15

A single carrot contains about one hundred

different kinds of phytochemicals—substances that plants

manufacture as part of their life processes. You may have heard

of beta-carotene, which gives carrots, pumpkins, and some

other fruits and vegetables their orange-yellow color. Dark green

leafy vegetables like spinach contain it too. Your body uses

beta-carotene to make vitamin A, which is required for pigments

important in vision and for healthy bones and teeth. Eating foods

rich in beta-carotene and some other phytochemicals also may

help ward off heart disease and certain cancers. On the other

hand, taking in too much beta-carotene—from supplements,

say—can cause digestive problems and even increase the cancer

risk in people who smoke. In this chapter we survey some simple

chemical basics that relate to the study of human biology—

including how certain substances serve as vital nutrients, present

health hazards, or both.

Chemistry of Life

2

DNA guides the processes that assemble atoms into the

parts of cells, and eventually into whole organisms (1.1–1.3).

Atoms are the nonliving raw materials for building living

things (1.3).

Properties of water are important in mechanisms that help

maintain homeostasis (1.1, 1.7).

Key ConCepts

LinKs to earLier ConCepts

Atoms and Elements

Atoms are the basic units of matter.

Each chemical element consists of a

single type of atom. Bonds between

atoms form molecules. Sections

2.1–2.4

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Bottom: Photodisc/Getty Images

Water and Body Fluids

Life depends on properties of water.

Substances dissolved in the water

of body fluids have major effects on

all body functions. Sections 2.5–2.7

Biological Molecules

Biological molecules include car-

bohydrates, lipids, proteins, and

nucleic acids. All contain atoms

of the element carbon. Sections

2.8–2.13

Homeostasis Preview

In this chapter we discuss two topics that bear directly on the

body’s ability to maintain the internal stability of homeostasis.

These are the properties of water and changes in the chemical

makeup of body fluids.

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