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67. Obligate anaerobes

68. Aerotolerant anaerobes

69. pH

70 media nutrient density

71. agar concentration

72. extremophiles

Explanation:

Anaerobes are microorganisms which do not require oxygen for their metabolic activities. The types of anaerobes based on metabolism are: obligate anaerobes; facultative anaerobes ; and aerotolerant anaerobes.

Some bacteria are anaerobes.

67. Obligate anaerobes do not require oxygen at all for their metabolism. They die in the presence of oxygen.

68. Aerotolerant anaerobes do not require oxygen as well but can also tolerate oxygen. they are unaffected by the presence or absence of oxygen

69. The pH of the medium affects the growth of bacteria. When pH becomes too low or too high, bacteria colonies begin to die.

70. when the nutrient concentration is high, growth rate of bacteria colony increases, but when it is low, bacteria colony growth decreases.

71. agar concentration limits the growth of bacteria colony. When the agar is very concentrated, that is the medium is hard, the bacteria colony is limited in their ability to move and vice versa.

72. Extremophiles is the name given to archaea that thrive in extreme conditions of temperature and pH. For example, the archaeal Methanopyrus kandleri strain 116 grows at 122 °C while the genus Picrophilus e.g., Picrophilus torridus has the ability to grow at a pH of 0.06.

1) gene flow

- it is described as the transfer of genes from one population to another population so that frequency of gene is increased.

-a zebra migrates to join a different herd of zebras.

2) natural selection

- a mechanism of evolutionary change in which individuals with advantageous traits survive and reproduce whereas the others ( those that can not adapt) eliminate from the population.

-competition for sunlight leads to taller trees.

3) mutation

- permanent change in the nucleotide sequence of dna ( genetic material) that could have harmful or useful consequences.

-the dna of a snake changes to make its venom stronger.

4) genetic drift - it is a random phenomenon ( that occurs by chance such as fire) that results in change in the gene frequency in a small population.    

-a grassfire randomly sweeps through a population of buffalo and kills most of the animals.

explanation: