Biology 12

SKILL FOCUS

Performing and recording

Analyzing and interpreting

Communicating results

Investigation 5 • B

158 MHR • Unit 2 Homeostasis

Pre-lab Question

How does the ear interpret sound waves?

Problem

How does distance affect hearing?

Prediction

Predict at what distance a person can no longer reliably

hear a series of numbers.

Materials

paper

container without a lid

Procedure

1.Select a quiet area that has a large amount of space

(such as an empty hallway).

2.On separate pieces of paper, write a series of five

random numbers. Be sure there is an equal

distribution of one-, two-, three-, and four-syllable

numbers in each group.

3.Place the pieces of paper in a container.

4.The person who chooses the numbers will read out

one group of five numbers to a partner who is 3 m

away. It is important that the reader try to maintain

the same tone and volume of voice throughout the

experiment.

5.The partner will write down the numbers he or she

hears.

6.Keep repeating the procedure at 3 m intervals until

the partner can no longer hear anything intelligible.

7.Graph the number of mistakes versus the distance

in a scatter plot. (Your teacher will distribute a

handout related to scatter plots.)

Post-lab Questions

1.At what distance could your partner no longer hear

the numbers reliably?

2.Compare your results with those of other lab groups

in the class. What are some of the reasons for

variation in the data?

Conclude and Apply

3.How does distance affect a person’s ability to hear

sounds?

4.What do you think would happen if you tried this

experiment outside? Explain your answer.

How Do We Hear?

Merkel discs, have flattened endings that respond

to light touch. There are also nerve endings wrapped

around hair follicles — they detect movements of

the hairs.

Other receptors, as shown in Figure 5.19, are

dendrites that are associated with specialized

structures. Meissner’s corpuscles respond to light

touch or texture. Usually found in sensitive areas

such as the fingertips, they allow you to tell the

difference between, for example, cotton and

leather. Krause end bulbs are similar to Meissner’s

corpuscles but are found in mucous membranes.

Pacinian corpuscles have a series of layers and

respond to deep pressure, stretching, tickling, and

vibration. Ruffini endings respond to heavy touch,

pressure, and stretching of the skin as well.

Meissner’s and Pacinian corpuscles are receptors

that initiate a rapid series of nerve impulses when

first stimulated. Other receptors may continue to

send impulses, but all are subject to adaptation.

Adaptationis the process by which a receptor

responds to a change in the environment, but if the

stimulus continues over a long period of time, we

lose awareness of it. This response explains why

we are aware of our clothes when we first put them

on, but after a few minutes we do not notice them.

In some cases the adaptation is a function of the

receptor, and in other cases the brain filters out the

sensations from our consciousness.

The fact that the skin is exposed to the outside

world presents a challenge in terms of maintaining

homeostasis. The skin is exposed to many hazards

that result in cuts, burns, and bruises, but the body

has a mechanism to repair them, as shown in

Figure 5.20 on page 160.