Required Practical: Investigating Animal Movement
Setup of Environmental Gradients: To test humidity, place distilled water in one half of the chamber base and a desiccant like anhydrous calcium chloride in the other. A gauze platform is placed above these to prevent the animals from coming into direct contact with the chemicals while allowing the air to reach the desired humidity.
Standardized Introduction: Introduce a significant sample size (e.g., 10 woodlice) through a central hole in the lid to ensure they start at a neutral point where both environments are equally accessible.
Temporal Monitoring: Allow the organisms to move freely for a set period (e.g., 10-15 minutes) before recording their final positions. This duration must be long enough for a response to occur but short enough to prevent total acclimation or exhaustion.
Replication and Averaging: The experiment should be repeated multiple times, cleaning the chamber between trials to remove any chemical trails (pheromones) that might influence the behavior of subsequent groups.
| Feature | Kinesis | Taxis |
|---|---|---|
| Directionality | Non-directional; random movement. | Directional; oriented to stimulus. |
| Mechanism | Change in speed or rate of turning. | Movement toward or away from source. |
| Example | Woodlice moving faster in dry air. | A moth flying toward a light source. |
Statistical Validation: Always expect to use the Chi-squared () test to analyze the results. This test determines if the observed distribution of animals in the chamber differs significantly from a theoretical 50:50 distribution (null hypothesis).
Control Variables: Be prepared to identify factors that must be kept constant, such as temperature and light intensity (when testing humidity), as these can act as confounding variables that influence animal behavior.
Handling Ethics: Mention the use of a soft paintbrush for moving organisms. This minimizes physical stress and injury, ensuring that the observed behavior is a response to the environment rather than a result of trauma.
Chemical Trails: A common error is failing to clean the chamber between trials. Woodlice can leave pheromone trails that lead others to follow them, which would skew the results toward a specific side regardless of the environmental stimulus.
Acclimatization Time: Students often record results too early. Organisms need time to detect the gradient and respond; however, waiting too long may lead to the organisms settling due to fatigue rather than preference.
Confusing Taxis and Tropism: Remember that taxis refers to the directional movement of a mobile animal, whereas tropism refers to the directional growth of a stationary plant.