1. What do you mean by unit membrane?
Not only the cell membrane but also the nucleus, chloroplast and mitochondria are double membranous, i.e. they are covered by two wall layers each of which, is consisting of protein-lipid-lipid-protein. This type of membrane is known as unit membrane.
2. What is fluid mosaic model of cell membrane?
As per this model all membranes of different cell organelles along with the plasma membrane is made up of double layer of lipid molecules in which proteins are embedded like the tiles of mosaic floors. This model is first proposed by Singer and Nicholson.
3. Mention the chemical nature of proteins present in plasma membrane with special reference to its functions.
Chemically the proteins present on plasma membrane are of two types:
- Lipoproteins—It functions as enzymes and ion channels.
- Glyco-proteins—It functions as receptor for hormone and neurotransmitters.
4. Classify the proteins as per their location on plasma membrane and mention each of their functions.
As per their location proteins are of 3 types:
- Intrinsic protein—These are located in the inner surface of membrane and serve mainly as enzymes.
- Extrinsic protein—These are located in the outer surface of membrane and contribute to the cytoskeleton.
5. Mention the function of SER and RER.
Functions of smooth endoplasmic reticulum (SER) are as follows:
- It is the site of steroid synthesis.
- It plays important role in skeletal and cardiac muscles.
Function of RER: It is the site of protein synthesis.
6. Name at least four lysosymes.
These are: Ribonuclease and deoxyribonuclease, phosphatase, collagenase and glycosidase.
7. What are the differences between microfilaments and microtubules?
Microtubules are long, hollow structure, 25 mm in diameter whereas microfilaments are solid fibres of 4-6 mm in diameter.
8. Enumerate different types of cell junction and each of their function.
On the basis of their function cell junctions are classified into 3 groups:
- Occluding junction or Zona occludens or tight junction—Prevent movement of ions and other molecules across the membrane.
- Anchoring junctions—These are of 3 types –
- Macula adherens or desmosome—act as a strong anchor between the cells/tissues which are subjected to mechanical stress like epidermis of skin.
- Zonula adherens or belt desmosome.
- Fascia adherens or strip desmosome.
- Communicating junctions—These are again of 3 types
- Gap junction- allows the speedy movement of Na+, K+, Ca+2, ATP, Sugar, amino acids, vitamins, etc. across the membrane.
- Plasmodesmata
- Chemical synapse.
9. How does lipid and water soluble substances diffuse through cell membrane?
Lipid soluble substances diffuse through lipid layer of membrane whereas water soluble substances diffuse through the channels present in cell membrane.3
10. What do you mean by voltage gated and ligand gated channels? Give example of each.
The ion channels, the gate(s) of which open or close by alteration in membrane potential, is known as voltage gated channels. Examples, Na+ and K+ or Ca++ channels present in cell membrane.
Whereas the ion channels, the gate(s) of which open or close in response to binding of channel proteins with some ligand molecules like neurotransmitters, hormone, intra-cellular Ca++, cAMP, G protein etc, is called as ligand gated channels. Example—Na+ and K+channels present in post-synaptic membrane of synapses.
11. What is facilitated diffusion? Give example.
It is a carrier mediated transport process in which carrier protein undergoes repetitive spontaneous configurational changes during which the binding site for the substance is alternatively exposed to the ECF and ICF and thereby allow the inward movement of substances inside the cell. Example—transport of glucose into RBC.
12. Define osmosis.
It is the passive flow of solvent, i.e. water across the selectively permeable membrane into a region of higher concentration of solute to which the membrane is impermeable.
13. Define osmotic pressure.
The tendency for movement of solvent molecules to a region of greater solute concentration can be prevented by applying pressure to the more concentrated solution. The pressure necessary to prevent this type of solvent migration is called the osmotic pressure.
14. What is osmolarity and osmolality?
Osmolarity is the number of osmoles per litre of solution. Whereas osmolality is the number of osmoles per kg of the solvent.
15. What is osmolality of normal human plasma? What is tonicity?
Osmolality of normal human plasma is 290 mosm/lit. The osmolality of a solution relative to plasma is called tonicity.4
16. How does hyperosmolality can produce coma?
It is by causing cellular dehydration.
17. What is solvent drag?
When water flows into or out of capillaries it carries dissolved particles with it. This force is known as solvent drag.
18. Define active transport process. What are their types?
When the transport of substances across the membrane takes place against their chemical or electrical or pressure gradient for which energy is required, this type of transport process is called active transport process. It is mainly of 2 types as follows:
- Primary active transport where energy is required directly.
- Secondary active transport in which the required energy is obtained from primary active transport.
19. Name the types of pump required for primary active transport with its site of location.
- Na+–K+ pump—Present in cell membrane of all parts of the body.
- Ca+2–pump—Present in sarcoplasmic reticulum of muscle cells.
- K+–H+pump—Present in the cells of the gastric mucosa and renal tubules.
20. How many types of carrier mediated transport processes are present in body? Name them with examples?
These are of three types which are as follows:
- Uniport—facilitated diffusion of glucose in renal tubules.
- Symport—secondary active transport of glucose in renal tubules coupled with Na+.
- Antiport – Na+– Ca++exchanger in muscle cell and also Na+- H+exchanger in renal tubules.
21. Define phagocytosis.
It is the process by which the extracellular substances like bacteria, dead tissue, foreign particles are engulfed and digested by the cells.5
22. What is the total amount of water in our body?
It is 42 litre in a 60 kg body weight person, i.e. 70 per cent of the body weight.
23. Why total body water is lower in female than male?
It is because of presence of relatively greater amount of subcutaneous fat in female body.
24. Name different compartments of ECF.
- Plasma—25 per cent
- Interstitial fluid—75 per cent
- Transcellular fluid—minute amount.
25. Name the method for measuring body fluid volume.
It is indicator dilution method.
26. What are the criteria of good indicator used for measuring body fluid volume?
These are as follows:-
- Must be non-toxic
- Must mix evenly throughout the compartments being measured.
- It should neither be reabsorbed nor be secreted.
- It should not alter the water distribution of the compartment being measured.
- It should be relatively easy to measure.
27. From the clinical point of view define acidosis and alkalosis.
Decrease blood pH, less than 7.35 is known as acidosis and increase blood pH, more than 7.45 is called alkalosis.
28. What is buffer? What is its chemical nature?
Buffer is a substance that has the ability to bind or release H+ ion in solution. Chemically it is a weak acid and its conjugated base.
29. Define homeostasis.
Maintenance of the constant internal environment of the body to enable its normal function is known as homeostasis.6
30. What do you mean by internal environment?
The ECF surrounding the body cells is called internal environment as the cellular function depends on this particular environmental condition.
31. What is negative feedback mechanism?
The homeostatic mechanism in which the final response becomes opposite to that of its initiating stimulus is known as negative feedback mechanism.
32. Define positive feedback mechanism.
The homeostatic mechanism in which the final response becomes similar to that of its initiating stimulus is known as positive feedback mechanism.
33. Does the positive feedback is harmful to the body?
Not always, in case of parturition, blood clotting and initiation of action potential positive feedback mechanism is operated which is not harmful to the body rather beneficial one.