On page 49-50, Dr. Moalem discusses the negative and positive aspects of the sun. He talks about how "the entire global ecology of planet depends on sufficient sunlight," and he explains how sunlight increases the levels of Vitamin D in our bodies. Conversely, Dr. Moalem explains the negative aspects of sunlight; he says that too much sun can cause environmental concerns like drought and health concerns like skin cancer and the destruction of the body's reserves of folic acid. This topic relates to our previous units on Photosynthesis and Ecology; in class, we learned that the sun provides energy for autotrophs to perform photosynthesis, providing us with food and air and contributing to our ecosystem.
This section relates to Big Idea IV: Biological systems interact, and these systems and their interactions possess complex properties. All biological systems depend on sunlight and their interactions with other organisms help them gain/ loss energy obtained from sunlight.
Dr. Moalem discusses some disorders caused by having too little (Vitamin D deficiency) or too much (skin cancer) sunlight. What are some other common diseases caused by the sun? Also, discuss the evolutionary mechanisms that humans have to deal with too much or too little sunlight. (e.g. skin color- Page 55)
(Ilakkiya Thanigaivelan, ithanig3@students.d125.org)
One of the most common conditions caused by the sun that almost everyone who goes outside has experienced is a sunburn. The UV lights literally "burn" the skin from lack of melanin. One way humans have evolved to cope with this is the development of melanin, the dark pigment within our skin which prevents the burn from occurring. Even though too much sun is bad for the skin and body, too little is just as bad. As mentioned in the book, lack of sunlight exposure causes vitamin D deficiency which can cause weak bones. There are many other conditions which can be caused by the sun such as age spots, moles, rashes, and worst of all skin cancer. Our relationship with the sun as humans is much like the basic Goldilocks principle. We need just the right amount of sunlight to be healthy and to do what evolution is intended to do, survive and reproduce. While our evolutionary mechanisms to aid us in receiving the right amount of sun have helped (tanning and a head of hair) it's never a bad idea to put on some sunscreen. I believe that this passage relates more to Big Idea #1. Exposure to the sun has created a variety of different phenotypes in the human species. As the book referenced, people closer to the equator tend to be darker because they are exposed to the sun much longer than that of northern people. But in order to deal with this lack of vitamin d, the darker skinned individuals have apolipoprotein E, a gene that "ensures that the amount of cholesterol flowing through the blood is cranked up. With more cholesterol available for conversion, dark-skinned people can maximize the use of whatever sunlight penetrates their skin"(Moalem 57)
ReplyDeleteTim Mielczarek tmielcz5@gmail.com
The sun is generally thought as one of the driving factors for life one earth because the sun is the source of energy. Plants use sunlight to do photosynthesis and produce food. The sun also warms the earth to create a habitable environment for all living species. However, as Dr. Moalem notes, the sun has many negative side effects on humans--- mainly health issues like skin cancer.
ReplyDeleteThis topic relates to Big Idea 4 because sunlight is essential to ecology. First, as I already described, the sun acts as a source of energy for plants. These autotrophs are the only organisms that can produce their own sugar, and autotrophs can only do this when they have sunlight. Another way the sun is essential to life on earth is creating an environment that is habitable. The sun keeps earth warm enough so that enzymes can function properly, but the sun is also far away enough from the earth to prevent the temperature from getting to hot and denaturing our enzymes.
Tim already talked about how the sun causes sunburn, probably the most common health issue associated with the sun. A second very well known issue is skin cancer, because ultraviolet light acts as a mutagen on skin cells. However, other health issues associated with over exposure to the sun include eye deterioration Wearing sunglasses or other eye protection is an easy way to prevent eye damage. Overexposure to the sun can also weaken the skin’s natural defenses, weakening the immune system.
Tim also noted the evolutionary history of pigmentation. However, I would like to add to his comments. According to a study conducted by Nina Joblonski and George Chaplin, “Human Skin pigmentation as an adaptation to UV radiation,” in May 2012, the different levels of pigmentation are a direct result of the level of UV radiation people get. Near the equator, the levels of UV radiation are higher; thus, people are darker because it provides photoprotection. Tim already talked about the adaptations people near the equator have to deal with the increased levels of sunlight. People are depigmented and have light skin in regions in UV radiation peaks once a year. Light skin is optimal for this seasonal spike in UV radiation and production of vitamin D. The article also notes why skin color varies so much among humans--- it is one of the easiest traits genes to mutate because of constant exposure to the sun.
(Dhruv Luthra, dluthra4@students.d125.org)