An apparatus for containing a liquid biological sample and for performing a biological process thereon comprises a sample area for receiving the sample, at least one reaction area in fluid communication with the sample area, a pneumatic area in pneumatic communication with the reaction area and the sample area, and a pneumatic port in the pneumatic area for connection of the apparatus to a pneumatic aspiration/dispensing pipette. The pneumatic aspiration/dispensing pipette provides for controlled flow of the liquid biological sample between the sample area and the reaction area. To reduce evaporative loss of the sample from the apparatus, a sample tower is provided in fluid communication with the sample area. A similar tower may be provided at the pneumatic port to reduce evaporative loss through the pneumatic area. A restricted orifice between the sample tower and the sample area holds the liquid sample in place during removal of the sample from the apparatus, counteracting the tendency of the liquid bolus to flow back toward the reaction area due to capillary forces. Also disclosed is a novel sealing arrangement which provides an effective pneumatic seal between the pneumatic port and a pneumatic aspiration/dispensing pipette without requiring the apparatus to include a separate "O" ring or other type of discrete sealing device.