- Explain how elements are organized on the periodic table.
- Explain the function of enzymes.
- Name the four main classes of organic molecules that are building blocks of life.
Check Your Understanding
- What are the main properties of all living things?
- What is homeostasis?
Introduction
Physicalscienceandbiologyaretwodifferentsubjectsinschool, soyoumightseethemastwo
unrelated sciences. However, understanding physical science is essential for understanding
biology. Living things are subject to the same physical laws of the universe as non-living
things. The rules that apply to chemical reactions in a test tube also apply to the chemical
reactions that take place inside your body. To understand how living things function, we
must have a little knowledge of physics and chemistry. This includes knowing what elements
are and how different molecules come together to form the components of life.
The Elements
Rocks, animals, flowers, and even your body, are made up of matter. Matteris anything
that takes up space and has mass. Matter makes up everything, living and nonliving.
Matter is composed of a mixture of elements. Elementsare substances that cannot be
broken down into simpler substances with different properties. Even chemical reactions
or physical processes, like heating or crushing, cannot break it down to release a simpler
substance. There are more than 100 known elements, and 92 occur naturally around us.
The others have been made only in the laboratory.
Elements are made up of identical atoms. Anatomis the simplest and smallest particle
of matter that still retains the chemical properties of the element. Atoms are so tiny that
only the most powerful microscopes can detect them. Atoms are the building block of all
elements, and of all matter. Each element has a different type of atom, and is represented
with a one or two letter symbol. For example, the symbol for oxygen is O and the symbol
for carbon is C.
Atoms themselves are composed of even smaller particles, including: the positively charged
protons, the unchargedneutrons, and the negatively chargedelectrons. Protons and
neutrons are located in the center of the atom, or the nucleus, and the electrons move
around the nucleus. How many protons and neutrons an atom has determines what element
it is. For example, Helium (He) always has two protons (Figure2.7), while Sodium (Na)