Plant

A plant is a form of life in the kingdom Plantae. Encompassing more than 250,000 species and taking on a vast variety of sizes, shapes, and behaviors, plants are characterized by generally shared traits such as having more than one cell, lacking locomotion, developing cellulose cell walls, and creating their own food using a process called photosynthesis. Existing on Earth for more than 440 million years, plants have become enormously diverse and occupy most habitats on the planet. Humans and other animals rely on plants for food, oxygen (a byproduct of photosynthesis), and a wide range of other products and activities that sustain and enrich life on Earth.

Defining Characteristics of Plants

Plants, the members of the kingdom Plantae, are forms of life that are not animals. Plantae includes more than 250,000 species, making it one of the largest kingdoms on Earth. These species also include an immense range of characteristics, making it difficult to define exactly what makes a living thing qualify as a plant. Some life forms, such as fungi and green algae, were once considered plants but were later disqualified as having too many dissimilar elements.

Most plants share several characteristics. Plants are multicellular, meaning they consist of more than one cell. Most plants move slowly, if at all, and have no parts for true locomotion such as the legs, fins, or wings of animals. Most plants grow from seeds and develop cellulose cell walls, hardened cellular formations that help the plant grow and maintain a solid structure. Perhaps the most important defining characteristic of most plants is photosynthesis, the ability to use air, sunlight, and water to create food.

Types and Parts of Plants

The two main types of plants are vascular and nonvascular. Vascular plants, such as trees and flowers, grow roots, stems, and leaves. These plant parts are formed from successive layers of cellulose created in the cells of the plant. Roots are long, thin body parts that reach into the ground, serving both to anchor the plant and to take in needed water and nutrients from the soil. Stems make up the bodies of vascular plants; stems may be very short and delicate, as in a clover, or extremely large and strong, as in a redwood tree. Plant leaves, generally green, are growths that help to produce food for the plant. The food and water in a vascular plant moves through the organism via special structures called xylem and phloem. Many vascular plants also produce flowers, which may contain reproductive materials such as pollen and seeds.

Meanwhile, nonvascular plants do not have clearly defined parts such as roots or stems and also lack xylem and phloem. Most nonvascular plants do not produce flowers. A common example of a nonvascular plant is moss, an erratically structured green growth that usually forms in moist, cool places.

Life Cycle and Food Production

Plants generally grow from seeds, pollen, or spores produced by earlier generations of that plant. These reproductive materials come in many shapes and sizes and function in different ways. Some are designed to fall directly and become embedded in the ground to allow growth to begin immediately. Other types are designed to blow in the wind and spread widely. Many plant seeds, pollen, and spores are spread by animals that use the plants for food. For instance, a squirrel may take an acorn (a seed-bearing nut from an oak tree) intending to eat it, but instead drop or misplace it in another location where the seed inside will eventually grow into a new tree.

Plants can grow, thrive, and spread because of photosynthesis, the process by which plants produce their own food. Green plant leaves contain a substance called chlorophyll that absorbs sunlight. The plant mixes the stored sunlight with water from its roots as well as carbon dioxide, a common gas in the air, to produce carbohydrates such as starch and sugar. These simple foods provide the plant with needed energy. The chemical reaction of photosynthesis is doubly helpful in that it also produces oxygen, a gas people and animals need to survive.

Habitats and Effects

Plants are some of the oldest and most durable forms of life on the planet. The fossil record shows that the first true plants most likely appeared during the Ordovician Period, more than 440 million years ago. Over the coming geologic eras, plants developed into their modern forms, such as simple mosses, creeping vines, colorful flowers, and towering trees. They also spread to most parts of the world and adapted to the various conditions they encountered. Today, plants may be found in widely varied habitats all over Earth, from steaming tropical rain forests to wintry boreal forests, from balmy wetlands to dry deserts. Different types of plants have developed special ways to survive in their particular environments. A well-known example is the cactus, which thrives in hot, arid locales by carefully storing and sparingly using water.

The effect of plants on Earth has been enormous. Plants are a vital link in the food chain as they can be consumed by animals and humans alike. In addition, the oxygen created by photosynthesis allows animals and humans to breathe. Humans have used plants in countless ways in the development of science and civilization, for food, building materials, fuel, medicine, paper, and innumerable forms of raw material. Scientists have used plants to study genetic inheritance, disease resistance, and many other important topics. Plants have also served to beautify the world, both in the wildness of nature and in carefully designed gardens and floral displays.

Bibliography

Ball, Jackie, Denise Vega, Uechi Ng, et al. The Plant and Animal Kingdoms: Plants.Discovery Channel School Science. Gareth Stevens Publishing. 4–5.

Kalman, Bobbie. Plants in Different Habitats. New York: Crabtree Publishing Company, 2006. 4–10.

Mauseth, James D. Botany: An Introduction to Plant Biology, Fifth Ed. Jones & Bartlett Learning, 2014. 2–3.

Speer, B.R. "Introduction to the Plantae: The Green Kingdom." University of California Museum of Paleontology. University of California, Berkeley, 9 Jul. 1997, www.ucmp.berkeley.edu/plants/plantae.html. Accessed 21 Nov. 2024.