Final answer:
Yes, it is true that black, green, oolong, and white teas all contain caffeine. The presence of caffeine varies among these teas and can provide stimulant effects by affecting neurotransmitter activity.
Step-by-step explanation:
The statement that black, green, oolong, and white tea all contain caffeine is true. These teas are all derived from the leaves of the Camellia sinensis plant, and the presence of caffeine in these teas varies depending on factors like the part of the plant used, the level of fermentation, and how the tea is processed.
Caffeine in teas is known to act as a stimulant by blocking the activity of adenosine, which affects neurotransmitter activity in the brain and can result in increased alertness and wakefulness.
An effective dose of caffeine is approximately 200 mg, which is about the amount found in two cups of strong coffee or tea.