While all energy on earth is derived from the sun in some way, humans cannot actually directly use energy from the sun for metabolic activity. Instead, humans consume plants or animals to obtain various chemical nutrients that we can convert into energy. These nutrients are produced by plants using energy directly from the sun, or from other animals using energy from consuming plants. The only direct application of energy from the sun in human metabolism is the production of vitamin D from a precursor molecule. One of the steps in the pathway that produces vitamin D requires solar energy, specifically UVB radiation, to make the reaction happen. This reaction actually occurs the same way in many different animals and fungi. Once this reaction takes place in the skin for animals, the product is sent to the liver then kidneys where further reactions take place to produce the final product, vitamin D.

The reaction that produces vitamin D relies on a protein that contains Iron in its active site. Vitamin D's primary role in the body is promoting uptake of calcium, phosphate, and magnesium. This makes it vital to maintaining healthy bones throughout life.

While humans can produce enough vitamin D with adequate amounts of sun exposure, the same UVB radiation that helps produce vitamin D also causes sun burn and can lead to skin cancer with too much exposure. Fortunately, humans only need moderate sun exposure to produce enough vitamin D for their daily needs and many foods in the USA are fortified with vitamin D so that we take it up through our diet without having to produce our own.

This is a great question Akron! Learning about how organisms including ourselves, process nutrients is an important topic, even more so in today’s world where diet and exercise are as popular as they’ve ever been.

As you may already know, photosynthesis is the process where plants and small organisms can use energy from sunlight to create their own nutrients. Plants, algae, plankton, and some other small organisms that process energy from the sun are called photoautotrophs.

Photoautotrophs is just a big word meaning, “organisms that obtain food using light.” Have you ever thought about why plants and organisms that process energy from the sun are usually green?Photosynthetic organisms use the light-absorbing molecule called chlorophyll to collect energy from the sun.

Chlorophyll is a pigment molecule that reflects green light, giving plants and algae their signature green color. Sunlight is taken up by chlorophyll. The sunlight is combined with water, as a source of electrons, to produce high energy molecules and oxygen. The high energy molecules are combined with carbon dioxide gas to create sugar!

Plants and algae do not like oxygen and get rid of it. This is great for us because we need oxygen and breathe it in!We do not like carbon dioxide and get rid of it when we breathe out, but plants and algae need it to make nutrients. This cycle is very important for how photosynthetic organisms and humans need each other to survive!

We also need plants to survive because we cannot create our own nutrients like they can. Humans and other animals need to eat nutrients like green vegetables, fibers, carbohydrates, proteins, vitamins, and minerals to obtain energy. These nutrients are combined with water to create high energy molecules, called ATP, to fuel our bodies.

However, our body only requires a certain level of nutrients. If we eat too much food, the body cannot break down all the nutrients efficiently and begins to store leftover nutrients as fat. Fat is an incredible source of energy, but it is much harder to break down than sugar. This is why it takes a lot of exercise and hard work to lose weight.

Water is used everywhere in the body and composes up to 60% of our bodies! Water helps regulate our temperature, keep our skin moist, and maintain healthy function in our organs. Our bodies lose water from breathing, sweating, and digesting food. Food and water are both combined for our body to run at optimal levels, just like you said. This is why it is extremely important to stay hydrated and to eat just the right amounts of healthy foods for our bodies to produce high amounts of energy.