Putting into practice what we have learnt
TIME PASSES quickly when you are having fun! I wish I could have seen your faces when you read that first sentence! Guess what, we are at the penultimate lesson for the 2018-2019 school year. Soon, those of you who are in grade 11 will be writing your exams. I hope that you have been working hard and are well prepared.
In this week’s lesson, as well as in the final one, we will be looking at ways to approach Question 1 on Paper 02 of your biology exam.
Question 1 seeks to test your knowledge of the practical principles of the subject and carries the most marks. Questions are based on topics such as diffusion and osmosis, enzymes, transpiration, respiration and photosynthesis. Practical skills such as the construction of tables to record data, the analysis of data recorded in graphs, construction of graphs from given data, and the planning and designing of experiments are also tested.
This means that if you have not been paying attention to the practical side of the subject, you are going to have difficulty answering Question 1.
EXAMPLES OF THE DIFFERENT TYPES OF QUESTIONS
The following graph shows the effect of temperature on the rate of respiration in yeast cells. Construct a table to show the data that is recorded in the graph. (4 marks)
In order to answer the question and obtain full marks, you will need to be able to interpret the graph and to use the information to construct a table.
CONSTRUCTED TABLE
TABLE SHOWING THE EFFECT OF TEMPERATURE ON THE RESPIRATION IN YEAST CELLS
Have you noticed that the requirements for constructing a table have been met? What are they?
1. There is a title, written in capital letters and placed at the top of the table.
2. The independent variable, the temperature, is placed in the first column; the second column contains the dependent variable, the number of bubbles produced per minute.
3. All units are placed in the headings.
4. All the data have the same number of decimal places.
5. The table is enclosed.
6. The values in the table match those on the graph.
EXAMPLES
(i) The graph shown describes the rate of respiration in yeast cells and is similar to the graph showing the effect of temperature on the rate of enzyme action. Suggest a reason for this.
Answer: Respiration in yeast is controlled by enzymes and, hence, any factor which affects the action of enzymes, e.g., temperature, will affect respiration in the same way.
(ii) Describe the trend in the rate of respiration as shown in the graph.
Answer: The rate of bubble production increases between 10oC and 40oC and decreases between 50oC and 70oC where it stops, as there is no production of bubbles.
(iii) Suggest a reason for this.
Answer: Respiration is controlled by enzymes, and enzymes are proteins and begin to become denatured at temperatures above 40oC; hence, there would be fewer enzyme molecules to react with the respiratory substrate. At 70oC, all the enzyme molecules are denatured and the respiration stops. Enzymes are proteins, and at high temperatures the active sites of the enzymes are altered, causing them to become denatured, preventing substrate molecules from binding with them.
(iv) (a) Is there an optimum temperature for the production of the bubbles?
Answer: Yes.
(b) If your answer to (a) is yes, what is the temperature?
Answer: 40oC.
(v) Create a list of the apparatus and materials that could be used to carry out this experiment.
Answer: (any 5 [mix of apparatus and materials] from this list will be accepted). Boiling tubes, water baths, thermometers, delivery tubes, timer, measuring cylinders, bungs with holes to fit delivery tubes, yeast solution (specific concentration), sugar, oil.
(vi) What could be a source of error for this experiment?
Answer: Temperature in the water bath not kept constant, inaccurate measurement of temperature.
(vii) Suggest a possible hypothesis for this experiment. Answer: Respiration is controlled by enzyme catalysed reactions, hence, the rate of respiration will increase up to the temperature at which the rate is optimum.
See you next week, and happy studying!
“Anyone who has never made a mistake has never tried anything new.” – Albert Einstein