Biology Now, 2e

Ingredients for Life ■ 41

agreed to let Miller work on the project for six

months, a year at the most. As it turned out, all

Miller needed was a few weeks.

Miller mixed the four gases together in a

large glass apparatus. He then zapped the swirl-

ing cloud of compounds with a continuous elec-

trical spark to mimic lightning strikes on early

Earth, which he surmised would break apart

the compounds (Figure 3.2). The process of

breaking existing chemical bonds and creat-

ing new ones is known as a chemical reaction.

The reactants (the gases, in this case) undergo

a chemical change and form new molecules,

called products. Some chemical reactions, like

the one Miller devised, require energy in order

to proceed. Others release energy.

After the first day of the experiment, a pink

liquid pooled in the bottom of the apparatus.

By the end of a week, it had turned “deep red and

Figure 3.1

Atomic structure

The electrons, protons, and neutrons of these hydrogen and carbon atoms are shown greatly enlarged

in relation to the size of the whole atom.

Q1: How many protons, electrons, and neutrons does the hydrogen atom shown here have?

What are the atomic number and the atomic mass number of the hydrogen atom?

Q2: What are the atomic number and the atomic mass number of the carbon isotope shown?

Q3: Nitrogen-11 is an isotope of nitrogen that has 7 protons and 4 neutrons. What are the

atomic number and atomic mass number of nitrogen-11?

Nucleus

Hydrogen atom Carbon atom

Protons

Electrons

Neutrons

+

+

+

+

+

+

–

–

–

–

–

–

–

–

+

+

Atomic

number

H

1

1

Hydrogen

C

6

12

Carbon

N

7

14

Nitrogen

O

8

16

Oxygen

Atomic

mass

number

turbid,” Miller reported. The color changes, he

later discovered, reflected the formation of new

products through chemical reactions.

To Miller and Urey’s pleased surprise, the

resulting red broth contained several biolog-

ically significant compounds, including five

amino acids, small molecules important to life.

HAROLD UREY

Harold Urey was an American chemist who won

the Nobel Prize in Chemistry in 1934 for the

discovery of an isotope of hydrogen. He was

the first to speculate that Earth’s early

atmosphere was composed of ammonia,

methane, hydrogen, and water vapor.