Final answer:
Humans directly respond to environmental changes by shivering when cold and sweating when hot, which are examples of responses to external stimuli. Organisms display responsiveness in various ways to ensure survival and maintain homeostasis. Plants, for instance, change their growth patterns in response to light, a phenomenon known as photomorphogenesis.
Step-by-step explanation:
The student's question pertains to how organisms respond to internal and external stimuli. An internal stimulus originates within an organism, like a plant absorbing water to prevent wilting. In contrast, an external stimulus comes from the organism's environment, such as light causing a plant to bend towards it or a human shivering in response to cold. The most clear example of how humans can respond directly to a change in the environment is by shivering when cold to generate heat, or sweating when hot to cool down. These responses help maintain homeostasis, which is the stability of internal conditions.
Responsiveness is a fundamental trait of living organisms, demonstrated by their ability to adjust to environmental changes. This may involve moving towards beneficial stimuli like food or away from harmful ones. Physical actions in response to environmental factors are part of an organism's survival mechanisms.
In the context of plants, they exhibit behaviors like photomorphogenesis and photoperiodism, which are growth and developmental responses to light, showcasing their sophisticated use of environmental cues despite being stationary organisms.