food tests

Question 1

reagent for reducing sugar

Answer 1

Benedict’s

Question 2

what does benedicts solution test for

Answer 2

glucose

Question 3

positive result of glucose

Answer 3

Brick red precipitate

Question 4

reagent for starch

Answer 4

iodine

Question 5

what does iodine test for

Answer 5

starch

Question 6

positive result for starch

Answer 6

blue-black

Question 7

reagent for protein/amino acids

Answer 7

biuret (a mixture of sodium hydroxide and copper sulfate)

Question 8

what does biuret test for

Answer 8

protein

Question 9

positive result for protein

Answer 9

lilac/purple

Question 10

reagent for fat

Answer 10

ethanol

Question 11

what is distilled water and ethanol used to test for

Answer 11

fat

Question 12

what is the positive result for fat

Answer 12

white emulsion (cloudy)

Question 13

give a reason for each of the following steps in the method, a thin layer of onion epidermis is used

Answer 13

help see individual cells

Question 14

give a reason for each of the following steps in the method, iodine solution is added to the onion epidermis

Answer 14

stain / see the parts of the cell

Question 15

give a reason for each of the following steps in the method, the cover slip is lowered onto the onion epidermis at an angle

Answer 15

prevent / reduce air bubbles

Question 16

cm -> micrometre

Answer 16

x 10000

Question 17

(of microscope image)

Answer 17

• include the magnification / scale
• do not draw overlapping cells
• draw (wider) cell walls
• draw all the cells present
• draw correct cell shapes
• label cell parts

Question 18

explain how:
- the immune systems of animals respond to a vaccination
- the immune response in farm animals prevents an outbreak of food poisoning in humans (6)

Answer 18

vaccination of animal
- white blood cells produce antibodies against salmonella
- antibodies are specific, complementary to salmonella, antigens
- antibodies bind to salmonella, antigens
secondary response in animal
- if infected antibodies are produced quickly or in large numbers
- white blood cells or antibodies would kill salmonella
- fewer pathogens in animals or in animal products
prevention of food poisoning in humans
- fewer pathogens eaten or in food
- number of bacteria never reaches a high enough level for infection to develop
- fewer toxins produced

Question 19

describe two aseptic techniques the scientists should have used in the investigation (petri dish bacteria)

Answer 19

• disinfect hands, work surface
• sterilise petri dish or culture medium
• pass inoculating loop through a flame

Question 20

explain why scientists use 37 °C but students must use 25 °C to incubate bacteria (3)

Answer 20

• 37 °C is human body temperature
• bacteria grows best at 37 °C
• 25 °C reduces growth of bacteria that are harmful to humans

Question 21

describe how the results in the figure above could be used to obtain a quantitative comparison of antibiotics A and B (petri dish colony)

Answer 21

• measure the diameter / radius of each clear area
• calculate / measure the area of each clear area

Question 22

suggest why antibiotic B no longer had an effect

Answer 22

bacteria must be resistant

Question 23

antibiotics treat food poisoning because they kill Salmonella bacteria inside the human body, some antibiotics work because they damage the bacterial cell wall, the bacteria die because the cells burst, explain why the cells burst (3)

Answer 23

• water enters the cell
• by osmosis
• no cell wall cannot withstand pressure of water