Cells called melanocytes that lie deep in the epidermis produce a pigment, called melanin, that gives skin its color. Exposure to ultraviolet light—from the sun or a tanning bed—causes melanocytes to produce more melanin, which they pass along to the skin cells above them, yielding a suntan. But why would sun exposure prompt this increased melanin production? What is the function of a tan, in other words?

To survive, the human body needs to maintain ________ and does so primarily through the means of self-regulation known as ______.

a. high energy output; positive feedback

b. adequate fat layers; exocrine secretion

c. bone density; muscle contraction

d. homeostasis; negative feedback

e. nerve signal transmission; hormonal secretion

The four basic types of tissue in the human body are:

a. epithelial, connective, muscle, nervous.

b. epithelial, blood, muscle, nervous.

c. skin, bone, muscle, nervous.

d. skin, connective, heart, nervous.

e. epithelial, bone, connective, muscle.

Muscle fibers that are striated and voluntary are found in:

a. cardiac muscle.

b. skeletal muscle.

c. smooth muscle.

d. rough muscle.

e. all four types of muscle.

Hormones and the glands or cells that secrete them make up the:

a. cardiovascular system.

b. respiratory system.

c. lymphatic system.

d. urinary system.

e. endocrine system.

Surface epidermal cells of the skin:

a. rapidly divide and are filled mostly with keratin.

b. never divide and remain in place through adult life.

c. rapidly divide and are in place only a short time.

d. are dead and filled with keratin.

e. rapidly divide and are filled with fat.

Cells called _____ build bone tissue, _____ maintain it, and _____ break it down.

a. osteoblasts; osteoclasts; osteocytes

b. osteoclasts; osteons; osteoblasts

c. osteoblasts; osteocytes; osteoclasts

d. osteons; osteocytes; osteoclasts

e. osteocytes; osteoblasts; osteoclasts

The essence of muscle contraction is that thick and thin muscle proteins:

a. slide past each other.

b. link irreversibly with each other.

c. are short enough to respond quickly.

d. stay completely separate.

e. pull in opposite directions.

No skeletal muscle can contract without first:

a. receiving a hormone signal.

b. checking on the status of nearby skeletal muscles.

c. lining up its actin and myosin filaments.

d. receiving a nervous system signal.

e. linking to a bone.