Tag: zoology

During tumorigenesis, cancerous cells undergo rapid cell division and compete with normal cells for nutrients.
Cancer cells spread to other parts of the body, a process called metastastize i.e., are not confined in area  of formation.
Cancer is the result of cells that uncontrollably grow and do not die.
So, statements A, B and C are correct.
Normal cells when grown in culture, will become growth inhibited, when they encounter another cell. This is contact inhibition and Cancer cells show no contact inhibition as they do not stop dividing and keep growing.
Thus, the correct answer is option (D), 'They show contact inhibition'.

Metastasis is the movement of spreading of cancer cells from one organ or tissue to another. Cancer cells usually spread through the blood or the lymph system. It is mainly caused due to the mutagens which cause a sudden heritable change in the DNA content which leads to fatal abnormalities.
So, the correct answer is option B.

Genes are found in the DNA of every cell of the human body. The functions of the cell, its growth pattern, divisions and life are all determined and control by the genes. Cancers in the human body are the result of mutations or changes in one or more genes in a cell leading to an abnormal protein or no protein at all. An abnormal protein in the cells causes them  to multiply uncontrollably and become cancerous. Any alteration in the tumour suppressor gene may result in cancer. 

Cancer cells are cells that divide rapidly, forming solid tumours or flooding the blood with abnormal cells. Malignant cancerous cells spread from their initial site to other organs or tissues resulting in metastasis. Cancer cells undergo invasion of local tissue i.e., direct extension and penetration by cancer cells into neighbouring tissues. Hence, cancer cells are characterised by uncontrolled growth, spreading to other body part and invasion of local tissue.

• A gene is the basic physical and functional unit of heredity. Genes are made up of DNA and DNA is present inside the nucleus.
• Mutations in genes can cause cancer by accelerating cell division rates or inhibiting normal controls on the system, such as cell cycle arrest or programmed cell death. As a mass of cancerous cells grows, it can develop into a tumour.
• Hence Transformation of a normal cell to cancer cell may start with changes in  Nucleus.
  
• So, the correct answer is 'Nucleus'.

The difference between normal tissues and cancer tissues is the rate of metabolism.  In normal cells, hundreds of genes intricately control the process of cell division. Normal growth requires a balance between the activity of those genes that promote cell proliferation and those that suppress it. However, in the case of cancer cells, they involve abnormal growth. Cells become cancerous after mutations accumulate in the various genes that control cell proliferation. Hence proliferation of cancer cell is not limited because of differing surface proteins and aberrant chromosomal complements. Thus, the correct answer is option D.

The ozone layer is mainly found in the lower portion of the stratosphere, from approximately 20 to 30 kilometres above Earth, which shields the earth from the sun's harmful ultraviolet radiations. Ozone gas is present in 10 ppm in this ozone layer.