Main->Readings->4th Grade Readings->Plants->Part 2
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Anatomy is the study of how living things are put together and what their parts are.
Seaweed and other algae do not have roots, flowers, or leaves. They do not have any tubes for water and food. Scientists believe they were the first type of plant to exist.
Ferns have leaves and they have tubes in their stems for water and food, but their root systems are simple and do not go very deep.
Seed plants, on the other hand, do have roots. They also have tubes in their stems for carrying water and food, and they have leaves.
Roots hold a plant in the ground and keep it from blowing away or washing away. But that is not their only job. Roots bring water and minerals from the soil. They do this through tiny root hairs which grow out from the main roots. One plant's roots may have millions of hairs.
There are tubes in the roots which carry the water and minerals to the rest of the plant. Some roots, such as carrots and beets, also store food for the plant.
There are two main types of root. In one type, the taproot system, a single large root grows straight down. In the other type, the fibrous root system, there are several main roots with many smaller branching roots. In the picture below, there is a picture of the roots of two weeds from Dr. Turner's garden. Number 1 has a taproot system, and Number 2 has a fibrous root system.
Stems hold up the rest of the plant. They support the leaves and flowers or cones. Because the cells of a plant are very stiff and strong, they can support a great deal of weight. Stems can be very thin, or they can be as thick as the trunk of a giant sequoia tree.
All plant stems, whether they are tree trunks or daisy stems, have a system of tubes which carry water and food to the rest of the plant. The tubes which carry water are called xylem (ZY-lem), and the tubes which carry food are called phloem (FLOW-em).
There are two main types of stem. One type is the green stem, which is thin, green, bends easily, and does not get thicker as the plant grows older. The other type of stem is the woody stem, which is stiff, does not bend easily, and grows taller and thicker every year.
In green stems, the tubes are arranged in bundles. In woody stems, the tubes are arranged in rings, with the food tubes in an outer ring and the water tubes nearer to the center.
Ferns, conifers, and flowering plants all have leaves. Leaves perform an important job, because they are the parts of the plant where most of the food is made.
Most leaves have several main parts. There are a central stalk (which is called the "petiole"), a flat part of the blade (the "lamina"), and veins, tubes which carry water and food in the leaf. Veins may run parallel to the stalk or they may branch out from it. Also, on the underside of the leaf there are tiny holes or doors, microscopic in size, called stomates. The stomates take in water and air, and also release air at night.
Leaves come in many shapes. There are two main types: needle leaves and broad leaves.
Many conifers have needle leaves, which are thin, pointed, and very tough. They do not lose much water to the air, which helps conifers survive in dry, cold areas.
Many trees which lose their leaves in the winter have broad leaves. Broad leaves are wider and expose more surface to the sun.
Broad leaves are divided into two types: simple and compound. A simple leaf, just as it sounds, is very simple: there is one main stalk and one main blade.
Simple Leaf (Maple)
In compound leaves, the leaf is divided into leaflets which are attached to the central stalk. It looks as if it has many leaves, but it is actually only one leaf.
Compound Leaf (Horse Chestnut)
At most times of the year, most plants do not have flowers or fruit, but they do have leaves. Therefore, when botanists want to identify a plant, they study its leaves. They look at several things:
If they know these things and they have a good plant guide, they can usually tell exactly what plant they are observing.
In the next section, you will learn about some special "leaves" which have a very important job in flowering plants.
Go on to Part 3: Making New Plants
This page last modified on October 19, 2002