80% @D. 7:01 PM mybb.qu.edu.qa 2 of 3 5-Which phase in a population growth curve

Question

80% @D. 7:01 PM mybb.qu.edu.qa 2 of 3 5-Which phase in a population growth curve is associated with no increase or decrease in population? a. lag phaso b. logarithmic phase e. stationary phase d. stop phase e. death phase 6-Which term best describes an organism that can't exist in the presence of oxygen? a. obligate acrobe b. facultative aerobe c. obligate anaerobe d. facultative anaerobe 7-Why are high temperatures, outside of the range that an organism is adapted to, potentially deadly? a high temperatures lead to too rapid growth b, high temperatures slow reproduction c. high temperatures change the shape of proteins d. high temperatures make lipid membranes brittle and fragile 8-What microbe can thrive and grow in the acidis environment of the human stomach? a. Staphylococcus aureus b. E. coli e. Helicobacter pylori d. Vibrio cholerae e. Streptococeus pyogenes

Explanation / Answer

Answer 5. Option (c) Stationary phase

Explanation:

The population growth curve is a logistic approach to study the bacterial growth. It has 4 distinct phases- lag phase, log phase, stationary phase and decline or death phase. In stationary phase, the bacterial growth is ceased. This is because as the bacterial population continues to grow during the prior phase (log phase), decreasing the available nutrients for the bacterial growth. Hence, during the statuonart phase there is no increase or decrease in the bacterial growth population.

Answer 6. Option (c) Obligate anaerobe

Explanation: Based on the oxygen tolerance of different microorganisms, they are classified as obligate or facultative anaerobes, aerobes, microaerophiles. Obligate anaerobes are those microorganisms which cannot tolerate oxygen. They lalacl vital ezymes like superoxide dismutase, catalase. Hence, they form reactive oxygen species, which are toxic for their survival.

Answer 7. Option (d) High temperatures make the lipid membrane brittle and fragile.

Explanation:

The lipid membrane is composed of cholesterol, fatty acids and glycoproteins. During high temperature, the lipid membrane gets destructed. This is unlikely in thermophiles (heat tolerant microorganisms) because they have high GC content and high amount of saturated fatty acids. Hence, normal microorganisms cannot survive high temperatures.

Answer 8. Option (c) Helicobacter pylori

Explanation:

Helicobacter pylori is a type of bacterium which can survive in acidic pH of stomach. It causes stomach ulcer by thriving in the acidic environment of stomach.

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