What are plants?
Plants are organisms that photosynthesize their food from the sun. They use energy from light to create sugars and build organic compounds such as cellulose. Plants are the primary producers in an ecosystem.
Differences between plants and algae
Algae are considered plants, but they are not classified in the same way as traditional plants. There is a large variety of algae which can be found both on land and in water. Algae can be unicellular or multicellular and range in size from microscopic to macroscopic.
The Viridiplantae, the green plants – green algae and land plants – form a clade. The Viridiplantae are the group of plants (both freshwater and terrestrial) and algae that includes many marine species. The chloroplasts of green plants are derived from cyanobacteria, suggesting they originated directly from endosymbiotic cyanobacteria. T
Brown algae (euglenids) and haptophyte do not have the same pigmentation as plants, but they possess chloroplasts with three or four surrounding membranes. Brown algae evolved from non-photosynthetic ancestors that formed endosymbiotic relationships with red algae rather than from cyanobacteria. .
Differences between plants and fungi
The classification of plants and fungi is not certain. Linnaeus originally classified the fungi in the plantae, but they were eventually placed within the Fungi Kingdom. There has been controversy about whether fungi should be placed in the Plantae or are instead protists. Molecular evidence shows that the most recent common ancestor of Fungi was more similar to that of Animalia than Plantae.
Plants are called autotrophs because they gain carbon through photosynthesis. In contrast, fungi are called heterotrophs because they gain carbon by breaking up and absorbing surrounding materials. Fruiting bodies are the reproductive structures of fungi and very different from those of plants.
Key plant characteristics
- Plants are organisms that give off their own energy via photosynthesis. They may either obtain this energy from the sun or some other source, like direct chemical reactions with minerals. The products of plants are proteins, carbohydrates, lipids, energy stores such as fats and oils and biomass.
- Plants are autotrophs that can use water, minerals and sunlight for free energy from the environment in order to make their own food products.
- Plants are primary producers in ecosystems and give many organisms oxygen as a byproduct of photosynthesis.
- Plant cells are distinguished by their cell walls containing cellulose, chloroplasts that perform photosynthesis, and a large central vacuole that holds water and keeps the plant turgid.
Photosynthesis
Photosynthesis is the chemical process by which plants make their own food from sunlight. This process requires light, water, and carbon dioxide. Plants produce their own food molecules by using the energy from light.
Chlorophyll, a green-colored, magnesium-containing pigment is essential to this process. It is generally present in plants’ leaves and other parts as well, and lends plants this deep green color.
When photosynthesis occurs, oxygen gas is released as a waste product. The process increases the activity of enzymes known as SHMT and CAT, which perform reduction and oxidation respectively.
Evolutionary history of plants
Scientists believe that plants evolved from green algae. They are thought to have originated in the ocean, where they use sunlight as food and oxygen produced by photosynthesis for their own respiration.
The chlorophyll that plants use for their own respiration and as a pigment in leaves was originally derived from algae, which are thought to have been adapted
Algal scum formed on the land 1,200 million years ago. It was not until the Ordovician Period that plants appeared on Earth. New evidence from the study of carbon isotope ratios in Precambrian rocks suggests 5000 years ago there were complex photosynthetic plants living on earth.
The theory is that the plants evolved from single-celled algae living in microbial mats . Primitive land plants emerged around 420 million years ago and diversified into many different types of plants.
Structure, growth, and development
In general, every plant is composed of roots, stems, leaves, flowers and fruits. These parts of the plant work together to process and release energy and water. Stems are responsible for moving water and carrying nutrients and food to all other parts of the plant, while leaves are responsible for absorbing carbon. Flowers or fruit fields contain ovaries on which seeds form.
Plant cells
Plant cells are made of cellulose, hemicellulose, and pectin. Cell division is characterized by the development of a phragmoplast in late-stage cytokinesis. Differentiation into different cell types occurs at the meristematic stage. The primary cell walls of plant cells are flexible and can expand as the cell grows.
Each type of tissue in a plant is comprised of specialized cells that carry out different functions, but share the same feature: primary cell walls which are flexible and can grow. Plant cells also have a secondary cell wall, which is inflexible.
