OpenStax Biology 2e Instructor Answer Guide
Biology 2e
Unit 2: The Cell
Chapter 6: Metabolism
Visual Connection Questions
1. Look at each of the processes, and decide if it is endergonic or exergonic. In each case, does
enthalpy increase or decrease, and does entropy increase or decrease?
A compost pile decomposing is an exergonic process; enthalpy decreases (energy is released)
and entropy increases (large molecules are broken down into smaller ones). A baby developing
from a fertilized egg is an endergonic process; enthalpy increases (energy is absorbed) and
entropy decreases. Sand art being destroyed is an exergonic process; there is no change in
enthalpy, but entropy increases. A ball rolling downhill is an exergonic process; enthalpy
decreases (energy is released), but there is no change in entropy.
2. If no activation energy were required to break down sucrose (table sugar), would you be able
to store it in a sugar bowl?
No. We can store chemical energy because of the need to overcome the barrier to its
breakdown.
, OpenStax Biology 2e Instructor Answer Guide
3. One ATP molecule’s hydrolysis releases 7.3 kcal/mol of energy (∆G = −7.3 kcal/mol of
energy). If it takes 2.1 kcal/mol of energy to move one Na + across the membrane (∆G = +2.1
kcal/mol of energy), how many sodium ions could one ATP molecule’s hydrolysis move?
Three sodium ions could be moved by the hydrolysis of one ATP molecule. The ∆G of the
coupled reaction must be negative. Movement of three sodium ions across the membrane will
take 6.3 kcal of energy (2.1 kcal × 3 Na+ ions = 6.3 kcal). Hydrolysis of ATP provides 7.3 kcal of
energy, more than enough to power this reaction. Movement of four sodium ions across the
membrane, however, would require 8.4 kcal of energy, more than one ATP molecule can
provide.
Review Questions
4. Energy is stored long-term in the bonds of _____ and used short-term to perform work from
a(n) _____ molecule.
c. glucose : ATP
5. DNA replication involves unwinding two strands of parent DNA, copying each strand to
synthesize complementary strands, and releasing the parent and daughter DNA. Which of the
following accurately describes this process?
a. This is an anabolic process
6. Consider a pendulum swinging. Which type(s) of energy is/are associated with the pendulum
in the following instances: i. the moment at which it completes one cycle, just before it begins
to fall back towards the other end, ii. the moment that it is in the middle between the two
ends, and iii. just before it reaches the end of one cycle (just before instant i.).
c. i. potential, ii. kinetic, iii. potential and kinetic
7. Which of the following comparisons or contrasts between endergonic and exergonic
reactions is false?
d. Endergonic reactions take place slowly and exergonic reactions take place quickly
Biology 2e
Unit 2: The Cell
Chapter 6: Metabolism
Visual Connection Questions
1. Look at each of the processes, and decide if it is endergonic or exergonic. In each case, does
enthalpy increase or decrease, and does entropy increase or decrease?
A compost pile decomposing is an exergonic process; enthalpy decreases (energy is released)
and entropy increases (large molecules are broken down into smaller ones). A baby developing
from a fertilized egg is an endergonic process; enthalpy increases (energy is absorbed) and
entropy decreases. Sand art being destroyed is an exergonic process; there is no change in
enthalpy, but entropy increases. A ball rolling downhill is an exergonic process; enthalpy
decreases (energy is released), but there is no change in entropy.
2. If no activation energy were required to break down sucrose (table sugar), would you be able
to store it in a sugar bowl?
No. We can store chemical energy because of the need to overcome the barrier to its
breakdown.
, OpenStax Biology 2e Instructor Answer Guide
3. One ATP molecule’s hydrolysis releases 7.3 kcal/mol of energy (∆G = −7.3 kcal/mol of
energy). If it takes 2.1 kcal/mol of energy to move one Na + across the membrane (∆G = +2.1
kcal/mol of energy), how many sodium ions could one ATP molecule’s hydrolysis move?
Three sodium ions could be moved by the hydrolysis of one ATP molecule. The ∆G of the
coupled reaction must be negative. Movement of three sodium ions across the membrane will
take 6.3 kcal of energy (2.1 kcal × 3 Na+ ions = 6.3 kcal). Hydrolysis of ATP provides 7.3 kcal of
energy, more than enough to power this reaction. Movement of four sodium ions across the
membrane, however, would require 8.4 kcal of energy, more than one ATP molecule can
provide.
Review Questions
4. Energy is stored long-term in the bonds of _____ and used short-term to perform work from
a(n) _____ molecule.
c. glucose : ATP
5. DNA replication involves unwinding two strands of parent DNA, copying each strand to
synthesize complementary strands, and releasing the parent and daughter DNA. Which of the
following accurately describes this process?
a. This is an anabolic process
6. Consider a pendulum swinging. Which type(s) of energy is/are associated with the pendulum
in the following instances: i. the moment at which it completes one cycle, just before it begins
to fall back towards the other end, ii. the moment that it is in the middle between the two
ends, and iii. just before it reaches the end of one cycle (just before instant i.).
c. i. potential, ii. kinetic, iii. potential and kinetic
7. Which of the following comparisons or contrasts between endergonic and exergonic
reactions is false?
d. Endergonic reactions take place slowly and exergonic reactions take place quickly
