Page 148 - Biology Form Two

Biology for Secondary Schools

proceeds to the next stage of aerobic
respiration, called Krebs’ cycle or Corks
citric acid cycle. If there is no oxygen, Conical flasks String
anaerobic respiration occurs.
Bean
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Test tubes seedling
Krebs’ cycle: This occurs in the
mitochondria. Krebs’ cycle starts with the
products of glycolysis, which are the two
molecules of pyruvic acid. The Krebs’ Pyrogallic acid Wet cotton wool Water
cycle involves a series of reactions and Conical flask A Conical flask B
produces carbon dioxide gas, water, and Figure 6.11: Experimental set-up to
ATP. demonstrate the significance of oxygen in

respiration
Activity 6.5: Investigate the
significance of oxygen in respiration 5. Cover each flask with a cork
holding a short glass tube.
Materials
Two conical flasks, cork, two test tubes, 6. Set up the experiment as shown
two glass tubes, bean seeds, cotton in Figure 6.11.
wool, pyrogallic acid, water, and string 7. Leave the experiment aside for
five days and make observations.
Procedure
1. Prepare two sets of bean seeds and 8. Prepare a short report about your

put them on a wet cotton wool in observation.
the conical flasks. Question

2. Put each set in a separate conical What conclusion can you make from
flask and label one flask as A and the experiment?
the other as B.

3. In conical flask A, suspend a test Activity 6.6: Demonstrate respiration
tube containing pyrogallic acid as in animals
shown in Figure 6.11. Pyrogallic Materials
acid absorbs oxygen in the air.
Mouse, bell jar, two conical flasks,
4. In conical flask B, put a test tube lime water, soda lime, thistle funnel,
with water. corks, delivery tubes, filter pump, and
petroleum jelly

142 Student’s Book - Form Two

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