Great question! There are two ways to think about your question. First, think about whether a human needs sunlight directly. How would you test this? One way would be to place that person in a room without any sunlight and see what happens. Of course, you would not do this to a person, but you can go through the "thought experiment" and make predictions.
It turns out that sunlight absorbed
through our skin is necessary in order for our
bodies to produce and use certain vitamins and
minerals. Our modern diets now supplement us with some of those (like the vitamin D in fortified milk). On the downside, too much sunlight (actually, only certain UV wavelength light in sunlight) can cause skin cancer (melanoma).
The second way to think about your question is in the "indirect sense." I bet you have studied the food web in class. As you know, plants need sunlight to produce energy through photosynthesis. And since plants form the foundation of the food web, what do you think would happen if suddenly there was not much sunlight available?
We definitely need the sun to survive, for many
reasons. Without the sun, our planet would get
extremely cold, and all living things on it would
Plants use the sun's energy for
photosynthesis, which is the process they use to make nutrients. All animals on Earth depend on
plants' ability to do that, either because they
eat the plants directly (like cows and humans) or
because they eat other animals that eat plants
(like cheetahs who eat gazelles, or humans who eat
chickens). If plants couldn't use the sun to make
nutrients, all living things on the planet would starve. There are many other things the sun does for us, as well. We definitely need it!
Yes, we definitely need the sun to survive. The sun provides the vast majority of the energy we need to live.
In outer space, away from the sun it is very cold -- about 450F below zero! Maybe someday our technology will be advanced enough to let us travel between our solar system and other stars. We might spend long periods of time away
from the sun, but we would still need to come back
to a star for energy at some (our sun is a star --
it just looks a lot bigger because it is closer).
The sun warms our atmosphere so it is a good
temperature for life as we know it. All the oil
and coal we burn is essentially energy from the
sun that was trapped in plants and animals that died and turned into oil and coal. Now we release that energy by burning the oil and coal. Wind energy comes from the sun heating the atmosphere and causing the air to move around.Yeah sun!
The short answer to your question is absolutely!
The long answer is not directly. Humans
need sunlight to make Vitamin D, which helps us absorb calcium from our food. You can take all the calcium supplements you want, but unless you have enough Vitamin D, they won't really help.
Calcium is important for building bones and making tooth enamel, and also for general good health, since calcium is important for muscle contraction and nerve function (nerves help with conscious thought, movement, body functions and collecting information from our environment like touch, smell, sound, taste, pain, etc).
New data from nutrition scientists suggests that many people do not get enough sunlight to make the Vitamin D they need to absorb calcium. (Sunscreen screens out the type of light needed to make Vitamin D.) I'm guessing that humans could probably survive without sunlight, although our bones wouldn't develop normally.
What we really need sunlight for, and what ALL animals on earth need
sunlight for, is the creation of food. Humans and other animals are called heterotrophs, which means "other" "feeding". Heterotrophs need to eat other
organisms to survive. If you're a vegetarian, the
organisms you are eating are plants. If you eat
meat, the organisms you are eating are animals,
and those animals probably ate plants, or ate
other organisms that ate plants. For example, cows
eat plants like grass and corn. Chickens eat
plants and insects and worms. Those insects and
worms got their food from plants, or from other
insects and bacteria that ate plants. This is
called a food chain, and it allows you to figure out the source of all your food.
Write down a list of everything you ate for lunch and figure out where that food came from. (You may need to get help from your teacher to do this.) For example, if you had a hamburger and fries: the bread in the bun was made of flour, which comes from plants. The beef came from cows, which eat plants. The lettuce, onions and tomatoes came from plants. The fries are potatoes, which are plants. If you had a Coke with it, the sugar in the Coke came from plants. If you do this, you'll soon realize that the ultimate source of ALL food is plants. How can plants make their own food? They are able to use
the energy in sunlight to make food from gas in the atmosphere and water and nutrients in the
soil. This is a process called "photosynthesis", which means "to make food" "from sunlight". It's pretty amazing, when you think about it, but it means that plants cannot live without sunlight.
So in this sense, humans and all heterotrophs need sunlight because we need plants for food and plants need sunlight. There are VERY few exceptions to this, and these animals live at the bottom of the ocean, or in other environments where there is no sunlight.
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