You observe a plant on your windowsill that is growing at an angle toward the outside. this is an example of a living thing

response to stimuli / tropism

Explanation:

The plants and animals always respond to stimuli. It is an innate character of all living things. When a bright light falls on the eye, it closes immediately. This is responding to the stimuli. When someone touches the leaves of touch-me-not plants it closes its leaves due to the external stimuli.

The plants respond to the light. Because it does photosynthesis in the presence of light. Therefore, the leaves and branches of the plants always bend towards the light. This process is called phototropism.

Similarly, the roots of the plants move towards gravity under the ground. This is called geotropism.

Besides phototropism and geotropism, other types of stimuli are there - hydrotropism(response to the water), chemotropism(response to certain chemicals).

That's why the plants growing on the windowsill move towards outside where light comes.