SKILL FOCUSInitiating and planningPredictingIdentifying variablesPerforming and recordingAnalyzing and interpretingInvestigation
DESIGN YOUR OWN
5 • CSowbugProblem
How can you demonstrate a particular invertebrate’s
responses to a chosen stimulus?Hypothesis
Based on your research, formulate a hypothesis stating
how the invertebrate will respond to the stimulus. The
hypothesis will form the basis of your experimental
design.CAUTION: Treat your invertebrate organism with
respect. Wash your hands after completing the
experiment.Invertebrate Response to External Stimuli
Different species have developed diverse homeostatic systems in order to survive.
These systems are adaptations that are the result of natural selection — they
developed because they were successful in the organism’s environment.
Therefore, a particular stimulus may result in different responses in different
species. To be able to conduct an experiment on the behaviour of an organism,
you should know about its natural environment and physiology. For example,
some invertebrate species are attracted to light, while others avoid it. The same
applies to water, heat, and a variety of other stimuli. This activity can be carried
out using any one of a number of invertebrate species, but one possibility is the
sowbug (Porcellio scaber), shown below.160 MHR • Unit 2 Homeostasis
blood clot scabFigure 5.20When a skin injury extends into the dermis, the first
reaction of the body is to restore the continuity of the skin. This
prevents the invasion of harmful bacteria that live on the skin.Blood flows out of
the wound until a
clot forms over it.A The wound is closed by the
formation of a scab. The scab
unites the wound edges to prevent
bacteria from entering. Blood
vessels dilate, and infection-fighting
cells speed to the wound site.