To Prepare And Show The Production Of Alcohol By Yeast

Question 1

Why must this investigation be carried out under anaerobic conditions?
(2)

Answer 1

Alcohol is only produced under anaerobic conditions

If aerobic conditions no alcohol will be produced

Question 2

How did you ensure conditions were anaerobic?

Answer 2

Layer of paraffin oil on top of boiled glucose solution and yeast

Question 3

Suggest a suitable control for this experiment.

Answer 3

Add no yeast

Question 4

How did you know fermentation was taking place?

Answer 4

Bubbles of carbon dioxide will be seen in the limewater

Question 5

Why might limewater be used in this experiment?

Answer 5

Limewater turns milky in the presence of carbon dioxide

Question 6

Name the molecule from which lactic acid is produced by glycolysis.

Answer 6

Pyruvate (pyruvic acid)

Question 7

In what part of the cell does the Krebs Cycle occur?

Answer 7

Mitochondrion

Question 8

Suggest how you would know the glucose is used up.

Answer 8

No more bubbles are produced

Question 9

Explain why boiled yeast is suitable as a control for this experiment?

Answer 9

Heat denatures enzymes

Question 10

Give an alternative control other than boiled or no yeast.

Answer 10

Distilled/deionized water

Question 11

What affect does the absence of limewater have on the experiment?

Answer 11

No affect on experiment

Question 12

Explain why the absence of limewater doesn’t affect the experiment?

Answer 12

Limewater is only present to test for carbon dioxide

Question 13

State one factor apart from temperature that must be kept constant when repeating the experiment, what needs to be the exact same when repeating the experiment.
(2)

Answer 13

Same concentration of glucose

Same concentration of yeast

Question 14

Name one industry that depends on fermentation.

Answer 14

Brewing/baking

Question 15

Name one end product of the brewing industry.

Answer 15

Alcohol

Question 16

Name one substance that yeast can use to make ethanol.

Answer 16

Sugar

Question 17

What substance, other than ethanol, is produced by the fermentation by yeast.

Answer 17

Carbon dioxide

Question 18

Suggest a suitable temperature for this experiment.

Answer 18

30 degrees Celsius

Question 19

Why does the production of ethanol eventually stop?

3

Answer 19

Sugar is used up

Alcohol kills yeasts

Yeast dies

Question 20

Name the reagent(s) used to demonstrate that alcohol (ethanol) has been produced and the colour change associated with a positive test,
(2)

Answer 20

Acidified potassium dichromate - orange to green

Iodoform test -Potassium iodide solution - colourless - then sodium hypochlorite solution - brown -orange then colourless - heat at 50-60 degrees then yellow crystals form

Question 21

Describe the iodoform test.

7

Answer 21

Filter the solution

Place some of filtrate into a test tube

Add an equal volume of potassium iodide solution - colourless

Add sodium hypochlorite solution - brown-orange colour then becomes colourless

Place test tube in a water bath at 50-60 degrees for 4 to 5 minutes

Remove test tube and allow to cool

Pale yellow crystals form of a chemical called iodoform which indicates ethanol is present

Question 22

Describe the discontinued test for alcohol.

3

Answer 22

Acidified potassium dichromate is added to the filtered solution

The test tube is placed in a warm water bath

If alcohol is present the colour changes from orange to green

Question 23

What substrate did you use?

Answer 23

Sugar/glucose