This set of Cell Biology Interview Questions and Answers for freshers focuses on “Movement of Substances Across Cell Membranes”.
1. The transport of water molecules from a solution to the cell cytoplasm occurs in _________
a) Hypertonic solution
b) Hypotonic solution
c) Isotonic solution
d) All of the mentioned
Explanation: When the concentration of solute in the solution is greater than that of cell interior, it is called hypertonic solution. When the concentration of solute in the solution is greater than that of cell interior, it is called hypotonic solution. When both the solution and the cell interior has equal concentration of solute, it is called isotonic solution. Water diffuses from hypotonic solution towards cell interior with more solute concentration.
2. Plasmolysis occurs in __________
a) Hypertonic solution
b) Hypotonic solution
c) Both hypotonic and hypertonic solution
d) Isotonic solution
Explanation: If a plant cell is placed in a hypertonic medium, its volume shrinks as the water diffuses out of the cell through the cell wall. The plasma membrane pulls away from the surrounding cell wall. This process of loss of water is called as plasmolysis and it leads to loss of support and wilt.
3. Which of the following channels depend on forces such as stretch tension applied on the membrane?
a) Voltage-gated channels
b) Mechano-gated channels
c) Ligand-gated channels
d) Tension-gated channels
Explanation: The conformational change of mechano- gated channels depend on mechanical forces that are applied to the membrane. These mechanical forces such as stretch tension forces the channel to open the pathway for the transport of ions and solutes.
4. How many H+ ions are transported by the vacuole H+-ATPase pump and the vacuole H+-phosphatase pump per hydrolysis of ATP and pyrophosphate respectively?
a) 1, 1
b) 1, 2
c) 2, 1
d) 2, 2
Explanation: The vacuole H+-ATPase pump and the vacuole H+-phosphatase pump are membrane proteins on the vacuole membrane that helps in the active transport of H+ ions inside the vacuole. With the hydrolysis of one ATP molecule, two H+ ions can pass through the H+-ATPase pump. However, with the hydrolysis of one pyrophosphate molecule, one H+ ion can pass through the H+-pyrophospatase pump.
5. The ion most abundant in cells and most permeable to cell membrane is ____________
Explanation: K+ is the ion that is found in most abundance in cells. It also has the greatest permeability through cell membrane and as a result, it is pumped faster than any other ion through the cell membrane by active or passive transport.
6. Facilitative transporter ___________
a) Helps in facilitated diffusion
b) Changes conformation
c) Transports molecules passively
d) Changes conformation, transports molecules and facilitated diffusion
Explanation: Facilitated diffusion is a method by which molecules are diffused across the cell membrane with the help of an intermediate protein called facilitative transporter. The diffusing substance binds selectively to this membrane-spanning protein that facilitates in diffusion process. It undergoes conformational change, exposing the solute to the other surface of the membrane.
7. GLUT1 is an example of ______________
a) Channel protein
b) Facilitative transporter
c) Active transporter
d) Lipid-anchored protein
Explanation: Humans consist of membrane-spanning proteins that help in the transport of glucose molecules through the cell membrane. These molecules have five isoforms from GLUT1 to GLUT5. It facilitates the diffusion of glucose from the bloodstream into the cell through facilitated diffusion.
8. The ratio of Na+ and K+ transported by Na+/K+-ATPase pump is ___________
Explanation: The sodium potassium pump is an active transporter that uses ATP to transport Na and K ions across a membrane. With each ATP used the pump exports 3 Sodium ions while it imports 2 Potassium ions into the cell.
9. Symport and Antiport is the classification of ____________
a) Primary active transport
b) Secondary active transport
c) Primary passive transport
d) Secondary passive transport
Explanation: Primary active transport involves hydrolysis of ATP or pyrophosphate or GTP to yied energy which helps in the transport of a particular molecule by utilization of that energy. Passive transport involves coupling the transport of one ion or molecule with the transport of another ion or molecule. It is of two types- Symport and Antiport. Symport refers to the pumping of two ions in the same direction of the cell membrane while Antiport refers to pumping of ions in the opposite direction.
10. Halobacterium salinarium uses the following for the active transport of ions to induce purple colour.
a) Light energy
d) Chemical energy
Explanation: Halobacterium salinarium is a halophilic archaebacterium, which takes on a purple colour when grown under anaerobic conditions. This is due to the presence of bacteriorhodopsin, a proton pump which depends on light energy. The absorption of light in the retinal group of bacteriorhodopsin results in conformational change and a proton from the retinal group moves to the cell exterior.
11. During salt stress condition in Arabidopsis, which of the following antiport proteins are used?
a) AvPI and AtNHX
b) AvPI and AtDBF
c) AvPI and AvPII
d) None of the mentioned
Explanation: AvPI (Arabidopsis vacuola protein I) and AtNHX (Arabidosis transporting H+ ion) are the antiport proteins present on the membrane of vacuole. During salt stress condition, there is an increase in Na+ ion in the cell, which leads to acidity in cell and may be harmful to plants. These antiport transport Na+ ion into the vacuole from cytoplasm coupled with the transport of H+ ion from vacuole to cytoplasm. This result in reduction of Na+ concentration in cytoplasm and reduction of acidity in salt-stress condition.
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