1. Introduction

An investigation of the effect of the UV Light on the growth of lemongrass.

4 students wanted to test the effects of UV Light on the growth of plants to see how much damage it can do to them if they stay too long in the sun.

The independent variable is the amount of time plants are exposed to the UV Light.
The dependent variable is the height of the plants after being exposed to the UV Light.
The constants are:
(a)  The type of plant used
(b)  The number of plants used per set-up
(c)  The intensity of UV light used
(d)  The amount of cotton wool used to grow the plant


Investigation of the effect of UV Light on the growth of plants.


UV Rays and Its Uses

UV radiation is part of the electromagnetic (light) spectrum that reaches the earth from the sun. It has wavelengths shorter than visible light, making it invisible to the naked eye. These wavelengths are classified as UVA, UVB, or UVC, with UVA the longest of the three at 320-400 nanometers (nm, or billionths of a meter). UVA is further divided into two wave ranges, UVA I, which measures 340-400 nanometers (nm, or billionths of a meter), and UVA II which extends from 320-340 nanometers. UVB ranges from 290 to 320 nm. With even shorter rays, most UVC is absorbed by the ozone layer and does not reach the earth.
Uses for UV light include getting a suntan, detecting forged bank notes in shops, and hardening some types of dental filling.You also see UV lamps in clubs, where they make your clothes glow. This happens because substances in washing powder "fluoresce" when UV light strikes them - they absorb the UV and then re-radiate the energy at a longer wavelength. Your teeth do the same thing!The lamps are sometimes called "black lights" because we can't see the UV coming from them.When you mark your possessions with a security marker pen, the ink is invisible unless you shine a UV lamp at it.Ultraviolet rays can be used to kill microbes. Hospitals use UV lamps to sterilise surgical equipment and the air in operating theatres.Food and drug companies also use UV lamps to sterilise their products.Suitable doses of Ultraviolet rays cause the body to produce vitamin D, and this is used by doctors to treat vitamin D deficiency and some skin disorders.
(Zeman, G. (2014, August 13). Ultraviolet radiation.)

Skin Cancer Caused By UV Rays
Both UVA and UVB, however, penetrate the atmosphere and play an important role in conditions such as premature skin aging, eye damage (including cataracts), and skin cancers. They also suppress the immune system, reducing your ability to fight off these and other maladies.By damaging the skin's cellular DNA, excessive UV radiation produces genetic mutations that can lead to skin cancer. Both the U.S. Department of Health and Human Services and the World Health Organization have identified UV as a proven human carcinogen. UV radiation is considered the main cause of nonmelanoma skin cancers (NMSC), including basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). These cancers strike more than a million and more than 250,000 Americans, respectively, each year. Many experts believe that, especially for fair-skinned people, UV radiation also frequently plays a key role in melanoma, the deadliest form of skin cancer, which kills more than 8,000 Americans each year.
Most of us are exposed to large amounts of UVA throughout our lifetime. UVA rays account for up to 95 percent of the UV radiation reaching the Earth's surface. Although they are less intense than UVB, UVA rays are 30 to 50 times more prevalent. They are present with relatively equal intensity during all daylight hours throughout the year, and can penetrate clouds and glass.
UVA, which penetrates the skin more deeply than UVB, has long been known to play a major part in skin aging and wrinkling (photoaging), but until recently scientists believed it did not cause significant damage in areas of the epidermis (outermost skin layer) where most skin cancers occur. Studies over the past two decades, however, show that UVA damages skin cells called keratinocytes in the basal layer of the epidermis, where most skin cancers occur. (Basal and squamous cells are types of keratinocytes.) UVA contributes to and may even initiate the development of skin cancers.
UVA is the dominant tanning ray, and we now know that tanning, whether outdoors or in a salon, causes cumulative damage over time. A tan results from injury to the skin's DNA; the skin darkens in an imperfect attempt to prevent further DNA damage. These imperfections, or mutations, can lead to skin cancer.
Tanning booths primarily emit UVA. The high-pressure sunlamps used in tanning salons emit doses of UVA as much as 12 times that of the sun. Not surprisingly, people who use tanning salons are 2.5 times more likely to develop squamous cell carcinoma, and 1.5 times more likely to develop basal cell carcinoma. According to recent research, first exposure to tanning beds in youth increases melanoma risk by 75 percent.

UVB, the chief cause of skin reddening and sunburn, tends to damage the skin's more superficial epidermal layers. It plays a key role in the development of skin cancer and a contributory role in tanning and photoaging. Its intensity varies by season, location, and time of day. The most significant amount of UVB hits the U.S. between 10 AM and 4 PM from April to October. However, UVB rays can burn and damage your skin year-round, especially at high altitudes and on reflective surfaces such as snow or ice, which bounce back up to 80 percent of the rays so that they hit the skin twice. UVB rays do not significantly penetrate glass.
(Skin Cancer Foundation. (n.d.). Retrieved January 22, 2015)

Skin Cancer Statistics
Common Cancer
In young American women between the ages of 20 and 35, and in adolescents and young adults between the ages of 15 and 29, melanoma is the second most common cancer.

Melanoma is the leading cause of cancer death in women ages 25 to 30 and is second only to breast cancer in women ages 30 to 34.

In the U.S., melanoma is currently the fifth most common cancer in men and the seventh most common in women of all age groups.

America's Highest Risk Population
Caucasian-Americans are 23 times more likely to develop melanoma than African-Americans. Worldwide, White populations have the highest risk of developing melanoma, and Asian populations have the lowest risk.

World's Highest Risk Countries
The world's highest incidence of melanoma is in Australia and New Zealand (more than twice as high as in North America). This may be due to how close these countries are to the equator, their greatly reduced ozone layer, and their population of mostly fair-skinned people.

Because of Australia's extensive skin cancer screening program, there has been a decrease in average tumor depth at the time of diagnosis.
(AIM At Melanoma. (n.d.). Retrieved January 22, 2015)

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