Biology 12

scab

new skin

cells

Materials

These will vary according to your experimental design.

Experimental Plan

1.Select an invertebrate species for your study.

Sample organisms may be found outdoors or

bought at a pet store or bait shop. After you have

made your choice, gather information on the

species to provide the background you will need to

design your experiment.

2.Choose a particular stimulus (such as heat, light,

water, etc.) that you predict will produce a

consistent response by the organisms.

3.Design an experiment that will show a positive or

negative response to the chosen stimulus by the

organisms. Be sure that your design has only one

experimental variable and that you eliminate as many

other variables as you can. Consider building an

apparatus to provide the necessary controls.

Checking the Plan

1.What will your independent variable be? What will

your dependent variable be?

2.How will you control other variables?

3.What measurements will you make?

4.How many trials will you carry out?

Data and Observations

Record your data in a suitable data table. Be sure you

have enough repetitions to make your results reliable.

Analyze

1.Did the animals in your experiment always behave in

the same way? Explain.

Conclude and Apply

2.Did the animals in your experiment show a

consistent response to the stimulus?

3.Very few experiments are free from possible sources

of error. What are some other factors that may have

affected the behaviour of the animals?

Exploring Further

4.A learned behaviour is different from a stimulus–

response reaction. How are they different?

To learn more about how certain stimuli affect

invertebrates, go to your Electronic Learning Partner.

ELECTRONIC LEARNING PARTNER

Chapter 5 The Nervous System • MHR 161

In 1998, scientists at the Salk Institute in La Jolla,

California, appeared to disprove a long-standing “fact” that

the human brain cannot grow new neurons once it reaches

adulthood. Since then, there is increasing evidence that

stem cells may be able to produce neurons. As you learned

in previous studies, stem cells are immature cells that can

divide repeatedly, producing many different kinds of tissues.

A team at McGill University in Montreal led by Freda Miller

has forced stem cells to send out neuronlike arms and to

express some of the same proteins that neurons do. They

have culled these stem cells from the skin of rats and the

scalps of adult humans. Perhaps one day researchers will

grow petri dishes full of neurons from a patient’s own skin!

The goal is to use transplanted neurons culled from skin

and bone marrow cells to repair damage caused by

Parkinson’s disease, Alzheimer’s disease, multiple sclerosis,

stroke, or head trauma.

BIO FACT

Skin cells beneath the scab begin to multiply and fill in the

gap. Eventually, the scab falls off to expose new skin. If a

wound is large, a scar may result from the formation of

large amounts of dense connective tissue fibres.

C