Why is it important not to open the lids of the Petri dish at the end of the experiment?

Why is it important not to open the lids of the Petri dish at the end of the experiment?

It does not prevent contamination, but slows its growth. Consequently contamination may go undetected until the cultures are incubated.

What is the purpose of holding the lid over the agar plate while inoculating?

Petri dish lids prevent dust from falling directly onto plates but allow diffusion of air around the edges. There are no direct air currents into the plate, and to enter, dust particles would have to rise vertically more than a centimeter. This does not often occur because of the density of the particles.

Why should the lid never be left open on a plate or tube?

Keep in mind that Petri dish lids prevent particulate matter and airborne bacteria from contacting the plate surface, while allowing the diffusion of air around the edges. Whenever a plate lid is removed, it should be held over the plate as a shield.

Why is it important for you to keep your media closed except only while inoculating fresh media?

Why is it important for you to keep your media closed except only while inoculating fresh media? To prevent the entrance of contaminants into your culture and the entrance of the culture into the environment.

Why did you not seal the plate completely?

Reason – The lid stops additional unwanted bacteria in the air contaminating the plate. Do not fully seal the lid, as this will stop oxygen reaching the bacterium, and this may encourage harmful anaerobic bacteria to grow.

Why is it important to invert the petri plates during incubation?

Petri dishes need to be incubated upside-down to lessen contamination risks from airborne particles landing on them and to prevent the accumulation of water condensation that could disturb or compromise a culture.

What is the purpose of flaming the loop before and after each use?

A wet loop with bacteria on it should first be held in the inner part of the flame to avoid spattering, and then heated until red hot in the outer part of the flame. Always flame the loop immediately before and after use! Allow it to cool before picking up an inoculum of bacteria (or you will kill the bacteria).

Why is it important to flame your inoculation loop before you do each streak on the agar plate?

Don’t forget to sterilize. Flame the loop or use a new disposable loop after you streak each quadrant. Using a new or sterilized loop allows you to effectively dilute the inoculum on the plate and obtain isolated colonies by spreading the inoculum thinner and more evenly.

Why is it important to flame the loop between streaks?

Flame the loop or use a new disposable loop after you streak each quadrant. Using a new or sterilized loop allows you to effectively dilute the inoculum on the plate and obtain isolated colonies by spreading the inoculum thinner and more evenly.

What is the main purpose of the streak plate procedure?

A streak plate involves the progressive dilution of an inoculum of bacteria or yeast over the surface of solidified agar medium in a Petri dish. The result is that some of the colonies on the plate grow well separated from each other. The aim of the procedure is to obtain single isolated pure colonies.

Why do we put the plates in the incubators at 25 C and not higher?

Inoculated agar plates are incubated at 25°C in school laboratories for no more than 24–48 hours. This encourages growth of the culture without growing human pathogens which thrive at body temperature (37°C).

Why is it important for you to flame your loop between inoculations?

To be properly sterilized, both the wire and the loop portions of the inoculating loop must be heated until red-hot. The non-glowing wire could still contain live bacteria that might contaminate the student’s cultures. The hot loop may create aerosols when it touches the culture.

How can I prevent my students from opening the plates?

8 You can seal plates around the whole circumference just before viewing if you think there is any risk that your students will open the plates. Or you can stop the growth of a culture completely by placing a piece of filter paper into the lid of the inverted plate.

Why are the plates incubated upside down in the laboratory?

See CLEAPSS Laboratory Handbook 15.2.10. 5 Plates are incubated upside down (agar up), so that condensation does not drip onto the plate and interfere with the developing microbes.

Why do I not see spots after the plate is developed?

If the solvent level in the developing jar is deeper than the origin (spotting line) of the TLC plate, the solvent will dissolve the compounds into the solvent reservoir instead of allowing them to move up the plate by capillary action. Thus, you will not see spots after the plate is developed.

How should inoculated plates be taped before incubation?

4 All inoculated plates must be taped before incubation to ensure they cannot be opened accidentally. Do this by fixing with 2 or 4 short strips of adhesive tape at opposite edges of the dish. Do not seal completely as this may promote the growth of anaerobic pathogens or prevent normal growth by restricting diffusion of oxygen.