Paper 62 Flashcards
Starch Test 5
dissolve in water,
few drops of iodine solution,
gently shake,
blue-black is present,
straw yellow is not
Glucose/reducing sugar Test 5
dissolve in water,
add 2cm3 of Benedict’s Reagent,
heat for 2-3 min at 80C
green/red/orange is present, (depending on concentration)
clear blue is not
Proteins Test 5
dissolve in water,
add Biuret reagent,
shake,
purple/mauve is present,
clear blue is not
Vitamin C Test 3
Add1cm3of DCPIP solutionto a test tube
Add a small amount of food sample (as a solution)
A positive test will show theblue colour of the dye disappearing
Lipids (fats and oils) Test 4
mix with ethanol,
gently shake,
pour mix into equal volume of water,
milky-white emulsion if present
Balloons and string were used to collect and measure the gas produced by the yeast
cells.
Suggest another, more accurate, method of collecting and measuring the gas. 3
syringe
(bung)+(delivery tube) +inverted measuring cylinder over water
downward displacement of water in a graduated container
Indicator to show that the gas produced is carbon dioxide and give the positive test result. 4
indicator: limewater
positive result: milky / white / cloudy
OR
Indicator: hydrogencarbonate
positive result: yellow
Describe how the method could be modified to prevent a change in the temperature of a
water-bath. 4
1 use thermostatically controlled water-baths ;
2 use a Bunsen burner AND thermometer (method outlined) / use a Bunsen burner and monitor the temperature ;
3 top up with, hot water / cold water / ice, and monitor /use a thermometer ;
4 insulate the container
(iv) Successful pollination results in fertilisation and the production of seeds.
Describe how you could test the seeds to show that they contain reducing sugars.
Include the result of a positive test. 2
method: add Benedict’s solution
positive test result: red / orange / yellow / green
Plan an investigation to determine the effect of temperature on the rate of transpiration
from leaves.
You may wish to include the apparatus listed and any other apparatus that you think is
suitable in your plan:
• leafy plants
• electronic balance
• thermometer
• string
• stop-clock (9)
Cut the stem of a leafy shoot (at an angle to increase the surface area) underwater to prevent air entering xylem
Fill a straw with water. Place your finger over one end of the straw to stop the water from running out.
Still under water, put the leafy shoot into the open end of straw and seal it with putty while removing it from water while keeping finger on straw.
Above water, seal vaseline. Make sure it is airtight and watertight before removing your finger from the straw.
Calculate the volume of water in the straw
Place shoot with straw next to a heater at 30℃ and set a timer to for 1 hour
Calculate the change in the volume of water after 1 hour
Repeat experiment at 20℃ and again at 10℃. Repeat experiment with all 3 temperatures multiple times and calculate the average water lost at each temperature in 1 hour. Be sure to use the same size shoot each time.
Wear gloves when cutting stem to avoid injury
Humidity also affects the rate of transpiration from leaves.
Suggest how you could decrease the humidity that the leaves are exposed to in a
transpiration investigation.
dehumidifier
Humidity also affects the rate of transpiration from leaves.
Suggest how you could incrse the humidity that the leaves are exposed to in a
transpiration investigation. 2
bowls of hot water around apparatus / place in plastic bag
State the test that could be used to show that starch was present in a sample of bread dough.
Give a positive test result. 2
add iodine (solution / reagent) ; blue-black (colour)
Plan an investigation to determine the effect of the mass of sugar on the volume of
carbon dioxide produced by a yeast suspension. 8
Stir in equal amounts of yeast with equal amounts of water in 3 test tubes, label one A, one B & one C.
dissolve in 4g of sugar in A and 8g of sugar in B, and put no Sugar in C
Put A B and C in thermostatically controlled waterbaths, make sure both temperatures are 37℃ and remain constant with a thermometer
Use 3 gas syringes to measure the volume of gas produced by A, B and C
Start a timer for 30 minutes
After 30 minutes, record the change in the syringe plunger positions
Repeat experiment multiple times and record the average results for each temperature
wear goggles and gloves to avoid burns from water baths
The student repeated the experiment described in 2(b) at a higher temperature. The
student left the plant for ten minutes at the new temperature before starting to measure
the rate of bubble production.
Suggest why the student waited for ten minutes before taking measurements.
idea of plant equilibrating to the new conditions
