Directions : The following five (5) items consist of two statements, Statement I and Statement II. Examine these two statements carefully and select the correct answer using the code given below. Statement I: Skin cancer is generally caused by the ultraviolet radiation. Statement II: Stratosphere allows ultraviolet radiation to enter the earth from the sun.
Statement I is true but Statement II is false
Understanding Skin Cancer and UV Radiation
The question asks us to evaluate two statements related to skin cancer and the role of the stratosphere concerning ultraviolet (UV) radiation. Let's break down each statement to determine its accuracy.
Statement I: Skin cancer is generally caused by the ultraviolet radiation
This statement talks about the link between ultraviolet radiation and skin cancer. Ultraviolet (UV) radiation is a form of electromagnetic radiation from the sun (and artificial sources like tanning beds). Scientific research has extensively shown that exposure to UV radiation is a primary cause of most skin cancers, including melanoma, basal cell carcinoma, and squamous cell carcinoma. UV radiation damages the DNA in skin cells, which can lead to uncontrolled cell growth and form cancerous tumors.
Therefore, Statement I is factually correct.
Statement II: Stratosphere allows ultraviolet radiation to enter the earth from the sun
This statement discusses the role of the stratosphere in relation to ultraviolet radiation. The stratosphere is a layer of Earth's atmosphere located above the troposphere. A crucial component within the stratosphere is the ozone layer. The ozone layer plays a vital role in absorbing most of the sun's harmful ultraviolet (UV) radiation, particularly UV-B radiation. Instead of allowing UV radiation to freely enter the Earth's surface, the stratosphere (with its ozone layer) acts as a protective shield, blocking a significant portion of it. Only a small amount of UV radiation, mainly UV-A, reaches the Earth's surface.
Therefore, Statement II is factually incorrect.
Evaluating the Options
Based on our analysis:
- Statement I is true.
- Statement II is false.
Let's look at the given options:
- Option 1: Both statements are individually true, and Statement II explains Statement I. (Incorrect, Statement II is false).
- Option 2: Both statements are individually true, but Statement II does not explain Statement I. (Incorrect, Statement II is false).
- Option 3: Statement I is true but Statement II is false. (Correct, matches our findings).
- Option 4: Statement I is false but Statement II is true. (Incorrect, Statement I is true and Statement II is false).
The option that correctly reflects the truthfulness of both statements is Option 3.
Conclusion on UV Radiation and Stratosphere
Statement I accurately describes the primary cause of skin cancer as ultraviolet radiation. Statement II incorrectly describes the role of the stratosphere; instead of allowing UV radiation to enter freely, the stratosphere's ozone layer absorbs most of the harmful UV rays.
Thus, Statement I is true, and Statement II is false.
Revision Table: Skin Cancer, UV, and Stratosphere
| Concept | Description | Relation to Statements |
|---|---|---|
| Skin Cancer | Abnormal growth of skin cells, often caused by DNA damage. | Linked to UV radiation (Statement I). |
| Ultraviolet (UV) Radiation | Energy from the sun; damages DNA in skin cells. | Primary cause of skin cancer (Statement I). Largely blocked by the ozone layer in the stratosphere (contradicts Statement II). |
| Stratosphere | Layer of atmosphere above the troposphere. | Contains the ozone layer which absorbs UV radiation (contradicts Statement II). |
| Ozone Layer | Region in stratosphere with high ozone concentration (\(\text{O}_3\)). | Absorbs most harmful UV-B radiation from the sun. |
Additional Information: UV Radiation and Earth's Atmosphere
Understanding the different types of UV radiation and how the atmosphere interacts with them is important:
- UV-A: Longest wavelength UV radiation. Reaches Earth's surface in significant amounts. Penetrates skin deeply, contributing to aging and wrinkling, and also plays a role in skin cancer.
- UV-B: Medium wavelength UV radiation. Most UV-B is absorbed by the ozone layer in the stratosphere. The UV-B that reaches the surface causes sunburn and is a major cause of skin cancer.
- UV-C: Shortest wavelength UV radiation. Extremely harmful, but completely absorbed by the ozone layer and other atmospheric gases before reaching the Earth's surface.
The ozone layer's absorption of UV-B is crucial for protecting life on Earth. Depletion of this layer (due to human-made chemicals like CFCs) increases the amount of harmful UV-B reaching the surface, leading to higher risks of skin cancer and other harmful effects.
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