Most animals synthesize their own ascorbic acid from ____.

If you're like most kids, you've probably heard at least one parent say, "Don't forget to take your vitamin!" or "Eat your salad — it's packed with vitamins!" But what exactly are vitamins?

Vitamins and minerals are substances that are found in foods we eat. Your body needs them to work properly, so you grow and stay healthy. When it comes to vitamins, each one has a special role to play. For example:

• Vitamin D in milk helps your bones.
• Vitamin A in carrots helps you see at night.
• Vitamin C in oranges helps your body heal if you get a cut.
• B vitamins in whole grains help your body make energy from food.

Vitamins Hang Out in Water and Fat

There are two types of vitamins: fat soluble and water soluble.

When you eat foods that contain fat-soluble vitamins, the vitamins are stored in the fat tissues in your body and in your liver. They wait around in your body fat until your body needs them.

Fat-soluble vitamins are happy to stay stored in your body for a long time. Then, when it's time for them to be used, special carriers in your body take them to where they're needed. Vitamins A, D, E, and K are all fat-soluble vitamins.

Water-soluble vitamins are different. These vitamins dissolve in water. When you eat foods that have water-soluble vitamins, the vitamins are not stored in your body. Instead, they travel through your bloodstream. Whatever your body doesn't use comes out when you urinate (pee).

So water-soluble vitamins need to be replaced often because they don't stick around! This crowd of vitamins includes vitamin C and the big group of B vitamins — B1 (thiamin), B2 (riboflavin), niacin, B6 (pyridoxine), folic acid, B12 (cobalamine), biotin, and pantothenic acid.

Vitamins Feed Your Needs

Your body is one powerful machine, capable of doing all sorts of things by itself. But when it comes to vitamins, it can use some help. That's where food comes in. Your body is able to get the vitamins it needs from the foods you eat because different foods contain different vitamins. The key is to eat different foods to get an assortment of vitamins. Though some kids take a daily vitamin, most kids don't need one if they're eating a variety of healthy foods.

Now, let's look more closely at vitamins — from A to K:

Vitamin A

This vitamin plays a really big part in eyesight. It's great for night vision, like when you're trick-or-treating on Halloween. Vitamin A helps you see in color, too, from the brightest yellow to the darkest purple. In addition, it helps your body fight infections by boosting your immune system.

Which foods are rich in vitamin A?

• milk fortified with vitamin A
• liver
• orange fruits and vegetables (like cantaloupe, carrots, sweet potatoes)
• dark green leafy vegetables (like kale, collards, spinach)

The B Vitamins

There's more than one B vitamin. Here's the list: B1, B2, B6, B12, niacin, folic acid, biotin, and pantothenic acid. Whew — that's quite a group!

The B vitamins are important in metabolic (say: meh-tuh-BAH-lik) activity — this means that they help get energy from the food you eat and set it free when your body needs it. So the next time you're running to third base, thank those B vitamins.

This group of vitamins also helps make red blood cells, which carry oxygen throughout your body. Every part of your body needs oxygen to work properly, so these B vitamins have a really important job.

Which foods are rich in vitamin B?

• whole grains, such as wheat and oats
• fish and seafood
• poultry and meats
• eggs
• dairy products, like milk and yogurt
• leafy green vegetables
• beans and peas
• fortified cereals

Vitamin C

This vitamin is important for keeping body tissues, such as gums, bones, and blood vessels in good shape. Vitamin C is key if you get a cut because it helps you heal. It also helps the body absorb iron from food. Kids need iron to prevent anemia.

This vitamin may also help your body fight off infections. If you get a cold, for instance, vitamin C can help shorten the amount of time you are sick.

Which foods are rich in vitamin C?

• citrus fruits, like oranges
• cantaloupe
• strawberries
• tomatoes
• broccoli
• cabbage
• kiwi fruit
• sweet red peppers

Vitamin D

No bones about it . . . vitamin D is the vitamin you need for strong bones! It's also great for forming strong teeth. Vitamin D lends a hand to an important mineral — it helps your body absorb the calcium it needs. Vitamin D is made in the skin when exposed to sunlight, or you can get it from the foods you eat.