Factors affecting plant growth
Plants usually rely on soil primarily for support and water, but they also obtain compounds of nitrogen , phosphorus , potassium, magnesium and other elemental nutrients from the soil.
The genome of a plant controls its growth. Biotic factors, such as temperature and available nutrients in the soil, also affect plant growth. Plants can be so crowded that no single individual produces normal growth.
The optimal plant growth is often hindered by animals, soil composition, lack of mycorrhizal fungi, and attacks from insects or plant diseases.
Annual plants grow and reproduce within one growing season. Biennial plants grow for two growing seasons but they usually reproduce in the second year. Perennials live for many years but once mature will usually reproduce annually.
Plants lose their leaves in the winter; many tropical plants lose their leaves during the dry season. Some plants grow less than 0.001 millimeters per hour while most trees grow 0.025 to .250 millimeters per hour.
Types of plants
Vascular plants
Plants with vascular tissues are called tracheophytes. The xylem and phloem transport water, nutrients, and sugars within the plant. This allows plants to grow taller by connecting nutrients and water to all parts of the plant. Non-vascular plants have no vascular tissues, and must live near water in order to survive.
Non-vascular plants
Non-vascular plants are plants that do not have xylem and phloem tissues which transport water and nutrients around the plant’s body. The lack of these tissues means that non-vascular plants cannot move water and nutrients to different parts of their body, so they are limited in what they can do.
Mosses are non-vascular plants because they do not have vascular tissue to transport water and nutrients. Mosses typically grow in moist environments where there is plenty of water available. They can absorb water directly through their leaves, and they also take up dissolved minerals from the soil.
Angiosperms
Angiosperms are the most widespread plants on Earth, with over 295,000 different species known. They are plants that have flowers that produce pollen, which has male parts and female parts. Angiosperm evolution has resulted in increasing levels of complexity, from the earliest algal mats through bryophytes to complex gymnosperms and angiosperms of today.
Gymnosperms
Gymnosperms are vascular plants that don’t make flowers. They rely on the wind to help spread their seeds. Some plants have seeds that grow on the surface of leaves. The pine tree is an example of a gymnosperm, as is the ginkgo tree. Ginkgo trees are essentially unchanged since ancient times, with some notable exceptions like height and bark texture.
Importance
Plants in human culture and history
From the beginning of human history, plants have played an important role in our lives. They provide us with food, shelter, and clothing. Plants are also central to many cultures and religions.
The relationship between humans and plants is complex, extending back even into our evolutionary history. Humans rely on plant domestication for food sources and agriculture which allowed settlements to develop further.
In modern everyday life, plants serve as symbols for many different things, including birthdays, holidays and memorials. Some plants symbolize losing or gaining life and are associated with religious ceremonies such as those that acknowledge a death.
Cultivation
Humans have been cultivating plants for food and other purposes for thousands of years. Plants are an important part of the human diet, providing essential nutrients that are required for survival. Agriculture is the source of most food consumed by humans today.
In addition to food crops, humans also cultivate plants for non-food items such as fibers, oils, dyes, and medicines. Hundreds of medicines are derived from plants, both traditional and modern medicines.
Finally, ornamental plants are the flowers and plants that are not of edible use or medicinal benefits but serve decorative purposes. Plants like Impatiens, Christopher Columbus Narcissus, Ivy Mater Plants and more are popular choices. Ornamental plants are not traditionally used for survival or to provide essential resources such as food or clean water.
Scientific and cultural uses
Plants have been used for scientific study and cultural purposes for centuries. Barbara McClintock studied inheritance over the course of her career, using plants. Her discoveries were groundbreaking as they led to a greater understanding of genetics.
Tree rings are an important dating tool in archeology. Every tree has a unique life cycle as defined by its alternating rings of the trunk which signify suitable environmental conditions, timing of different seasons, and annual fruiting. Trees with the same type of rings but different duration can be dated between specific periods of time and because no two trees have the same pattern, we can determine annual average temperatures.
