1.1.2: Organisms Studied in Botany

Learning Objectives

Describe the importance of plants in the study of botany and list other organisms that typically included in the study of botany.

Botany is the scientific study of plants and organisms that were historically considered plantlike. It helps us understand why plants are so vitally important to the world. Plants start the majority of food and energy chains, they provide us with oxygen, food and medicine. Most plants are what you typically think of: multicellular eukaryotic organisms that are ancestrally terrestrial and photosynthesize. In the process of photosynthesis, these organisms produce their own food, using sunlight, carbon dioxide, and water into organic molecules, or food. However, some organisms ecologically are considered plant-like due ot their role in nature. For example, green slugs, Elysia chlorotica (see Figure \(\PageIndex{1}\)) collect chloroplasts from algae and use them for their entire life as food producers. Therefore, green slugs, while technically classified as animals, have plantlike characteristics.

Figure \(\PageIndex{1}\): Green slug Elysia chlorotica captures chloroplasts from the alga Vaucheria litorea.

Plants are in the domain Eukarya and in the kingdom Plantae. There are about 320,000 species of plants that have been named so far. They fill our terrestrial ecosystem and provide food and shelter for animals. Plants cells contain chloroplasts, which conduct photosynthesis. They are thus autotrophic, synthesizing their own organic carbon. In addition, most of the plant cell is filled with a large membrane-bound structure, the central vacuole, which functions in store. Plant cells are surrounded by rigid cell walls containing cellulose. Plants are multicellular, composed of like cells that function as tissue. Their leaves, stems, and roots function as organs. Plants can be small like duckweed or large like the giant sequoia (Figure \(\PageIndex{2}\)).

Figure \(\PageIndex{2}\). On top, two species of duckweeds (Wolffia globosa and Spirodela polyrhiza). . On the bottom, Giant Sequoias from King Canyon National Park. Copyright Eric Guinther (CC BY-SA 3.0) for top image, Kammy Algiers (CC-BY) bottom image.

While fungi are neither closely related to plants, nor do they share key characteristics (like photosynthesis), they are sometimes included in the study of botany. Perhaps this is because the fruiting bodies that some fungi use for reproduction (such as mushrooms) may seem plantlike in the sense that they a stationary structures emerging from the soil. Fungi are heterotrophic, meaning that they feed on other organisms to obtain organic carbon. Unlike animals, which ingest their food, fungi secrete digestive enzymes to breakdown large molecules surrounding them. They then absorb the smaller molecules. Fungal cells are surrounded by rigid cell walls that contain the polysaccharide chitin. Some fungi are unicellular while other are multicellular. Although fungi and plants are not closely related, their are intertwined ecologically. For example, mycorrhizae are fungi that grow in or on plant roots and assist with nutrient absorption. Additionally, fungi often decompose dead plant material, releasing nutrients back into the soil and promoting further plant growth.

Other organisms studied in botany are "protists", which have complex, eukaryotic cells but are not plants, animals, or fungi. Some "protists", like slime molds, resembling fungi in the sense that they are heterotrophic. Other "protists" superficially resemble plants in that they conduct photosynthesis and are autotrophic. These are collectively called algae, but they arise from many different groups, and some are not closely related to plants at all. Multicellular algae are sometimes called seaweeds. Most algae have cell walls, which may or may not contain cellulose.

Photosynthetic prokaryotes, which have simple cells, are sometimes studied in botany as well. For example, cyanobacteria, are commonly called blue-green algae, but this is a misnomer because true algae are eukaryotes. Instead, cyanobacteria are photosynthetic bacteria, that often form filaments of cells. Bacteria that are pathogens of plants may also be included in the study of botany. Viruses, which are infectious particles that contain protein and nucleic acid, can also infect plant cells. Unlike plants, fungi, "protists", and prokaryotes, viruses are not technically considered organisms because they are not composed of cells.

Attribution

Curated and authored by Kammy Algiers and Melissa Ha using 1.1 Plants, Botany, and Kingdoms from Introduction to Botany by Alexey Shipunov (public domain)