This set of Food Microbiology Multiple Choice Questions & Answers (MCQs) focuses on “Microorganisms Growth Factors – Water Activity”.
1. In the cell system, thiocyanate is converted to hypothiocyanate with the help of _______ enzyme.
a) Lactose oxidase
b) Lactic acid oxidase
c) Lactoperoxidase
d) Lactic peroxidase
View Answer
Explanation: Lactoperoxidase causes the oxidation of the reactants through the peroxide method. This is a 2-way flow reaction that takes place in the aqueous cytoplasm. The membrane surrounding the cytoplasm allows water to flow into the cell as well as from the cell into the environment.
2. The net flow of water out of the cytoplasm may give rise to _______
a) Plasmolysis
b) Cell Suicide
c) Production of more ribosomes
d) Cell Division
View Answer
Explanation: When a cell is placed in a hypertonic solution (solution in which the solute concentration is higher than in the cell), the cell loses water. This makes the pressure decrease and the cell protoplasm shrinks away from the cell wall.
3. Bound water does not contribute to the water activity.
a) True
b) False
View Answer
Explanation: The moisture in the food is present in the free form and the bound form. Bound water is associated with the hydration of hydrophilic entities and the dissolution of solutes. It does not help in biological functions and therefore does not take part in the water activity.
4. Cytolysis can be prevented by the ______ in bacteria and fungi.
a) Ribosomes
b) Cell wall
c) Nucleus
d) Periplasm
View Answer
Explanation: Cytolysis is the bursting of the cell when placed in a hypotonic solution (solution in which the solute concentration is less than in the cell). Hence, excess water goes into the cell causing it to swell and burst. The rigid cell wall prevents the cell from bursting.
5. Bacteria that are able to survive under subzero temperature sometimes have polyols in the cytoplasm which act as _________
a) Fuel
b) Heat Producers
c) Energy Currency
d) Antifreeze
View Answer
Explanation: A polyol is an organic compound with many hydroxyl groups. Since they are mostly carbohydrates, they prevent the deterioration of biological entities at subzero temperatures. They also support some of the glycoproteins that play a role in antifreeze.
6. What is the full form of ERH?
a) Equilibrium Redlich Heat
b) Equilibrium Relative Heat
c) Equilibrium Relative Humidity
d) Equilibrium Redlich Humidity
View Answer
Explanation: Equilibrium Relative Humidity or ERH is numerically equal to water activity (aw). ERH is represented as a fraction in the form:
aw = P/P0 = (1/100) ERH where P is the partial pressure of the water with the atmosphere in equilibrium with the reactants whereas P0 is the partial pressure of the atmosphere in equilibrium with pure water at a given temperature T.
7. The _______ component of the water potential is related to the effects of solutes in the solution.
a) Solution
b) Humidity
c) Heat
d) Osmotic
View Answer
Explanation: Osmotic pressure is also known as solute pressure. The presence of solutes causes the overall water potential to decrease. Ψs is expressed in bars and it a negative quantity. The osmotic component may contribute to the cytolysis or plasmolysis of the cell.
8. The lowering of water activity can lead to a longer lag phase and a shorter growth phase.
a) True
b) False
View Answer
Explanation: All chemical and biological reactions need an aqueous environment. If the water activity i.e. the amount of water required for the functioning of cells is reduced, the growth will be adversely affected. Also, the size of the final population will decrease. The drying of the internal components of the cell may take place and the fluidity of the cell membrane is not maintained.
9. The _______ component of the water potential is concerned with the interaction of water molecules with surfaces.
a) Pressure
b) Matric
c) Gravitational
d) Osmotic
View Answer
Explanation: The matric potential is caused due to the forces of attraction on water. It can be shown with the help of capillary tubes. The forces between water and the solute particles give rise to surface tension. The forces can also be related to the cell wall and colloidal surfaces. Ψm can be considered to be negligible in case of plants.
10. Paramecia perform osmoregulation with the help of ________
a) Contractile Vacuole
b) Oral Groove
c) Cilia
d) Food Vacuole
View Answer
Explanation: Paramecia are fresh water organisms and hence are present in a hypotonic solution as compared to their body. This might result in excess water flowing inside the cell and rupturing it. This can be controlled by osmoregulation. Paramecia have 2 contractile vacuoles, one at each end. The contractile vacuole swells up when water enters the body and ruptures when its maximum capacity is reached. This causes the expulsion of water to the surrounding.
11. ____________ solutes are produced in increased concentrations to get the cell in equilibrium with the environment when the surrounding water activity is decreased.
a) Hard
b) Mixed
c) Regulatory
d) Compatible
View Answer
Explanation: Osmotic pressure in the environment increases as water activity decreases. To keep the cell in equilibrium with the environment, it is essential that the water activity in the cell is decreased and the osmotic pressure increased. This can be done with the help of compatible solutes like mannitol in fungi and amino acids in bacteria. These solutes do not interfere with the cytoplasmic functions.
12. Microbes that are able to grow on dry foods are called _________
a) Haemotolerant
b) Xerotolerant
c) Halotolerant
d) Osmotolerant
View Answer
Explanation: Low water activities can give rise to three types of foods. Xerotolerant microbes can grow on dry foods with extremely low water activity. They can survive even after food preservation concerning reduction of water activity. Halotolerant microbes are those which thrive in spite of high salt concentrations whereas osmotolerant species can survive in the presence of high concentrations of unionized compounds.
13. What instrument can be used to measure the water activity by measuring the ERH of the atmosphere in which the sample is kept?
a) Hair Hygrometer
b) Barium Scale
c) Barometer
d) Mercury Manometer
View Answer
Explanation: The hair hygrometer is a humidity sensor which is based on adsorption and the mechanical humidity sensing technique. Hair contracts or expands based on the air humidity and the hygrometer uses this very concept. The hair strands are connected to a clock driven drum which then measures the humidity with a needle which is moved by the expansion or contraction of the hair.
Sanfoundry Global Education & Learning Series – Food Microbiology.
To practice all areas of Food Microbiology, here is complete set of Multiple Choice Questions and Answers.
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