Page 151 - Biology Form Two

Biology for Secondary Schools

Obligate anaerobes from contracting and relaxing due to
These are organisms which can only its toxicity and can also cause pain.
live and respire in the absence of When this occurs, oxygen is required
oxygen. They die in the presence of to oxidise lactic acid into water and
FOR ONLINE READING ONLY
oxygen. Examples include Bacteroides carbon dioxide. The oxygen required
and Clostridium species. in such a situation is known as oxygen
debt.
Facultative anaerobes

These are organisms which can respire Oxygen debt causes the animal to
both in the presence and in the absence breathe rapidly and deeply in order to
of oxygen. Examples of such organisms get enough oxygen required to convert
include yeast and bacteria species such lactic acid to carbon dioxide and water.
as Escherichia coli. Some of the lactic acid is converted to

In plants and yeast, anaerobic respiration glucose. Breathing goes back to normal
is also called fermentation. It involves when the acid has been broken down.
breaking down glucose by bacteria or
fungi to form alcohol, carbon dioxide Activity 6.8: Investigate on anaerobic
and energy. This is represented by the respiration in yeast

following equation:
Materials
C H O → 2C H OH + 2CO + Energy Yeast, glucose solution, two test tubes,
6
5
2
2
12
6
delivery tube, weighing scale, clamps,
Glucose → Ethanol + Carbon dioxide +Energy cork, measuring cylinder, oil, and lime
In animals, anaerobic respiration leads to water
the formation of lactic acid and energy, Procedure
as shown in the following equation: 1. Mix 2 grams of yeast with 5 ml
C H O → 2C H O + Energy of glucose solution in a test tube.
6
3
6
3
12
6
Glucose → Lactic acid + Energy 2. Pour some oil on the surface of
the mixture. Oil prevents oxygen
Anaerobic respiration occurs when from entering the mixture.
the body’s oxygen supply does not
meet the needs. For example, during 3. Put some lime water into another
a vigorous activity such as sports, test tube.
lactic acid is accumulated in the 4. Set up the apparatus as shown in
muscles. The accumulation of lactic Figure 6.14.
acid in the muscles prevents them

Student’s Book - Form Two 145

05/10/2024 15:36:46
BIOLOGY FORM 2 NEW.indd 145 05/10/2024 15:36:46
BIOLOGY FORM 2 NEW.indd 145