Page 1 Summary: Introduction to Survival and Response
This page introduces the fundamental concepts of survival and response in organisms, focusing on taxes and kineses. It begins by defining key terms essential for understanding the topic.
Vocabulary:
- Stimulus: A detectable change in the internal or external environment of an organism.
- Response: The result of a stimulus detected by a receptor, which may involve movement or behavioral change.
- Receptor: An organ or specialized cell that can detect the change causing the stimulus.
- Taxis: A simple response whose direction is determined by the direction of the stimulus.
- Kinesis: A response where the organism doesn't move directly towards or away from a stimulus but changes its speed and rate of direction change.
The page explains that the ability to respond to stimuli is a characteristic of life that enhances survival chances. It outlines the basic process of stimulus and response:
stimulus → receptor → coordinator → effector → response
This process can involve either chemical control or nerve cells. The text emphasizes that organisms with more appropriate responses have a greater chance of survival and passing on their genes.
Highlight: The ability to respond to stimuli is crucial for survival, allowing organisms to avoid dangers and find resources.
The page then delves into more detailed explanations of taxes and kineses:
Taxes are classified as positive (towards the stimulus) or negative (away from the stimulus) and are named based on the nature of the stimulus.
Example: Single-celled algae exhibit positive phototaxis by moving towards light, which is essential for their photosynthesis and survival.
Kineses are described as responses where the organism's movement is not directly towards or away from the stimulus. Instead, the organism changes its speed and rate of direction change.
Highlight: Kineses are particularly important when a stimulus is less directional, such as with humidity or temperature gradients.
The page concludes with an example of kinesis in woodlice, illustrating how this behavior helps them maintain optimal moisture conditions and increases their chances of survival.
