Question

Results A. Effect of UV Radiation Record the results for each plate at follows (see images below): (-) no growth 1+ light growth 2+ medium growth 3+ heavy growth Also, note any differences in appearance of growth on cach of the plates. 15 30 60 ates)

Answer 1

1. No, UV exposure with the lid on did not have any effect on bacterial growth as uv does not penetrate through glass or plastic.

2. From the given plates lid off 0 sec =+3 ( heavy growth) lid off 15 sec= +2 ( medium growth) and lid off 30 and 60 sec =+1 ( light growth) and. Lid on 60 sec =+3 ( heavy growth). The lowest growth is in case of exposure for 60 sec without lid.

3. In case of exposure for lesser time , the colonies are more sense and with increase in exposure time the colonies are rather scattered.

4. Exposure to UV results in the formation of thymine dimers in the bacterial DNA, and thus transcription and protein formation in bacteria is inhibited and so the bacteria cannot survive or divide any further.

1. A. Hospitals are home for a wide variety of pathogenic strains, as patients with different diseases visit. Exposure of rooms to UV when not in use prevents the growth of such bacteria and other microorganisms by the above mentioned mechanism and thus helps in sterilization of the rooms.

B. Uv lights are used only when the room is not in use as exposure to UV can cause mutations in human DNA as well which might lead to diseases such as cancer. Hence sterilization of rooms with UV is done in the absence of humans.

2. If the plates were exposed to visible light alone there will be heavy growth of bacteria.

3. Since heavy growth was observed in plate with lid on, it can be assumed that UV light didn't pass through the lid and thus didn't affect the growth of bacteria.

4. It is essential to expose the bacteria for different time durations as shorter exposure time still allows the growth of few colonies, hence the exposure time should be optimised to completely prevent bacterial growth and achieve sterilization.