B1.5 The respiratory system, breathing and respiration - Respiration in yeast

Question 1

Aerobic respiration

Answer 1

Cell respiration which happens in the presence of oxygen in the mitochondria of the cell, in animals and plants

Question 2

Anaerobic respiration

Answer 2

Cell respiration which happens in the absence of oxygen

Question 3

Fermentation

Answer 3

Anaerobic respiration in plant and yeast cells which produces ethanol and carbon dioxide

Question 4

Word equation for fermentation

Answer 4

Glucose -> carbon dioxide + ethanol (+energy)

Question 5

Uses of fermentation

Answer 5

The manufacture of bread and alcoholic drinks

Question 6

Glucose

Answer 6

A simple sugar that is an important energy source in living organisms, the only reactant for the fermentation reaction

Question 7

Carbon dioxide (CO2)

Answer 7

A byproduct of fermentation, can be used to make bread and contributes to alcohol production

Question 8

Anaerobic respiration in yeast practical

Answer 8

Anaerobic respiration can be demonstrated by removing oxygen from the surroundings of yeast, the products of fermentation can then be observed

Question 9

Removing oxygen

Answer 9

Adding an oil layer will prevent a solution of yeast obtaining oxygen from the air

Question 10

Sterilisation

Answer 10

It is important that the equipment and glucose solution is sterile, as this could lead to contamination which would affect the results of the experiment

Question 11

Temperature

Answer 11

Should be controlled and kept warm for yeast fermentation, a set temperature condition can be achieved using a water bath

Question 12

Yeast solution

Answer 12

The solution that is required for this practical consists of yeast, water and sterile glucose, with a suspended layer of oil above the solution

Question 13

Acclimatisation

Answer 13

It is important that the yeast solution is given time to settle, particularly when there may still be oxygen present in the solution which would lead to aerobic respiration and affect the results

Question 14

Bung and delivery tube

Answer 14

The yeast solution should be in a boiling tube with a bung attached to a delivery tube, this allows the gas products of fermentation to be collected

Question 15

Limewater test

Answer 15

A solution that can confirm the presence of carbon dioxide, if CO2 is bubbled in limewater it will cause the solution to change from colourless to a milky or cloudy precipitate

Question 16

Water displacement

Answer 16

A method that can be used to measure the rate of fermentation by how much carbon dioxide is produced, carbon dioxide will displace water from an inverted measuring cylinder that can be recorded

Question 17

Carbon dioxide bubbles

Answer 17

Yeast will produce bubbles of carbon dioxide when undergoing fermentation, CO2 gas will travel down the delivery tube and will form bubbles in an inverted measuring cylinder that is full of water

Question 18

Measuring rate of fermentation

Answer 18

By measuring how much water has been displaced from the measuring cylinder over a set period of time, the volume of carbon dioxide and the rate of carbon dioxide production (or fermentation) can be determined

Question 19

Dependent variable

Answer 19

The variable that is measured, in this case it is the rate of fermentation or volume of carbon dioxide produced by yeast for a set duration

Question 20

Independent variable

Answer 20

The variable that is changed, in this case it could be the temperature that the yeast is fermented at or the type of sugar that is used as a food source for yeast

Question 21

Control variables

Answer 21

The variables that should be kept the same, in this case it could be the time each test is recorded for, the volume of solutions, the concentration of glucose

Question 22

Expected results for changed temperature

Answer 22

The rate of fermentation, which is the amount of carbon dioxide produced over a set time, will be greatest when yeast is kept at an optimum temperature