What is photoperiodism and tropisms on plants?
Photoperiodism
Photoperiodism is the reaction of organisms to the length of day or the length of night occurring in both plants and animals.
A lot of flowers use photoreceptor proteins like phytochrome or cryptochrome to sense seasonal changes in the length of day or the length of night which send signals to the flower.
Flowering plants that have these receptors are called long-day plants or short-day plants, although the receptor is prompted by the length of the night, not the length of the day.
Tropism
Tropism is a biological phenomenon that describes the movement or turning of a plant in response to an environmental or biological stimulus. 
Light, gravity, chemicals, water, colors, temperature, and contact can influence plants to grow in a certain direction based on their need for different factors.
Plants are capable of direct physical movement directionally (taxis) or non-directionally (kinesis).
Tropism is the movement or curvature caused by an external stimulus that determines the direction of movement. External stimulus such as light or gravity can cause a plant to grow a certain direction. The plants will grow in the opposite direction of gravity, up. They will also grow towards the light. Photoperiodism is the physiological reaction of plants to the length of day or night. Plants such as short or long day plants are examples of such. Long day plants are plants that only flower when the day is longer than a certain amount of hours and short day plants are plants that will flower only when the day is shorter than a certain amount of hours.
