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United States Department of Agriculture

Agricultural Research Service

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All About Plants
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How Does Your Garden Grow?
All About Plants

Who Needs Plants

Image of palm treePlants can be found all over the Earth. You can find them at the top of mountains and in the oceans. They grow in the cold polar regions, in the hot dry deserts and everywhere in between. All life on Earth depends on plants. If there were no plants, there would be no life. Plants provide us with food, clothing, shelter, medicine, and energy. They produce gases for our atmosphere and help to keep it clean. I guess you could say that plants are important. 
What Do Plants Need?

In order for plants to grow and be healthy they need six things. They need light, nutrients, water, the right temperature, space to grow and gases in the air. Plants get all of these things from their environment. Plants that come from seeds have four main structures that help them get what they need from their environment. From the bottom up, they have roots, stems, leaves, and flowers. 
Rooting Around

Two of the things a plant needs, water and nutrients, are retrieved from the soil through the root system. Nitrogen and minerals such as calcium, sulfur, potassium, magnesium, and phosphorus dissolve in water and are absorbed by the roots of a plant through root hairs. Most plants have billions of root hairs which are tiny structures near the end of the roots. The end of the root is called the root tip. It has a slimy cap to help the root push through the soil as it grows. A plant's root system is generally about as big as the rest of the plant. It anchors and stabilizes the plant.
There are two kinds of plant root systems: fibrous root systems and taproot systems. A fibrous root system looks like a tangled up wad of string. It's actually a network of branching roots. In a fibrous root system there is no main root. Grass is a good example of a plant with this type of root system. In a taproot system there is a long, thick main root that grows deeply into the soil. Branching off from this taproot are smaller roots. A dandelion has a taproot system. Image of a Fibrous Root
Fibrous Root
Image of a Taproot

Not only do roots absorb water and minerals, and anchor and stabilize the plant, they hold soil in place. Roots are nature's net to keep soil from washing away when it rains. Try out When Water Hurts inMud Pie Science or Down and Dirty to get a first hand look at how roots keep a grip on soil. 

In some plants, tubes, or phloem, from the stem extend into the roots and the plant is able to store food in the root system. Sugar, or glucose, is transported through the phloem to the roots where it is changed to starch and stored. 
Beam Me Up!

The stem of the plant supports and transports. It supports the leaves and flowers so that they are in the sunlight and it transports water, nutrients, and food. Stems can be long or short, thick or thin, rigid or flexible.

Stems transport water, nutrients, and food through two types of tubes. The phloem, which are mentioned above, carry food (glucose) from the leaves to the other parts of the plant. The xylem carry the water and nutrients from the roots to the leaves.

"Leaf" Me Alone

Leaves come in many sizes, shapes, and colors. They have a petiole which connects the leaf to the stem, and veins that carryimage of a leaf nutrients and water throughout the leaf. The main part of the leaf is called the blade, and on the underside of the blade are tiny holes called stomata. Stomata allow air to move in and out of the leaf. Plants that grow in shady areas often have large leaves which help them get as much sunlight as possible. Plants must have light to make their food. Just like us, without food a plant cannot survive.

Leaves are a kind of kitchen for the plant because this is where the plant makes its food (glucose). It is here, in the leaves, that plants are able to take solar energy (sunlight) and make food energy. This process is called photosynthesis. The word photosynthesis comes from two Greek words, photo meaning "light" and synthesis meaning "putting together".

Photosynthesis occurs in tiny structures within the plants' cells called chloroplasts. Chloroplasts contain a chemical called chlorophyll which traps the sun's energy. Chlorophyll is the chemical that gives leaves their green color. During photosynthesis, a plant uses the sun's energy (light) to put together water and a gas called carbon dioxide to make glucose and oxygen. The glucose gives the plant energy to grow and the oxygen is given off into the air. 
Not Just Another Pretty Face

Without flowers there would be no more plants. They are the reproductive part of the plant where seeds are produced in fruits. Most flowers have the male and female part needed to produce seeds. The stamens are long, skinny stalks. These are the male parts. They contain millions of tiny pollen grains which are the male sex cells, or sperm.

Image of inner structure of a flowerThe stamens surround the female part, or pistil. The bottom of the pistil which is the ovary contains one or more ovule. The ovule hold the egg which is the female sex cell. The top part of the pistil is usually sticky. A seed is formed when a sperm and egg unite.

In order for a seed to form, pollen must be transferred from the stamen to the sticky part of the pistil. This occurs in a couple of ways. Flowers can pollinate themselves, or wind may carry the pollen from one flower to another. Sometimes Diagram of the inner structure of a flowerpollen is carried by insects. An insect will land on a flower and some of the pollen will rub off on its body. When the insect lands on another flower, some of the pollen gets stuck to the sticky part of the pistil. This process is called pollination.

Another diagram of the inner structure of a flowerOnce pollination has occurred, a tube grows down from the pollen grain to the ovary. A sperm cell from the pollen then travels down the tube to an ovule. Here the sperm cell joins with an egg which then develops into a seed. Sometimes the ovule develops into a thick fruit that covers and protects the seed or seeds. A fruit is the part of the plant that contains the seed. Apples, oranges, bananas, strawberries, and peaches are all common fruits. Image of red, green, and yellow peppers each sliced in half We even call them fruits. But what about tomatoes, peppers, cucumbers, and string beans? We call them vegetables, but don't they contain the seeds of the plant?

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Last Modified: 12/29/2016
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