Thursday, 7 January 2016

Most recent asked Cell Biology Interview Questions and Answers

51. What are differentiations of the cell membrane?
In some types of cells, the cell membrane present differentiations that are necessary for the specific functions of the cells. The main differentiations are the microvilli and the structures for reinforcement of adhesion or union between cells (cell junctions).
Microvilli are multiple external projections of the membrane resembling glove fingers. This differentiation is found in cells of tissues where it is advantageous to increase the size of the surface in contact with the exterior, for example, in the enteric (intestinal) epithelium for absorption of nutrients.
Membrane differentiations for reinforcement of adhesion between cells occur mainly in epithelial tissues where the need for coverage and impermeability requires cells to be “glued” to neighbouring cells. These differentiations can be interdigitations, desmosomes, tight junctions (zonula occludens), zonula adherens (adherens junctions) and gap junctions.

52. What is the relation between concentration gradient and active and passive transport?
Passive transport is the movement of substances across membranes in favor of their concentration gradient, i.e., from a more concentrated region to a less concentrated region. Active transport, in the other hand, is the transport of substances across membranes against their concentration gradient, from a less concentrated to a more concentrated region. In passive transport, because it is spontaneous, there is no energy spending; the active transport however requires energy (work) to occur.
Active transport is a work to maintain or increase the concentration gradient of a substance between two regions while passive transport acts in a manner to reduce the concentration gradient.

53. What are the three main types of passive transport?
The three main types of passive transport are simple diffusion, osmosis and facilitated diffusion.
Cell Membrane Review - Image Diversity: passive transport

54. What is the energy source used in active transport through biological membranes?
The energy necessary for active transport (against the concentration gradient of the transported substance) to occur comes from ATP molecules. The active transportation uses chemical energy from ATP.

55. What is the difference between simple and facilitated diffusion? Facilitated by which type of molecule does the term “facilitated” mean?
Simple diffusion is the direct passage of substances across the membrane in favor of their concentration gradient. In facilitated diffusion the movement of substances is also in favor of their concentration gradient but the substances move bound to specific molecules that act as “permeabilizers”, i.e., facilitators of their passage through the membrane.
Cell Membrane Review - Image Diversity: facilitated diffusion

56. How does the intensity of simple diffusion vary in relation to the concentration gradient of the moved substance?
The higher the concentration gradient of a substance the more intense its simple diffusion will be. If the concentration gradient diminishes the intensity of simple diffusion diminishes too.

57. How does the intensity of facilitated diffusion vary in relation to the concentration of the moved substance? What is the limiting factor?
Likewise simple diffusion facilitated diffusion is more intense when the concentration gradient of the substance increases and less intense when the gradient lessens. In facilitated diffusion however there is a limiting factor: the quantity of the permeases that facilitate the transport through the membrane. Even in a situation in which the concentration gradient of the diffusing substance increases, if there are not enough permeases to perform the transport there will be no increase in the intensity of the diffusion. This situation is called saturation of the transport proteins and it represents the point in which the maximum transport capacity of the substance across the membrane is achieved.

58. Without saturation of transport proteins and under same concentration gradient how can the speed of simple diffusion be compared to the speed of facilitated diffusion?
The action of facilitator proteins in facilitated diffusion makes this type of diffusion faster than simple diffusion under equal concentration gradients of the moved substance.

59. How does facilitated diffusion present similarities with enzymatic chemical reactions?
One of the main examples of facilitated transport is the entrance of glucose from the blood into cells. Glucose from blood binds to specific permeases (hexose-transporting permeases) present in the cell membrane and by diffusion facilitated by these proteins it enters the cell to play its metabolic functions.
Facilitated diffusion resembles chemical catalysis because the transported substances bind to permeases like substrates bind to enzymes and in addition after one transport job is concluded the permease is not consumed and can perform successive other transports.

60. What are some examples of biological activities in which osmosis plays important role?
Hemolysis (destruction of red blood cells) by entrance of water, the hydric regulation in plants and the entrance of water in the xylem of vascular plants are all examples of biological phenomena caused by osmosis.
Excessive dilution of the blood plasma makes, by osmosis, the entrance of too much water in red blood cells and then the destruction of these cells (hemolysis). Osmosis also is the main process for maintenance of the flaccid, turgid or plasmolytic states of plant cells. Osmosis is one of the forces responsible for the entrance of water in plant roots since root cells are hypertonic in comparison to the soil.

More Questions & Answers:-
Page1 Page2 Page3 Page4 Page5 Page6 Page7 Page8 Page9

No comments:

Post a Comment