Respiration questions (cont'd)
Monacia Williams, Contributor

Well, hello again! Last week I included in the lesson some questions on anaerobic respiration and I invited you to write answers for them. Did you? I hope so because through the exercise you are able to test yourself to determine how well you understand the material that you are studying. As you study the different topics you need to practise answering as many questions as you can. When you do this you are guaranteeing that you will get a good grade in the exam.

Before we begin to review the answers, let us take another look at the question. You must ensure that you understand the question before you attempt to answer if.

Did you notice that:

• there were two sets of apparatus?
• while both sets of apparatus had yeast in glucose solution, Apparatus Y had boiled, cooled glucose, while Apparatus X had only glucose?
• Apparatus Y had a layer of oil on top of the mixture?

If you did, then you are on the right track! This will be of great help in answering the questions.

Now, let us see how well your answers correspond with those that I will now give.

Answers

(a)(i) Aim: To compare the rate of carbon dioxide production in aerobic and anaerobic respiration.

• (ii) What is the purpose of the oil in the test tube of Apparatus Y?
  The oil will form a barrier preventing air with oxygen from entering the yeast and glucose solution, ensuring that aerobic respiration will not take place.
• What is the purpose of the use of boiled glucose in Apparatus Y?
  Boiling removes all the air with oxygen that might have been trapped in the glucose mixture, so this ensures that aerobic respiration will be prevented from occurring.
• What is the purpose of using equal volumes of glucose solution?
  This is to ensure that the conditions in both tubes only have one variable, the presence/absence of oxygen.

(iii) One other precaution that should have been taken:

• The experimental set-up should have been placed into a water bath to avoid fluctuations in temperature.
• The solution in Apparatus Y could have been tested with diazine green indicator. This becomes pink when there is no oxygen present.

(b)(i) A better way of presenting these results would be to use graphs. This makes it much easier to compare the two sets of results.

(ii)The number of bubbles produced per minute:

• For Apparatus X, it was 3.25 bubbles per minute.
• For Apparatus Y, it was 1.2 bubbles per minute (the answers were obtained by dividing the two totals by 20).

(iii) The difference between the results in Apparatus X and Apparatus Y was due to:

• Respiration in Apparatus X was aerobic, while in Apparatus Y it was anaerobic.
• Aerobic respiration produces more carbon dioxide and produces this at a faster rate than anaerobic respiration.
• The carbon in the glucose in Apparatus X is broken down completely to carbon dioxide, while in Apparatus Y some of the carbon remains in the alcohol that is also produced.

(iv) Outline of the steps:

• Remove a small amount of the glucose.
• Add an equal quantity of Benedict's solution.
• Heat in a water bath.
• Record the colour change.

How well did you do? Very well? Congratulations! Not so well? Compare the answers and try to identify the reason(s) for the differences and work hard to eliminate those reasons. Next week, we will look at gaseous exchange in humans and plants as well as respiratory surfaces.

Remember read up on all the relevant laboratory exercises in your text. Become familiar with them; you will be glad you did!

Corporal Richard McPherson (right), of the Jamaica Constabulary Force, speaks to Cumberland High School students, Rene Allen and Kemar Adams, on the qualifications needed to become a JCF member during a career fair at Portmore Missionary Church. - Anthony Minott/Freelance Photographer