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Q12:
How is a cancerous cell different from a normal cell?
Solution :
Biological Basis of Cellular Transformation
The fundamental distinction between a normal cell and a cancerous cell lies in the regulation of the cell cycle and the homeostatic control mechanisms governing proliferation. Normal cells maintain a controlled state of division, whereas cancerous cells exhibit a loss of contact inhibition and uncontrolled neoplastic growth.
Step 1: Comparative Analysis of Cellular Properties
The following table delineates the physiological and genetic deviations of cancerous cells compared to normal counterparts:
| Characteristic | Normal Cell | Cancerous Cell |
|---|---|---|
| Contact Inhibition | Present; stops division upon contact with neighboring cells [Regulation via Cell Adhesion Molecules]. | Absent; cells continue to divide, resulting in piling up and tumor formation. |
| Cell Cycle Control | Strictly regulated by cyclin-dependent kinases (CDKs) and checkpoints. | Deregulation; mutations in proto-oncogenes/tumor suppressor genes ($p53$, $Rb$) lead to unregulated mitosis. |
| Telomerase Activity | Limited; leads to cellular senescence after a fixed number of divisions (Hayflick limit). | High; activation of telomerase allows for indefinite division (immortality). |
| Metastasis | Fixed in tissue of origin (anchorage dependence). | Capable of invasion and metastasis; cells detach and migrate via circulatory/lymphatic systems. |
Step 2: Graphical Representation of Growth Kinetics
The following SVG illustrates the uncontrolled proliferation observed in a neoplastic cell line versus the regulated growth of a normal cell line.
Step 3: Molecular and Physiological Justifications
- Loss of Contact Inhibition: In healthy tissues, physical contact triggers signaling pathways that inhibit the $G_1$ to $S$ phase transition. Cancerous cells harbor mutations in genes responsible for these inhibitory pathways, such as the cadherin-mediated cell-cell junctions, enabling uninhibited growth.
- Neoplastic Transformation: Cancerous cells undergo "transformation," where proto-oncogenes (responsible for normal growth) are mutated into oncogenes, and tumor-suppressor genes (which repair DNA or trigger apoptosis) are inactivated. This leads to a loss of the apoptotic response, where cells that should undergo programmed cell death instead persist and propagate mutations.
- Metastasis: Unlike normal cells that require a basement membrane for structural anchoring [Anchorage dependence], malignant cells secrete enzymes such as matrix metalloproteinases (MMPs) to digest the extracellular matrix, facilitating migration into the bloodstream.
Final Solution: A cancerous cell differs from a normal cell primarily through the loss of contact inhibition, the evasion of programmed cell death (apoptosis), the capacity for indefinite replication due to activated telomerase, and the ability to undergo metastasis by bypassing the requirement for anchorage dependence.
More Questions from Class 12 Biology Human Health and Disease EXERCISES
- Q1: What are the various public health measures, which you would suggest as safeguard against infectious diseases?
- Q1: What are the various public health measures, which you would suggest as safeguard against infectious diseases?
- Q2: In which way has the study of biology helped us to control infectious diseases?
- Q2: In which way has the study of biology helped us to control infectious diseases?
- Q3(a): How does the transmission of each of the following diseases take place? (a) Amoebiasis
- Q3(a): How does the transmission of each of the following diseases take place? (a) Amoebiasis
- Q3(b): How does the transmission of each of the following diseases take place? (b) Malaria
- Q3(b): How does the transmission of each of the following diseases take place? (b) Malaria
- Q3(c): How does the transmission of each of the following diseases take place? (c) Ascariasis
- Q3(c): How does the transmission of each of the following diseases take place? (c) Ascariasis
- Q3(d): How does the transmission of each of the following diseases take place? (d) Pneumonia
- Q3(d): How does the transmission of each of the following diseases take place? (d) Pneumonia
- Q4: What measure would you take to prevent water-borne diseases?
- Q4: What measure would you take to prevent water-borne diseases?
- Q5: Discuss with your teacher what does ‘a suitable gene’ means, in the context of DNA vaccines.
- Q5: Discuss with your teacher what does ‘a suitable gene’ means, in the context of DNA vaccines.
- Q6: Name the primary and secondary lymphoid organs.
- Q6: Name the primary and secondary lymphoid organs.
- Q7(a): The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form: (a) MALT
- Q7(a): The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form: (a) MALT
- Q7(b): The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form: (b) CMI
- Q7(b): The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form: (b) CMI
- Q7(c): The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form: (c) AIDS
- Q7(c): The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form: (c) AIDS
- Q7(d): The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form: (d) NACO
- Q7(d): The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form: (d) NACO
- Q7(e): The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form: (e) HIV
- Q7(e): The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form: (e) HIV
- Q8(a): Differentiate the following and give examples of each: (a) Innate and acquired immunity
- Q8(a): Differentiate the following and give examples of each: (a) Innate and acquired immunity
- Q8(b): Differentiate the following and give examples of each: (b) Active and passive immunity
- Q8(b): Differentiate the following and give examples of each: (b) Active and passive immunity
- Q9: Draw a well-labelled diagram of an antibody molecule.
- Q9: Draw a well-labelled diagram of an antibody molecule.
- Q10: What are the various routes by which transmission of human immuno-deficiency virus takes place?
- Q10: What are the various routes by which transmission of human immuno-deficiency virus takes place?
- Q11: What is the mechanism by which the AIDS virus causes deficiency of immune system of the infected person?
- Q11: What is the mechanism by which the AIDS virus causes deficiency of immune system of the infected person?
- Q12: How is a cancerous cell different from a normal cell?
- Q13: Explain what is meant by metastasis.
- Q13: Explain what is meant by metastasis.
- Q14: List the harmful effects caused by alcohol/drug abuse.
- Q14: List the harmful effects caused by alcohol/drug abuse.
- Q15: Do you think that friends can influence one to take alcohol/drugs? If yes, how may one protect himself/herself from such an influence?
- Q15: Do you think that friends can influence one to take alcohol/drugs? If yes, how may one protect himself/herself from such an influence?
- Q16: Why is that once a person starts taking alcohol or drugs, it is difficult to get rid of this habit? Discuss it with your teacher.
- Q16: Why is that once a person starts taking alcohol or drugs, it is difficult to get rid of this habit? Discuss it with your teacher.
- Q17: In your view what motivates youngsters to take to alcohol or drugs and how can this be avoided?
- Q17: In your view what motivates youngsters to take to alcohol or drugs and how can this be avoided?
CBSE Solutions for Class 12 Biology Human Health and Disease
Chapters in CBSE - Class 12 Biology
- Reproduction in Organisms
- Human Reproduction
- Reproductive Health
- Principles of Inheritance and Variation
- Molecular Basis of Inheritance
- Evolution
- Strategies for Enhancement in Food Production
- Microbes in Human Welfare
- Biotechnology: Principles and Processes
- Biotechnology and Its Applications
- Organisms and Populations
- Ecosystem
- Biodiversity and Conservation
- Environmental Issues
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