Which foods are rich in vitamin D?

• milk and other dairy fortified with vitamin D
• fish
• egg yolks
• liver
• fortified cereal

Vitamin E

Everybody needs E. This hard-working vitamin protects your cells and tissues from damage. It is also important for the health of red blood cells.

Which foods are rich in vitamin E?

• whole grains, such as wheat and oats
• wheat germ
• leafy green vegetables
• vegetable oils like sunflower, canola, and olive
• egg yolks
• nuts and seeds

Vitamin K

Vitamin K is the clotmaster! Remember the last time you got a cut? Your blood did something special called clotting. This is when certain cells in your blood act like glue and stick together at the surface of the cut to help stop the bleeding.

Which foods are rich in vitamin K?

• leafy green vegetables
• dairy products, like milk and yogurt
• broccoli
• soybean, canola, and olive oils

When your body gets this vitamin and the other ones it needs, you'll be feeling A-OK!

Nutrients are chemical substances found in every living thing on Earth. They are necessary to the lives of people, plants, animals, and all other organisms. Nutrients help break down food to give organisms energy. They are used in every process of an organism’s body. Some of the processes are growth (building cells), repair (healing a wound), and maintaining life (breathing).

Plants and other autotrophs absorb nutrients from soil and water. Autotrophs are organisms that can make their own food. The most important nutrients they need are carbon, hydrogen, and oxygen. Other nutrients needed by plants are nitrogen, phosphorous, potassium, calcium, magnesium, and sulfur.

From these basic nutrients, plants and other autotrophs synthesize, or create, their own nutrients, such as sugars. The human body can also synthesize some nutrients, such as amino acids. However, most organisms need nutrients created by autotrophs. People and animals get most of their nutrients from food.

Essential nutrients are nutrients that the human body is unable to synthesize. They must be obtained from food or water. Essential nutrients include carbohydrates, proteins, fats, vitamins, and minerals.

Carbohydrates, proteins, and fats are all part of a group of essential nutrients called macronutrients. “Macro-” means large, and these are the nutrients humans need in the largest amounts. Foods that are high in macronutrients include potatoes, which are high in carbohydrates; nuts, which are high in proteins; and avocados, which are high in fats.

Each macronutrient supplies a specific amount of energy. We know how much energy is in a kind of food by how many calories it has. A calorie is a unit of energy. Think of calories like gallons of fuel in a tank: If your car can go 20 kilometers by using one gallon of fuel and you are taking a 40-kilometer trip, you know that you need two gallons of fuel. Calories are fuel in the human body.

Vitamins and minerals are part of a group of essential nutrients called micronutrients. “Micro-” means small; humans need micronutrients in small amounts. Vitamins have names like vitamin A, vitamin C, and vitamin D. Vitamins contain the element carbon, which means they are organic compounds. Minerals, such as calcium and iron, come from the earth or environment. Minerals do not contain carbon, meaning they are inorganic compounds.

Nutrients in the Environment

Nutrients accumulate, or build up, in the environment. Nutrient-rich soil or water contains large amounts of nitrogen, carbon, phosphorus, sulfur, and potassium. These nutrients can come from natural sources, like plant and animal remains. As plants and animals die, they decompose. Decomposition releases nutrients into the environment.

Human activity also adds nutrients to soil and water. Many factories use nutrients to help preserve their products. Nutrients are either released as gas into the atmosphere, or as liquid. Either way, the nutrients enter the water cycle.

Sewage and wastewater are also full of nutrients such as carbon. Wastewater is often used on golf courses, where it enters local creeks as runoff. Treated wastewater is sometimes released directly into the environment.

Fertilizers, used in agriculture, are rich in carbon, nitrogen, and phosphorus. Farmers use fertilizers on crops such as grains, fruits, and vegetables. Phosphorus-based fertilizers are also used on golf courses, parks, and even neighborhood lawns.

