Watch the following pipetting video (1min 43sec):

video
Links to an external site.

Complete the following sentences:

When drawing up volume into a pipette tip, the plunger button should be depressed to the ______
[ Select ]
Second
First
_______ stop position.

When dispensing a sample from a pipette tip, the plunger button should be depressed to the______
[ Select ]
Second
First
_______stop position.

Question

Watch the following pipetting video (1min 43sec):

video
Links to an external site.

Complete the following sentences:

When drawing up volume into a pipette tip, the plunger button should be depressed to the ______ 
[ Select ]
Second
First
 _______ stop position.

When dispensing a sample from a pipette tip, the plunger button should be depressed to the______
[ Select ]
Second
First
 _______stop position.

BlackTom AI · Accepted Answer

The question involves understanding the two-step operation of a micropipette during liquid handling.

First blank: When drawing up volume into a pipette tip, you must depress the plunger to the first stop position before aspirating. This creates the correct volume in the tip; going only to the primary (first) stop prevents drawing in too much air or liquid, and going past the second stop could introduce an over-aspiration risk or cause liquid to be drawn too far into the shaft. Therefore, the appropriate completion is 'First'.

Second blank: When dispensing a sample from a pipette tip, you should depress the plunger to the second stop position to expel all the liquid from the tip. The second stop ensures residual liquid in the tip and the tip’s bore is pushed out, maximizing accuracy and minimizing leftover liquid. Hence the correct completion is 'Second'.

Why other intuitions would be incorrect: If you used 'Second' for drawing up, you would risk drawing up too much volume or drawing liquid beyond the intended volume, compromising accuracy and potentially contaminating the pipette. If you used 'First' for dispensing, you might leave some liquid trapped in the tip, again reducing accuracy and not delivering the full intended volume. Overall, the standard practice is first stop to aspirate, second stop to dispense, which aligns with the typical stepwise control of a micropipette.

BCMB20005_2025_SM1 Week-1 Pre-Lab Quiz

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