Parts of a Plant
Just as people have tissues and organs, plants also have specialized tissues and structures. The tissues and structures make up two broad systems: the shoot system and the root system. The shoot system is made up primarily of leaves, stems, and reproductive structures (e.g., flowers, fruit, seeds, etc.) and the root system is made up of roots. Each of these structures has characteristics that help it to carry out its major function.
Leaves are the mostly flat green parts of plants.
The flat part of a leaf is called the lamina (also known as the leaf blade). The part of the leaf which attaches to the stem is called the petiole (also called a leaf stalk). Most, but not all, leaves have these parts.
Leaves are typically large and flat so that they can expose as many of their chloroplasts to sunlight as possible.The role of a leaf is to:
- provide a place for photosynthesis to occur; and
- be involved in transpiration of water.
Some leaves, however, have specialized functions giving them unusual shapes and colours. Some you might not even recognize as leaves! The thin needles on pine trees and other conifers are actually leaves. Their small surface area combined with a waxy covering helps these leaves to minimize water loss.
Have you ever seen a Poinsettia plant in the winter holidays like the one below?
What appear to be red flowers are actually specialized structures called bracts. The flowers are the little yellow things in between the red bracts. Bracts are specialized leaves which help to attract pollinators such as bees and birds to the flowers. Many flowers are attractive to animals, such as birds and bees, which transfer pollen (containing the sperm) from one flower to another. Due to their role in helping to spread pollen, these animals are known as pollinators.
The stem is a structure which forms the core of the shoot system. The stem is divided into two parts; nodes and internodes. Nodes are where buds grow into leaves, stems, or flowers and internodes are the parts of the stem in between the nodes (see Figure 8). In most plants, stems are found above the ground, but for some plants, such as potatoes, stems are also found below the ground. The part of the potato plant we eat, called a tuber, is actually a specialized underground stem which stores nutrients for the plant.
The role of the stem is to:
- provide support for the plant
- provide a place for leaves, flowers and fruit to grow;
- keep leaves facing towards sunlight;
- transport water and nutrients up from the roots and transport the products of photosynthesis down from the leaves; and
- store nutrients.
Humans have many uses for plant stems. We extract sugar from sugar cane stems and make maple syrup from the sap (sugar and water) found in maple tree stems (we call tree stems trunks).
Paper and wood also come from tree stems, as do cinnamon and cork which are both made from the bark (outer layer) of tree stems.
The root system is the system of structures typically, but not always, found below the ground.
The role of roots is to:
- anchor the plant to the ground;
- take up water and minerals needed for growth and development;
- store food and nutrients; and
- provide a means of reproduction called vegetative (asexual) reproduction.
Although roots are generally below ground, they do require some oxygen to stay alive. Generally, this small quantity of oxygen is found naturally between the grains of soil, but if the soil is saturated (filled with water), the oxygen is forced out. Without the needed oxygen underground, the plants will start to produce roots above ground. Roots can be thin and hair-like (fibrous roots) (A), short and thick (taproots) (B), or somewhere in between (e.g., buttress roots) (C).