Fertilizer not absorbed by plants accumulates in the soil. Nutrients from fertilizer can also leech into groundwater or runoff. Nutrient-rich runoff flows into creeks, rivers, and bays. Ponds, lakes, and even the ocean can absorb huge amounts of nutrients, especially nitrogen and phosphorus.

Balance of Nutrients

Nutrients such as carbon, oxygen, and nitrogen make all life possible. Nutrient-poor areas cannot support much biodiversity. Bogs, for instance, are nutrient-poor wetlands found in cool climates. The soil of bogs is much more acidic than fertile, or nutrient-rich, soil. Few species of plants can grow in the nutrient-poor soil of bogs. With fewer species of plants available, the ecosystem is unable to support a large variety of other organisms, such as animals and fungi.

The introduction of nutrients into an environment can make the ecosystem healthy and fertile. Upwelling is the natural process of cold, nutrient-rich water being pushed to the upper layers of the ocean. Upwelling brings a huge supply of nutrients to fish, seaweeds, and marine mammals. Economic activity also depends on upwelling. The fisheries off the western coast of South America, for instance, depend on the annual upwelling of the Pacific Ocean to bring nutrients to fish and shellfish stocks.

Excess Nutrients

Although life depends on nutrients, too many nutrients can have a negative impact on an ecosystem. Algal blooms, for instance, are caused by excess nutrients. They can actually prevent the natural nutrient flow in an aquatic ecosystem.

Algal blooms form as excess nutrients, from natural and manmade sources, accumulate in a body of water. When the conditions are just right, algae, bacteria, and other microbes bloom, or multiply quickly. The rapid reproduction uses almost all the nutrients in the water. The bloom forms a thin mat near the surface of the water, preventing light from reaching below.

The organisms in many algal blooms are not eaten by other organisms, so they are not part of the food web. An algal bloom uses up important nutrients—including oxygen—without contributing to the aquatic environment. Some algal blooms even contain toxic microbes. This type of algal bloom is called a harmful algal bloom (HAB). Without light and oxygen, plants die quickly. An algal bloom uses up nutrients and prevents the development of plants that fish and other living things depend on for survival.

Algal blooms can die off as quickly as they form. The dead algae and other microbes sink to the bottom of the body of water. Sunlight and nutrients can once again enter the ecosystem. However, bacteria that help decay the algal bloom now absorb most of these nutrients. It can take weeks or even months for an ecosystem to recover from an algal bloom.

Algal blooms can reduce nutrients in an area to such a degree that the area is known as a dead zone. This means that few organisms can survive in the environment. Dead zones do not have enough nutrients to support a food web.

Excess Nutrients in the Chesapeake Bay

Dead zones are a frequent problem for the Chesapeake Bay, a huge estuary on the East Coast of the United States. This region is home to 13.6 million people. Its watershed includes the large urban areas of Washington, D.C., and Baltimore and Annapolis, Maryland.

The western corridor of the Chesapeake Bay is highly industrialized. The eastern corridor is home to many farming communities. Runoff from factories, homes, and farms has polluted the bay with excess nutrients.

The size and duration of dead zones in the Chesapeake Bay vary. They depend on the season and the weather. During heavy rains, more nutrients are washed into the bay. During the spring and summer, farms fertilize their crops, leading to more nutrient runoff. About one-third of the excess nutrients in the Chesapeake Bay is the result of air pollution. Burning fossil fuels releases carbon and nitrogen into the air. Eventually, these nutrients return to the soil and water through the water cycle.

People and businesses can control the nutrients they release. At home, people can help by using phosphorus-free fertilizer and preventing lawn waste from washing into the gutter. Native plants help filter water and stop debris from washing into a watershed. Making sure septic systems don’t have leaks, safely disposing of household chemicals (like paint and batteries), and minimizing activities that erode soil also help prevent algal blooms.

Factories and farms can help control the amount of nutrients released into the environment by following safety standards and reducing runoff.