Which type of seeker is defined by having an organic radar transmitter and receiver?

The correct choice is an active seeker, as it is characterized by having its own organic radar transmitter and receiver. This enables the seeker to emit signals and then analyze the reflected echoes to determine the range, speed, and angle of the target. The independence provided by the internal transmitter and receiver allows for greater accuracy in tracking moving targets and enhances target acquisition capabilities.

By using its own radar system, an active seeker can illuminate a target and perform tracking while being less reliant on external sources, which can be a significant advantage in combat scenarios. This autonomously functioning system is particularly beneficial in environments where electronic countermeasures by the enemy might disrupt signals from other types of seekers.