Lab 20 - Physical methods of control (UV)

Question 1

what is the electromagnetic spectrum?

Answer 1

a spectrum of “light” or electromagnetic radiations

Question 2

what are electromagnetic radiations?

Answer 2

different wavelengths with different energies

Question 3

radiations with lower wavelengths have ____ energy

Answer 3

radiations with lower wavelengths have higher energy

Question 4

what do radiations do to DNA?

Answer 4

damage DNA

Question 5

what is ultraviolet (UV) light?

Answer 5

non-ionizing radiation

Question 6

what does UV do?

Answer 6

it forms thymine dimers - it interferes with DNA replication causing mutations and possibly leads to cell death

Question 7

what are the 2 repair pathways from UV damage to DNA?

Answer 7

photoreactivation and excision repair

Question 8

does UV light penetrate far into solid material? what is it used to disinfect?

Answer 8

no, UV light does not penetrate very far into solid material, so it is used to disinfect smooth surfaces and clear liquids

Question 9

what is UV disinfection employed for?

Answer 9

UV disinfection is employed in food service settings, forensic laboratories, and water treatment facilities.

Question 10

what are x-rays and gamma rays?

Answer 10

ionizing radiations

Question 11

are x-rays and gamma rays energetic? what happens?

Answer 11

they are so energetic that they convert water molecules to highly reactive hydroxyl radicals that damage DNA and other cellular components

Question 12

what do the hydroxyl radicals in x and gamma rays cause?

Answer 12

the hydroxyl radicals cause double-stranded DNA to break, resulting in mutations that make the microorganism unable to survive and reproduce

Question 13

how far do x and gamma rays penetrate?

Answer 13

they penetrate significantly into most normal materials

Question 14

what are x and gamma rays used for?

Answer 14

they are used to sterilize medical devices and to reduce microorganism contamination of meats, fresh fruits, vegetables, and other foods.

Question 15

what did we do for the experiment?

Answer 15

1. We divided the plates into two, control and UV light.
2. We used a sterile swab and applies the bacteria to the entire surface 3 times in all different directions.
3. We covered the control part with an index card and put the plate under a UV light.

Question 16

what were our results?

Answer 16

• in Staphylococcus epidermidis, there was a lot of growth in the control half and less growth on the UV half. But there was still growth on both halves.
• in Bacillis subtilis, there was equal growth on both sides.
• In serratia marcescens, there was a lot of growth on the control, but a little bit of growth on the UV side.

Question 17

why was there equal growth on both the control and UV half of B. subtilus?

Answer 17

because it produces endospores

Question 18

which bacteria were affected by bacteria? which weren’t?

Answer 18

S. epidermidis and Serratia marcecens were affected by UV.
B. subtillus wasn’t affected by UV