through the electron transport chain from
photosystem II to photosystem I.
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The Calvin Cycle
Class __________________
Date ______________
(pages 212–214)
14. What does the Calvin cycle use to produce high-energy sugars?
The Calvin cycle uses ATP and NADPH from the light-dependent reactions to produce
high-energy sugars.
15. Why are the reactions of the Calvin cycle also called the light-independent reactions?
The Calvin cycle does not require light.
16. Circle the letter of each statement that is true about the Calvin cycle.
a. The main products of the Calvin cycle are six carbon dioxide molecules.
b. Carbon dioxide molecules enter the Calvin cycle from the atmosphere.
c. Energy from ATP and high-energy electrons from NADPH are
used to convert 3-carbon molecules into higher-energy forms.
d. The Calvin cycle uses six molecules of carbon dioxide to
produce a single 6-carbon sugar molecule.
Factors Affecting Photosynthesis
(page 214)
17. What are three factors that affect the rate at which photosynthesis occurs?
a. Availability of water
b. Temperature
c. Intensity of light
18. Is the following sentence true or false? Increasing the intensity of light decreases the
false
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rate of photosynthesis.
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Class __________________
Date ______________
WordWise
Answer the questions by writing the correct vocabulary terms from Chapter 8
in the blanks. Use the circled letter from each term to find the hidden word.
Then, write a definition for the hidden word.
1. What is the process called by which plants use the sun’s energy to
make high-energy sugars?
p
h
o
t
o
s
y
n
t
h
e
s
i
s
2. What is the stage of photosynthesis called in which plants use the
energy that ATP and NADPH contain to build high-energy sugars?
C
a
l
v
i
n
c
y
c
l
e
3. What are the reactions of the first stage of photosynthesis called?
l
i
g
h
t
–
d
e
p
r
e
a
c
t
i
o
n
s
e
n
d
e
n
t
4. What is the region called where the Calvin cycle takes place?
s
t
r
o
m
a
5. What is an organism called that obtains energy from the food it
consumes?
h
e
t
e
r
o
t
r
o
p
h
6. What is one of the principal chemical compounds that living things
use to store energy?
a
d
e
n
o
s
i
n
e
t
r
i
p
h
o
s
p
h
a
t
e
7. What is an organism called that makes its own food?
a
u
t
o
Definition:
256
r
o
p
h
pigment
A pigment is a light-absorbing molecule.
Guided Reading and Study Workbook/Chapter 8
© Pearson Education, Inc. All rights reserved.
Hidden word:
t